Anatomy - 45 - Osteology of the Pelvis; Anal Triangle

Label the following pelvic variations. Possible answers are: Android, Anthropoid, Gynecoid, and Platypelloid. Which are most common in males? Which are most common in females?

A. Android B. Gynecoid C. Anthropoid D. Platypelloid A and C are most common in males. A and B are most common in white females and B and D are most common in black females. Overall, B is the most common type in females.

A 22-year old victim of an automobile accident has damaged structures that from the boundary of the perineum. Which structure is spared? A. sacrospinous ligament B. sacrotuberous ligament C. ischial tuberosities D. tip of the coccyx E. pubic tuberosities

A. The sacrospinous ligament. The sacrospinous ligament is higher in the pelvis and is not part of the perineum.

Does the inferior hypogastric plexus carry autonomic or somatic nerves?

Autonomic nerves. The inferior hypogastric plexus carries sympathetic and parasympathetic nerves ONLY. There are no somatic nerves involved.

A 29 year-old woman is admitted to a hospital because the birth of her child is several days overdue. During childbirth, her pelvic diaphragm is torn. Paralysis in which muscle will result? A. Piriformis B. Rectus abdominis C. Obturator internus D. Levator ani E. Coccygeus

D. Levator Ani. The only muscles in this list that are part of the pelvic diaphragm are the levator ani and the coccygeus. Because the levator ani is closer to the vagina (which is presumably where the tearing occurred) we would expect levator ani to be more correct than coccygeus.

The greater pelvis is defined as the area bounded: A. superiorly by the pelvic brim B. inferiorly by the pelvic diaphragm C. anteriorly by the hip bones D. posteriorly by the coccyx E. laterally by the illium

E. The greater pelvis is synonymous with the false pelvis. It is bound by the ala or wing of the ilium. The ilium runs posteriorly and laterally of the false pelvis area, making E the correct answer. Most of the answers refer to the boundaries of the true pelvis.

True or false: the coccygeus is one of the levator ani muscles.

False. The coccygeus is not one of the levator ani muscles; however, the coccygeus, combined with the three levator ani muscles, are collectively called the pelvic diaphragm.

True or false: the pectinate line and anorectal junction are two different names for the same structure.

False. The pectinate line and the anorectal junction are two different structures. The pectinate line is about 2/3 of the way down the anus, closer to the superficial area/perineum. The anorectal junction, on the other hand marks the junction between the rectum and anus. It is the line between them and is marked by the anorectal angle.

True or false: While the perineum does follow the contours of the tissue between the coccyx and pubic symphysys, it is basically flat.

False. The perineum is a diamond that is "hinged" at the juncture of the urogenital and anal triangles. In other words, it slopes (90 degree angle) toward both the coccyx and pubic symphysis. See the attached image for a graphical illustration.

True or false: Just like the joints between the Ilium, Ischium, and Pubis, the joint between the Ilium and the Sacrum is fused.

False. The sacro-iliac joint is NOT a fusion. For this reason, there are very strong ligaments that hold this joint together, preventing the weight of the body from driving the sacrum (like a wedge) between the bones of the hip.

True or false: the umbilical artery is completely obliterated in adults. It no longer exists as a blood vessel.

False. While much of the umbilical artery obliterated, there is still a blood vessel there. The umbilical artery gives rise to the superior vesicular artery, which supplies the bladder.

Of the following pelvic variations, which is best for child bearing? Android, Anthropoid, Gynecoid, and Platypelloid.

Gynecoid. Dr. Kramer explained that although Platypelloid looks like the best option (the most wide), in discussions with gynecologists, they agree that babies' heads engage the gynecoid pelvis better than the Platypelloid pelvis.

What important function is executed by the levator ani muscles, particularly the puborectalis?

It helps to maintain the anorectal angle. This is the angle that the rectum forms with the anus. If the angle is affected, a person can become fecally incontinent. All of the levator ani muscles participate in maintaining the anorectal angle; however the puborectalis is most important.

Anatomically, the shape of the perineum is a diamond composed of two triangles. What are the lateral borders of the diamond? What is the anterior border of the diamond? What is the posterior border of the diamond? What are the names of the two triangles?

Lateral Border - the pubic tuberosities Anterior Border - the pubic symphysis Posterior Border - the coccyx Anterior Triangle - Urogenital Triangle Posterior Triangle - Anal Triangle

What is a good "rule of thumb" that generally allows you to distinguish between a male and female pelvis?

Male - the "V" shape made between your index and middle fingers should, when placed over the pubic symphysis, approximate the pubic width of the male pelvis. See attached image. Female - the "V" shape made between your thumb and index finger should, when placed over the pubic symphysis, approximate the pubic width of the female pelvis. See attached image.

There is only one anastamosis of the portal and systemic venous systems that occurs within the pelvis. Where does it occur?

Near the anal canal.

Where, in the anorectal area, would you find the pectinate line? Where would you find the anorectal junction?

Pectinate Line - the pectinate line is found about 2/3 of the way down the anus (down meaning closer to the anal opening). The pectinate line does not mark the boundary between the anus and rectum. Anorectal Junction - the anorectal junction marks the boundary between the anus and rectum. It is found at the anorectal angle, the point at which the puborectalis wraps around the rectum/anus, forming a sling.

What spinal nerves supply both the autonomic and somatic nerves of the rectum?

S 2, 3, and 4. Keeps the poo off the floor

What four spinal nerves form the sacral plexus? What are the two main nerves formed by this plexus?

S1, 2, 3, and 4. This plexus forms the sacral nerve and the pudendal nerve. According to Dr. Kramer, these are the two main nerves of the sacral plexus.

Are sacral splanchnic nerves sympathetic or parasympathetic nerves? How about pelvic splanchnic nerves?

Sacral Splanchnic Nerves - Sympathetic Pelvic Splanchnic Nerves - Parasympathetic

Unlike many anatomical structures, the pelvis lies at an angle (with the true pelvis facing anteriorly). In a standing person, describe the direction of the sacrotuberous and sacrospinous ligaments relative to the ground.

Sacrotuberous - the sacrotuberous ligament runs roughly perpendicular to the ground in a person who is standing. In other words, it runs roughly parallel to the plane of the standing person's body. Sacrospinous - the sacrospinous ligament runs roughly parallel to the ground in a person who is standing. Basically, the sacrotuberous and sacrospinous ligaments are roughly perpendicular to each other, with the sacrospinous ligament running roughly parallel to the ground.

Of the following anal sphinctors, which are under voluntary control? What nerve innervates the voluntary sphinctors? Sphinctor Ani Externus; Sphinctor Ani Internus; Corrugator Cutis Ani.

Sphinctor Ani Externus. This sphinctor contains three parts: deep, superficial, and subcutaneous. Branches of the pudendal nerve innervate these sphinctors.

Of the following anal sphinctors, which are under involuntary control? What nerve innervates the involuntary sphinctors? Sphinctor Ani Externus; Sphinctor Ani Internus; Corrugator Cutis Ani.

Sphinctor Ani Internus and Corrugator Cutis Ani. Both of these sphinctors are smooth muscle sphinctors that are under autonomic control. These sphinctors are innervated by pelvic autonmic plexi.

What artery travels from the true pelvis into the false pelvis (Dr. Kramer described it as the "only one" that does this)?

The Iliolumbar Artery.

Describe the importance of the anorectal angle.

The anorectal angle prevents the anus and rectum from lining up as one contiguous tube. This "kink" in the rectum/anus is called the anorectal angle. The anorectal angle is important in maintaining fecal continence. The levator ani, particularly the puborectalis, relax during defecation and urination, allowing feces to pass through the rectum and anus. See the attached images and text for more information.

What ligaments stabilize the sacro-iliac joint?

The anterior and posterior sacro-iliac ligaments.

Who's perineum is larger, the average male or the average female? Why?

The average female has a larger perineum. The lateral boundaries of the perineum are the pubic tuberosities. Because, as discussed earlier in Dr. Kramer's lecture, the female pelvis has a wider gap between the pubic tuberosities, it makes sense that a female perineum would be larger (in area) than a male perineum.

What important blood vessel division occurs at/near the level of the sacro-iliac joint?

The division of the common iliac artery into internal and external branches (the internal and external iliac arteries).

What is the false pelvis? What occupies the space contained within the false pelvis?

The false pelvis is the area superior to the true pelvis. It is defined laterally and superiorly by the wings of the Ilium. Abdominal viscera occupies the space of the false pelvis. In the attached image, the false pelvis is the area shaded in light green.

What structures mark the end of the rectum and the beginning of the anus?

The levator ani muscles. The rectum ends where it perforates these muscles.

What collection of muscles (three muscles that are collectively called by one name) cover the obturator internus?

The levator ani. The levator ani is composed of the following three muscles: Iliococcygeus, Puborectalis, and Pubococcygeus.

What forms the anterior border of the true pelvic cavity?

The lower half of the Ilium, Ischium, and Pubis.

What forms the lateral border of the true pelvic cavity?

The lower half of the Ilium, Ischium, and Pubis.

What forms the inferior border of the true pelvic cavity?

The muscular pelvic diaphragm.

Why are external hemorrhoids more painful than internal hemorrhoids?

The pectinate line divides the tissues around the rectum and anus into two groups. The groups have different innervation, vascularization, and correspond to different embryological structures (endoderm and ectoderm). The innervation of the two segments cause the difference in hemorrhoid pain. Internal hemorrhoids lie in tissue that is innervated by visceral nerves. These do not sense pain as acutely as the somatic innervation present in the tissues where external hemorrhoids arise. The pectinate line is essential to understanding the differences between internal and external hemorrhoids.

What is the significance of the pectinate line (anal/rectal)?

The pectinate line separates the embryological endoderm from embryological ectoderm. The pectinate line also marks the division between visceral innervation and somatic innervation. Additionally, different arteries feed the tissues on each side of the pectinate line. See the table in the attached image for more details.

What forms the superior border of the true pelvic cavity?

The pelvic brim or pelvic inlet.

What is the perineal body?

The perineal body is a fibromuscular mass that lies at the central point of the perineum. Several muscles come together at the perineal body.

Describe the position of the perineum relative to the pelvic diaphragm.

The perineum is defined to the be the space inferior to the pelvic diaphragm that is also positioned between the legs. In the attached image, the perineum is shaded in blue.

What important anastamosis occurs near the rectum?

The portalcaval anastamosis. This is where the arteries and veins of the rectum combine, forming an anastamosis between the portal system and systemic circulation.

What pelvic bone predominantly bears the weight of the abdomen?

The pubic bone.

What do we mean when we say that the rectum perforates the levator ani muscles?

The rectum doesn't pierce these muscles. These muscles wrap around the anus (particularly the puborectalis).

The weight of the body on the pelvis should cause it to rotate. What two ligaments prevent the pelvis from rotating?

The sacrospinous and sacrotuberous ligaments.

What forms the posterior border of the true pelvic cavity?

The sacrum and coccyx.

What is the pelvic brim? Which bones of the pelvis contribute to it?

The superior boundary of the true pelvis. The ilium, sacrum, and pubis all contribute to the pelvic brim. In the attached image, it is outlined in red.

What nerve and artery supply and drain the rectum?

The superior rectal artery and vein.

True or false: Because humans quit moving their "tails" (most likely) millions of years ago, the coccygeus will probably not have much of a muscle belly.

True. The coccygeus will probably just look like faschia - - it is unlikely to have much of a muscle belly.

Label the following image.

1. Circumflex Iliac Artery 2. Internal Iliac Artery 3. Inferior Epigastric Artery 4. Common Iliac Artery 5. Umbilical Artery 6. Obturator Artery 7. Internal Pudendal Artery 8. Middle Rectal Artery

Label the following muscles of the pelvic diaphragm.

1. Coccygeus 2. Iliococcygeus 3. Pubococcygeus 4. Puborectalis

Label the following image.

1. Iliac Crest 2. Anterior Superior Iliac Spine 3. Ischial Spine 4. Ischial Tuberosity

Label the following image.

1. Inferior Gluteal Artery 2. Superior Gluteal Artery 3. Lateral Sacral Artery 4. Iliolumbar Artery

Label the following image. Also, consider that attached table.

1. Nerve to the Piriformis 2. Nerve to the Obturator Internus 3. Nerve to Levator Ani These are all so close to the spinal nerves that they take direct branches from the spinal nerves.

Label the following image.

1. Obturator Internus 2. Piriformis 3. Sacrotuberous Ligament 4. Obturator Internus 5. Piriformis 6. Sacrotuberous Ligament (cut) 7. Coccygeus

Label the following image. What is the specific name for this anatomical "view?"

1. Pubococcygeus 2. Puborectalis 3. Coccygeus 4. Pubococcygeus 5. Puborectalis 6. Ischial Tuberosity 7. Ischial Spine 8. Coccygeus 9. Pubic Symphysis Dr. Kramer specifically said not to worry about the series of very specific muscles named between 1 and 2, 4 and 5. This position is called the lithotomy (I think that's what he called it) position.

Label the following image.

1. Sacro-iliac joint 2. Pubic Symphysis 3. Anterior Sacro-iliac Ligament 4. Posterior Sacro-iliac Ligament

Label the following image.

1. Sciatic Nerve 2. Pudendal Nerve and Inferior Gluteal Artery 3. Nerve to Levator Ani and Coccygeus 4. Nerves to Piriformis 5. Coccygeus 6. Nerve to Obturator Internus

The tendonous arch of the levator ani is the thickening of obturator faschia that stretches between two important landmarks. What are these landmarks?

1. The Pubic Symphysis. 2. The Ischial Spine.

What four muscles comprise the inferior border of the lesser pelvis? Collectively, what are they called?

1. The coccygeus 2. The pubococcygeus 3. The iliococcygeus 4. The puborectalis Collectively, these are called the pelvic diaphragm - - they form the inferior border of the lesser pelvis.

What four landmarks define the true pelvic cavity?

1. The pelvic brim (or pelvic inlet) 2. The muscular pelvic diaphragm 3. The lower half of the Ilium, Ischium, and Pubis 4. The sacrum and coccyx

What do we mean by the term "caval?"

"Caval" is synonymous with "systemic." In the case of anastamoses between the portal system and the systemic venous circulation, only one is found in the pelvis. It is commonly called the portocaval anastamosis.