PROCEDURE

As biohazard bags may leak, always keep organs inside donor covering on top of the dissection tables or in biohazard bags within the organ box under the table.  Do not place the bags or organs directly on the floor or on chairs.

Landmarks across the abdomen most commonly follow the 'quadrant system'. This consists of an imaginary transverse line at the level of the umbilicus (the transumbilical plane) and a sagittal line at the midline. These divide the abdomen into a right upper quadrant, left upper quadrant, right lower quadrant and left lower quadrant. Physician notes often refer to quadrants to describe the location of clinical complaints (Netter251).

In the clinic you may also encounter the more detailed 'regional system' of nine squares in a tic-tac-toe pattern centered on the umbilicus. This is in less common use than the quadrant system (Netter251).

2. Fold back the blue drape and unzip/open the body bag, but do not unclip the inner plastic covering the donor.

These donors are under dissection by the Dental program and the inner layers should remain covering the donors to prevent dehydration while we are working.

3. Remove the abdominal organs on their tray from the translucent organ box under the table and use the area on top of the donors covered legs as your work area.

4. Take the abdominal organs out from the biohazard bag on their tray and arrange the organs on the tray into their correct orientations/positions.
    (Figure325) (Netter270) (Photo3003)

In this lab session we will be reviewing (reminding!) you of abdominal organ organization and examining internal structures of the gastrointestinal organs.

5. Begin at the superior aspect of the GI block and observe the liver, which occupies the upper right quadrant and extends across the midline into the upper left quadrant.
    (Figure325) (Netter270) (Photo3003)

6. Lift the inferior margin of the liver and identify the gallbladder.
    (Figure328) (Netter276)

The gallbladder is located just inferior to the right lobe of the liver and continues posteriorly behind the inferior border of the liver. 

The green coloration from the gallbladder is a result of the acidic pH of the chemicals used during embalming. The greenish chemical coloration often leaches out and stains surrounding tissues. In the living, the gallbladder has a bluish coloration. Bilious vomit is yellow-green in color  due to intrinsic yellow color of bile as well as contact of the bile with the stomach contents. 

Gallbladder removal is a relatively common surgical procedure, thus depending on the clinical history of the individual there may or may not be a gallbladder present. If the gallbladder is absent in your donor, examine the gallbladder of a nearby table.

7. Identify the stomach in the upper left quadrant  and examine the following.
    (Figure329) (Netter276) (Photo3003)

The esophageal entry point to the stomach is at the region called the cardia. To the immediate left of the esophageal opening is the fundus of the stomach.  The main portion of the stomach is called the body, and the region just prior to entering the duodenum is called the pylorus.

At the end of the pyloric part of the stomach find the pyloric sphincter where it joins the first part of the duodenum.  This can be felt as a muscular thickening of the wall at that point (and will be examined in detail below).

8. Continue from the pyloric sphincter into the duodenum, which consists of four parts

Superior (part 1): This is the transverse segment close to the stomach, and attachment region for the hepatoduodenal ligament containing the bile duct.

Descending (part 2): This segment takes a turn and descends inferiorly (retroperitoneal).

Horizontal (part 3): This segment traverses across to the left forming a 'C' shape curve with the previous segments. Within that curve lies the head of the pancreas.

Ascending (part 4): This segment turns superiorly and joins to the jejunum and may not be clearly visible.

This point is where the 4th part of the duodenum transitions from retroperitoneal to intraperitoneal and becomes the jejunum.

This point is held in place by the suspensory ligament of the duodenum (aka ligament of Treitz) in the mesentary spanning from the duodenum-to-jejunum junction to the diaphragm (transected during organ removal).

This ligament is where the small bowel transitions to intraperitoneal and serves as the clinical demarcation of upper and lower gastrointestinal tract.

9. Observe the pancreas with the head located in the 'C' curve of the duodenum and tail pointing towards the hilum of the spleen.

The spleen is in the upper left quadrant. The spleen is an abdominal organ (i.e. present in the abdominal cavity), but is not an organ of the gastrointestinal system. The spleen is a lymphoid organ important in immune responses and in elimination of aging erythrocytes.

The breakdown product of erythrocytes is bilirubin which is excreted via the biliary system of the liver.  Excessive bilirubin in the blood causes jaundice.

10. The small intestines continue into a series of loops of jejunum and ileum.
    (Figure330) (Netter270) (Photo3037) (Photo3003)

Loops of intestine are attached to the posterior abdominal wall by sheets of mesentery containing arteries, nerves, and veins supporting the organs. This mesentery connects along one side of the tube of intestines from the stomach to anus, commonly called the mesenteric border. The margin facing away from the mesentery is the anti-mesenteric border.

Surgically, anastomosis incisions along the mesenteric aspect are at risk of disrupting blood supply while anti-mesenteric incisions are less likely to disrupt supply. (Figure366)

11. Push all of the small intestine loops to the left and identify the start of the large intestine in the lower right quadrant.
    (Figure330) (Netter272)

The large intestine consists of several parts that you should identify.

Cecum - located just inferior to the ileocecal junction between the ileum and cecum nestled within the right iliac fossa. On the surface of the cecum note the tenia coli (longitudinal bands of smooth muscle) and their continuation on the rest of the parts of the colon. (Figure331) (Netter280)

Tenia coli - The tenia coli represent the outer longitudinal muscles that lie on the cecal surface and continue from it through all parts of the colon. When these muscular bands contract, bulges or out-pouches called haustra are formed. (Figure331) (Netter280)

Appendix - The appendix is attached to the inferior end of the cecum. If you have difficulty follow one of the tenia coli inferiorly as these all lead directly to the start of the appendix. (Figure331) (Netter280)

In some individuals the appendix may have been removed to treat appendicitis, thus it may not be present in every donor.

Also in some individuals fat filled peritoneal bags called omental appendices (or appendices epiploicae) may be present within the mesentery covering the colon. These are most commonly found in the transverse and sigmoid colon regions below.

Ascending colon - this ascends along the right margin of the abdomen and is secondarily retroperitoneal. It ends at the right colic (hepatic) flexure. Alongside the ascending colon is a 'gutter' formed by where it fuses with the right wall, this is the right paracolic gutter. (Figure330) (Netter272)

Transverse colon - The ascending colon turns to the left forming the transverse colon that crosses the abdominal cavity to end at the left wall. At the left wall the colon turns inferiorly, with this bend called the left colic (splenic) flexure and is the start of the descending colon. The transverse colon is suspended in the greater omentum and its position can vary between individuals depending on the size of the omentum. (Figure332) (Netter272) (Photo3037) 

Transverse mesocolon - Posterior to the transverse colon, connecting the transverse colon to the posterior wall, is a sheet of mesentery. This sheet is called the transverse mesocolon. (Figure330) (Netter272)

12. Push the small intestine loops to the right and examine the organization of the large intestine along the left quadrant.
    (Figure333) (Netter272) (Photo3037)

Descending colon - The descending colon begins at the left colic (splenic) flexure and extends inferiorly along the left abdominal wall (it is secondarily retroperitoneal). Alongside the descending colon is a 'gutter' formed by where it fuses with the left wall called the left paracolic gutter.

You may observe small 'ballooning' pouches on the descending colon which are diverticula. These are much smaller than haustra and typically bulge out from the larger haustra pouches. Diverticuli are quite common in the elderly and when inflamed or infected cause diverticulitis.

Sigmoid colon - The descending colon forms a 'S' like loop called the sigmoid colon in the lower left pelvic cavity (this is an intraperitoneal structure).

Rectum - the sigmoid colon ends in the rectum (which is not yet visible and will be examined in the pelvis section of the course).

PROCEDURE - Gastrointestinal System

13. Use scissors to make a longitudinal incision in the stomach along the anterior surface continuing the incision superiorly through the attached section of the esophagus.
    (Figure344a)

The gastric and gastro-omental arteries run along the lesser and greater curvature respectively, avoid cutting these as you open the anterior surface.

14. If there are stomach contents present, clean these out with a moist towel or wash with running water in one of the sinks as needed.

15. Spread open the stomach and examine the internal wall to identify:
    (Figure345) (Netter277)

Gastroesophageal sphincter (also known as the lower esophageal sphincter) - The gastroesophageal sphincter is present at the junction of the stomach and esophagus, but lacks any distinct anatomic features at rest and is what is called a 'physiological sphincter'.

In the lumen, may be able to see the change from a stratified squamous epithelium of the esophagus to the simple columnar epithelium of the stomach which occurs in a zigzag line (z-line), although tissue disruption post-mortem often makes this indistinct.

A physiological sphincter is one that is indistinguishable from the rest of the lumen wall in its resting arrangement, but upon specific neural control the muscle of the sphincter contracts forming a small ridge closing off the lumen.

Dysfunction of the physiological control of the gastroesophageal sphincter causes gastroesophageal reflux ('heartburn') and if occurring repetitively causes gastroesophageal reflux disease (GERD) scarring the mucosa of the esophagus.

The upper esophageal sphincter is also a physiological sphincter at the junction of the pharynx and esophagus, which opens as part of the swallowing process.

Cardia - The small region of stomach just inside the stomach after the gastroesophageal opening.

Fundus - The fundus is the region of the stomach to the left and superior to the esophageal opening.

Body - The body is the central region of the stomach making up the largest area of the stomach.

Pylorus - This region of the stomach is the terminal segment just prior to the entry point to the duodenum.

Rugae - These are folds in the inner surface of the stomach (gastric folds). Rugae allow the stomach to expand dramatically with a large meal. Rugae are flattened in the fully distended stomach.

16. Continue the longitudinal incision into the duodenum, following around the superior, descending, and a few centimeters into the horizontal segment of the duodenum.
    (Figure344b)

When opening the duodenal wall try to avoid cutting any of the any major vessels or ducts.

17. Using fingers palpate and open the pyloric sphincter, feeling the thick muscular orifice that forms this sphincter.

The pyloric sphincter is a clear anatomic sphincter, in contrast to the physiological sphincter of the gastroesophageal spincter.

18. Spread open the duodenum and examine the internal wall to identify the plicae circulares.
    (Figure346) (Netter279)

These are large folds in the internal wall of the duodenum (absent in superior segment of the duodenum).  Unlike rugae, plicae circulares are permanent and do not flatten with distention.

19. Use a blunt probe to follow the bile duct inferiorly towards the duodenum identifying the approximate point at which it contacts/enters the duodenum.
    (Figure346) (Netter288)

Just as the bile duct reaches the duodenum it is joined by the main pancreatic duct. The pancreatic duct extends the length of the pancreas with multiple branches receiving secretions from different parts of the pancreas. Most of the secondary duct branches are too small to see with the naked eye.

20. Examine the inner wall of the duodenum at approximately the point where the bile duct makes contact for the duodenal papilla.

This is an elevation of the mucosa on the medial wall of the duodenum and formed by the shared opening of the bile duct and main pancreatic duct.

There is typically a fold, or hood, on the wall superior to the papilla, although this varies considerably in size between individuals and can be indistinct.

21. Make a 10cm longitudinal incision in the wall of the proximal jejunum and another in the distal ileum and compare the internal wall in these two regions.
    (Netter279)

You may need to clean/wash any intestinal contents to allow you to see the interior wall.

Observe that the mucosal folds are larger and closer together in the jejunum compared to the ileum. 

Note however, the difference in fold arrangement is often indistinct post-mortem as all of the tract is in a relaxed non-distended state. This means the ileum folds are no longer flattened.

22. Make an approximately 10cm longitudinal incision in the anterolateral wall of the cecum and examine the internal wall.
    (Figure347) (Netter281)

You may need to clean/wash any intestinal contents to allow you to see the interior wall.

Ileocecal valve - This is the opening to the ileum, present on the medial wall of the cecum.

The muscularis externa in this region is slightly thicker forming a 'valve' that regulates flow of material from the ilium to caecum (approximately 2 liters of fluid passing daily). This thickening is rarely observable at the gross anatomy level.

Appendix opening - if the appendix is present, the opening is typically slightly inferior to the ileocecal valve. 

23. Examine the appendix (if one was present in your donor).

In some individuals the appendix may have been removed to treat appendicitis, thus it may not be present in every donor.

The appendix has a small segment of mesentery, the mesoappendix, spanning the appendix to ileum. This encloses the blood, nerve and lymphatic supply of the appendix.

24. Make an approximately 10-15cm long incision in the wall of the descending colon along the center of one of the tenia coli and examine the internal wall.

If you observed any diverticula place your incision such that you will be able to observe those from the inside.

You may need to clean/wash any intestinal contents to allow you to see the interior wall.

Observe the inner bulges of the haustra and the smooth inner lining of the colon.

Polyps are also common in elderly, so you may observe small protrusions into the lumen from the wall of the colon. These can look like small masses protruding from the wall or small mushroom shaped protrusions.

25. Return to the liver and examine the superior surface of the liver where the falciform and coronary ligaments are attached.
    (Netter284)

These ligaments serve as attachments of the liver to the diaphragm (coronary ligaments) and anterior abdominal wall (falciform ligament). The weight of the liver is supported by these attachments preventing the heavy liver 'crashing' inferiorly in the abdominal cavity.

26. Rotate to examine the inferior surface, taking care not to break vessel/ducts of the portal triad.
    (Figure348) (Netter284)

You should observe a roughly H shaped impression on the inferior surface of the liver.

The transverse part of the H marks the porta hepatis where branches of the hepatic artery, hepatic portal vein, and bile duct gains access to the liver.

The H impression also marks the separations of the liver lobes examined next.

Liver subdivisions of the liver have some variations in terminology.

The highest precision system is the segmental system (Couinaud classification) which divides the liver into 8 segments each supplied by a portal triad segmental branch (which arise from the main left/right branches). This is mostly of need for specialist liver surgery.

Anatomically, the liver is divided into a left lobe, right lobe, caudate lobe, and quadrate lobe, corresponding primarily to identifiable surface features.

Surgically, the liver is considered as a left part and a right part, corresponding to the left and right hepatic artery territories. (Figure365)

27. Examine the posterior surface of the liver to the right of the right arm of the H to identify the right anatomic lobe of the liver.
    (Figure348) (Figure365) (Netter284) (Netter287)

The right anatomic lobe is also demarcated by the line of the falciform ligament on the anterior surface of the liver.

The right anatomic lobe is the largest liver lobe approximately 6 times the size of the left anatomic lobe.

The bulk of the right anatomic lobe is supplied by the right hepatic artery and the right portal vein, and sends bile out the right hepatic duct.

28. Examine the posterior surface of the liver to the left of the left arm of  the H to identify the left anatomic lobe.
    (Figure348) (Figure365) (Netter284) (Netter287)

The left anatomic lobe is also demarcated by the line of the falciform ligament on the anterior surface liver.

The left anatomic lobe is supplied by the left hepatic artery and the left portal vein, and sends bile out the left hepatic duct.

29. Examine between the two arms of the H impression for the 'accessory' lobes of the liver, the caudate lobe posterior to the porta hepatis and the quadrate lobe anterior to the porta hepatis.
    (Figure348) (Figure365) (Netter284) (Netter287)

The quadrate lobe receives blood supply from the left hepatic artery (and left portal vein).

The caudate lobe receives mixed supply from both left and right hepatic arteries (and portal veins).

Surgically the liver is divided into a 'right part' and a 'left part' which line up with major vasculature, but are slightly different from the anatomic lobes. The left part of the liver extends past the falciform ligament to include the caudate and quadrate lobes (Couinaud segments 1, 4a, and 4b), essentially an imaginary line extended from the gallbladder across the superior surface. This simplifies conceptual thinking as the left part is supplied by the left hepatic artery, and the right part is supplied by the right hepatic artery.

30. Examine the posterior surface and observe the short segment of the inferior vena cava within the liver containing the openings for the right, left and middle hepatic veins.
    (Figure348) (Netter284) (Netter287)

In some cases where the hepatic vein entry points are deep you may need to make a short vertical incision in the wall of the inferior vena cava on the superior aspect of the vessel and spread the opening to see inside.

All of the blood that has traversed the liver, whether it originated from the hepatic arteries or the portal veins, returns to the inferior vena cava via the left and right hepatic veins. 

31. Observe the gallbladder which is forms the right arm of the roughly H shaped posterior impression on the liver.
    (Figure348) (Netter284) (Netter287)

Observe how the superior aspect of the gall bladder is in direct contact with the liver and the major part is covered by peritoneum.

The gallbladder is though to receive nerve fibers that also contact the right diaphragm, such that pain from the gallbladder (e.g. from cholecystitis) often refers to the right scapula (Murphy's sign), although the mechanism of this referred pain is poorly understood. This proposed mechanism is consistent with the scapula being innervated by the same cervical levels as the diaphragm.

Gently palpate the gall bladder to determine if there are any gallstones present. These will feel like hard 'rocks' that vary from a few millimeters across to over a centimeter across. They are very common with a 30-40% chance of some stones being present in your donor.

32. Make an incision in the superior aspect of the gallbladder and squeeze out bile content.

If bile stones are present wash and examine some of those.  The size, shape, coloration and composition of gallstones vary widely based on the chemical composition of the stones.

Most cases of gallstones are asymptomatic, but obstructive cholecystitis can be caused by small stones making their way down the biliary duct system and getting stuck. The typical block location is the narrowing at the hepatopancreatic ampulla (of vater) which is the narrowest point in the biliary system from the gallbladder out into the duodenum.

Remove and wash all of the gallstones if any are present and bring them to the support table where there will be a small glass jar. This is to add the stones to the laboratory pathology collection for future teaching use.

CLINICAL EXERCISE - Liver Resection

-- The liver has four major lobes, but similar to the lung also subdivides into eight discrete segments with independent vascular supply (these are called Couinaud segments or simply hepatic segments, the boundaries of these segments are not important at the moment). A discretely localized cancer in the liver can be managed by resection of the segment containing the mass.

- In this clinical exercise, you will perform a hepatic segment wedge resection. For the steps to perform:
                                          ------ click here ------>

33. Using the 6" knife in your tools tray, make an anterior to posterior cut separating a section of the far right lobe of the liver.
    (Photo3063) (Photo3063a)

A dry knife tends to 'catch' on soft tissues, thus this knife will cut most effectively if the knife and groove being cut are liberally moistened with wetting agent.

34. Make two additional anterior to posterior slices through the right lobe of the liver each approximately 1cm thick.
    (Photo3063b) (Photo3063c)

35. Examine the surface of the cross sectional slices through the liver.
    (Photo3064)

Cross sectional surfaces of the liver should have relatively uniform parenchyma with cross section cuts through small to medium portal triads and hepatic veins. The magnifier in your special tools box may help you observe smaller triad/vessel cross-sections.

Within the portal triads there is a bile duct (usually light green), an hepatic artery branch (smaller, thick wall) and a portal vein branch (larger with thin wall). The portal triads are subsidiary branches of the main ducts/artery/vein traveling together down to microscopy diameters. The triads travel within each of the segments of the liver.

The hepatic veins are the output of the liver and travel between liver segments. These veins not accompanied by bile ducts or hepatic artery branches. Thus, an isolated vein is likely an hepatic vein.

In some donors, you might observe large 'patches', as large as several inches in size, that have a different coloration tone than the surrounding liver (usually darker). These are most likely an hepatic hemangioma, which is a tumor formed by a tangle of blood vessels. The hepatic hemangioma is benign, often asymptomatic, and quite common (~5% of individuals). (Photo3064a)

Liver sclerosis is also common and can manifest as smaller pale patches dispersed throughout the cross-section representing sclerotic (scar) tissue in the liver.

CLINICAL EXERCISE - Simple continuous suturing

- Any surgical intervention involves an opening through the integument and deeper structures that must be closed to repair the structure or prevent infection. The most traditional and common method of closing an opening is by suture (additional methods utilizing staples and surgical adhesives depending on the procedure).

- In this clinical exercise, you have the chance to practice simple continuous suturing in your donor. A video of simple continuous suturing is available in the introduction section of the Dissector and can be brought up with this link ------ video ------>

- For the steps to perform:
                                         ------ click here ------>

35. Review the overall vasculature connections of the gastrointestinal tract foregut, midgut, and hindgut.

Remember that arteries are named based on their distribution target. Where the vessel originates is useful to observe, but always trace where a particular vessel is going when trying to make an identification.

Foregut - Celiac trunk (Photo3010)

Midgut - Superior mesenteric artery (Photo3011)

Hindgut - Inferior mesenteric artery (Photo3012)

Venous return - Portal venous system (Photo3013)

36. Review the overall neural connections of the gastrointestinal tract foregut, midgut, and hindgut

The gastrointestinal tract receives both sympathetic (thoracolumbar) and parasympathetic (craniosacral) innervation. These extrinsic autonomic systems regulate the function of the intrinsic neural system of the gastrointestinal tract, the enteric nervous system.

Foregut (parasympathetic) - Vagus
Foregut (sympathetic) - Greater splanchnic (T5-9)
                                    - Celiac ganglia

Midgut (parasympathetic) - Vagus
Midgut (sympathetic) - Lesser splanchnic (T10-11)
                                    - Superior mesenteric ganglia

Hindgut (parasympathetic) - Pelvic splanchnic
Hindgut (sympathetic)  - Least splanchnic (T12)
                                        (+Lumbar splanchnic L1-2)
                                      - Inferior mesenteric ganglia

In reality there is cross-talk between ganglia and the respective nerves, so the higher level neural control of the gut is more complicated than the simplistic presentation classically described above.  Where relevant, the course will delve into some of those complexities.

The enteric nervous system is distributed throughout the walls of the gastrointestinal tract in thousands of microscopic ganglia and axons. The enteric nervous system is capable of independent function. Thus, the enteric nervous system will function in the absence of 'top down' autonomic innervation from the central nervous system.

37. When finished, place your organs back into the biohazard bag (without the tray) and return them to the translucent organ storage box under the table.

The tray can be placed on the platform/tub under the organ box.

38. Clean the work area, zip up the donor body bag, and re-cover the donor with the blue drape.

Post-Lab Daily Clinical Review Cases

Each lab has several multiple choice practice cases to reinforce understanding of the material within the lab and associated lectures. These are optional to review at home for consolidating and testing understanding.

Case 01

Case 02

Case 03

Case 04

CHECKLIST

Soft Structures

Liver
    Left, right, quadrate, and caudate lobes
    Porta hepatis
    Left and right hepatic veins

Duodenum
    Superior segment
    Descending segment
    Horizontal segment
    Ascending segment
    Plicae circulares
    Duodenal papilla

Stomach
    Gastroesophageal junction
    Fundus
    Body
    Pylorus
    Pyloric sphincter
    Rugae

Pancreas
    Head
    Neck/Body
    Tail

Jejunum

Ileum

Cecum
    Ileocecal valve
    Appendix opening

Appendix
    Mesoappendix