Anatomy Pelvis Pelvic

Fertilization normally takes place in the ampulla of the uterine tube. This is the middle segment of the uterine tube, and it is the longest and widest segment. The infundibulum is the funnel-shaped distal end of the uterine tube, and the isthmus is the narrowest part of the uterine tube which connects directly to the uterus. The uterine lumen is the site of implantation, not fertilization. Finally, the cervical canal is the pathway out of the uterus at its inferior end-- it would not be an appropriate site for fertilization or implantation.

The trigone of the bladder is bounded by the openings of the left and right ureteric orifices superolaterally, the interureteric crest between the openings of the ureters and the internal urethral orifice inferiorly. The urachus is the structure that joins the apex of the fetal bladder to the umbilicus. After birth, it becomes the median umbilical ligament.

This question is phrased in a slightly tricky way, so it's important to break it down before looking at the answers. There are two things to think about here. First, you need to decide if a structure is part of the uterus. If it is part of the uterus, then you need to decide if it is shed during menstruation. The correct answer will be a structure that is part of the uterus but is not shed during menstruation. Answers about structures that are not shed during menstruation because they are not part of the uterine wall are incorrect. The myometrium is our correct answer. It is the middle muscular component of the uterine wall and it is not shed during menstruation. The endometrium is the inner mucosal coat of the uterus. It exhibits many characteristic changes during the menstrual cycle and all but its stratum basalis is shed during menstruation. The mesometrium is the mesentary of the uterus which forms the major part of the broad ligament of the uterus. It is not even part of the uterine wall, so it's not the answer to look for. Cervical mucosa lines the cervix, which is the inferior portion of the uterus. This mucosa is shed during menstruation. Finally, the uterus does not have rugae - rugae are the folds found in the lining of the vagina (and stomach).

The cervix is the inferior end of the uterus that projects into the vagina. This means that the vagina comes up and wraps around the cervix, creating the vaginal fornix. There are multiple fornices at the top of the vagina: anterior, posterior, and lateral. The cervical canal is the passageway through the cervix to the vagina. The uterine lumen is the hollow center of the uterus. The rectouterine and uterovesicular pouches are two peritoneal folds found in the pelvic cavity. The rectouterine pouch is a peritoneal fold extending across the floor of the pelvic cavity from the sacrum (beside the rectum) to the uterus. The uterovesicular pouch is a peritoneal fold extending from the uterus to the bladder.

In a vasectomy, the ductus deferens is ligated or excised. This means that the fluid that is then ejaculated from the seminal vesicles, prostate, and bulbourethral glands has no sperm. The sperm simply degenerate in the epididymis and the proximal ductus deferens. It would not be a good idea to ligate the ejaculatory duct or the seminal vesicle because that might compromise the patient's ability to ejaculate. Just remember, another name for the ductus deferens is the vas deferens, so it make sense that the procedure to ligate this structure is called a vasectomy.

There are two true statements here. First, the prostate gland encircles the urethra. It circles around the first part of the urethra, the prostatic urethra. This is why urinary retention is one symptom of prostatic hypertrophy--if the prostate is enlarged, it may close around the urethra, occluding this passage and preventing urine from exiting the bladder. The prostate gland is also extraperitoneal. Remember: the rectovesicular pouch, a fold of peritoneum that hangs between the bladder and rectum, is the lowest extent of the peritoneal cavity in males . But, the prostate is found on the posterior side of the bladder, below the point where the peritoneal membrane created this fold. So, it is an extraperitoneal organ.
The lobes of the prostate are: anterior, posterior, lateral, and middle. Finally, the prostate would not be imaged using an intravenous urogram. In an intravenous urogram, a patient is given IV contrast, and radiographic images are taken as the contrast is excreted, passing through the kidneys, ureters, and bladder. Since the prostate is not part of this excretory pathway, it would not be viewed through this method.

Remember, the pectinate line (the line in the anus where mucosa changes to skin) is the dividing line for lymphatic drainage. Structures above the pectinate line drain into the inferior mesenteric and internal iliac nodes. Structures below the pectinate line drain into the superficial inguinal nodes. Since the tumor is in the cutaneous (skin) region of the anal canal, it is going to be drained by the superficial inguinal nodes. This means that these nodes would be the first site of metastases.

The pudendal nerve is found about 2 cm lateral to the anal canal. Therefore, it is the structure most likely to be damaged by the stab wound. The crus of the penis is the lateral part of the corpus cavernosum found at the base of the penis. It is anterior, not lateral, to the anal canal. The perineal body is a structure found in the female only--it is a fibromuscular mass found in the plane between the anal canal and the perineal membrane that serves at the convergence of several muscles. It is anterior to the anal canal. The inferior rectal artery is a branch of the internal pudendal artery that delivers blood to the inferior part of the rectum. It would not be injured by the stabbing because it is located on the surface of the rectum, not 2 cm lateral to the anal canal. Finally, the vesicular bulb is a structure of erectile tissue located on either side of the vestibule of the vagina, attached to the perineal membrane. So, it would be anterior to the site of the stabbing.

Remember: The rectouterine and vesicouterine pouches are the two pouches created by draping the peritoneum over the pelvic organs. These pouches are the two lowest extents of the peritoneal cavity, so to answer this question, you just need to decide which one goes lower. Since the uterus is folded over the bladder, the rectouterine pouch can extend to a slightly lower level than the vesicouterine pouch, which makes C the correct answer. The pararectal fossa is formed by lateral reflections of perineum over the superior one third of the rectum; this space gives the rectum room to fill with feces. The paravesicular fossa is a space near the bladder that allows the bladder to expand. Why is the rectovesicular pouch incorrect? It's only found in males, not females! (But, if the question had asked about males, the rectovesicular pouch would have been the correct answer.)

The pectinate line is the place where the lining of the anal canal changes from skin to mucosa. It is also a landmark that divides the lymphatic drainage, vascular supply, and innervation of the anal canal. Lymph coming from structures above the pectinate line drains to the inferior mesenteric lymph nodes or the internal iliac nodes. Lymph from structures below the pectinate line travels to the superficial inguinal lymph nodes.
As far as vasculature and nerves go... Superior to the pectinate line, arterial blood comes from the superior rectal artery and drains to the portal system through the superior rectal veins. This area is innervated by the inferior hypogastric plexus (autonomic innervation). Inferior to the pectinate line, blood comes from the inferior rectal arteries and is drained into the caval system. Innervation here comes from the inferior rectal nerves (somatic innervation).
The anorectal junction is the point where the rectal ampulla narrows due to a U-shaped sling created by the puborectalis muscle. This area is superior to the pectinate line. The white line is a transitional area inferior to the pectinate line that represents some subtle changes as the mucosal lining becomes "regular" skin. Finally, the cutaneous zone is the area of skin at the very end of the rectum.

The mesovarium, mesometrium, and mesosalpinx are the three peritoneal sections that create the broad ligament. The mesosalpinx covers the uterine tube and hangs below it to meet with the mesovarium. The mesovarium covers the ovary and ovarian ligament. It extends posteriorly from the mesosalpinx like a shelf. The mesometrium makes up the rest of the broad ligament.
The ovarian ligament is located in the broad ligament but is not part of the broad ligament. It is a round cord that attaches the ovary to the uterus just below the point where the uterine tube enters the uterus. The round ligament of the uterus reaches the lateral surface of the uterus below the uterine tube. It is continuous with the ovarian ligament and it holds the fundus of the uterus forward. The suspensory ligaments of the ovary are peritoneal folds that cover the ovarian neurovascular supply as these vessels pass over the pelvic brim to reach the ovary. Finally, the uterosacral ligament connects the isthmus of the uterus to the sacrum. It is important for the support of the uterus, and it is found in the rectouterine fold.

Remember that the prostatic urethra travels through the prostate gland. So, if the periurethral zone of the prostate hypertrophied, the nearby prostatic urethra would be occluded. The central and peripheral zones of the prostate are not as close to the urethra. If they enlarged, they would not restrict the flow of urine quite as much. The ejaculatory duct is the duct formed once the ductus deferens joins with the duct of the seminal vesicle. It passes through the prostate gland, but its enlargement would have no effect on the prostate or the urethra. Finally, the seminal vesicle is a sac on the posterior surface of the bladder which is superior to the prostate gland. It produces seminal fluid, and changes in the seminal vesicle should not alter the flow of urine.

The pectinate line is the line of transition between the mucosal lining of the anal canal and the skin lining of the anal canal. So, this is the point where the mucosal zone ends and the skin begins. The white line is a transitional zone between the pectinate line and "regular" skin where there are some more subtle changes in the epithelial lining of the anal canal. But the pectinate line is the line that demarcates the major transition from mucosal lining to skin.

The rectovesicular pouch is a reflection of the peritoneum between the rectum and the bladder. It can only be found in males because females have the uterus sitting between the rectum and the bladder. This means that females have two pouches created by reflections of peritoneum draped over the pelvic viscera: the rectouterine and vesicouterine pouches. The ischioanal fossa is the fat filled space located lateral to the anal canal and inferior to the pelvic diaphragm. It has an anterior recess that extends superior to the perineal membrane and sphincter urethrae muscle, and it is found in both males and females. The genital hiatus is also found in both sexes--it is the place where the urethra/vagina and anus exit the pelvic diaphragm. The ischiocavernosis muscle compresses the corpus cavernosum of the penis or clitoris. Finally, the sphincter urethrae encircles and compresses the urethra in both sexes.

The prostate is located on the posterior side of the bladder. Since the rectum is behind the bladder and prostate, you can image the prostate by placing an ultrasound transducer in the rectum and pressing it against the anterior wall. Then, the ultrasound transducer will be against the prostate gland.

There are usually three transverse rectal folds in the lower rectum. These are specializations of the circular layer of musculature that are designed to support fecal mass. Although circular folds is somewhat descriptive of the transverse rectal folds, this is not the best answer. Anal columns are longitudinal folds of mucosa over rectal vessels. They are found on the inner wall of the anal canal. Anal valves are the folds of mucosa that join the anal columns at their inferior ends.

The ovary is entirely covered by a layer of peritoneum called the mesovarium. The mesovarium, along with the mesometrium and the mesosalpinx, creates the broad ligament. Because the ovary is completly encased in peritoneum, it would be outlined on a CT with intraperitoneal contrast material. The prostate, seminal vesicles and vagina are located below the rectovesicular pouch or rectouterine/vesicouterine pouches. So, they are not associated with the peritoneal cavity and would not be seen on the CT scan. Although peritoneum drapes over the rectum, forming the rectovesicular fold in males and the rectouterine fold in females, the rectum would not be clearly outlined by the intraperitoneal contrast since it is not covered by peritoneum on all sides.

The shaft of the penis is an analog of the shaft of the clitoris, while the labia majora is derived from the same embryonic structures as the scrotum. The other three answer choices list structures that come from comparable embryonic structures in the male and female. See Netter Plate 389 for a picture of the homologous structures in males and females!

The cervix of the uterus is anterior to the rectum. Since the cervix is the inferior part of the uterus that is protruding into the vagina, it should feel like a firm structure upon palpation. The bladder is the most anterior organ in the pelvis, in front of the uterus and rectum. So, the bladder would not be directly in front of the anterior wall of the rectum. The body of the uterus lies upon the bladder, so it is too far in front of the anterior rectal wall to be palpated. The pubic symphysis is the joint connecting the two pubic bones. It forms the anterior boundary of the pelvis, and would be too far forward to palpate through the rectum. Although the vagina is directly anterior to the rectum, it would not feel like a distinct and firm structure upon palpation.

The duct of the seminal vesicle carries seminal fluid, a basic fluid containing fructose. The contents of the seminal fluid buffers the acid in the vagina and provides nutrients for sperm. The duct of the seminal vesicle joins with the ampulla of the ductus deferens (which is carying sperm) to form the ejaculatory duct. This is the first place where seminal fluid mixes with sperm. Sperm is first formed in the seminiferous tubules. They then travel from the head to the tail of the epididymis, through the ductus deferens, into the ejaculatory duct where they mix with seminal fluid, into the prostatic urethra, through the rest of the urethra, and then out the penis. So, all of the other answer choices are places that are important for the passage of sperm.

The ejaculatory duct travels through the prostate and opens into the prostatic urethra. So, it is likely that this duct might get removed or damaged during the surgery. The duct of the seminal vesicle and the ductus deferens are the two ducts that join to make the ejaculatory duct. They both lie on the posterior surface of the bladder and would not be interrupted by the surgery. The fossa navicularis is a dilation in the penile urethra. It would not be harmed by surgery in the prostatic urethra. Finally, the seminferous tubules are the tubules in the testes where sperm are formed.

The pectinate line is more than the line where the mucosal lining of the anal canal changes to skin. It is also a key dividing point for the flow of lymph in the anal canal. Above the pectinate line, lymph flows to the inferior mesenteric and internal iliac lymph nodes. Below the pectinate line, lymph flows to the superficial inguinal lymph nodes. So, the pathology report tells you that the tumor must be somewhere below the pectinate line since the superficial inguinal lymph nodes are the only nodes involved. The only answer representing a tumor below the pectinate line is A, the cutaneous portion of the anal canal. The proximal and distal rectum represents a space far above the pectinate line, and the mucosal zone of the anal canal is, by definition, above the pectinate line. At the pectinate line itself, lymph should be flowing to all the sets of nodes, and it would be unlikely that a tumor at the pectinate line would involve only the superficial inguinal lymph nodes.