USMLE Step 1 Qs (3)

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Quizzes Created: 14 | Total Attempts: 3,051

Questions: 50 | Attempts: 147 | Updated: Mar 22, 2023

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1.

The process of unlocking the fully extended knee in preparation for flexion requires initial contraction of which of the following muscles?
- A.
  
  Gastrocnemius, soleus, and plantaris muscles
- B.
  
  Hamstring muscles
- C.
  
  Popliteus muscle
- D.
  
  Quadriceps femoris muscle
- E.
  
  Sartorius muscle and short head of the biceps femoris muscle
Correct Answer
C. Popliteus muscle

Explanation
To unscrew a knee from its locked and slightly hyperextended position, the popliteus muscle contracts and causes medial rotation of the tibia or, if the foot is planted, lateral rotation of the femur. This movement frees the medial femoral condyle from its posterior position on the tibial condylar surface. The quadriceps femoris then relaxes, and knee flexion occurs by contraction of the hamstring muscles, assisted by the short head of the biceps femoris, sartorius, gracilis, and gastrocnemius muscles.

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2.

A 22-year-old male who belongs to a weekend football league presents in the ER. He was running with the ball when a defender tackled him in the midthigh. The patient reports that when he got up, his thigh hurt, so he sat out the rest of the game. When walking to the car, his posterior thigh was extremely painful and swollen. After his shower, he noticed it was becoming discolored with increased swelling. You are concerned about the presence of a hematoma and a disruption of the arterial blood flow to the hamstring muscles. An arteriogram is performed and the vessels in question (arrows) show good filling by contrast. These blood vessels are
- A.
  
  Descending branches of the inferior gluteal artery
- B.
  
  Perforating branches of the deep femoral artery
- C.
  
  Perforating branches from the obturator artery
- D.
  
  Perforating branches of the femoral artery
- E.
  
  Posterior femoral artery
Correct Answer
B. Perforating branches of the deep femoral artery

Explanation
Perforating branches of the deep femoral artery are the principal blood supply to the posterior thigh. The other arteries supply anterior, medial, and gluteal regions of the thigh.

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3.

The muscles of the anterior compartment of the leg are innervated primarily by which of the following nerves?
- A.
  
  Deep fibular
- B.
  
  Lateral sural cutaneous
- C.
  
  Saphenous
- D.
  
  Superficial fibular
- E.
  
  Sural
Correct Answer
A. Deep fibular

Explanation
The common fibular (peroneal) nerve bifurcates into superficial and deep branches. The deep fibular nerve innervates all muscles of the anterior compartment of the leg. The superficial fibular nerve emerges from the deep fascia and descends in the lateral compartment, where it innervates the peroneus longus and brevis muscles before dividing into median dorsal cutaneous and intermediate dorsal cutaneous nerves, which supply the distal third of the leg, dorsum of the foot, and all the toes. The saphenous nerve (the terminal branch of the common femoral nerve) distributes cutaneous branches to the anterior and medial aspects of the leg as well as to the dorsomedial aspect of the foot. The sural nerve follows the course of the lesser saphenous vein and becomes the lateral sural cutaneous nerve to supply the anterolateral aspect of the foot.

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4.

The tendon of which of the following muscles is involved when the tuberosity of the fifth metatarsal bone is avulsed in an inversion fracture?
- A.
  
  Abductor digiti minimi
- B.
  
  Peroneus brevis
- C.
  
  Peroneus longus
- D.
  
  Tibialis anterior
- E.
  
  Tibialis posterior
Correct Answer
B. Peroneus brevis

Explanation
The peroneus (fibularis) brevis, a pronator and everter of the foot, inserts into the tubercle at the base of the fifth metatarsal. The peroneus longus passes under the tarsal arch to insert onto the plantar aspect of the first metatarsal. The tibialis posterior inserts onto the navicular bone, whereas the tibialis anterior inserts into the first cuneiform and first metatarsal. The abductor digiti minimi inserts onto the proximal phalanx of the fifth toe.

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5.

In a presurgical patient, the great saphenous vein was cannulated in the vicinity of the ankle. During the procedure, the patient experienced severe pain that radiated along the medial border of the foot. Which of the following nerves was accidentally included in a ligature during this procedure?
- A.
  
  Medial femoral cutaneous nerve
- B.
  
  Saphenous nerve
- C.
  
  Superficial fibular nerve
- D.
  
  Sural cutaneous nerve
- E.
  
  Tibial nerve
Correct Answer
B. Saphenous nerve

Explanation
The saphenous nerve accompanies the great saphenous vein along the medial aspect of the leg and foot as far as the great toe. The superficial fibular nerve innervates the central portion of the dorsum of the foot. The sural cutaneous nerve innervates the lateral aspect of the foot. The medial and lateral plantar branches of the tibial nerve supply the sole of the foot.

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6.

A 22-year-old male who belongs to a weekend football league was running with the ball when a defender tackled him mid-lower limb from the side. After the tackle, he felt that the knee was hurt and went to the emergency room. From an MRI of the knee, the lateral meniscus is uniformly black; however, the medial meniscus has a tear (lucent area within the meniscus). Which of the following is the reason why the medial meniscus is more susceptible to damage than the lateral meniscus?
- A.
  
  The medial meniscus is attached to the popliteus muscle tendon, which can move into a position making it more susceptible.
- B.
  
  The medial meniscus is attached to the medial (tibial) collateral ligament, which holds it relatively immobile, making it more susceptible.
- C.
  
  The medial meniscus is attached to the anterior cruciate ligament, which holds it relatively immobile, making it more susceptible.
- D.
  
  The only reason the medial meniscus is more susceptible to damage is that the knee usually gets hit laterally, causing more torsion on the medial meniscus.
Correct Answer
B. The medial meniscus is attached to the medial (tibial) collateral ligament, which holds it relatively immobile, making it more susceptible.

Explanation
The medial meniscus is attached to the medial collateral ligament. It is relatively immovable and, therefore, unable to evade damage such as occurred in this case. The medial meniscus is clearly not attached to the popliteus muscle or to the anterior cruciate ligament.

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7.

A physician examines a patient who complains of pain and paresthesia in the left leg. The distribution of the pain—running down the medial aspect of the leg and the medial side of the foot and including the great toe—is suggestive of a herniated intervertebral disk. The physician links the distribution of symptoms with nerve L4 and concludes that herniation has occurred at which location?
- A.
  
  L3–L4 intervertebral disk
- B.
  
  L4–L5 intervertebral disk
- C.
  
  L5–S1 intervertebral disk
- D.
  
  S1–S2 intervertebral disk
- E.
  
  Insufficient data to determine
Correct Answer
A. L3–L4 intervertebral disk

Explanation
The deep incisure in the inferior border of the pedicle ensures that the spinal nerve associated with that vertebra will exit through the intervertebral foramen well above the intervertebral disk so that it will not be affected by a herniation at that level. However, a posterolateral herniation (the usual direction) will impinge on the next lower nerve as it courses toward its associated intervertebral foramen. In this case, pain was distributed along the medial side of the leg and foot as far as the great toe—the distribution of the saphenous branch of the femoral nerve (L4). Herniation of the third lumbar intervertebral disk between vertebral bodies L3–L4 would affect nerve L4.

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8.

Refer to the photomicrographs below in answering these questions. The low-magnification micrograph is on top and is from the same organ as the high-magnification micrograph located below it. In the top panel, the cells located in the region marked with the asterisk and those in the region delineated with the star and dashes have which of the following characteristics in common?
- A.
  
  Embryologic origin from intermediate mesoderm
- B.
  
  Storage of appreciable quantities of product
- C.
  
  Dependence on anterior pituitary regulation
- D.
  
  Are essential for life
- E.
  
  Release of stress-related hormones
Correct Answer
E. Release of stress-related hormones

Explanation
The photomicrograph shows the histology of the adrenal gland showing the cortex (*) and medulla (– – –), which both release stress-related hormones [i.e., glucocorticoids and catecholamines (norepinephrine and epinephrine)]. The adrenal cortex originates from the intermediate mesoderm, whereas the adrenal medulla forms from neural crest. Adrenocortical cells are under the influence of corticotrophs in the anterior pituitary. Adrenocortical cells import cholesterol and acetate and produce the hormones shown in the table below. The zona glomerulosa (A) is found immediately beneath the capsule (E) and is followed by the zona fasciculata (B) and zona reticularis (C) as one moves toward the medulla (D). However, in all zones the cells do not store appreciable quantities of hormones, there is an absence of secretory granules, and the steroid hormones are released by diffusion through the plasma membrane without use of the exocytotic process used by most glands, including the adrenal medulla. The cells of the adrenal medulla (D) may be considered as modified postganglionic sympathetic neurons. Adrenal medullary cells synthesize and secrete norepinephrine, epinephrine, and enkephalins in response to stimulation of preganglionic sympathetic fibers that travel through the abdomen in the splanchnic nerves and innervate the gland. The adrenal cortical hormones are viewed as essential for life because of their regulation of metabolism. In Addison's disease there is a progressive destruction (hypotrophy) of the adrenal cortex (zones A, B, and C). The result in the patient is asthenia (lack of strength, overall weakness, and fatigue), anorexia, nausea, vomiting, weight loss, hypotension, and low blood sugar.
The adrenal hormones are listed in the table below:
Zone Secretion Target Regulartory Factors
Zona glomerulosa Mineralocorticoids (aldosterone) Collecting tubules Angiotensin II
Zona fasciculata Glucocorticoids (cortisol, hydro-cortisone) and weak androgens Gluconeogenesis by the liver ACTH (adrenocortico-tropic hormone)
Zona reticularis Glucocorticoids and weak androgens Androgens are precursors of estradiol in the fetus ACTH
Medulla Norepinephrine and epinephrine Preparation for "flight or fight" Preganglionic sympathetic fibers from the splanchnic nerves

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9.

Refer to the photomicrographs below in answering these questions. The low-magnification micrograph is on top and is from the same organ as the high-magnification micrograph located below it. In Addison's disease, which of the following would be a direct effect of the disease?
- A.
  
  Hypertrophy of zone A only
- B.
  
  Hypertrophy of zones A, B, and C only
- C.
  
  Hypotrophy of zones A, B, and C only
- D.
  
  Hypotrophy of zones A, B, C, and D only
- E.
  
  Hypertrophy of zones A and B only
Correct Answer
C. Hypotrophy of zones A, B, and C only

Explanation
The photomicrograph shows the histology of the adrenal gland showing the cortex (*) and medulla (– – –), which both release stress-related hormones [i.e., glucocorticoids and catecholamines (norepinephrine and epinephrine)]. The adrenal cortex originates from the intermediate mesoderm, whereas the adrenal medulla forms from neural crest. Adrenocortical cells are under the influence of corticotrophs in the anterior pituitary. Adrenocortical cells import cholesterol and acetate and produce the hormones shown in the table below. The zona glomerulosa (A) is found immediately beneath the capsule (E) and is followed by the zona fasciculata (B) and zona reticularis (C) as one moves toward the medulla (D). However, in all zones the cells do not store appreciable quantities of hormones, there is an absence of secretory granules, and the steroid hormones are released by diffusion through the plasma membrane without use of the exocytotic process used by most glands, including the adrenal medulla. The cells of the adrenal medulla (D) may be considered as modified postganglionic sympathetic neurons. Adrenal medullary cells synthesize and secrete norepinephrine, epinephrine, and enkephalins in response to stimulation of preganglionic sympathetic fibers that travel through the abdomen in the splanchnic nerves and innervate the gland. The adrenal cortical hormones are viewed as essential for life because of their regulation of metabolism. In Addison's disease there is a progressive destruction (hypotrophy) of the adrenal cortex (zones A, B, and C). The result in the patient is asthenia (lack of strength, overall weakness, and fatigue), anorexia, nausea, vomiting, weight loss, hypotension, and low blood sugar.

The adrenal hormones are listed in the table below:
Zone Secretion Target Regulartory Factors
Zona glomerulosa Mineralocorticoids (aldosterone) Collecting tubules Angiotensin II
Zona fasciculata Glucocorticoids (cortisol, hydro-cortisone) and weak androgens Gluconeogenesis by the liver ACTH (adrenocortico-tropic hormone)
Zona reticularis Glucocorticoids and weak androgens Androgens are precursors of estradiol in the fetus ACTH
Medulla Norepinephrine and epinephrine Preparation for "flight or fight" Preganglionic sympathetic fibers from the splanchnic nerves

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10.

The activity of the cell labeled with the star is regulated by which of the following?
- A.
  
  Follicle-stimulating hormone (FSH)
- B.
  
  Luteinizing hormone (LH)
- C.
  
  FSH releasing factor
- D.
  
  Inhibin
- E.
  
  Androgen-binding protein
Correct Answer
B. Luteinizing hormone (LH)

Explanation
The cell marked with a star is a Leydig cell (i.e., interstitial cell) and is regulated by luteinizing hormone (LH), also known as interstitial cell-stimulating hormone (ICSH), secreted by gonadotrophs in the anterior pituitary. Leydig cells are located between seminiferous tubules and are responsible for the production of testosterone. Sertoli cells function in a nutritive and supportive role somewhat analogous to the glial cells of the CNS. The Sertoli cells produce inhibin, which feeds back on the anterior pituitary and hypothalamus to regulate FSH release. Testosterone is modified by binding to androgen-binding protein (ABP), which is synthesized by the Sertoli cells. The testosterone is necessary for the maintenance of spermatogenesis as well as the male ducts and accessory glands. ABP is regulated by FSH, testosterone, and inhibin. Sertoli cells have extensive tight (occluding) junctions between them that form the blood-testis barrier. Sertoli cells communicate with adjacent cells through gap junctions and extend from outside the blood-testis barrier (basal portion) to luminal to the blood-testis barrier (apical portion). During spermatogenesis, derivatives of spermatocytes cross from the basal to the adluminal compartment across the zonula occludens between adjacent Sertoli cells. Each Sertoli cell is, therefore, associated with multiple spermatogenic cells.

The testis is composed of seminiferous tubules containing a number of spermatogenic cells undergoing spermatogenesis and spermiogenesis. The cells labeled with the arrowheads are spermatogonia, the derivatives of the embryonic primordial germ cells. The spermatogonia are of three types (not distinguishable in the photomicrograph): type A dark cells (Ad), type A pale cells (Ap), and type B cells. Type Ad cells are precursors that divide to form Ad and Ad progeny or Ad and Ap progeny. The Ap cells give rise to B spermatogonia that are capable of differentiating into primary spermatocytes. These cells comprise the basal layer and undergo mitosis (spermatocytogenesis) to form primary spermatocytes, which have distinctive clumped or coarse chromatin (marked by arrows). Secondary spermatocytes are formed during the first meiotic division and exist for only a short period of time because there is no lag period before entry into the second meiotic division that results in the formation of spermatids. The spermatids begin as round structures and elongate with the formation of the flagellum. This last part of seminiferous tubule function is the differentiation of sperm from spermatocytes (spermiogenesis) and is complete with the release of mature sperm into the lumen of the tubule.

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11.

Which of the following statements correctly describes the cells marked with asterisks?
- A.
  
  They divide during each wave of spermatogenic cell division
- B.
  
  They are found in a 1:1 relationship with spermatogonia, spermatocytes, and spermatids
- C.
  
  They undergo spermatocytogenesis to form spermatocytes
- D.
  
  They undergo meiosis and and produce the haploid number associated with the gametes
- E.
  
  They form tight junctions with each other to establish the blood-testis barrier
Correct Answer
E. They form tight junctions with each other to establish the blood-testis barrier

Explanation
The cell marked with a star is a Leydig cell (i.e., interstitial cell) and is regulated by luteinizing hormone (LH), also known as interstitial cell-stimulating hormone (ICSH), secreted by gonadotrophs in the anterior pituitary. Leydig cells are located between seminiferous tubules and are responsible for the production of testosterone. Sertoli cells function in a nutritive and supportive role somewhat analogous to the glial cells of the CNS. The Sertoli cells produce inhibin, which feeds back on the anterior pituitary and hypothalamus to regulate FSH release. Testosterone is modified by binding to androgen-binding protein (ABP), which is synthesized by the Sertoli cells. The testosterone is necessary for the maintenance of spermatogenesis as well as the male ducts and accessory glands. ABP is regulated by FSH, testosterone, and inhibin. Sertoli cells have extensive tight (occluding) junctions between them that form the blood-testis barrier. Sertoli cells communicate with adjacent cells through gap junctions and extend from outside the blood-testis barrier (basal portion) to luminal to the blood-testis barrier (apical portion). During spermatogenesis, derivatives of spermatocytes cross from the basal to the adluminal compartment across the zonula occludens between adjacent Sertoli cells. Each Sertoli cell is, therefore, associated with multiple spermatogenic cells.

The testis is composed of seminiferous tubules containing a number of spermatogenic cells undergoing spermatogenesis and spermiogenesis. The cells labeled with the arrowheads are spermatogonia, the derivatives of the embryonic primordial germ cells. The spermatogonia are of three types (not distinguishable in the photomicrograph): type A dark cells (Ad), type A pale cells (Ap), and type B cells. Type Ad cells are precursors that divide to form Ad and Ad progeny or Ad and Ap progeny. The Ap cells give rise to B spermatogonia that are capable of differentiating into primary spermatocytes. These cells comprise the basal layer and undergo mitosis (spermatocytogenesis) to form primary spermatocytes, which have distinctive clumped or coarse chromatin (marked by arrows). Secondary spermatocytes are formed during the first meiotic division and exist for only a short period of time because there is no lag period before entry into the second meiotic division that results in the formation of spermatids. The spermatids begin as round structures and elongate with the formation of the flagellum. This last part of seminiferous tubule function is the differentiation of sperm from spermatocytes (spermiogenesis) and is complete with the release of mature sperm into the lumen of the tubule.

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12.

A 53-year-old woman has a paralysis of the right side of her face that produces an expressionless and drooping appearance. She is unable to close her right eye, has difficulty chewing and drinking, perceives sounds as annoyingly intense in her right ear, and experiences some pain in her right external auditory meatus. Physical examination reveals loss of the blink reflex in the right eye on stimulation of either cornea and loss of taste from the anterior two-thirds of the tongue on the right. Lacrimation appears normal in the right eye, the jaw-jerk reflex is normal, and there appears to be no problem with balance. The inability to close the right eye is the result of involvement of which of the following?
- A.
  
  Zygomatic branch of the facial nerve
- B.
  
  Buccal branch of the trigeminal nerve
- C.
  
  Levator palpebrae superioris muscle
- D.
  
  Superior tarsal muscle (of Müller)
- E.
  
  Orbital portion of the orbicularis oculi muscle
Correct Answer
A. Zygomatic branch of the facial nerve

Explanation
The palpebral portion of the orbicularis oculi muscle (innervated by the zygomatic branch of the facial nerve) produces the blink, whereas the orbital portion is involved in "scrunching" the eye shut. The buccal branch of the facial nerve innervates muscles of facial expression (including the buccinator muscle) between the eye and the mouth, whereas the buccal branch of the trigeminal nerve is sensory. The levator palpebrae superioris muscle, which elevates the upper eyelid, is innervated by the oculomotor nerve, whereas the involuntary superior tarsal muscle is supplied by sympathetic nerves.

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13.

A 53-year-old woman has a paralysis of the right side of her face that produces an expressionless and drooping appearance. She is unable to close her right eye, has difficulty chewing and drinking, perceives sounds as annoyingly intense in her right ear, and experiences some pain in her right external auditory meatus. Physical examination reveals loss of the blink reflex in the right eye on stimulation of either cornea and loss of taste from the anterior two-thirds of the tongue on the right. Lacrimation appears normal in the right eye, the jaw-jerk reflex is normal, and there appears to be no problem with balance. Which of the following is the branch of the facial nerve that conveys secretomotor neurons involved in lacrimation?
- A.
  
  Chorda tympani
- B.
  
  Deep petrosal nerve
- C.
  
  Greater superficial petrosal nerve
- D.
  
  Lacrimal nerve
- E.
  
  Lesser superficial petrosal nerve
Correct Answer
C. Greater superficial petrosal nerve

Explanation
The greater superficial petrosal nerve leaves the facial nerve (CN VII) at the geniculate ganglion. It carries secretomotor neurons from the superior salivatory nucleus to the pterygopalatine ganglion and joins along the way with the sympathetic deep petrosal nerve to become the nerve of the pterygoid canal.

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14.

A 70-year-old woman is seen in Outpatient Neurology complaining of strange feelings and numbness in both lower extremities below the knees. She walked with a wide-based gait, slamming her right foot down heavily and dragging her left foot. Subsequent examination revealed diminished two-point discrimination, proprioception, and vibratory senses, especially below the knees. Pain and temperature sensations were intact. Motor examination revealed hyperactive knee and ankle-jerk reflexes with spastic weakness most obvious on the left. The patient tended to tilt to the left when standing with her eyes closed. The afferent fibers involved in this case ascend in the spinal cord in which of the following?
- A.
  
  Lateral spinothalamic tract
- B.
  
  Cuneate fasciculus
- C.
  
  Cuneocerebellar tract
- D.
  
  Anterior spinothalamic tract
- E.
  
  Fasciculus gracilis
Correct Answer
E. Fasciculus gracilis

Explanation
The fasciculus gracilis consists of afferent fibers carrying information concerning two-point discrimination, vibration, and joint/limb position from the lower extremities and inferior trunk. The cuneate fasciculus (fasciculus cuneatus) carries the same modalities from the superior trunk and upper extremities. Classically, light touch is the modality assigned to afferents in the anterior spinothalamic tract, whereas afferents of the lateral spinothalamic tract convey information regarding pain and temperature. Fibers in the cuneocerebellar tract convey proprioception from the upper extremity.

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15.

A 70-year-old woman is seen in Outpatient Neurology complaining of strange feelings and numbness in both lower extremities below the knees. She walked with a wide-based gait, slamming her right foot down heavily and dragging her left foot. Subsequent examination revealed diminished two-point discrimination, proprioception, and vibratory senses, especially below the knees. Pain and temperature sensations were intact. Motor examination revealed hyperactive knee and ankle-jerk reflexes with spastic weakness most obvious on the left. The patient tended to tilt to the left when standing with her eyes closed. Further studies revealed that the patient's symptoms were due to a chronic vitamin B₁₂ deficiency (pernicious anemia). This results in decreased activity of B₁₂-dependent enzymes, including methylmalonic CoA mutase, essential for maintenance of myelin sheaths. Demyelinization in which of the following motor pathways would produce the observed symptoms?
- A.
  
  Lateral corticospinal tract
- B.
  
  Vestibulospinal tract
- C.
  
  Lower motor neurons (ventral horn cells)
- D.
  
  Rubrospinal tract
- E.
  
  Tectospinal tract
Correct Answer
A. Lateral corticospinal tract

Explanation
Demyelinization would most profoundly affect the function of well-myelinated large neurons of the lateral corticospinal tract, as well as the lower motor neurons originating in the ventral horn of the spinal cord. However, because reflex pathways were intact and hyperactive, the disease process must be confined to the upper motor neurons of the corticospinal tract. The lateral corticospinal tract carries messages from the contralateral motor cortex to lower motor neurons in the ventral horn of the spinal cord. Loss of this pathway results in spastic, rather than flaccid, paralysis. The other tracts (vestibulo-, rubro-, and tecto-spinal) are composed of fine, sparsely myelinated neurons and would be less affected by the anemia.

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16.

A mammogram of a woman, age 48, reveals macrocalcification within the right breast, indicating the need for biopsy. The surgeon visually and manually examines the breast with negative results. The surgeon closely examines the nipple for indications of ductal carcinoma. At surgery for the biopsy, a locator needle is inserted into the region of macrocalcification and the position confirmed by mammography. The surgeon incised the skin and dissected a block of tissue about the needle. The pathology report indicated ductal carcinoma with microinvasion necessitating surgery. Both patient and surgeon agreed that a modified radical mastectomy offered the best prognosis in her case. At surgery for mastectomy, the surgeon carries the dissection along the major pathway of lymphatic drainage from the mammary gland. The major lymphatic channels parallel which of the following?
- A.
  
  Subcutaneous venous networks to the contralateral breast and abdominal wall
- B.
  
  Tributaries of the axillary vessels to the axillary nodes
- C.
  
  Tributaries of the intercostal vessels to the parasternal nodes
- D.
  
  Tributaries of the internal thoracic (mammary) vessels to the parasternal nodes
- E.
  
  Tributaries of the thoracoacromial vessels to the apical (subscapular) nodes
Correct Answer
B. Tributaries of the axillary vessels to the axillary nodes

Explanation
The lymphatic drainage of the mammary gland, which follows the path of its blood supply, generally parallels the tributaries of the axillary, internal thoracic (mammary), thoracoacromial, and intercostal vessels. Because about 75% of the breast lies lateral to the nipple, the more significant lateral and inferior portions of the breast drain toward the axillary nodes. The smaller medial portion drains to the parasternal lymphatic chain paralleling the internal thoracic vessels, whereas the very small superior portion drains toward the nodes associated with the thoracoacromial trunk and the supraclavicular nodes.

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17.

A mammogram of a woman, age 48, reveals macrocalcification within the right breast, indicating the need for biopsy. The surgeon visually and manually examines the breast with negative results. The surgeon closely examines the nipple for indications of ductal carcinoma. At surgery for the biopsy, a locator needle is inserted into the region of macrocalcification and the position confirmed by mammography. The surgeon incised the skin and dissected a block of tissue about the needle. The pathology report indicated ductal carcinoma with microinvasion necessitating surgery. Both patient and surgeon agreed that a modified radical mastectomy offered the best prognosis in her case. At surgery for mastectomy, the surgeon carries the dissection along the major pathway of lymphatic drainage from the mammary gland. The surgery appears to have been successful. However, the patient is found to have winging of the scapula when the flexed arm is pressed against a fixed object. This indicates injury to which of the following nerves?
- A.
  
  Axillary
- B.
  
  Long thoracic
- C.
  
  Lower subscapular
- D.
  
  Supraclavicular
- E.
  
  Thoracodorsal
Correct Answer
B. Long thoracic

Explanation
The serratus anterior muscle (protractor and stabilizer of the scapula) is innervated by the long thoracic nerve (of Bell), which arises from roots C5 to C7 of the brachial plexus. During modified radical mastectomy, this nerve is usually spared to maintain shoulder function. However, its location places it in jeopardy during the lymphatic resection. The suprascapular nerves are sensory branches of the cervical plexus. The axillary nerve, deep in the brachial portion of the axilla, innervates the deltoid muscle. The thoracodorsal nerve, which arises from the posterior cord of the brachial plexus, innervates the latissimus dorsi. The lower subscapular nerve innervates the teres major muscle and a portion of the subscapularis muscle.

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18.

A firefighter, age 34 and a nonsmoker, complains of bouts of dizziness at times of intense exertion. His history reveals having been exposed to intense smoke six months ago when his breathing apparatus malfunctioned during a job. He is scheduled for a pulmonary function test. Regarding the "pump handle" movement during respiration, which of the following statements is correct?
- A.
  
  There is a decrease in the anterior-posterior diameter of the chest
- B.
  
  No movement occurs at the costovertebral joints
- C.
  
  There is an increase in the superior-inferior diameter of the chest
- D.
  
  Movement occurs at the sternomanubrial joint
- E.
  
  The primary change in dimension of the chest occurs in the transverse diameter
Correct Answer
D. Movement occurs at the sternomanubrial joint

Explanation
Contraction of the intercostal muscles causes rotation of the costovertebral joints and elevation of the sternal ends of the upper (2–6) ribs. Along with slight movement of the sternomanubrial joint, particularly in the young, this "pump-handle movement" increases the anteroposterior (AP) diameter of the chest. The transverse diameter of the thoracic cavity increases when contraction of the intercostal muscles also elevates the midportion of the ribs (bucket-handle movement). Contraction of the diaphragm increases the vertical diameter of the thoracic cavity.

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19.

A firefighter, age 34 and a nonsmoker, complains of bouts of dizziness at times of intense exertion. His history reveals having been exposed to intense smoke six months ago when his breathing apparatus malfunctioned during a job. He is scheduled for a pulmonary function test. When the patient was asked to exhale forcibly and maximally, the volume of expiration was constant but the rate of flow was diminished, indicating airway constriction likely due to bronchospasm. The smooth muscle of the bronchial airways is innervated by which of the following nerves?
- A.
  
  Intercostal nerves
- B.
  
  Phrenic nerves
- C.
  
  Thoracic splanchnic nerves
- D.
  
  Vagus nerve
Correct Answer
D. Vagus nerve

Explanation
Innervation of the bronchial smooth muscle is mediated by parasympathetic neurons carried by the vagus nerve. These nerves also stimulate secretion from the bronchial glands. Excessive vagal activity may initiate bronchospasm or the asthmatic syndrome.

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20.

A 36-year-old male office worker comes to the clinic complaining of general weakness and shortness of breath. He also relates a rapid, throbbing pulse after climbing a flight of stairs. Which of the following correctly pertains to normal mitral valve function?
- A.
  
  The papillary muscles are rudimentary and have no major function
- B.
  
  It prevents regurgitation of blood during ventricular relaxation
- C.
  
  The chordae tendineae and papillary muscles prevent eversion of the valve cusps
- D.
  
  The papillary muscles contract to close the valve
Correct Answer
C. The chordae tendineae and papillary muscles prevent eversion of the valve cusps

Explanation
During the cardiac cycle, differential pressures between the atria and ventricles open and close the atrioventricular valves. The papillary muscles attach the chordae tendineae to the heart wall and provide an important dynamic mechanism to ensure the competence of the valves. During the ejection phase of ventricular systole, shortening of the papillary muscle compensates for the decrease in the ventricular chamber size and thereby, prevents eversion of the atrioventricular valve leaflets, thereby preventing regurgitation during ventricular systole.

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21.

A 64-year-old man is brought into the emergency room after experiencing more than 3 h of increasing chest pain that was unrelieved by rest, antacids, or nitroglycerin. He complains of nausea without vomiting. Further questioning reveals a two-year history of exertional angina pectoris (pressing chest pain that often radiated along the inner aspect of the left arm when the patient climbed one flight of stairs). Propranolol, which reduces the response of the heart to stress, and nitroglycerin, which dilates systemic veins as well as coronary arteries, had been prescribed previously. On physical examination he is found to be acyanotic (normal blood oxygenation), tachypneic (rapid breathing), tachycardiac (rapid pulse rate) with a regular rhythm, and diaphoretic (sweating). This patient's tachycardia probably is mediated by reflex arcs associated with decreased cardiac output and possibly reduced blood pressure. The visceral efferent (motor) pathway of this cardiac response is mediated by which of the following?
- A.
  
  Carotid branches of the glossopharyngeal nerves
- B.
  
  Greater splanchnic nerves
- C.
  
  Phrenic nerves
- D.
  
  Sympathetic cervical and thoracic cardiac fibers
- E.
  
  Vagus and recurrent laryngeal nerves
Correct Answer
D. Sympathetic cervical and thoracic cardiac fibers

Explanation
The afferent limb of the cardiac reflex is mediated by the carotid branch of the glossopharyngeal nerve (CN IX) from the aortic body and sinus as well as by the vagus nerve (CN X) from the aortic body. The efferent limb, which is carried by the sympathetic division of the autonomic nervous system, mediates increases in heart rate and strength of heart beat through release of norepinephrine at the postganglionic effector site. The sympathetic cardiac accelerator fibers, affecting primarily the ventricles, are derived from the superior, middle, and inferior cervical ganglia (cervical cardiac nerves) as well as from the upper four thoracic ganglia (thoracic cardiac nerves), whence they converge on the cardiac plexus before reaching the heart. Parasympathetic fibers derived from CN X and its recurrent laryngeal branch decrease heart rate and stroke volume through release of acetylcholine, principally in the vicinity of the sinuatrial node.

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22.

A 64-year-old man is brought into the emergency room after experiencing more than 3 h of increasing chest pain that was unrelieved by rest, antacids, or nitroglycerin. He complains of nausea without vomiting. Further questioning reveals a two-year history of exertional angina pectoris (pressing chest pain that often radiated along the inner aspect of the left arm when the patient climbed one flight of stairs). Propranolol, which reduces the response of the heart to stress, and nitroglycerin, which dilates systemic veins as well as coronary arteries, had been prescribed previously. On physical examination he is found to be acyanotic (normal blood oxygenation), tachypneic (rapid breathing), tachycardiac (rapid pulse rate) with a regular rhythm, and diaphoretic (sweating). In angina pectoris, the pain radiating down the left arm is mediated by increased activity in afferent (sensory) fibers contained in which of the following?
- A.
  
  Carotid branch of the glossopharyngeal nerves
- B.
  
  Greater splanchnic nerves
- C.
  
  Phrenic nerves
- D.
  
  Thoracic splanchnic nerves
- E.
  
  Vagus nerve and recurrent laryngeal nerves
Correct Answer
D. Thoracic splanchnic nerves

Explanation
Afferent innervation from the heart and coronary arteries travels to the cardiac plexus along the sympathetic pathways. Once the afferent fibers pass through the cardiac plexus, they run along the cervical and thoracic cardiac nerves to the cervical and upper four thoracic sympathetic ganglia. Having traversed these ganglia, the fibers gain access (via the white rami communicantes) to the upper four thoracic spinal nerves and the corresponding levels of the spinal cord. The visceral afferent fibers associated with the vagus nerve are associated with reflexes and do not carry nociceptive information. The greater, lesser, and least splanchnic nerves convey visceral afferents from the abdominal region.

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23.

A 64-year-old man is brought into the emergency room after experiencing more than 3 h of increasing chest pain that was unrelieved by rest, antacids, or nitroglycerin. He complains of nausea without vomiting. Further questioning reveals a two-year history of exertional angina pectoris (pressing chest pain that often radiated along the inner aspect of the left arm when the patient climbed one flight of stairs). Propranolol, which reduces the response of the heart to stress, and nitroglycerin, which dilates systemic veins as well as coronary arteries, had been prescribed previously. On physical examination he is found to be acyanotic (normal blood oxygenation), tachypneic (rapid breathing), tachycardiac (rapid pulse rate) with a regular rhythm, and diaphoretic (sweating). The patient is admitted to a coronary care unit for tests and observation. An electrocardiogram reveals a pattern consistent with a small ventricular posteroseptal infarct from ischemic necrosis that resulted from inadequate blood supply. In the diagram of a normal heart shown below, the coronary artery most likely to be involved in a posteroseptal infarct (as in this patient) is indicated by which letter?
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
Correct Answer
D. D

Explanation
The artery labeled D in the diagram accompanying the question represents the posterior interventricular (descending) artery, which supplies blood to the posterior portions of the interventricular septum as well as to the posterior wall of the right ventricle. This artery usually is a branch of the right coronary artery, and the diagnosis of this patient's disorder is consistent with the results of the ECG, which indicates a posterior septal infarct. The anterior interventricular artery (C) arises from the left coronary artery (A) and supplies the anterior portion of the interventricular septum and the anterior walls of both ventricles. The posterior interventricular artery (D) usually anastomoses with the anterior interventricular artery (C) near the apex of the heart. The circumflex artery (B) circles toward the back of the heart in the coronary sulcus and may occasionally give rise to the posterior interventricular artery (D). The right marginal artery (E) is a branch of the right coronary artery.

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24.

A 64-year-old man is brought into the emergency room after experiencing more than 3 h of increasing chest pain that was unrelieved by rest, antacids, or nitroglycerin. He complains of nausea without vomiting. Further questioning reveals a two-year history of exertional angina pectoris (pressing chest pain that often radiated along the inner aspect of the left arm when the patient climbed one flight of stairs). Propranolol, which reduces the response of the heart to stress, and nitroglycerin, which dilates systemic veins as well as coronary arteries, had been prescribed previously. On physical examination he is found to be acyanotic (normal blood oxygenation), tachypneic (rapid breathing), tachycardiac (rapid pulse rate) with a regular rhythm, and diaphoretic (sweating). To improve the blood flow to the interventricular septum, a coronary bypass procedure is elected. During surgery the anterior interventricular artery is located and prepared to receive a graft. Which of the following is the vessel lying adjacent to the anterior interventricular artery?
- A.
  
  Anterior cardiac vein
- B.
  
  Coronary sinus
- C.
  
  Great cardiac vein
- D.
  
  Middle cardiac vein
- E.
  
  Small cardiac vein
Correct Answer
C. Great cardiac vein

Explanation
The great cardiac vein accompanies the anterior interventricular (descending) artery. The anterior cardiac veins pass across the right coronary sulcus to drain directly into the right atrium. The middle cardiac vein lies in the posterior interventricular sulcus with the posterior descending artery. The small cardiac vein accompanies the right marginal vein and the right coronary artery. The coronary sinus, accompanying the circumflex artery in the left coronary sulcus, receives the great, middle, and small cardiac veins before draining into the right atrium.

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25.

A 64-year-old man is brought into the emergency room after experiencing more than 3 h of increasing chest pain that was unrelieved by rest, antacids, or nitroglycerin. He complains of nausea without vomiting. Further questioning reveals a two-year history of exertional angina pectoris (pressing chest pain that often radiated along the inner aspect of the left arm when the patient climbed one flight of stairs). Propranolol, which reduces the response of the heart to stress, and nitroglycerin, which dilates systemic veins as well as coronary arteries, had been prescribed previously. On physical examination he is found to be acyanotic (normal blood oxygenation), tachypneic (rapid breathing), tachycardiac (rapid pulse rate) with a regular rhythm, and diaphoretic (sweating). A section of superficial vein removed from the lower portion of the patient's leg is grafted from the aorta to the coronary artery just distal to the site of occlusion. In coronary bypass surgery, which of the following statements is true?
- A.
  
  The proximal end of the vein is anastomosed to the aorta
- B.
  
  The distal end of the vein is anastomosed to the aorta
- C.
  
  The orientation is unimportant because aortic pressure is always higher than venous pressure
- D.
  
  The orientation is unimportant because the vein is being used as an artery
- E.
  
  The orientation would be important only if a coronary vein were being bypassed
Correct Answer
B. The distal end of the vein is anastomosed to the aorta

Explanation
In a coronary bypass procedure, the distal end of the vein graft is anastomosed to the aorta so that the presence of a valve or valve leaflets in the graft will not obstruct the flow of coronary blood. In recent years, the reversed saphenous vein graft from the calf has been the choice for this procedure. This vein is closer in size to the coronary arteries than one taken from the thigh

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26.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). Diffuse pain referred to the epigastric region and radiating circumferentially around the chest is the result of afferent fibers that travel via which of the following nerves?
- A.
  
  Greater splanchnic
- B.
  
  Intercostal
- C.
  
  Phrenic
- D.
  
  Vagus
Correct Answer
A. Greater splanchnic

Explanation
Visceral afferent pain fibers from the gallbladder travel through the celiac plexus, thence along the greater splanchnic nerves to levels T5–T9 of the spinal cord. Thus, pain originating from the gallbladder will be referred to (appear as if coming from) the dermatomes served by T5–T9, which include a band from the infrascapular region to the epigastrium.

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27.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). The patient receives a general anesthetic in preparation for a cholecystectomy. A right subcostal incision is made, which begins near the xiphoid process, runs along and immediately beneath the costal margin to the anterior axillary line, and transects the rectus abdominis muscle and rectus sheath. At the level of the transpyloric plane, the anterior wall of the sheath of the rectus abdominis muscle receives contributions from which of the following?
- A.
  
  Aponeuroses of the internal and external oblique muscles
- B.
  
  Aponeuroses of the transversus abdominis and internal oblique muscles
- C.
  
  Aponeuroses of the transversus abdominis and internal and external oblique muscles
- D.
  
  Transversalis fascia
- E.
  
  Transversalis fascia and aponeurosis of the transversus abdominis muscle
Correct Answer
A. Aponeuroses of the internal and external oblique muscles

Explanation
The rectus sheath is formed by the aponeuroses of the abdominal wall musculature. Between the costal margin and the umbilicus, the aponeurosis of the internal oblique muscle splits; one portion passes anterior and the other posterior to the rectus abdominis muscle. The aponeurosis of the external oblique muscle fuses with the anterior leaflet of the aponeurosis of the internal oblique muscle to form the anterior wall of the rectus sheath. The aponeurosis of the transversus abdominis muscle fuses with the posterior leaflet of the aponeurosis of the internal oblique muscle to form the posterior wall of the rectus sheath. Approximately midway between the umbilicus and symphysis pubis, the aponeuroses of the internal oblique and transversus abdominis muscles pass anterior to the rectus abdominis muscle to contribute to the anterior leaf of the rectus sheath. This abrupt transition results in a free edge to the posterior rectus sheath, known as the arcuate line (of Douglas). Between this line and the pubis, only the transversalis fascia separates the rectus abdominis muscle from the peritoneum. It is here, where the inferior epigastric artery gains access to the rectus sheath, that ventral lateral (spigelian) herniation may occur.

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28.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). Exploration of the peritoneal cavity disclosed a distended gallbladder. Where is the gallbladder located?
- A.
  
  Between the left and caudate lobes of the liver
- B.
  
  Between the right and quadrate lobes of the liver
- C.
  
  In the falciform ligament
- D.
  
  In the lesser omentum
- E.
  
  In the right anterior leaf of the coronary ligament
Correct Answer
B. Between the right and quadrate lobes of the liver

Explanation
The gallbladder lies on the inferior surface of the liver between the right and quadrate lobes. The caudate lobe lies posteriorly between the right and left lobes. The falciform ligament, a portion of the lesser omentum, attaches to the liver at the incisura between the quadrate and left lobes as well as along the fissure for the round ligament. Toward the superior surface of the liver, the falciform ligament splits to form the left and right coronary ligaments, which define the bare area of the liver. The coronary ligaments come together again to form the gastrohepatic ligament of the lesser omentum.

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29.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). The lesser omentum is incised close to its free edge, and the biliary tree is identified and freed by blunt dissection. The liquid contents of the gallbladder are aspirated with a syringe, the fundus incised, and the stones removed. The entire duct system is carefully probed for stones, one of which is found to be obstructing a duct. In view of the observation that the patient is not jaundiced, which of the following is the most probable location of the obstruction?
- A.
  
  The bile duct
- B.
  
  The common hepatic duct
- C.
  
  The cystic duct
- D.
  
  Within the duodenal papilla proximal to the juncture with the pancreatic duct
- E.
  
  Within the duodenal papilla distal to the juncture with the pancreatic duct
Correct Answer
C. The cystic duct

Explanation
Obstruction of any portion of the biliary tree will produce symptoms of gallbladder attack. If the common hepatic duct or bile duct is occluded by stone or tumor, biliary stasis with accompanying jaundice occurs. In addition, blockage of the duodenal papilla (of Vater), distal to the juncture of the bile duct with the pancreatic duct, can lead to complicating pancreatitis. If only the cystic duct is obstructed, jaundice will not occur because bile may flow freely from the liver to the duodenum. Bile duct obstruction also may arise as a result of pressure exerted on the duct by an external mass, such as a tumor in the head of the pancreas.

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30.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). The biliary duct system is carefully dissected. The cystic artery and cystic duct both are identified, ligated, and divided, the duct at a point about an eighth of an inch from its juncture with the common hepatic duct. The gallbladder is then freed from the inferior surface of the liver by blunt dissection and removed. However, the operative field suddenly fills with arterial blood. To locate and ligate the bleeder, hemorrhage should be controlled by which of the following procedures?
- A.
  
  Ligating the common hepatic artery
- B.
  
  Ligating the proper hepatic artery distal to the origin of the right gastric and gastroduodenal arteries
- C.
  
  Ligating the left hepatic artery, especially if there are additional (aberrant) left hepatic arteries present
- D.
  
  Ligating the hepatic portal vein
- E.
  
  Temporarily compressing the hepatic pedicle
Correct Answer
E. Temporarily compressing the hepatic pedicle

Explanation
Compressing the hepatic pedicle and its contained vascular structures between the forefinger placed in the omental foramen (of Winslow) and the thumb placed anteriorly is a convenient way to stem extrahepatic hemorrhage until the source of bleeding can be located and ligated. The blood supply to the liver is variable; several potential anastomotic loops exist between branches of the extrahepatic arterial system. Thus, ligation of the common hepatic artery proximal to the gastroduodenal artery will enable arterial blood to reach the liver from branches of the splenic artery (via anastomotic left and right gastroepiploic arteries) and the superior mesenteric artery (via the anastomotic inferior and superior pancreaticoduodenal arteries). Ligation of the proper hepatic artery proximal to the origin of the right gastric artery will enable arterial blood to reach the liver from branches of the celiac artery (via anastomotic left and right gastric arteries). However, ligation distal to the juncture of the right gastric artery will terminate most of, if not all, the blood supply to the liver and incur a danger of ischemia, if not necrosis, of hepatic tissue. Because accessory or aberrant hepatic arteries usually are not sources of collateral blood supply to the liver, they cannot be relied on to provide intrahepatic anastomotic connections.

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31.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). It is ascertained that an accessory right hepatic artery inadvertently had been torn. There is no choice but to ligate the accessory artery. Which of the following will be the most likely effect of this ligation?
- A.
  
  Ischemic necrosis of the quadrate lobe of the liver
- B.
  
  Ischemic necrosis of a discrete portion of the right lobe of the liver
- C.
  
  No necrosis in any lobe because of the integrity of the hepatic portal vein
- D.
  
  No necrosis in any lobe because of extrahepatic collateral blood supply
- E.
  
  No necrosis in any lobe because of intrahepatic collateral blood supply
Correct Answer
B. Ischemic necrosis of a discrete portion of the right lobe of the liver

Explanation
Because few intrahepatic arterial anastomoses exist, ligation of a left or right hepatic artery or of an aberrant (accessory) hepatic artery will result in ischemic necrosis of the region of the liver supplied by that vessel. The left hepatic artery supplies the left lobe and the quadrate lobe, as well as half the caudate lobe. The right hepatic artery supplies the right lobe and the other half of the caudate lobe; it also usually supplies the gallbladder through the cystic artery. No major extrahepatic anastomotic connections distal to the right gastric artery exist, and the hepatic portal vein has far too low a partial pressure of oxygen to supply the metabolic requirements of liver parenchyma.

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32.

A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). The subcostal incision, which parallels the costal margin anteriorly, is closed in layers. The patient is allowed up on her first postoperative day; on the third day the drain (which shows no bile leakage) is withdrawn, and on the tenth day the patient is discharged. As a result of the location and direction of the incision, one might expect healing to result in which of the following?
- A.
  
  Loss of blood supply and necrosis of a portion of the rectus abdominis muscle
- B.
  
  Significant paralysis of a portion of the rectus abdominis muscle
- C.
  
  Minimal scarring
- D.
  
  Negligible possibility of subsequent abdominal herniation
Correct Answer
B. Significant paralysis of a portion of the rectus abdominis muscle

Explanation
The rectus abdominis muscle receives an abundant collateral blood supply. The nerve supply to the rectus abdominis muscle is derived from abdominal extensions of the lower seven intercostal nerves and from the iliohypogastric nerve. These nerves run between the internal oblique and transversus abdominis muscles to reach the lateral border of the rectus sheath, which they pierce to reach the rectus abdominis muscle. Consequently, a subcostal incision from the xiphisternal angle to the anterior axillary line is apt to sever one or two of these nerves and thus paralyze a significant portion of the ipsilateral rectus abdominis muscle. An affected patient may be predisposed to subsequent abdominal herniation. Although the direction of an incision along the costal margin is perforce perpendicular to the dermal cleavage lines (of Langer) and thus may produce discomfort and healing with significant scarring, such an incision is justified by the required operative exposure that it provides.

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33.

A 37-year-old man with a history of alcohol abuse was seen in the emergency room complaining of stomach cramps in the region of the umbilicus. He reported several recent incidents of vomiting that contained no noticeable blood, although he had in the past vomited bright red blood. He insisted that he had been on the wagon for the past several months. Physical examination revealed a mass about the umbilicus with indications of periumbilical peritoneal inflammation. His white blood cell count was high and he had a temperature of 39.4°C (103°F). He was admitted to the surgical service for emergency reduction of an umbilical hernia with suspected strangulation. The crampy abdominal pain referred to the umbilical region and knowledge of peritoneal structure would lead the examining physician to suspect that which of the following was most likely the strangulated section of gut?
- A.
  
  Ascending colon
- B.
  
  Descending colon
- C.
  
  Small intestine
- D.
  
  Sigmoid colon
- E.
  
  Stomach
Correct Answer
C. Small intestine

Explanation
The umbilical region is innervated by the tenth intercostal nerve. The afferent nerve fibers from the jejunum and ileum as well as from the ascending colon and transverse colon travel through the superior mesenteric plexus and along the lesser splanchnic nerve to spinal nerves T10 and T11. Thus, pain originating from these portions of the gastrointestinal tract will refer pain to the umbilical region. The ascending colon and descending colon, which are secondarily retroperitoneal, are unlikely to be involved in the umbilical herniation. The mobile transverse colon could be involved, but the referred pain would tend to be subumbilical, not periumbilical.

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34.

A 37-year-old man with a history of alcohol abuse was seen in the emergency room complaining of stomach cramps in the region of the umbilicus. He reported several recent incidents of vomiting that contained no noticeable blood, although he had in the past vomited bright red blood. He insisted that he had been on the wagon for the past several months. Physical examination revealed a mass about the umbilicus with indications of periumbilical peritoneal inflammation. His white blood cell count was high and he had a temperature of 39.4°C (103°F). He was admitted to the surgical service for emergency reduction of an umbilical hernia with suspected strangulation. After the herniated segment of gut was placed into the abdominal cavity, its color changed from purple to pink, which indicated that the vasculature was functional. The small intestine normally receives significant collateral circulation from which of the following arteries?
- A.
  
  Descending branch of the left colic artery
- B.
  
  Renal arteries
- C.
  
  Splenic artery
- D.
  
  Superior pancreaticoduodenal artery
Correct Answer
D. Superior pancreaticoduodenal artery

Explanation
The jejunum and ileum receive their principal blood supply from the superior mesenteric artery. A strong collateral circulation is derived from the superior pancreatic artery, a branch of the pancreaticoduodenal artery that arises from the hepatic branch of the celiac artery. The superior pancreatic artery anastomoses with the inferior pancreatic artery, the first branch of the superior mesenteric artery. The collateral circulation is weak between the right colic artery and the ileal branches. There are no possibilities for superior mesenteric anastomoses from the splenic, the descending branch of the left colic, or renal arteries.

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35.

A 37-year-old man with a history of alcohol abuse was seen in the emergency room complaining of stomach cramps in the region of the umbilicus. He reported several recent incidents of vomiting that contained no noticeable blood, although he had in the past vomited bright red blood. He insisted that he had been on the wagon for the past several months. Physical examination revealed a mass about the umbilicus with indications of periumbilical peritoneal inflammation. His white blood cell count was high and he had a temperature of 39.4°C (103°F). He was admitted to the surgical service for emergency reduction of an umbilical hernia with suspected strangulation. On manual exploration of the abdominal cavity, the liver was felt to be hard and nodular. This, in addition to the history of hematemesis, indicated that control of the portal hypertension was necessary. In a patient with cirrhosis of the liver, venous hypertension would be expected in which of the following veins?
- A.
  
  Hepatic vein
- B.
  
  Renal vein
- C.
  
  Short gastric veins
- D.
  
  Suprarenal vein
Correct Answer
C. Short gastric veins

Explanation
The short gastric veins are branches of the splenic vein and, therefore, would experience the portal pressure. The short gastric veins also anastomose with the esophageal veins and produce esophageal varices. The hepatic vein, between the liver and inferior vena cava, drains the liver and is not part of the portal system. There are no communications between the portal system and the renal or suprarenal veins.

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36.

A middle-aged woman describes flushing, severe headaches, and a feeling that her heart is "going to explode" when she gets excited. At the beginning of a physical examination her blood pressure (130/85) is not significantly above normal. However, on palpation of her upper left quadrant, the examining physician notices the onset of sympathetic signs. Her blood pressure (200/135) is abnormally high. A subsequent CT scan confirms the suspected tumor of the left adrenal gland. The patient is scheduled for surgery. The symptoms that the patient correlated with the onset of excitement were due to nervous stimulation of the adrenal glands. The adrenal medulla receives its innervation from which of the following nerves?
- A.
  
  Preganglionic sympathetic nerves
- B.
  
  Postsynaptic sympathetic nerves
- C.
  
  Preganglionic parasympathetic nerves
- D.
  
  Postganglionic parasympathetic nerves
- E.
  
  Somatic nerves
Correct Answer
A. Preganglionic sympathetic nerves

Explanation
The adrenal medulla is innervated from thoracic levels of the spinal cord mediated by preganglionic sympathetic nerve fibers traveling in the lesser and least splanchnic nerves, with some contribution from the greater splanchnic and lumbar splanchnic nerves. Because both the adrenal medulla and postganglionic sympathetic neurons are adrenergic and derived from neural crest tissue, the homology of the chromaffin cells and postganglionic sympathetic neurons is apparent. There appears to be no parasympathetic innervation to the adrenal medulla and no innervation whatever to the adrenal cortex.

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37.

A middle-aged woman describes flushing, severe headaches, and a feeling that her heart is "going to explode" when she gets excited. At the beginning of a physical examination her blood pressure (130/85) is not significantly above normal. However, on palpation of her upper left quadrant, the examining physician notices the onset of sympathetic signs. Her blood pressure (200/135) is abnormally high. A subsequent CT scan confirms the suspected tumor of the left adrenal gland. The patient is scheduled for surgery. The adrenal gland is located, and the venous drainage is ligated to prevent life-threatening quantities of adrenalin from entering the bloodstream on manipulation of the gland. Normally, the left adrenal venous drainage is into which of the following veins?
- A.
  
  Inferior vena cava
- B.
  
  Left azygos vein
- C.
  
  Left inferior phrenic vein
- D.
  
  Left renal vein
- E.
  
  Superior mesenteric vein
Correct Answer
D. Left renal vein

Explanation
The venous drainage from each adrenal gland tends to be through a single vein. The left adrenal gland usually drains into the left renal vein superior to the point where the gonadal vein enters the left renal vein. The left adrenal vein usually anastomoses with the hemiazygos vein and may provide an important route of collateral venous return. The right adrenal gland usually drains directly into the inferior vena cava.

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38.

While moving furniture, an 18-year-old man experiences excruciating pain in his right groin. A few hours later he also develops pain in the umbilical region with accompanying nausea. At this point he seeks medical attention. Examination reveals a bulge midway between the midline and the anterior superior iliac spine, but superior to the inguinal ligament. On coughing or straining, the bulge increases and the inguinal pain intensifies. The bulge courses medially and inferiorly into the upper portion of the scrotum and cannot be reduced with the finger pressure of the examiner. It is decided that a medical emergency exists, and the patient is scheduled for immediate surgery. Nausea and diffuse pain referred to the umbilical region in this patient most probably are due to which of the following?
- A.
  
  Compression of the genitofemoral nerve
- B.
  
  Compression of the ilioinguinal nerve
- C.
  
  Dilation of the inguinal canal
- D.
  
  Incarceration of a loop of small bowel
- E.
  
  Ischemic necrosis of the cremaster muscle
Correct Answer
D. Incarceration of a loop of small bowel

Explanation
The diffuse central abdominal pain in the patient presented is probably referred pain from the loop of small bowel incarcerated within the herniated peritoneal sac. Compression of the bowel results in compromise of the blood supply and subsequent ischemic necrosis. The visceral afferent fibers from the distal small bowel travel along the blood vessels to reach the superior mesenteric plexus and lesser splanchnic nerves, which they follow to the T10–T11 levels of the spinal cord. The pain, therefore, is referred to (appears as if originating from) the T10–T11 dermatomes, which supply the umbilical region. Because the gut develops as a midline structure, visceral pain tends to be centrally located regardless of the adult location of any particular region of the gut. As a result of dilation of the inguinal canal by the hernial sac, however, the patient also experiences localized somatic pain mediated by the iliohypogastric, ilioinguinal, and genitofemoral nerves.

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39.

While moving furniture, an 18-year-old man experiences excruciating pain in his right groin. A few hours later he also develops pain in the umbilical region with accompanying nausea. At this point he seeks medical attention. Examination reveals a bulge midway between the midline and the anterior superior iliac spine, but superior to the inguinal ligament. On coughing or straining, the bulge increases and the inguinal pain intensifies. The bulge courses medially and inferiorly into the upper portion of the scrotum and cannot be reduced with the finger pressure of the examiner. It is decided that a medical emergency exists, and the patient is scheduled for immediate surgery. During surgery, one would expect to find which of the following arteries in the inguinal region?
- A.
  
  Aberrant obturator (if present)
- B.
  
  Deep circumflex iliac
- C.
  
  External iliac
- D.
  
  External pudendal
- E.
  
  Inferior epigastric
Correct Answer
B. Deep circumflex iliac

Explanation
The deep circumflex iliac artery, which arises from the internal iliac artery opposite the inferior epigastric artery, parallels the inguinal ligament as it courses toward the anterosuperior iliac spine. The external pudendal and superficial epigastric arteries are branches of the femoral artery that supply, respectively, the superficial pubic (hypogastric) region, the inguinal regions, and the anterior surfaces of the scrotum or labia majora. The inferior epigastric artery, a branch of the external iliac artery, courses superomedially beneath the aponeuroses of the abdominal wall to gain access to the rectus sheath by passing anterior to the arcuate line (of Douglas). An aberrant obturator artery (present in about 30% of the population) usually arises from the inferior epigastric artery and courses inferiorly deep to the pubic ramus to the obturator foramen.

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40.

While moving furniture, an 18-year-old man experiences excruciating pain in his right groin. A few hours later he also develops pain in the umbilical region with accompanying nausea. At this point he seeks medical attention. Examination reveals a bulge midway between the midline and the anterior superior iliac spine, but superior to the inguinal ligament. On coughing or straining, the bulge increases and the inguinal pain intensifies. The bulge courses medially and inferiorly into the upper portion of the scrotum and cannot be reduced with the finger pressure of the examiner. It is decided that a medical emergency exists, and the patient is scheduled for immediate surgery. The external oblique aponeurosis is incised and the superficial ring is opened. The inguinal canal is then opened by blunt dissection. Abdominal wall structures that usually contribute directly to the spermatic cord include which of the following?
- A.
  
  External oblique muscle
- B.
  
  Falx inguinalis
- C.
  
  Internal oblique muscle
- D.
  
  Rectus sheath
- E.
  
  Transversus abdominis muscle
Correct Answer
C. Internal oblique muscle

Explanation
Several abdominal structures are involved in the formation of the spermatic cord. The deep fascia contributes the external spermatic fascia. Although some references include the external oblique muscle or aponeurosis, no contribution is derived from that layer owing to a hiatus in the aponeurosis. The cremaster muscle, a contribution of the internal oblique muscle, joins the spermatic cord as the inguinal canal passes through that layer. The transversus abdominis muscle, which usually terminates as the falx inguinalis just superior to the deep ring, contributes to the cremaster muscle in less than 5% of all males. The transversalis fascia contributes the internal spermatic fascia.

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41.

While moving furniture, an 18-year-old man experiences excruciating pain in his right groin. A few hours later he also develops pain in the umbilical region with accompanying nausea. At this point he seeks medical attention. Examination reveals a bulge midway between the midline and the anterior superior iliac spine, but superior to the inguinal ligament. On coughing or straining, the bulge increases and the inguinal pain intensifies. The bulge courses medially and inferiorly into the upper portion of the scrotum and cannot be reduced with the finger pressure of the examiner. It is decided that a medical emergency exists, and the patient is scheduled for immediate surgery. At this point in the surgical procedure, it is noticed that a nerve has been inadvertently sectioned. This nerve exited through the superficial inguinal ring and was applied to the anterior aspect of the spermatic cord. Which of the following is the most likely result of this operative error?
- A.
  
  Inability to produce spermatozoa in the right testis
- B.
  
  Impotence
- C.
  
  Loss of the cremasteric reflex on the right side
- D.
  
  Loss of the dartos response to cold
- E.
  
  Loss of sensation over portions of the base of the penis and anterior scrotum
Correct Answer
E. Loss of sensation over portions of the base of the penis and anterior scrotum

Explanation
The ilioinguinal nerve exits the abdominal wall through the superficial inguinal ring, where it is applied to the anterior surface of the spermatic cord. Section of this nerve will result in paresthesia over the base of the penis and scrotum. The femoral branch of the genitofemoral nerve innervates the upper medial surface of the thigh, where it mediates the afferent limb of the cremasteric reflex. The efferent limb of this reflex is carried by the genital branch of the genitofemoral nerve, which lies within the cremaster layer. The dartos response, which is sympathetic, arises from the sacral sympathetic chain and reaches the pudendal nerve via gray rami communicantes.

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42.

A 24-year-old woman seeking assistance for apparent infertility has been unable to conceive despite repeated attempts in five years of marriage. She revealed that her husband had fathered a child in a prior marriage. Although her menstrual periods are fairly regular, they are accompanied by extreme lower back pain. The lower back pain during menstruation experienced by this woman probably is referred from the pelvic region. The pathways that convey this pain sensation to the central nervous system involve which of the following?
- A.
  
  Hypogastric nerve to L1–L2
- B.
  
  Lumbosacral trunk to L4–L5
- C.
  
  Pelvic splanchnic nerves to S2–S4
- D.
  
  Pudendal nerve to S2–S4
Correct Answer
A. Hypogastric nerve to L1–L2

Explanation
The visceral afferent fibers that mediate sensation from the fundus and body of the uterus, as well as from the oviducts, tend to travel along the sympathetic nerve pathways (via the hypogastric nerve and lumbar splanchnics) to reach the upper lumbar levels (L1–L2) of the spinal cord. Thus, uterine pain will be referred to (appear as if originating from) the upper lumbar dermatomes and produce apparent backache. The visceral afferent fibers that mediate sensation from the cervical neck of the uterus travel along the parasympathetic pathways (via the pelvic splanchnic nerves [nervi erigentes]) to the midsacral levels (S2–S4) of the spinal cord. In this instance, pain originating from the cervix will be referred to the midsacral dermatomes and produce pain that appears to arise from the perineum, gluteal region, and legs.

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43.

A 24-year-old woman seeking assistance for apparent infertility has been unable to conceive despite repeated attempts in five years of marriage. She revealed that her husband had fathered a child in a prior marriage. Although her menstrual periods are fairly regular, they are accompanied by extreme lower back pain. Which of the following would be found immediately inferior to the left cardinal (lateral cervical) ligament?
- A.
  
  Ovarian neurovascular bundle
- B.
  
  Uterine tube
- C.
  
  Round ligament of the uterus
- D.
  
  Ureter
- E.
  
  Uterine artery and vein
Correct Answer
D. Ureter

Explanation
The ureter, lying just medial to the internal iliac artery in the deep pelvis, passes from posterior to anterior immediately inferior to the lateral cervical ligament. This ligament contains the uterine artery and vein to which the ureters pass inferior approximately midway along their course between internal iliac artery and uterus. The ureter continues inferior to the anterior portion of the lateral cervical ligament (where it can sometimes be palpated through the walls of the vagina at the lateral fornices) to gain access to the base of the urinary bladder. The close association between uterine vessels and ureter is of major importance during surgical procedures in the female pelvis.

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44.

A 24-year-old woman seeking assistance for apparent infertility has been unable to conceive despite repeated attempts in five years of marriage. She revealed that her husband had fathered a child in a prior marriage. Although her menstrual periods are fairly regular, they are accompanied by extreme lower back pain. The patient is scheduled for a hysterosalpingogram, in which radi-opaque material is injected into the uterus and uterine tubes. Examination of subsequent radiographs discloses bilateral spillage of the contrast medium into the peritoneal cavity, an indication of which of the following?
- A.
  
  The uterine tubes are normal
- B.
  
  The mesonephric ducts failed to form properly
- C.
  
  The paramesonephric ducts failed to form properly
- D.
  
  There is a rectouterine fistula
- E.
  
  There is a vesicovaginal fistula
Correct Answer
A. The uterine tubes are normal

Explanation
The uterus is formed by fusion of the paired paramesonephric ducts. The uterine tubes are the unfused portions of these ducts. Patency of the uterine tubes may be ascertained by hysterosalpingography, wherein radiopaque material is injected into the uterine cavity and uterine tubes through a catheter inserted into the external cervical os. Radiographs delineate the cavity of the body of the uterus and the uterine tubes. Spillage of the contrast material through the abdominal ostia into the peritoneal cavity demonstrates normal patency of the uterine tubes. The abdominal ostia of the uterine tubes permit passage of infection, air, and spermatozoa into the female peritoneal cavity. The rare rectouterine fistula would result in the appearance of contrast media in the rectum. A vesicovaginal fistula between the vagina and urethra or bladder would not be evident on a hysterosalpingogram.

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45.

A 24-year-old woman seeking assistance for apparent infertility has been unable to conceive despite repeated attempts in five years of marriage. She revealed that her husband had fathered a child in a prior marriage. Although her menstrual periods are fairly regular, they are accompanied by extreme lower back pain. The most important measurement of the pelvic outlet, indicating the least dimension, is the transverse midplane diameter. It is measured between which of the following?
- A.
  
  Ischial spines
- B.
  
  Ischial tuberosities
- C.
  
  Lower margin of the pubic symphysis to the sacroiliac joint
- D.
  
  Sacral promontory to the inferior margin of the pubic symphysis
Correct Answer
A. Ischial spines

Explanation
The transverse midplane diameter is measured between the ischial spines. It can be approximated by the somewhat greater transverse diameter measured between the ischial tuberosities. The distance from the lower margin of the pubic symphysis to the sacroiliac joint defines the sagittal diameter, which is usually the greatest dimension and, therefore, unimportant.

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46.

A 45-year-old plumber presented in the clinic complaining of long-standing pain in the elbow. Subsequent examination revealed normal flexion/extension at both the elbow and the wrist but weakened abduction of the thumb and extension at the metacarpophalangeal joints of the fingers. These symptoms were found to be caused by entrapment of the posterior interosseus nerve. Which of the following muscles could be expected to demonstrate normal contraction?
- A.
  
  Extensor indices
- B.
  
  Extensor digitorum
- C.
  
  Extensor carpi radialis longus
- D.
  
  Abductor pollicis longus
- E.
  
  Extensor digit minimi
Correct Answer
C. Extensor carpi radialis longus

Explanation
All of the muscles listed above are innervated by the posterior interosseus branch of the radial nerve (the terminal part of the deep radial nerve). Extensor carpi radialis longus, however, is innervated by a muscular branch of the radial nerve proximal to the origin of the deep branch. Its function would, therefore, be preserved in entrapment of the posterior interosseus nerve.

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47.

A 45-year-old plumber presented in the clinic complaining of long-standing pain in the elbow. Subsequent examination revealed normal flexion/extension at both the elbow and the wrist but weakened abduction of the thumb and extension at the metacarpophalangeal joints of the fingers. These symptoms were found to be caused by entrapment of the posterior interosseus nerve. Which of the following muscles could itself cause entrapment of the posterior interosseus nerve?
- A.
  
  Extensor carpi ulnaris
- B.
  
  Extensor indices
- C.
  
  Anconeus
- D.
  
  Extensor digitorum
- E.
  
  Supinator
Correct Answer
E. Supinator

Explanation
Each of the muscles listed above is innervated by the deep branch of the radial nerve or its terminal portion, the posterior interosseus nerve. The deep radial nerve passes between the deep and superficial layers of the supinator muscle and lies on a bare area of the radius where it may be compressed by action of the supinator or damaged by a fracture of the radius.

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48.

A 67-year-old woman slipped on a scatter rug and fell with her right arm extended in an attempt to ease the impact of the fall. She experienced immediate severe pain in the region of the right collar bone and in the right wrist. Painful movement of the right arm was minimized by holding the arm close to the body and by supporting the elbow with the left hand. There is marked tenderness and some swelling in the region of the clavicle about one-third of the distance from the sternum. The examiner can feel the projecting edges of the clavicular fragments. The radiograph confirms the fracture and shows elevation of the proximal fragment with depression and subluxation (underriding) of the distal fragment. Traction by which of the following muscles causes subluxation (the distal fragment underrides the proximal fragment)?
- A.
  
  Deltoid muscle
- B.
  
  Pectoralis major muscle
- C.
  
  Pectoralis minor muscle
- D.
  
  Sternomastoid muscle
- E.
  
  Trapezius muscle
Correct Answer
B. Pectoralis major muscle

Explanation
The horizontal direction of the fibers of the clavicular head of the pectoralis major muscle draws the humerus medially and causes the distal fragment of the bone to sublux. The sternal head of this muscle also has the effect of pulling the arm medially, an effect that is normally offset by the strutlike action of the clavicle.

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49.

A 67-year-old woman slipped on a scatter rug and fell with her right arm extended in an attempt to ease the impact of the fall. She experienced immediate severe pain in the region of the right collar bone and in the right wrist. Painful movement of the right arm was minimized by holding the arm close to the body and by supporting the elbow with the left hand. Internal bleeding can be a complication if the subluxed bone fragment tears a vessel and punctures the pleura. Which of the following vascular structures is particularly vulnerable in a clavicular fracture?
- A.
  
  Axillary artery
- B.
  
  Brachiocephalic artery
- C.
  
  Lateral thoracic artery
- D.
  
  Subclavian artery
- E.
  
  Thoracoacromial trunk
Correct Answer
D. Subclavian artery

Explanation
Because large and important neurovascular structures pass between the clavicle and first rib, including the subclavian artery, clavicular fracture may produce life-threatening bleeding into the pleural cavity. The axillary artery is the continuation of the subclavian after it has cleared the first rib, so neither this vessel nor its thoracoacromial branch is likely to be threatened by clavicular fracture. There is no brachiocephalic artery on the left side, and on the right its terminal point is marked by its bifurcation into common carotid and subclavian arteries proximal to the fracture site.

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50.

A 67-year-old woman slipped on a scatter rug and fell with her right arm extended in an attempt to ease the impact of the fall. She experienced immediate severe pain in the region of the right collar bone and in the right wrist. Painful movement of the right arm was minimized by holding the arm close to the body and by supporting the elbow with the left hand. Marked swelling is noted about the palmar aspect of the wrist. Persistent flexion of the fingers and apparent shortening of the middle finger is seen. There is paresthesia (sensory dullness) over the palmar aspect of the thumb, index finger, middle finger, and a questionable portion of the ring finger, yet when the wrist is gently flexed, intense pain spreads over this area. Sensation over the palm seems normal. The partial flexion of the fingers in this case is best explained by which of the following?
- A.
  
  Compression of the radial artery
- B.
  
  Compression of the recurrent branch of the median nerve
- C.
  
  Impingement of the flexor tendons by a dislocated carpal bone
- D.
  
  Paralysis of the dorsal interossei muscles
- E.
  
  Paralysis of the flexor digitorum superficialis muscle
Correct Answer
C. Impingement of the flexor tendons by a dislocated carpal bone

Explanation
A fall on the extended hand will frequently dislocate the lunate bone anteriorly. This dislocated bone may then impinge on the tendons of the extrinsic digital flexor muscles and thereby prevent flexion of the fingers. Compression of the median nerve in the carpal tunnel cannot explain this observation because the prime flexors of the digits are the extrinsic flexors (flexors digitorum superficialis and profundus), which receive their innervation in the forearm, well proximal to the injury. The dorsal interossei, innervated by the ulnar nerve, are digital extensors. The recurrent branch of the median nerve innervates the thenar muscles.

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USMLE Step 1 Qs (3)

The process of unlocking the fully extended knee in preparation for flexion requires initial contraction of which of the following muscles?

The muscles of the anterior compartment of the leg are innervated primarily by which of the following nerves?

The tendon of which of the following muscles is involved when the tuberosity of the fifth metatarsal bone is avulsed in an inversion fracture?

In a presurgical patient, the great saphenous vein was cannulated in the vicinity of the ankle. During the procedure, the patient experienced severe pain that radiated along the medial border of the foot. Which of the following nerves was accidentally included in a ligature during this procedure?

Refer to the photomicrographs below in answering these questions. The low-magnification micrograph is on top and is from the same organ as the high-magnification micrograph located below it. In Addison's disease, which of the following would be a direct effect of the disease?

The activity of the cell labeled with the star is regulated by which of the following?

Which of the following statements correctly describes the cells marked with asterisks?

A 36-year-old male office worker comes to the clinic complaining of general weakness and shortness of breath. He also relates a rapid, throbbing pulse after climbing a flight of stairs. Which of the following correctly pertains to normal mitral valve function?