Abdomen Lab 6a

1. Dissect the organs of the posterior body wall, remember these structures are retroperitoneal:

   • Kidneys

   • Aorta and its branches

   • IVC and its tributaries

2. Have a detailed look at the diaphragm muscle, and the muscles of the posterior body wall

3. 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.

Identify the following:

• Adrenal (suprarenal) vessels:

  • 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

HELPFUL HINTS

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

• Lumbar vv.

• Middle sacral v.

• Common iliac vv.

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.

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)