Dissect the organs of the posterior body wall, remember these structures are retroperitoneal:
Kidneys
Aorta and its branches
IVC and its tributaries
Have a detailed look at the diaphragm muscle, and the muscles of the posterior body wall
Dissect out and identify the nerves of the posterior body wall
Using blunt dissection and scraping, remove the remaining peritoneum and extraperitoneal fat to identify the following:
Kidneys - lateral to vertebrae T12-L3; use scissors and your fingers to remove the parietal peritoneum and perirenal fat from over and around the kidneys respectively
Ureters - use forceps to free the ureters from the parietal peritoneum and fat; extend from the renal pelvis to the urinary bladder, you will not be able to follow the ureters to the bladder at this time.
Adrenal (suprarenal) glands - positioned on the superior pole of each kidney; pale in color and somewhat triangular shaped
Abdominal aorta - use forceps to dissect through the parietal peritoneum to reveal the aorta (and neighboring vena cava and branches); the abdominal aorta courses longitudinally to the left of the midsagittal line, on the anterior surface of the vertebral bodies
Inferior vena cava - courses longitudinally to the right of the midsagittal line, also on the anterior surface of the vertebral bodies
Iliac crest - palpate its internal surface
Diaphragm - move the liver and stomach to different positions to see the diaphragm
Appreciate the distribution of the lymphatics of the posterior abdominal wall. Lymph nodes may be difficult to find. Recall that lymphatics usually follow the course of venous drainage and thus, you should probably be able to intuit where the lymph in these lymph nodes came from.
Kidneys - left and right; observe that the right kidney is slightly lower than the left kidney due to the presence of the liver in the upper right quadrant of the abdomen (we’ll cut open the kidneys in the next block)
Perirenal fat - each kidney is embedded in a substantial layer of fat; with your fingers, shell out the kidneys from the perirenal fat
Adrenal glands - each adrenal gland is separated from the superior pole of each kidney by a layer of connective tissue; use forceps or your fingers to separate the adrenal glands from the kidneys, but leave the adrenal blood vessels intact!
Ureters - cross the psoas major m. and course deep to the gonadal vessels en route to the true pelvis (urinary bladder); use forceps to delineate both ureters, but do not cut the ureters!
It may be difficult to differentiate the adrenal glands from the perirenal fat pad so look carefully.
Identify the following:
Superior suprarenal a. - arises from the inferior phrenic a.
Middle suprarenal a. - arises from the aorta
Inferior suprarenal a. - arises from the renal a.
Suprarenal v. - usually drains to the renal v.; only one vein compared to the three arteries; the veins are asymmetric
The adrenal vessels are fairly thin and may be difficult to identify. It is difficult to find 3 distinct adrenal arteries so do what you can.
Use forceps to reveal and identify the following:
Abdominal aorta - courses longitudinally to the left of the midsagittal line, on the anterior surface of the vertebral bodies; the bifurcation of the abdominal aorta is at the L4 vertebra
Inferior phrenic aa. - paired arteries that arise immediately inferior to the diaphragm; first paired branches from the abdominal aorta; give superior suprarenal aa. to the suprarenal glands
Celiac trunk - T12 vertebral level; unpaired artery; supplies the foregut
Superior mesenteric a. - L1 vertebral level; unpaired artery; supplies the midgut
Inferior mesenteric a. - L3 vertebral level; unpaired artery; supplies the hindgut
Middle suprarenal a. - paired arteries from the abdominal aorta, near the level of the celiac trunk; supplies the suprarenal glands
Renal aa. - L1 vertebral level; paired arteries that originate between the superior and inferior mesenteric aa.; the left renal a. is shorter than the right renal a.; multiple arteries are frequently encountered (expect variation); give rise to the inferior suprarenal a. Gonadal (testicular/ovarian) aa. - L2 vertebral level; paired arteries that arise inferior to the renal aa. and superior to the inferior mesenteric a.; cross anterior to the ureters and external iliac vessels
Lumbar aa. - four paired arteries that course laterally across the sides of vertebrae L1-L4; segmental blood supply of the lumbar region
Median sacral a. - unpaired artery that arises from the abdominal aorta at its bifurcation into the common iliac aa.
Common iliac aa. - paired arteries from the distal end of the aorta at the L4 vertebral level; each bifurcates into the external and internal iliac aa.
Use forceps to reveal and identify the following branches of the inferior vena cava:
Right renal v. - shorter than the left renal v.
Right suprarenal v. - drains the right adrenal gland; only one suprarenal v. drains each adrenal gland compared to the three adrenal aa. that supply each gland
Left renal v. - crosses anterior to the aorta and just inferior and posterior to the superior mesenteric a.
Left suprarenal v. - one vein also drains the left adrenal gland
Left gonadal (testicular/ovarian) v. - drains the left gonad into the inferior border of the left renal v.
Right gonadal v. - drains the right gonad into the inferior vena cava
You may not be able to see the inferior phrenic vv. and hepatic vv. because the liver will be in the way. Also, note that the superior and inferior mesenteric vv. are not tributaries to the inferior vena cava, rather they are tributaries to the portal venous system.
Rupture of an aneurysm (localized enlargement) of the abdominal aorta causes severe pain in the abdomen or back. If unrecognized, a ruptured aneurysm has a mortality of nearly 90% because of heavy blood loss. Surgeons can repair an aneurysm by opening it, inserting a prosthetic graft (such as one made of Dacron) and sewing the wall of the aneurysmal aorta over the graft to protect it. Aneurysms may also be treated by endovascular catheterization procedures.
In this section, we will be looking at the muscles of the posterior abdominal wall, including the diaphragm, as well as their associated structures.
If you haven’t done so already, you should cut out part of the liver to free up some space and to better visualize the adjacent viscera. Preserve the part of the liver attached to the porta hepatis and the gallbladder.
The diaphragm is a dome shaped muscle that separates the thoracic cavity from the abdominal cavity. If not already cut, cut the peritoneal reflections from the diaphragm muscle to the liver. To cut those reflections, use your fingers to locate them and scissors to cut them. This procedure will mobilize (free) the liver so that it may be moved away from the diaphragm.
Identify the following:
Central tendon - remnant of the transverse septum, observe the opening for the inferior vena cava (vena caval hiatus)
Muscular part - observe the openings for the esophagus (esophageal hiatus) and the aorta (aortic hiatus)
Right crus - originates lateral to the aortic hiatus; loops around the esophagus to form the esophageal hiatus, the physiologic sphincter of the esophagus
You may observe a muscle slip coursing inferomedially from the right crus of the diaphragm to the duodenojejunal junction - this is the suspensory ligament of the duodenum
Left crus - move the stomach and spleen away from the diaphragm; the left crus is lateral to the aortic hiatus; fleshy fibers contribute to the medial arcuate ligament
Median arcuate ligament - formed by the right and left crura arching over the aorta
Medial arcuate ligaments - tendinous thickenings of the diaphragm; form the openings for the psoas major mm.
Lateral arcuate ligaments - tendinous thickenings of the diaphragm; form openings for the quadratus lumborum mm.
The medial and lateral arcuate ligaments may be better visualized from the thorax side of the diaphragm depending on the ease with which you can move around your cadaver’s abdominal viscera.
Use forceps and your fingers to remove the parietal peritoneum and fat from both sides of the posterior abdominal wall to identify the following:
Psoas major m. - long muscle attached to the bodies and transverse processes of L1-L5 vertebrae
Overlaps the medial portion of the quadratus lumborum m. and crosses anterior to the sacroiliac joint; passes inferior to the inguinal ligament to insert on the lesser trochanter of the femur
The lumbar plexus of nerves arises from the lumbar transverse processes, exits the intervertebral foramina, and emerges between the psoas major muscle fibers, where they arise from the lumbar transverse processes
Psoas minor m. - this thin muscle courses anteriorly on and medial to the psoas major m.; inserts distally on the pecten pubis (the psoas minor m. is sometimes absent)
Quadratus lumborum m. - quadrilateral-shaped muscle that is lateral and deep to the psoas major m.
Iliolumbar ligament - courses from the ilium to the lumbar vertebrae along the attachment of the quadratus lumborum m.
Iliacus m. - located in the iliac fossa of the pelvis; attaches to the iliac fossa and courses distally to the lesser trochanter of the femur (may be covered by a considerable amount of fat)
Use forceps to remove residual fat from the posterior abdominal wall to dissect the following nerves. Dissect all of the following nerves long their entire course, then return to the nerves in the listed sequence to identify them by name. Again, expect variation.
Subcostal n. (T12 spinal cord segment) - scrape/dissect through the peritoneum and fascia inferior to rib 12; emerges inferior to the lateral arcuate ligament and descends on the anterior surface of the quadratus lumborum m. before passing through the transversus abdominus m. laterally
Lumbar plexus - emerges laterally from the muscle belly of the psoas major m.; locate the following nerves lateral to the psoas major m.:
Iliohypogastric and ilioinguinal nn (both L1 spinal cord segment) - diverge from their common trunk at the lateral, superior border of the psoas major m.; course across the quadratus lumborum m. prior to crossing the transversus abdominis m. above the iliac crest; may arise as a single nerve and split within the layers of the abdominal wall musculature
Genitofemoral n. (L1-L2 spinal cord segments) - located on the anterior surface of the psoas major m. (the only nerve that emerges from the anterior surface of the psoas major m.); divides on the distal portion of the psoas major m. into the genital branch (exits the abdomen through the deep inguinal ring) and the femoral branch (courses with the external iliac a. on route to the thigh)
Lateral femoral cutaneous n. (L2-L3 spinal cord segments) - located along the lateral border of the psoas major m., where the psoas major m. crosses the iliac crest; crosses the iliacus m. before passing deep to the inguinal ligament en route to the thigh
Femoral n. (L2-L4 spinal cord segments) - located deep and lateral to, and often overlapped by, the psoas major m. near its union with the iliacus m.; courses deep to the inguinal ligament en route to the thigh
Obturator n. (L2-L4 spinal cord segments) - probe the fat deep and medial to the inferior portion of the psoas major m. near the sacral promontory to reveal the obturator n.