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Schedule

Lab 6 -GI Tract Removal, Urogenital System, Posterior Abdominal Wall

Suggested reading:
Gray's Ch. 4 (340-403)

Primary Lab Objectives and Goals:

  1. Identify the three major arteries that supply the gut: the celiac trunk, and superior and inferior mesenteric arteries. Examine the blood supply of the sigmoid colon. Cut all of these arteries and prepare the gut for removal.

  2. Examine the external anatomy of the gut, and view the inner structures that allow you to understand differences in anatomy.  Understand the differences in arcades of vessels and fat in the different regions, and the unique anatomical features of the colon.

  3. Study the arrangement of the branches of the superior mesenteric artery supplying the jejunum and ileum.

  4. Identify the divisions of the digestive tract.  Carefully trace your way from the stomach to the duodenum, ilium, jejunum, cecum, and then the ascending, transverse and descending colon (the sigmoid colon may be hard to find). Understand the flow of digestive contents.

  5. Locate the gonadal, renal, and suprarenal vessels. Understand blood flow into the kidneys and pelvis. Focus on the developmental movements of those organs.

  6. Section the kidney and trace the ureters from the kidneys to the bladder. Understand the blood flow into the kidneys and the urine flow from renal structures (pyramids and calyces) to the bladder.

  7. Examine the pouches formed by the reflections of the peritoneum on the pelvic viscera.
  1. Examine the diaphragm and note the passage of the major vessels and structures passing through the openings.

 

Procedure:

1. GUT REMOVAL

NOTE: Before severing the arteries, carefully study their positions. You will need to re-identify them later. You may wish to tie them with string to make this easier.

  1. Sever the three primary branches of the celiac trunk (the left gastric, splenic, and hepatic arteries) close to their origins .
  2. Do the same to the superior and inferior mesenteric arteries.

HINT: the superior mesenteric artery is directly below the celiac trunk. You may cut through both without realizing it, so carefully examine the aorta to identify these trunks.

 

 

  1. Trace the branches of the inferior mesenteric artery to the sigmoid colon (sigmoid arteries) and the rectum (superior rectal artery).
  1. Mobilize the sigmoid colon, noting the extent of the sigmoid mesocolon and any lymph nodes within the mesocolon.
 
  1. Tie off the esophagus and sigmoid colon with two strings at each end (see diagram below).
  2. Cut between each pair of ties at each end

NOTE: It is VERY important that you use TWO strings, about ½ inch apart, at each end of the gut. This is to prevent the spillage of gut contents into the abdominal cavity. This can be especially unpleasant in the area of the sigmoid colon. You will need to reach your hand deep into the abdominal cavity towards the pelvis in order to find the sigmoid colon. When you choose a section, make sure that it is not “full”. If it is, find another gut section close by that you can tie off and cut instead.

 
  1. Remove the entire gastrointestinal tract between these two points, together with its glandular derivatives (liver and pancreas) and the spleen.

NOTE: While you are removing the GI tract, try to identify the inferior mesenteric artery and cut it cleanly. Sometimes this becomes torn very close to the aorta, which makes it difficult to find afterwards.

You may also have to leave a small piece of liver attached to the hepatic veins entering the inferior vena cava. Do not cut any vessels or nerves until you understand where they come from and go to.

 

 

 

2.  STRUCTURES OF THE GI TRACT

  1. Examine the external anatomy of the GI tract, delineating regions of the gastrointestinal system supplied by the superior and inferior mesenteric arteries

Atlas Images:

 

 

  1. To examine the internal anatomy, tie off small segments (~5-10 inches each) from each region of the GI tract (duodenum, jejunum, ileum, and colon) and cut a longitudinal opening (as shown below) to reveal the inner surface.

NOTE: Check with your lab instructor to determine whether the GI tract of your cadaver is suitable for internal examination - some cadavers may have GI tracts that can be opened along their entire length.

  1. Clean out each opened section by running it under water in the large steel sinks. Matter should be removed from the sinks with paper towels to prevent clogging.
  2. Within the duodenum find the openings of the pancreatic and biliary ducts.
  3. Note the differences between the small intestine with its villi and small pouches, and the colon with no villi and large pouches.  These differences have key clinical significance and are important to visualize in lab. 
  4. Look for aggregates of lymph nodules (visible as pale, white patches) in the walls of the small intestine.

Atlas Images:

 

 

 

3. SUPERIOR MESENTERIC ARTERY

  1. Compare the arrangement of the terminal branches of the superior mesenteric artery (vasa recta) to the jejunum and ileum.
  2. When your group has finished examining the gut, place the entire gut into a plastic bag for storage.  

 

 

 

 

4. POSTERIOR ABDOMINAL WALL

  1. Examine the posterior abdominal wall. 
  2. Locate the stubs of the three midline gut arteries you transected (the celiac trunk, superior and inferior mesenteric arteries).

NOTE: In about 50 percent of all cadavers, a dilation called the cisterna chyli is present at the point where the somatic and visceral lymphatics join.  The lymphatic system is exceedingly variable, and almost any named lymph trunk is apt to take the form of a plexus.

  1. Look in the area between the abdominal aorta and IVC, at the approximate level of the celiac trunk/superior mesenteric artery, to determine whether a cisterna chyli is present in your cadaver.  If your cadaver does not have a cisterna, find a neighbor whose cadaver does and examine it.

Atlas Images:

 

 

 

5. VESSELS OF THE KIDNEYS

  1. Remove the parietal peritoneum covering the posterior abdominal wall.
  2. Trace the renal arteries from the aorta laterally to the kidneys.
  3. Trace the suprarenal arteries from the kidneys to the suprarenal glands of the superior pole of the kidneys.
  4. Trace the testicular or ovarian arteries from just below the renal arteries on the aorta and follow them down to the pelvis (you will look at them in detail later).
  5. Trace the corresponding veins on each side.  
  6. Note the differing pattern of venous drainage on the left versus right sides.
  7. Find the accompanying gonadal veins coming off the left renal vein and IVC respectively.

Atlas Images:

 

  1. Delicately clean the fatty capsule of the left kidney away from the friable (easily crumbled) suprarenal gland.  
  2. Review the suprarenal gland's nervous and vascular connections.
  3. Attempt to section a suprarenal gland and distinguish the medullary substance from the less vascular cortex.

Atlas Images:

 

 

 

6. SECTION THE KIDNEYS

  1. Section the left kidney in the frontal plane and study its internal anatomy.

    NOTE: the kidney is usually covered in a thick layer of fat, even in thin individuals. The easiest way to get the kidney out is to simply stick your fingers into the fat until you feel the kidney. Then grab it and ease it out of its fatty layer.

  1. Note the blood supply to the ureter.
  2. Follow the ureter into the pelvis to where it connects to the bladder at the ventral wall near the pubic symphysis.

You will examine the bladder in more detail in a later lab. 

  1. Trace urine flow from pyramids to minor calyces, to major calyces, to the renal pelvis, to the ureter, to the bladder.

Atlas images:

 

 

 

7. POUCHES

FUNCTIONAL ANATOMY

The celoem does not extend far into the true pelvis: thus, there is a peritoneal “roof” to the pelvic basin. This “roof” is indented from below by various organs and vessels. In the male, the peritoneum dips caudally between the bladder and rectum to form a rectovesical  pouch;  this is divided into a vesicouterine pouch and a rectouterine pouch by the uterus in the female.

  1. Find the rectovesical pouch in the male, and the vesicouterine and rectouterine pouches in the female.
  2. Examine a neighbor's cadaver of the opposite sex.

Atlas Images:

 

 

 

8. OPENINGS IN THE DIAPHRAGM

  1. Examine the diaphragm
  2. Note the aortic and esophageal openings, and the opening in the central tendon for the inferior vena cava.
  3. Determine the vertebral levels at which each opening is positioned.
 

 

 

Clinical correlations

 

1. Perforating peptic ulcers

Duodenal and stomach ulcers are generally caused by Helicobacter pylori or ulcerogenic drugs such as Non-Steroidal Antiinflammatories, and are characterized by atacks of nausea, heartburn and epigastric pain, which become worse when the stomach is empty, and are relieved by eating food and taking antacids. If these mucosal erosions are allowed to progress they may burn through the duodenal or stomach walls, resulting in a perforating ulcer and spilling stomach contents and acids into the body cavity causing acute abdominal pain. Anterior perforations can lead to chemically triggered and then bacterial peritonitis, and posterior perforations cause bleeding from compromise of the gastroduodenal artery as it passes posteriorly to the first portion of the duodenum to the greater curvature of the stomach, hence immediate surgical intervention is needed.

 

2. Appendicitis

Appendicitis is generally caused by blockage of the lumen of the vermiform appendix, and development of infection and inflammation in the sac distal to it. The classical presentation of appendicitis includes acute onset of a loss of appetite, nausea and constipation, with pain beginning in the epigastric and umbilical region and transfering to the lower right quadrant of the abdomen, with the area of most acute pain at McBurney's point – a point one third of the way to the umbilicus on a line joining the right anterior superior iliac spine to the umbilicus. The usual surgical approach, a small McBurney’s incision perpendicular to this spinoumbilical line at McBurney’s point, should provide access to the appendix while preserving maximal muscle and nerve function, although particular care should be taken in women of childbearing age to ensure that the symptoms are not attributable to conditions of the reproductive tract, since the incision cannot be easily extended into this region.

Atlas Image:

 

 

 

 

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