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Pelvis Walls and Floor - Lecture Notes
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Pelvis Walls and Floor
Posterior to the urinary bladder in the midline is the rectum in the male pelvis.
In the male, the prostate gland is resting on the pelvic floor, with the urinary bladder located superiorly. The deep dorsal vein from the penis passes inferior to the pubis, dumping into the prostatic venous plexus around the prostate gland. The peritoneum extends from the anterior wall and over the superior surface of the urinary bladder, reflecting posteriorly for a distance before reflecting to the rectum. In the male, the peritoneal reflections form just one pouch between the rectum and the urinary bladder and is known as the rectovesticle pouch. This is the lowest point in the peritoneal cavity in the male and will collect fluids in the peritoneal cavity.
The bladder rests on the prostate gland, which in turn, rests on the pelvic floor. Prostate gland encompases the urethra and runs right through the core of the prostate gland. The prostatic portion of the urethra is the part of the urethra that run through the prostate. The portion of the urethra that pass through the pelvic floor is called the membranous part of the urethra. The portion that runs through the penis is called the spongy or penile part of the urethra. In the female, only the membranous part of the urethra exist, passing through the pelvic floor.
Muscle fibers around the internal opening of the urethral are circular and does have sphincter action. When the male becomes sexually aroused, these sphincter muscles contract and prevent urine from escaping from the bladder. At time of ejaculation, the sphincter is closed tightly. The prostate gland has a very thick outer capsule and is subdivided into lobes, depending on the urologist/clinician; most common is the central vs. peripheral designations of portions of the prostate. Ureters in both sexes pass through the external bladder wall at an oblique angle; this helps to prevent reflux of urine back into the ureter. During distension, the bladder wall puts pressure on the ureter to prevent reflux.
The spermatic cord ends as it leaves the inguinal canal and the vas deferens leaves the vasculature and goes into the true pelvis. The vas deferens comes in from either side of the ureters. The vas deferens dilates and froms the ampulla, and goes towards the midline; they do not unite but move just superior to the prostate gland. Flanking the two ampula of the vas deferens on either side are the seminal vesticles. Sperm cells never enter the seminal vesicles (it is a misnomer). Seminal vesicles are a single tube that is highly convoluted structure, forming the gland. Each seminal vesticle has a small duct that unites with the ampulla on their respective sides, forming the ejaculatory ducts. So right at the surface of the prostate gland are the two ejaculatry ducts which pierces the prostate gland and run into the prostatic urethra. The ejaculatory duct contains contents of the vas deferens (sperm and fluids) and contents of the seminal vesticles. Inferior in the muscles of the deep pouch are the bulbourethral glands.
Digital rectal exam touches the posterior lobe of the prostate gland. Median lobe causes the most clinical issues in terms of benign enlargement of the prostate gland (benign prostatic hypertrophy), which will occur in 80-90% of males in their 8th decade of life. As the prostate gland enlarges, it will encroach into other structures, either superiorly or encroaching into the urethra. The stenosis of the urethra results in weak stream of urine and frequent urination, often at night. Enlarged prostate may also cause a raised ridge in the urinary bladder, causing urine to pool and resulting in increased risk of urinary bladder infections. Treatment includes removal of part of the prostate gland.
In the posterior wall of the urethra is the urethral crest that runs through the length of the prostatic urethra. Midway along the porstatic urethra is the seminal colliculus where the urethral crest widens and where 3 openings reside. The 2 ejaculatory ducts open into the seminal colliculus. The single third opening is the prostatic utricle – this is an embryonic vestige of the vagina of the female and has no function in the male. On the sides of the urethral crest on the posterior wall are a series of several prostate ducts. So at this point in the prostatic urethra, all the components of semen are formed; the fluids of the bulbourethral glands are not included. The prostate gland has smooth muscle that contracts during ejaculation, compressing the prostatic urethra, and help propelling the semen. Sperm, and secretions from the testes and epididymus contain 10% of semen. Seminal vesticles contributes 60% of semen: mucoid, fructose, citric acid and other nutrients, prostaglandins (react with cervical mucous to make environment more conductive to sperm movement; reverse peristalsis especially in the uterine tube move the sperm towards egg; sperm in upper vagina can reach the distal tube in 5 minutes), fibrinogen (clotting factor to retain sticky mucoid consistency to hold semen into upper vagina). Prostate contributes 30% of semen: Alkaline, thin, milky; citrate, phosphate, calcium, profibrinolysin (converted to fibrinolysin which, after some minutes causes lysis of the mucoid clot of semen)
Male sexual response can be divided into erection, emission, ejaculation, and detumescence. Erection is mediated by the parasympathetic innervation to uncoil arteries in the penis. Erection is maintained by the Buck’s fascia constricting the deep dorsal veins. Emission is the formation of semen and mixing in the prostatic urethra. This is in control of the sympathetic system. Ejaculation follows emission within seconds. Defined as propulsion of semen from prostatic urethra out through the penile urethra. The parasympathic system mediates ejaculation. Detumescence is the return of the penis to the flaccid state and is mediated by the sympathetic system. The female sexual response is relatively unknown. Women can experience an erection and detumescence but what happens in between is unclear but is much more complicated than in the male. The female is much more psychological in the sexual response than in the male.
Piriformis muscle is a posterior muscle that takes origin on the sacrum and comes out of the greater sciatic foramen and passes to the femur. The obturator internus tendon exits the lesser sciatic forament and passes to the femur. Obturator internis fascia splits to form the pudendal canal. It also has a thickening of the fascia that runs from the pubis to the ischial spine called the tendonous arch. The tendonous arch proves attachments to muscles in the pelvic diaphram. Fibers in the pelvic diaphram that attach from the pubis to the coccyx is called the pubococcygeus muscle. Fibers from the tendenous arch to the coccyx is called the iliococcygeous muscle. These two muscles are not really separate and make up the levator ani muscle. Deep in the pelvis, parallel with piriformis, attaching from the ischiospine to the coccyx, is called the ischiococcygeus or the coccygeus muscle. The ischiococcygeus, pubococcygeus, and iliococcygeus make up the pelvic diaphragm. Therefore, the levator ani is not exactly the pelvic diaphragm as it is missing the ischiococcygeus muscle. Fibers of pubococcygeus that don’t make it to the coccyx that meet up with fibers from the other side, forming a sling around the anal rectal junction (forming a funnel), is called the puborectalis. The puborectalis is a subdivision of the pubococcygeus that forms the anal-rectal sling in the pelvic floor, pulling the anal-rectal junction towards the pubis.
The puborectalis is responsible for making the angle between the rectum and anal canal. It is also important in retaining fecal continence. This muscle is a voluntary muscle but the sympathetic nervous system keeps its flexed unless overridden voluntarily. If relaxed, the angle between the rectum and anal canal approaches 180 degrees, fecal incontinence may occur.
Between the two parts of the pubococcygeus muscle on the pubis, there is a gap in the pelvic floor that is closed by the genital hiatus that is closed by the urogenital diaphragm. The urogenital diaphragm is the peritoneal membrane, the muscles of the deep pouch, and the fascia on the superior ascpect of the deep pouch (which is muscular fascia). Therefore, the deep pouch is a potential space and is part of the the urogenital diaphragm. There are 2 gaps for the deep dorsal nerve, and for the urethra. The urogenital diaphragm is on a different plane than the pelvic diaphragm and actually continue to the pubic rami on either side and the pelvic diaphragm overlaps urogenital diaphragm. But, together, they close the pelvic outlet.
The autonomic plexus in the pelvis.
There is a somatic nerve plexus formed by the ventral rami of the spinal nerves S1-S5. These nerves plus the lumbosacral trunk from the lumbar plexus form the sacral plexus. Primary innervation from the sacral plexus is into the lower limb. The pudendal nerve also comes out of the sacral plexus and contains contributions from S2-S4. The piriformis muscle forms the posterior wall behind the sacral plexus.
The internal iliac artery demonstrates the greatest branching variation in the human body; branches can only be named by determining where they go. The bifurcation of the aorta occurs around L4 and forms the left and right common iliac arteries. The common iliac divides into the internal and external iliac arteries. The internal iliac divides into an anterior and posterior division. The posterior division branches into 3 arteries. The iliolumbar artery branches from the posterior division of the internal iliac and ascends back into the false pelvis along the lumbar vertebrae, supplying blood to the muscles on the false pelvis. The lateral sacral arteries travel to the lateral aspect of the sacrum, supplying the sacral plexus, piriformis, and to the terminal portions of the spinal cord (cauda equina). The superior gluteal is the largest branch that leaves the pelvis via greater siatic foramen between the lumbosacral trunk and S1.
The anterior division gives off several branches. The obturator artery exits the pelvis and goes down to the medial thigh and is paired with the obturator nerve through the obturator foramen. The umbilical artery comes off the anterior division and gives off the superior vesticle arteries, before being fibrous, reflecting into the anterior abdominal wall as the median fold. In the female, a vaginal branch from the anterior division goes to the vagina. The uterine artery branches off the vaginal artery and crosses superior to the ureter. The inferior vesticle artery branches off the anterior internal iliac in the male, but in females, it is believed not to exist. The middle rectal artery is a small branch, contributing to the anastomosis with the superiorectal artery. The inferior gluteal and the internal pudendal artery are the major branches of the anterior division of the internal iliac; these two arteries leave the pelvis.
In the female, a vaginal branch from the anterior division goes to the vagina. The urinary artery branches off the vaginal artery and crosses superior to the ureter. The uterine artery is of clinical significance because it is very closely related with the ureter. During a hysterectomy, it is important to clamp the uterine artery; however, if the ureter gets clamped in the ligature as well, then that’s just not cool. Ureters can go into spasm with very little manipulation that can cause a short term ligature. “Water goes under the bridge” – ureters goes under the uterine artery.
In the male, find the organ the vessel goes to and name the artery after the location of the organ.
The prostate is supplied by inferior vesticle arteries.
Kegal exercises tone and maintain muscles of the pelvic floor. This is especially important for vaginal delivery when the pelvic floor gets distended and would need to be toned to prevent damage to the pelvic floor.
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