Block 7 Anatomy Perineum Xtrnal Genital Umich W Xpl

Explanation
The sacrospinal ligament connects the sacrum to the ischial spine. Together with the sacrotuberous ligament, it converts the greater and lesser sciatic notches into greater and lesser sciatic foramina. However, it is not near the perineum--it is more important as a landmark that creates the greater and lesser sciatic foramina which helps to organize the structures exiting the pelvis.
The bounderies of the perineum are as follows. Anterior: pubic symphysis; Anterolateral: ischiopubic rami; Lateral: ischial tuberosities; Posterolateral: sacrotuberous ligament; Posterior: tip of the coccyx. These boundaries create two triangles in the perineum: the urogenital triangle and the anal triangle. The urogenital triangle is the anterior subdivision, bounded by the pubic symphysis, ischiopubic rami, and the posterior margin of the perineal membrane, which corresponds to an imaginary line between the two ischial tuberosities. The anal triangle is the posterior division of the perineum. It starts off where the urogenital triangle ends: at the posterior margin of the perineal membrane. Then, it is bounded by the sacrotuberous ligament and the tip of the coccyx.
It's important to look at these triangles and orient yourself to them using the bones in your bone set--you'll realize that the perineum is not contained in one flat plane; instead, the triangles are at angles to each other.

Explanation
The perineal body is an irregular fibromuscular mass located at the center of the posterior border of the perineal membrane. It is the site where many muscles converge, including bulbospongiosus, external anal sphincter, and the superficial and deep transverse perineal muscles. This is found only in females; the male homolog for this structure is the central tendinous point.
Frenulum is a word that refers to a small fold, and there are two in the female perineum, so this isn't even specific enough to be a good answer. The frenulum of the clitoris is a structure lying deep to the clitoris, formed by the deep labia minora. This structure is not near the posterior border of the perineal membrane; it is clearly in the urogenital triangle. There is also a frenulum of the labia minora which is just anterior to the perineal body, also in the urogenital triangle. Although the frenulum of the labia minora is sort of superficial to the center of the posterior border of the perineal membrane, the question is asking for a structure that is closely associated with the perineal membrane. This means that structures of the external genitalia will be wrong answers. The posterior labial commissure is another structure of the external genitalia which is located over the posterior border of the perineal membrane, and it's also a wrong answer for the same reason. The anococcygeal ligament is a ligament that attaches the external anal sphincter to the coccyx. It is located in the anal triangle. The pubovesicular ligament attaches the bladder to the pubic bone. It is more associated with the pelvic viscera as opposed to the perineum.

Explanation
The deep artery supplies the corpus cavernosum of the penis/clitoris, which is the major erectile body. It is one of the two terminal branches of the internal pudendal artery, with the other one being the dorsal artery of the penis/clitoris. This artery supplies superficial structures. The artery of the bulb supplies blood to the bulb of the penis and the bulb of the vestibule. Although the bulbs are erectile tissue, the corpus cavernosum is the main erectile body. The posterior labial/scrotal artery supplies exactly what you would guess--the posterior labia or scrotum. It is a branch of the perineal artery. Finally, the superficial external pudendal artery supplies the skin and superficial fascia of the upper medial thigh, as well as the skin of the pubic region. It is a superficial branch of the femoral artery.

Explanation
The bulbs of the vestibule/bulb of the corpus spongiosum are pieces of erectile tissue that attach to the perineal membrane. They are covered by the bulbospongiosis muscle. The ischiopubic rami, pubic symphysis, and ischial tuberosities are bony structures important for defining the boundaries of the perineum. The crura of the corpora cavernosa attach to the ischiopubic rami and the perineal membrane.

Explanation
The ejaculatory duct is a duct which courses through the prostate gland and contains only semen. Remember, semen is the combination of sperm from the ductus deferens, seminal fluid from the seminal vesicle, and secretions of the prostate gland. The ejaculatory duct is formed by the union of the duct of the seminal vesicle and the ampulla of the ductus deferens, and it is the site where sperm and seminal fluid mix. The prostatic urethra is also contained in the prostate gland, and it carries semen, but it also carries urine out of the bladder. The membranous urethra is the continuation of the prostatic urethra outside of the prostate gland, and it carries both semen and urine as well. The seminal vesicle is a structure on the posterior surface of the bladder that produces seminal fluid. The ductus deferens is a passageway that carries sperm from the epididymis to the ejaculatory duct.

Explanation
Males and females have analogous erectile bodies. The three main erectile bodies in males are 2 corpus cavernosa and a corpus spongiosum. Females have 2 corpus cavernosa plus 2 vestibular bulbs which are analogs to the corpus spongiosum. So, females actually have more erectile bodies than males. Development differs, however, in many other ways. Remember: the gubernaculum pulls the testes to descend into the scrotum, but the ovaries stop their descent and remain in the pelvis. The urogenital folds fuse in males to create the raphe of the penis. However, they stay open in females to create the labial minora and perineal raphe. Finally, the phallus elongates in males but not in females.

Explanation
There are four portal-caval anastomoses in the body. First, between the superior rectal veins in the portal system and the middle and inferior rectal veins in the caval system. Second, between the esophageal veins that go to the left gastric vein (portal) and the esophageal veins that go to the azygos system (caval). Third, between the paraumbilical veins of the portal system and the veins of the anterior abdominal wall that drain into the inferior vena cava. Fourth, between the colic veins of the portal system and the retroperitoneal veins of the caval system. So middle rectal is the right answer. The superior gluteal vein, renal vein, and inferior phrenic vein are all part of the caval system; the splenic vein is part of the portal system.

Explanation
The ischioanal fossa is a space found on both sides of the anal canal. It is bounded laterally by the obturator internus, superiorly by the pelvic diaphragm, and medially by the pelvic diaphragm and anus. It is the area that is lateral to the anal canal and inferior to the pelvic diaphragm. The anterior recesses are the parts of the ischioanal fossa that extend above the perineal membrane, and the posterior recesses extend deep to the sacrotuberal membrane and superior to the gluteus maximus. The genital hiatus is the place where the pelvic diaphragm splits to allow the urethra/vagina and anus to pass through. The pudendal canal travels from the lesser sciatic foramen, where its contents enter the perineum. It contains the internal pudendal artery, internal pudendal vein, and pudendal nerve.

Explanation
The bounderies of the perineum are as follows. Anterior: pubic symphysis; Anterolateral: ischiopubic rami; Lateral: ischial tuberosities; Posterolateral: sacrotuberous ligament; Posterior: tip of the coccyx. The spine of the ischium, which projects into the pelvis toward the lateral pelvic wall, does not make up a boundary of the perineum

Explanation
Since the urine is leaking through the ventral side of the penis, it must be leaking through a defect in the spongy urethra. The spongy urethra is contained in the corpus spongiosum, so it follows that the corpus spongiosum must be open. The membranous urethra is a brief portion of the urethra extending from the bottom of the prostate to the top of the corpus spongiosum. A defect here would not cause leakage on the ventral surface of the penis. The corpora cavernosa are erectile bodies that lie beside the corpus spongiosum. They are not involved with the flow of urine or the urethra. The glans of the penis is at the tip - if this structure failed to close, there would be abnormal leakage from the tip of the penis, not the ventral surface.

Explanation
When performing a transvaginal pudendal nerve block, the ischial spine is palpated through the wall of the vagina and the needle is then passed through the vaginal mucous membrane toward the ischial spine. Eventually, the needle pierces the sacrospinous ligament, at which point the pudendal nerve is bathed with anesthetic. Remember--the pudendal nerve is within the pudendal canal, and it wraps around the ischial spine before it delivers its branches. So, administering the nerve block at the ischial spine allows a physician to anesthetize all the branches of the pudendal nerve. This is a very important landmark that you want to remember!
Also remember--the pudendal nerve block does not need to be administered transvaginally. In a perineal pudendal nerve block, the ischial tuberosity is palpated through the buttock and the needle is inserted into the pudendal canal about one inch deep medial to the ischial tuberosity. The anesthetic can then be injected to bathe pudendal nerve. In this case, a different anatomical landmark, the ischial tuberosity, is used to deliver the nerve block
Arcus tendineus levator ani is the origin for levator ani. It is a specialization of the fascia of obturator internus which runs from the spine of the ischium to the superior pubic ramus. The coccyx is the most inferior portion of the vertebral column--it is found on the posterior wall of the pelvis. The lateral fornix of the vagina is the space found lateral to the cervix as it protrudes into the vagina. The obturator foramen is a large foramen on the anterior side of the pelvis, formed by the pubic and ischial rami. It is a site of attachment for obturator externus and internus. None of these structures are appropriate landmarks to use when performing a pudendal nerve block.

Explanation
An episiotomy is an incision made in the perineum to enlarge the distal end of the birth canal and to prevent serious damage to the perineal structures. This procedure is often performed when there is a risk of tearing the birth canal due to a breech or forceps delivery. When performing a median episiotomy, a cut is made immediately posterior to the vagina, through the perineal body. If this cut went too far, the physician might cut through the external anal sphincter or the rectum. So, external anal sphincter is the correct answer.
It's important to remember that episiotomies are often made in the posterolateral direction, not on the midline. If the incision tears further during the delivery, a median incision is more likely than a posterolateral incision to extend posteriorly through the external anal sphincter, and the rectum. Consequently, a posterolateral incision is considered safer by some.
The bulbospongiosus muscle, ischiocavernosus muscle, and sphincter urethrae are anterior to the area that is cut during an episiotomy. The sacrospinous ligament extends from the sacrum to the ischial spine--it is deep to the perineum and should not be involved with this procedure.

Explanation
Erection is mediated by parasympathetic nerves, and the pelvic splanchnic nerves are the parasympathetic nerves that innervate the smooth muscle and glands of all pelvic viscera. So, the pelvic splanchnic nerves are the nerves contributing the fibers to the prostatic plexus which innervate penile/clitoral erectile tissue to cause erection.
None of the other listed nerves carry parasympathetic fibers which could innervate the penis and cause erection. Additionally, none of these other nerves contribute to the prostatic plexus, which is an extension of the inferior hypogastric plexus. The deep perineal nerve is the a branch of the perineal nerve that innervates all the muscles of the urogenital triangle. The dorsal nerve of the penis/clitoris is a branch of the pudendal nerve that provides sensory innervation to the skin of the shaft of the penis/clitoris. The genitofemoral nerve provides motor innervation to the cremaster muscle and sensory innervation to the skin of the anterior scrotum/labium majus and the upper medial thigh. Finally, the pudendal nerve is the major nerve of the perineal region. Its branches include the inferior rectal nerve, perineal nerve, and the dorsal nerve of the penis/clitoris.

Explanation
The rectal venous plexus is one of the four portal/systemic anastomoses. Blood from the portal system can flow into the venous system at this junction. This means that portal blood, from the superior rectal vein, could flow through the rectal venous plexus, into the inferior rectal vein and into the systemic venous drainage. Now, you just need to figure out what the inferior rectal vein drains into. And it drains into the internal pudendal vein, so that's the answer. See Netter plate 370 for a picture illustrating this concept of the portal/systemic anastomosis in the rectum.
The external iliac vein is one of the two branches of the common iliac vein (along with the internal iliac vein). However, the internal iliac vein and its tributaries (including the pudendal vein) are much more important in draining the pelvic structures. The inferior gluteal vein is a branch of the anterior division of the internal iliac vein--it drains gluteus maximus. The inferior mesenteric vein is part of the portal venous system--it gives rise to the superior rectal veins, but not the inferior rectal veins!

Explanation
The perineum and the external genitalia, including the labia majora and scrotum, drain to the superficial inguinal lymph nodes. However, in the male, remember that the testes do not drain to the superficial inguinal lymph nodes! The lymphatic vessels for testes travel in the spermatic cord and drain the testes into the lumbar nodes (ovaries also drain to lumbar nodes).
The lumbar nodes drain the internal pelvic organs; the sacral nodes drain the prostate gland, uterus, vagina, rectum, and posterior pelvic wall; the external iliac nodes drain the lower limb; the internal iliac nodes drain the pelvis and gluteal region.

Explanation
The pudendal canal travels from the lesser sciatic foramen to the deep transverse perineus muscle. The ischial spine marks the posterior limit of the pudendal canal, so that's the correct answer. If you weren't sure about that, you might also notice that the physician here is trying to perform a transvaginal pudendal nerve block. This means that the physician will be using the ischial spine as a landmark and inserting the needle near this prominence, coating the pudendal nerve with anesthesia before it gives off its branches.
The coccyx is the inferior end of the vertebral column; it is on the posterior wall of the pelvis. The ischial tuberosity (not to be confused with the ischial spine!) protrudes posteroinferiorly from the body of the ischium. It is the attachment for the sacrotuberous ligament. The ischiopubic ramus is the articulation between the ischial ramus and the inferior pubic ramus in the anterior pubis. The obturator groove is a groove on the inferior surface of the superior pubic ramus. It marks the area of passage of the obturator vessels and nerve in the obturator canal.