Schedule  

Lab 10 - Pelvic contents

Pre-lab Exercise: Surface Anatomy of the Pelvis and Perineum

Primary Lab Objectives and Goals:

  1. Examine the inner surface of the rectum and the anal canal and locate the external anal sphincter.
  2. Examine the pelvic autonomic plexuses. Understand the connection of these plexuses to the autonomic nervous system (re-examine the sympathetic trunk in this context).
  3. Trace the ureters to the bladder to understand the path of urine flow and structures that either cross or are crossed by the ureters. Along the inner surface of the bladder, locate the ureteric openings, trigone, and the internal urethral orifice. Identify the sphincter urethrae and understand urine flow into the urethra.

  4. In cadavers that have a prostate, identify the seminal vesicles, vas deferens, ejaculatory duct, and rectovesical pouch.  Explore and understand the connections between these structures and the urethra and prostate.

  5. In cadavers that have/had a uterus, locate the uterus and uterine tubes, cervix, and vagina. Find the transverse cervical ligament (of the uterus), vesicouterine and rectouterine pouches.

  6. Trace branches of the internal iliac artery. Though there is variation, it is important to understand which organs or regions are served by parts of this artery.

  7. Trace the roots and major branches of the lumbosacral plexus. Note that some of these nerves go to the body wall and others to the lower limb. 

  8. Identify the muscles of the pelvic diaphragm: puborectalis, pubococcygeus, and iliococcygeus, and coccygeus (also called ischiococcygeus). Identify as well, the obturator internus which is not part of the pelvic diaphragm, but part of the pelvic wall. Locate the sacrospinous and sacrotuberous ligaments.  Understand how these structures work together to support the pelvic contents

 

Dissection Instructions

1. RECTUM AND ANAL CANAL

  1. Examine the clean inner surface of the rectum (MOVIE -courtesy of UMich) and anal canal (MOVIE - courtesy of UMich). The anus, like the urethra, is closed by an involuntary internal anal sphincter of smooth muscle, as well as a voluntary external anal sphincter derived from the body-wall musculature.

Atlas Images:

 
  1. Use your fingers to carefully separate the rectum from the more ventral organ (bladder or uterus).
  2. Note the autonomic nerve fibers (pelvic splanchnic nerves) passing forward on either side of the rectum to the bladder and pelvic organs. These fibers pass ventrally from the sacral region to reach the target organs.
  3. Contrast this with the vessels traveling medially from the side wall of the pelvis --the blood supply of the rectum will be studied in more detail below.

 

2. BLADDER AND URETHRA

  1. Pull the bladder away from the pubis.
  2. Note that the connective tissue in the retropubic space (the area between the bladder and pubis) is loose and filled with fat.
  3. Locate the condensations of connective tissue at the neck of the bladder that form ligamentous cords firmly anchoring the bladder to the pubis.
  4. Trace the ureters to the lateral corners of the bladder.

Cadavers with a prostate:

Cadavers with a uterus:

  1. Identify the two small openings of the ureters and the internal urethral orifice.
  2. Look for the trigone, the triangular region defined by the two ureteral orifices and the internal urethral orifice.
  3. Insert the tip of a probe into the orifice of the ureter.
  4. Note the diagonal course of the ureters through the wall of the bladder.
  5. In cadavers with a prostate, locate the external sphincter urethrae muscle below the prostate gland, but above the perineal membrane.
  6. Compare the urethral sphincters in cadavers with a prostate and cadavers with a uterus. Note, that in cadavers with a uterus, the presence of the vagina typically reduces the external sphincter urethrae to a U-shaped slip of muscle tissue running over the top of the urethral orifice.

Cadaver with a prostate:

Cadaver with a uterus:

FUNCTIONAL ANATOMY:

The loose connective tissue in the retropubic space permits mobility of the expanding bladder and cushions it from the pubic bones.

The diagonal course of the ureters through the wall of the bladder ensures that their distal ends are pressed shut when the bladder is distended. This prevents backflow of urine into the ureters. The three openings of the bladder form a triangle: the trigone, the triangular area of smooth mucosa bounded by the ureteric openings and the internal urethral orifice.

 

3. PROSTATE AND SEMINAL VESICLES (cadavers with a prostate)

  1. Identify the three parts of the urethra: prostatic urethra, membranous urethra, and spongy urethra.
  2. Examine the interior of the prostatic urethra.
  3. On the dorsal wall of the urethra, look for a small opening in the midline of the longitudinal urethral crest. This is the prostatic utricle.

NOTE - the utricle is a midline structure, and the two ejaculatory ducts (mentioned below) are just lateral to the utricle. Depending on the manner in which these structures were sectioned when the pelvis was hemisected, they may have been obliterated, or they may be visible on just one side of your cadaver.

  1. On either side of the utricle, find the two pinpoint openings of the ejaculatory ducts.
  2. Using a dissecting needle, attempt to probe the ejaculatory duct from the prostate back to the seminal vesicles. PLAY MOVIE to review this genital tract (courtesy of UMich).

Atlas Images:

FUNCTIONAL ANATOMY:

The ejaculatory duct conveys sperm and seminal fluid from the ductus deferens and seminal vesicle into the urethra. The prostate adds secretions via twenty or thirty small ducts visible as small openings along the length of the prostatic urethra.

f. Dissect the seminal vesicles and the ductus deferens out of the rectovesical fascia, located in the rectovesicle pouch between the bladder and the rectum.

Atlas Images:

 

4.  UTERUS, CERVIX, AND VAGINA (cadavers with a uterus)

  1. Examine the uterus and find its fundus and body.
  2. Identify the walls of the uterus: the internal endometrium, the thick and muscular myometrium, and the external perimetrium.
  3. From the superior part of the uterus, trace the uterine tube (fallopian tube) toward the ovary and find its various portions: isthmus, ampula, infundibulum, and the finger-like fimbriae.
  4. Inferior to the uterus, identify the cervix and locate the external os (connection between the cervix and vagina).
  5. In the superior portion of the vagina, probe the posterior fornix- the vaginal recess dorsal to the cervix. Note that the posterior fornix is in close association to the peritoneum of the rectouterine pouch. PLAY MOVIE to review this genital tract (courtesy of UMich).
  6. Identify the transverse cervical ligament along the base of the broad ligament, its attachment to the side of the uterus, and the uterine artery contained within it.

HINT– the transverse cervical ligaments are a meshwork of tissue rather than a defined ligament. In the act of dissecting to see the uterine artery and ureter, much of this ligament will be lost. Dissect carefully with awareness of where this structure is in order to appreciate its structure.

Atlas Images:

 

5a. INTERNAL ILIAC ARTERY- ANTERIOR DIVISION

  1. From the abdominal aorta, find the left and right common iliac arteries.
  2. The common iliac artery branches into the external iliac artery (going to the lower limb) and the internal iliac artery going to the pelvis.
  3. The veins in this region are large and cross in front of the arteries. If the veins are blocking the view of arteries, the veins can be removed.
  4. Find and identify the branches of the anterior division of the internal iliac artery (MOVIE of the pattern in a female -courtesy of UMich):
    1. Umbilical artery – find its obliterated remnant in the medial umbilical ligament and the superior vesical arteries, which branch from the patent portion of the umbilical artery. Branches from the superior vesical artery supply the bladder.
    2. Obturator artery – passes through the obturator canal
    3. Uterine artery (cadavers with a uterus)- passes through the transverse cervical ligament, superior to the ureter, and supplies the uterus.
    4. Vaginal artery (cadavers with a uterus)- is a branch of the uterine artery. The vaginal artery supplies the vagina.
    5. Inferior vesical arteries (cadavers with a prostate)- (equivalent to the vaginal artery) supply the bladder, seminal vesicle, ductus deferens, and prostate.
    6. Internal pudendal artery - passes through the greater sciatic foramen inferior to the piriformis muscle, and accompanied by the pudendal nerve.
    7. Middle rectal artery – identify by tracing it to the rectum.
    8. Inferior gluteal artery – exits the pelvis by passing through the greater sciatic foramen inferior to the piriformis muscle.

NOTE – the branching pattern of the internal iliac artery can be variable, not only between individuals, but sometimes even within a single individual (the right side might differ from the left). Be sure to keep this in mind as you do your dissection and find the arteries by tracing them to their target.

Cadavers with a uterus:

Cadavers with a prostate:

 

5b. INTERNAL ILIAC ARTERY- POSTERIOR DIVISION

  1. Find and identify the branches of the posterior division of the internal iliac artery:
    1. Iliolumbar artery - ascends between the obturator nerve and the ventral rami of spinal nerves L4 and L5
    2. Lateral sacral artery - running across Sl-S3
    3. Superior gluteal artery - between the lumbosacral trunk and S1 before passing through the greater sciatic foramen, superior to the piriformis muscle.
   

 

6. SACRAL PLEXUS

  1. Use your fingers to dissect the rectum away from the anterior surface of the sacrum and coccyx.
  2. Identify the rather large nerves of the sacral plexus of nerves (MOVIE - courtesy of UMich).
  3. Identify the following:
    1. lumbosacral trunk
    2. sciatic nerve
    3. ventral rami of S1-S4
    4. pudendal nerve You found the pudendal nerve in the ischioanal fossa. Understand that the pudendal nerve leaves the pelvis through the greater sciatic foramen, just posterior to coccygeus muscle, courses ventrally and enters the ischioanal fossa through the lesser sciatic foramen.

Cadavers with a uterus:

Cadavers with a prostate:

 

7a. PELVIC DIAPHRAGM: LEVATOR ANI (MOVIE - courtesy of UMich)

FUNCTIONAL ANATOMY: The pelvic diaphragm is body wall muscle and hence is innervated by ventral rami (S2-S4, pudendal nerve).

  1. Retract the rectum, bladder, prostate and seminal vesicles or uterus medially.
  2. Use blunt dissection to remove any remaining fat and connective tissue from the superior surface of the pelvic diaphragm. 
  3. Identify the three muscles that form the levator ani muscle:
    • Puborectalis muscle – its proximal attachment is the body of the pubis.
    • Pubococcygeus muscle – its proximal attachment is the body of the pubis. Its fibers run generally parallel to the puborectalis but more lateral. It attaches to the coccyx and the anococcygeal raphe.
    • Iliococcygeus muscle – its proximal attachment is the tendinous arch of the levator ani (also known as the fascia of the obturator internus). It attaches distally to the coccyx and the anococcygeal raphe.

NOTE – when you identify the muscles of the levator ani, make note also of the obturator internus muscle, part of which is visible above and below the tendinous arch from which the levator ani takes it origin. This is a helpful landmark for orienting yourself to the pelvis and perineum.

Atlas Images:

FUNCTIONAL ANATOMY:

The puborectalis forms the lateral boundary of the urogenital hiatus. It also forms a “puborectal sling” around the rectum that when contracted pulls the rectum and perineal body forward thus causing the anorectal flexure. During defecation, the puborectalis muscle relaxes, the anorectal flexure straightens, and the elimination of fecal matter is facilitated.

 

7b. POSTERIOR PELVIC DIAPHRAGM and PELVIC WALL (MOVIE - courtesy of UMich)

  1. Identify the (ischio)coccygeus muscle, which completes the pelvic diaphragm posteriorly. Its proximal attachment is the ischial spine and distally it attaches to the lateral border of the coccyx and the lowest part of the sacrum.

HINT– the coccygeus muscle parallels the sacrospinous ligament, one of two pelvic ligaments that form the boundaries for the greater and lesser sciatic foramina.

  1. Identify the obturator internus muscle, which forms part of the lateral wall of the pelvic cavity.

HINT - The proximal attachment of the obturator internus is the margin of the obturator foramen and the inner surface of the obturator membrane. Superior to the tendinous arch of the levator ani muscle, the obturator internus forms the lateral wall of the pelvic cavity. Inferior to the tendinous arch, the obturator internus forms the lateral wall of the ischioanal fossa in the perineum.

 

Atlas Images:

 

CLINICAL NOTES

Prostatic hyperplasia

Because the prostate lies inferior to the bladder and because the urethra passes through the prostate, enlargement of the prostate due to benign swelling (benign prostatic hypertrophy) or cancer can have profound effects on urination in men.  When the prostate swells it puts pressure on the bladder leading to the frequent need to urinate.  Men with BPH or other prostatic changes may produce smaller amounts of urine more frequently.  In addition, because the swollen prostate can compress the urethra it is often harder for men with BPH or other prostatic changes to produce a steady flow of urine or to initiate urination. Given what you have learned about pouches in the pelvis and the order in which organs are found, what would be the best way to digitally examine a patient for prostatic swelling?

 

Urethral Rupture

Unilateral rupture of the spongy (penile) urethra into the perineal cleft (the potential space between Colle’s and Gallaudet’s fascia) will first result in urine collection in the perineum and the scrotal sac on the same side as the rupture. Since the scrotal septum is not completely fused, continued urine collection will eventually spill into the perineum and scrotal sac on the other side as well.

Compare the image on the left showing spongy (penile) urethral rupture with the image on the right showing an intact urethra. 

 

Culdocentesis

To examine and collect abnormal fluid in the pelvis of female patients doctors perform culdocentesis.  In this procedure generally a needle is passed through the posterior fornix of the vagina.  Fluid is withdrawn through that needle. See the figure below.  Should the patient be prone or supine during this procedure?

Iliac artery occlusion
The internal iliac artery supplies blood to pelvic organs and to gluteal muscles that run from the pelvis to the femur and move the hip joint.  If the internal iliac artery is occluded, obstructed, or narrowed, blood flow to the gluteals can be reduced.  This vascular insufficiency can lead to pain. Cramping, and discomfort.  This is often referred to as buttock claudication and can be misinterpreted as neurological in origin. 

 

 

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