Dissector Answers - Duodenum, Pancreas, Liver, & Gallbladder

Learning Objectives:

Upon completion of this session, the student will be able to:

  1. Identify and describe the parts and peritoneal relationships of the duodenum and pancreas.
  2. Describe the pattern of common vasculature of the duodenum and pancreas.
  3. Trace the potential collateral blood flow between celiac and superior mesenteric arterial territories, and between superior and inferior mesenteric arterial territories.
  4. Trace the pathway of common entry of the bile ducts and pancreatic ducts into the 2nd part of the duodenum.
  5. Identify parts of the liver and describe the relationships of its portal venous, hepatic arterial, and hepatic venous circulation.
  6. Identify the structures passing into and out of the porta hepatis and some of the most common variations on this pattern.
  7. Describe the peritoneal relationships of the liver and gallbladder.
  8. Explain the discrepancy between the external lobulation of the liver and the true internal segmentation of the liver based on the branching of the intrahepatic arteries, veins, and ducts.

Learning Objectives and Explanations:

1. Identify and describe the parts and peritoneal relationships of the duodenum and pancreas. (W&B 458-466, N268, N279, N279, TG5-26,TG5-01,TG5-26)

Because of their close functional and spatial relationships, as well as a shared blood supply, it is logical to consider the duodenum and the pancreas together.

The duodenum (Latin, duodeni = 12 each) (N268, TG5-01) is the connecting pipe between the stomach and the small intestine. (FYI: both "du-uh-DEE-num" and "du-AH-de-num" are correct pronunciations.) It is mostly retroperitoneal. The exceptions are the first 2cm of the first part (ampulla, duodenal cap) and the duodenojejunal junction. (The latter is not technically part of the duodenum.) The duodenum has four parts: (N279, N279, TG5-26B.TG5-26C)

For the opposite viewpoint of the above list, from the duodenum's "perspective", see N298 or TG5-26.

The pancreas (Greek, pankreas = sweetbread) is an accessory digestive organ. It is retroperitoneal, except for its tail. It makes enzymes that aid in chemical digestion of food. (This is its "exocrine" role. The pancreas also has an "endocrine" role with insulin, glucagon, and all that business.) It is also divided into four parts:

2. Describe the pattern of common vasculature of the duodenum and pancreas. (W&B 463-465, NN301,N304, TG5-27B,TG5-27C)

Both the duodenum and the pancreas receive blood from the celiac trunk and the superior mesenteric artery. They serve as a site for anastomosis between these two large systems. The body and tail of the pancreas are supplied mostly by branches of the splenic artery, namely the great, superior, caudal, and dorsal pancreatic arteries.

3. Trace the potential collateral blood flow between celiac and superior mesenteric arterial territories, and between superior and inferior mesenteric arterial territories. (W&B 463-465, 487, NN301,N304,N306,N307,TG5-13,TG5-14,TG5-27B,TG5-27C)

As described above, there is collateral circulation between the celiac and superior mesenteric arterial territories as they both supply the head of the pancreas and the duodenum. Collateral circulation between the superior mesenteric and inferior mesenteric arterial territories occurs via the marginal artery, which is effectively a very large arterial arch that supplies the entire colon (not discussed in Moore).

4. Trace the pathway of common entry of the bile ducts and pancreatic ducts into the 2nd part of the duodenum. (W&B 461, 470-472, N294,N298,N295,TG5-24B,TG5-24C,TG5-26)

This image is not to scale with regard to the size of the gallbladder relative to the other organs. Connectivity is also not anatomically accurate, but is meant to be illustrative.

Fresh bile from the liver drains out via the right and left hepatic ducts, which join to become the common hepatic duct. Stored bile leaves the gall bladder via the cystic duct. (Please note that bile from the liver also enters the gallbladder via the cystic duct, by traveling retrograde, when the GI tract does not need bile to aid in digestion of food and bile is therefore stored.) The common hepatic duct joins the cystic duct to form the common bile duct. (Greek, kystis = bladder, pouch)

The main pancreatic duct begins in the tail of the pancreas and receives tributaries all along its path to the head of the pancreas. Often there is also a separate accessory pancreatic duct (N 298), which drains independently into the duodenum via the lesser (minor) duodenal papilla.

Usually, the main pancreatic joins the common bile duct right before entering the duodenum, so they both dump their contents via the greater (major) duodenal papilla (comprised of the ampulla of Vater, or hepatopancreatic ampulla, and the sphincter of Oddi). There is variation in this anatomy, for example, independent dumping of the pancreatic and common bile ducts into the duodenum via separate papillae (N N295).

5. Identify parts of the liver and describe the relationships of its portal venous, hepatic arterial, and hepatic venous circulation. (W&B 466-468, N287,N289,N310,N301,N312,N289,N291,TG5-19,TG5-21,TG5-22A,TG5-22B,5-28)

Surfaces: Anatomical lobes (see #8 below):

The gallbladder, IVC, ligamentum teres, ligamentum venosum, and porta hepatis all combine to form an H-shape on the liver's visceral surface (W&B 466, N289,TG5-21). The anatomical lobes can be described with respect to this group of structures:

The liver receives arterial blood from the aorta via the celiac trunk, which gives off the common hepatic artery (N310 or TG5-19) as a branch. This artery gives off the proper hepatic artery (N301 or TG5-27), which then divides into the right and left hepatic arteries. Further branching occurs as the arteries supply the hepatic tissue.

The liver also receives the portal vein (N312 or TG5-28), which brings nutrients and other compounds absorbed from the GI tract to be stored and/or processed. Within the liver, the portal vein divides into right and left branches of the portal vein, then further into segmental branches.

The portal venous and hepatic arterial circulation are closely related structurally, with very similar branching patterns within the right lobe. The other lobes have similar branching as well, but are subject to more variation than the right. (The bile ducts also follow this pattern, but of course they are transporting their contents in the other direction.) (N289,N288,N291,TG5-22,TG5-23) This total arrangement is similar in concept to the pulmonary circulation, where the pulmonary arteries, bronchial arteries, and bronchioles have similar branching patterns. Continuing that line of thought, the hepatic veins are similar to the pulmonary veins in that they reside between lobes (segments) and drain blood from two or more adjoining areas.

6. Identify the structures passing into and out of the porta hepatis and some of the most common variations on this pattern. (N287,N315,N309,N310,N301,N307,TG5-19,TG5-21,TG5-27,TG5-35)

The porta hepatis allows passage of the portal vein, hepatic artery, hepatic bile ducts, lymphatic vessels, hepatic nerve plexus (N287 or TG5-27). It is similar to a "hilum", like in the lung or a lymph node. There is also branching of the portal vein and hepatic artery that occurs in the porta hepatis. (N315,N319,TG5-22A,TG5-22B)

As for variations, we are mostly talking about the arterial supply here. In 83% of the cases, the proper hepatic artery arises from the common hepatic artery and branches into right and left hepatic arteries. In 14% of people the right hepatic artery is an independent branch of the SMA and has nothing to do with the common hepatic artery. In 18% of people the left hepatic artery comes from the left gastric artery, either as an accessory to the "normal" left hepatic artery or as the only left hepatic artery. (Note that these situations with the right and left hepatic arteries are not mutually exclusive, which explains why these don't add up to 100%.) Finally, 4% of the time the common hepatic artery is itself a branch of the SMA, but from there the anatomy is "normal". (W&B 475, N310,N301,TG2-25)

When on this topic, we also have to consider the cystic artery, which is a VERY important structure to find during a cholecystectomy. Usually, the cystic artery is a branch of the "normal" right hepatic artery (72%). Of course, if you have one of those 14% where the right hepatic artery comes from the SMA, you would expect the cystic artery to be a branch of that "funky" right hepatic artery (13%). Other uncommon variations include: cystic artery as branch of a normal proper hepatic artery (6%), cystic artery from left hepatic artery, crossing anterior to the bile duct(s) (3%), and cystic artery as an independent branch of the gastroduodenal artery, again crossing anterior to the duct (3%). (W&B 476, N295,TG2-25).


For more than you ever wanted to know about anatomical variation, the University of Iowa has a great site, an "Illustrated Encyclopedia of Human Anatomic Variation". Here is a quick and dirty link to the section on abdominal arteries (including the hepatic arteries).
7. Describe the peritoneal relationships of the liver and gallbladder. (W&B 467-468)

The liver develops in the ventral mesogastrium, between the stomach and the body wall (check out W&B 441). The connection between the liver and the body wall remains as the falciform ligament (N287,TG5-21) in the adult, while the connection between the liver and the stomach remains as the lesser omentum (N275,TG5-18). The falciform ligament encloses the ligamentum teres hepatis (N229,TG5-21), the remnant of the umbilical vein that brought oxygenated blood from the placenta to the fetal heart. The falciform ligament stretches from the umbilicus to the liver as a double-layered fold. Upon reaching the liver, the layers diverge, with one covering the visceral surface and the other covering the diaphragmatic surface of the liver. (Don't get confused... these are both still visceral peritoneum.) The layer that covers the diaphragmatic surface reflects onto the body wall (and turns into parietal peritoneum) forming the anterior layer of the coronary ligament (W&B 466, Figure 6-40 A). The layers of peritoneum covering the visceral part of the liver also diverge, forming the posterior layer of the coronary ligament (N287,TG5-21). Where these anterior and posterior layers meet are the right and left triangular ligament. (Latin and English combo, falciform = shaped like a scythe or sickle, Latin, teres = round)

8. Explain the discrepancy between the external lobulation of the liver and the true internal segmentation of the liver based on the branching of the intrahepatic arteries, veins, and ducts. (W&B 468-469, N289,TG5-23)

The anatomical lobes of the liver, which are based on external appearance, differ slightly from the functional (surgical) lobes of the liver, which are based on distribution of the portal vein, hepatic arteries, and hepatic bile ducts. The line of division between left and right is created by the gallbladder and the IVC (one side of the "H" we discussed above). This line divides the liver into right and left portal lobes (older terminology). There is also a third part, the posterior part of the liver, which is the anatomical caudate lobe. It used to be divided into right and left caudate lobes, but now they are combined.

When all is said and done, the liver has 8 functional segments:

posterior part:
posterior segment (I)
left part:
left lateral division:
lateral segment (II)
lateral anterior segment (III)
left medial division:
medial segment (IV)
right part:
right medial division:
anterior medial segment (V)
posterior medial segment (VIII)
right lateral division:
anterior lateral segment (VI)
posterior lateral segment (VII)

Hint: Don't memorize this. Just know that the functional division is different from the anatomical division, and that it is based on blood supply and bile drainage.


Cultural enrichment: Check out these sections from the 1918 version of Gray's Anatomy of the Human Body! Some of the terms are (of course) out-of-date, but the illustrations are timeless.
The Liver - The Pancreas - The Portal System of Veins - The Abdominal Aorta - Surface Anatomy of the Abdomen - Surface Markings of the Abdomen

Questions and Answers:

9. Is the superior (1st) part of the duodenum peritoneal or retroperitoneal? (N275,N279,TG5-18,TG5-26)

Both. The first 2 cm has a mesentery, the hepatoduodenal ligament. The rest of the superior part of the duodenum is retroperitoneal.

9a. What is the suspensory muscle of the duodenum? ( N270,TG5-26)

The suspensory muscle of the duodenum (also known as the ligament of Trietz) is a thin sheet of muscle fibers derived from the right crus of the diaphragm that suspends the fourth part of the duodenum (the duodenojejunal flexure or junction) from the posterior abdominal wall.

10. What is the relation of the horizontal (3rd) part of the duodenum to the superior and inferior mesenteric arteries? (N279,TG5-26)

The 3rd part of the duodenum is crossed anteriorly by the SMA and vein. It is superior to the IMA.

11. Carefully trace the common bile duct as it courses behind the first part of the duodenum and the head of the pancreas to the medial wall of the second part of the duodenum. Does an artery cross it? (N304,TG5-27)

The posterior superior pancreaticoduodenal artery from the gastroduodenal artery passes anterior to the duct as it passes to the right, then travels inferiorly posterior to the common bile duct.

12. How does the posterior arcade differ from the anterior arcade? (NN301,N304,TG5-27B,TG5-27C)

The posterior arcade is further away from the duodenum, so its vasa recta to the duodenum must be longer.

12a. Do you find veins with the arterial arcades of the pancreas and duodenum? (NN301,N304,TG5-27BTG5-27C)

The respective veins travel with the arteries of the duodenum and pancreas. They drain to the superior mesenteric vein and/or the portal vein.

13. Does the splenic vein receive the inferior mesenteric vein? (N311,N312,N313,TG5-14,TG5-28)

Yes... well... sometimes. The splenic vein receives the inferior mesenteric vein in slightly more than a third of individuals, while inferior mesenteric vein first unites with superior mesenteric vein in approximately one third of individuals. In the remaining individuals (slightly less than a third), the three veins unite at the same point to form the portal vein.

13a. Do you have an accessory pancreatic duct? (N279,TG5-26)

Do you? Most people do. The small accessory pancreatic duct drains the upper part of the head of the pancreas to the lesser duodenal papilla within the wall of the descending (2nd) part of the duodenum.

14. Do you find a lesser duodenal papilla? Are there differences between it and the greater duodenal papilla.? (N279,TG5-26)

The lesser duodenal papilla can usually be found superior and anterior to the greater duodenal papilla. The accessory pancreatic duct opens here.

15. Into which part of the duodenum do the common bile and pancreatic ducts open? (N279,TG5-26)

The descending (2nd) part of the duodenum.

15a. Where is the inferior vena cava? (N287,N310,TG5-19)

The inferior vena cava lies embedded within the posterior surface of the liver.

16. Where are the cystic veins? (N312,N313,TG5-28)

Small cystic veins pass from the gallbladder into the liver through the bed of the gallbladder. There is an anterior and posterior branch.

17. What are the fetal functions of the round ligament of the liver (ligamentum teres hepatis, a remnant of the obliterated umbilical vein), and the ligamentum venosum? (N229,TG5-21B,TG5-21C)

The round ligament of the liver was the umbilical vein that carried well-oxygenated and nutrient rich blood from the placenta to the fetus. The ligamentum venosum is the fibrous remnant of the fetal ductus venosus that shunted blood from the umbilical vein to the IVC, short-circuiting the liver before birth.

18. Identify the hepatic veins. How many are there? (N265,TG5-34)

Hepatic veins are formed by the union of the central veins of the liver and open into the IVC just inferior to the diaphragm. There are three: left, right and middle hepatic veins.

19. Did you find any hepatic lymph nodes? (N315,TG5-35)

The superficial lymphatics can be found in the subperitoneal fibrous capsule of the liver.

20. Review all of the tributaries of the portal vein and completely organize its drainage pattern. What organs does it drain? (N312,TG5-28)

The portal vein collects low oxygen, high nutrient blood from the GI tract and spleen.

21. Is there any relationship between this intrahepatic pattern and the division of the liver into right and left lobes based on external appearance? (N289,TG5-23)

See #8 above.

 

Updated: 11January 2012