Anatomy Dissection Classes

• Abdominal cavity
• Stomach & intestines
• Liver, gall bladder, pancreas & spleen
• Self-directed learning

The aim of this class is to explore the greater sac of the peritoneal cavity, noting (i) the position of organs covered by peritoneum, (ii) the mesenteries, ligaments and omenta which suspend organs from the abdominal wall or connect them to each other, (iii) the compartments, spaces, pouches, and recesses of the cavity where air, blood or other body fluids might collect.

By the end of the class you should appreciate how the "essential services" of mobile organs may reach them (via mesenteries, ligaments and omenta) and how the organs may be approached surgically without damaging these folds. You should also appreciate where the lesser sac of the peritoneal cavity lies and how it communicates with the greater sac.

In the abdomen:

• the falciform and triangular ligaments of the liver;
• the subphrenic spaces;
• the coronary ligaments, the bare area of the liver;
• the hepatorenal pouch;
• the stomach and lesser omentum;
• the epiploic foramen and its boundaries;
• the gastrophrenic ligament;
• the gastrosplenic and lienorenal ligaments;
• the left phrenicocolic ligament;
• the greater omentum and transverse mesocolon;
• the paracolic gutters;
• the attachments of the roots of the mesentery;
• the peritoneal recesses into which internal herniae may form;

• the rectovesical pouch;

• the uterus and broad ligaments, the recto-uterine pouch (pouch of Douglas), and the uterovesical pouch;

• the folds raised by the urachus, the obliterated umbilical arteries and the inferior epigastric arteries.

Background reading - read the sections in your textbook on:

• the abdominal and pelvic peritoneum
• the greater and lesser sacs
• the general arrangements of the abdominal viscera

Before beginning the dissection, examine the isolated organs and prosections on display. Consider their size and shape. Check their position in the abdomen. Identify:

1. the stomach;
2. the liver and gall bladder;
3. the spleen;
4. the duodenum and pancreas;
5. the kidneys;
6. the jejunum and ileum;
7. the caecum; appendix; ascending, transverse, descending and sigmoid colon; the rectum.

When in situ, which of these organs lie retro-peritoneally on the posterior abdominal wall?

Parietal peritoneum lines the walls of the abdominal cavity. It clothes the anterior and posterior abdominal walls, the under surface of the diaphragm and the cavity of the pelvis. What is the nerve supply of the parietal peritoneum?

The visceral peritoneum is continuous with the parietal peritoneum. It leaves the posterior abdominal wall to invest certain viscera. In some cases, it passes in front of the organ (e.g. duodenum), in other cases it leaves the posterior abdominal wall as two leaves lying together to form a mesentery which completely invests the organ (e.g. small intestine). The upper parts of the pelvic organs (rectum, uterus, bladder) project into the abdominal cavity and are therefore covered by visceral peritoneum which hangs down in depressions or pouches between them.

In both sexes the peritoneal cavity is completely closed, as is the abdominal cavity in the male. However, in the female, the abdominal cavity communicates with the exterior through the uterine tubes, the uterus and vagina.

Begin by locating and identifying the falciform ligament which runs from the anterior wall of the abdominal cavity to the liver. Its free border contains the ligamentum teres. Of what is the ligamentum teres a remnant?

Now examine the exposed abdominal viscera within the peritoneal cavity. You must appreciate that the disposition of the viscera within the cavity varies considerably in normal subjects. Also, adhesions may be present, due to pathological processes. What is an adhesion?

It is therefore important that you study as many specimens as possible, both male and female. If adhesions are present, ask for help!

DORSAL ABDOMINAL WALL with lines of peritoneal reflections.

The mobile organs, liver, stomach, spleen, small intestine, transverse colon, pelvic colon - have been removed and the cut edges of mesenteries and ligaments are shown. Retro-peritoneal organs remain in situ. Label them.

Find the greater omentum and the transverse colon attached to its posterior surface. Gently raise the great omentum and transverse colon. You will find that the transverse colon is attached to the posterior abdominal wall by the transverse mesocolon (mesocolic shelf), thereby dividing the abdominal cavity into a supracolic compartment and an infracolic compartment.

The supracolic compartment lies between the diaphragm above and the transverse mesocolon below. Identify the liver and gall bladder, the stomach, duodenum and spleen. Note the hepatic and splenic flexures of the colon at the right and left extremities of the transverse mesocolon.

Transverse sections through the abdomen: the lower diagram showing the lesser sac below the level of the greater curvature of the stomach; the upper diagram showing the arrangement at the level of the Foramen of Winslow (epiploic foramen).

Between the liver and the diaphragm is the subphrenic space. Run your hand into this narrow space (from the front) and note that it is divided into right and left parts by the falciform ligament. Your hand is prevented from running right over the top of the liver by the reflection of peritoneum that connects the liver to the diaphragm. This is the coronary ligament. There is a "bare area" between the liver and diaphragm, bounded by the coronary ligament.

Under the liver you will find the subhepatic channel. Its inferior limit is the transverse mesocolon. On the right, there is a deep, narrow space limited behind by the dorsal abdominal wall and the right kidney. This space is known as the hepato-renal pouch (of Rutherford Morison). Note that it is directly continuous with the right paracolic gutter (see below). The hepato-renal pouch is of surgical importance. Why?

Find the stomach. Note the hepato-gastric (gastro-hepatic) ligament, thin and veil-like, which suspends the lesser curvature of the stomach from the liver. This ligament continues onto the first part of the duodenum as the hepato-duodenal ligament. These two ligaments (hepato-gastric and hepato-duodenal) are together known as the lesser omentum. Identify the free margin of the lesser omentum on its right side. Identify the three structures at the free border and make a note of their relation one to another.

Pass a finger behind the free edge of the lesser omentum. Your finger will enter an opening, the epiploic foramen (of Winslow), which leads into a recess of the peritoneal cavity, situated behind the stomach, the lesser sac (omental bursa).

With your finger still in the epiploic foramen, describe its boundaries:

Locate the greater curvature of the stomach. A peritoneal fold attaches it superiorly to the diaphragm. This is the gastrophrenic ligament. To the left, the fold runs to the spleen, as the gastrosplenic ligament. The left gastroepiploic artery runs in the ligament. From the spleen, this same fold continues to the posterior abdominal wall where it attaches, in the region of the left kidney, forming the lienorenal ligament. The splenic artery runs in the ligament. At the lower end of the stomach, the fold runs between the greater curvature and the transverse colon, and is called the gastrocolic ligament. Identify these various ligaments which arise from the greater curvature.

Run your hand into the upper left side of the abdomen and find the spleen. Put your hand between the diaphragm and spleen and gently draw the spleen forwards on its pedicle. Move your hand behind the spleen and you should feel the upper pole of the left kidney. The lienorenal ligament runs between the spleen and kidney.

The infracolic compartment (greater sac) lies below the transverse mesocolon and contains the main mass of intestinal coils. Projecting forwards in the midline is the prominence made by the lumbar vertebrae and the associated psoas muscles. This median "watershed" is flanked on either side by the iliolumbar fossa. The whole cavity is therefore shallowest in the midline and deepest laterally.

Find the beginning of the large intestine in the right iliac fossa. The ascending colon runs upwards to the hepatic flexure, below the liver. The transverse colon runs between hepatic and splenic flexures. Once again, define its mesentery and the greater omentum. The splenic flexure is at a higher level than the hepatic. This is associated with the great bulk of the liver on the right. Find the small transverse fold of peritoneum between the splenic flexure and the diaphragm, the phrenico-colic ligament. Note that there is no phrenicocolic ligament on the right. The descending colon runs vertically down to the pelvic brim where it continues as the sigmoid (pelvic) colon. Find the left and right paracolic gutters on the lateral aspects of the ascending and descending colons.

How do they differ?

Make a note of their communications. Why is this clinically important?

The small intestine lies in the concavity of the colon and is suspended by the mesentery from the posterior abdominal wall. Confirm that the duodenum has no mesentery. The attachment of the mesentery begins at the duodenojejunal flexure and slopes downwards and to the right, to the right sacroiliac joint. Examine the mesentery and note the pattern of the blood vessels within it. Describe any differences you see between the pattern of blood vessels to the jejunum and those to the ileum.

Discuss with a demonstrator the paraduodenal fossae. They may be the site of "internal herniae". Explain such herniae.

A more common type of internal hernia is a hiatus hernia. What is this?

Examine the infracolic compartment between the ascending and descending parts of the colon. It is divided into left and right parts by the oblique attachment of the mesentery to the posterior abdominal wall. The left infracolic compartment communicates with the pelvis. Why is this important?

Trace the small intestine to its termination in the right iliac fossa. Locate the caecum and the appendix (if present!). Find the meso-appendix. It contains some important vessels. Which ones?

The pelvic peritoneal cavity is continuous with the abdominal peritoneal cavity. Define the pelvic brim. Trace the sigmoid colon down into the pelvis. It is suspended by the sigmoid mesocolon, which attaches it to the pelvic wall in an inverted "V" arrangement over the division of the left common iliac artery. Locate the rectum. Note that it is retroperitoneal.

In the male, define the upper surface of the bladder. Try to locate the vas deferens, the ureter and the seminal vesicles. Define the rectovesical pouch of the peritoneum.

In the female, define the recto-uterine pouch (of Douglas). Define the uterus, uterine tubes, ovaries and the broad ligament. Find the bladder and the uterovesical pouch.

NOTES ON VISCERAL SENSATION

1. Sensation from viscera can be crudely divided into "normal" (usually associated with motility and/or distension) and "abnormal" (i.e. painful).
2. (a) "Normal" sensory information from viscera is transmitted through the visceral sensory fibres of the parasympathetic nervous system.

Where are the cell bodies of the relevant peripheral axons:

2. "Painful" sensory information from viscera is transmitted through the visceral sensory fibres of the sympathetic nervous system.

Where are the cell bodies of these peripheral fibres?

Painful sensations from the viscera are vaguely localised to the median plane, no matter the location of the viscus.

BUT.....

1. All viscera are invested with a layer of the lining of the body cavity, i.e. visceral pleura, pericardium, peritoneum. The sensory supply to this visceral membranous layer is by the visceral sensory fibres described above.

The parietal layers of these membranes are, however, innervated by sensory branches of somatic nerves. Therefore, if the pathology comes to include the parietal membranous layer, the pain now localises well, because it signals through the somatic systems.

Thus, early in acute appendicitis, when only the vermiform appendix and visceral peritoneum are inflamed, pain is felt in the central abdomen; as soon as parietal peritoneum in the right iliac fossa is involved, the pain localises to the fossa. However, one does not experience a pain "in the appendix", or even "in the parietal peritoneum", but in the fossa, i.e. associated with the somatic structures of the abdominal wall.

This phenomenon is known as referred pain. It explains why, for example, cardiac pain is felt in the left arm (among other places); or gall bladder pain in the right shoulder; or ureteric pain in the external genitalia. If you do not understand upon what innervation patterns these particular referrals are based, find out.

Objectives

1. Describe the gross anatomy, understand the function and demonstrate the relations of the following structures: stomach, duodenum, jejunum, ileum, caecum, appendix, ascending colon, transverse colon descending colon and sigmoid colon.
2. Describe the blood supply, lymph drainage and innervation of the gastrointestinal tract.
3. Relate the blood supply and lymphatic drainage of the gastrointestinal tract to its development.
4. Describe the origin, course, distribution and relations of the arteries supplying the abdominal viscera.
5. Outline the venous drainage of the gastrointestinal tract.
6. Describe the lymphatic drainage of the gastrointestinal tract.
7. Compare the blood supply of the jejunum and ileum
8. Define the portal venous system and explain its main function.
9. Define the portosystemic anastomoses; explain their clinical significance and list the main sites at which such anastomoses occur.
10. Discriminate between sympathetic and parasympathetic nerves in terms of their origin, organisation and function.
11. Describe the pathways by which autonomic fibres reach the abdominal viscera.

Background reading - read the sections in your textbooks on:

• the abdominal organs
• the arterial supply, venous and lymphatic drainage of the alimentary canal
• the innervation of the gastrointestinal tract
• the development of the gastrointestinal tract and its derivatives

The lesser sac is now open. Pass a hand behind the stomach, into the lesser sac. Pass a finger of the other hand through the foramen of Winslow and make contact. Define the boundaries of the lesser sac. Behind the stomach, on the posterior abdominal wall, identify the following:

the pancreas;

the splenic artery;

the left kidney and adrenal gland.

The stomach is a muscular bag, fixed at both ends, much of which lies under cover of the lower ribs.

On the stomach identify the following:

Is the cardiac orifice an "anatomical" sphincter?

Is the pylorus an "anatomical" sphincter?

Now find the greater and lesser curvatures. Identify the blood vessels closely related to these two curvatures.

Concentrate on the lesser curvature (both anterior and posterior surfaces). Branches of the anterior (left) and posterior (right) vagus may be seen sinking into the muscular wall of the stomach. What are the nerves of Latarjet and what is their function?

Study the relations of the stomach. Name at least six.

What is Troisier's sign?

Three arteries leave the aorta and pass ventrally to supply the gastrointestinal tract. The most cranial one, the coeliac trunk, supplies the foregut and its two derivatives (liver, pancreas) and the spleen. The second one, the superior mesenteric, passes within the mesentery to supply the midgut. The last one, the inferior mesenteric, runs into the transverse mesocolon to supply the hindgut.

The coeliac trunk.

This is the artery of the foregut, and its three branches supply the gastrointestinal tract down to the opening of the common bile duct into the duodenum, plus the liver, spleen and pancreas.

Label the diagram of the coeliac trunk and its branches overleaf.

Define the coeliac trunk in your cadaver as it arises for the aorta, at the upper border of the pancreas.

At what vertebral level is the coeliac trunk given off?

Note the coeliac ganglia. They lie on each side of the coeliac trunk.

Locate the three branches of the coeliac trunk. The left gastric artery enters the lesser omentum and runs along the lesser curvature of the stomach. Find the splenic artery as it runs to the left, along the upper border of the pancreas. Look for the hepatic artery as it passes downwards and to the right behind the peritoneum of the posterior abdominal wall before entering the lesser omentum.

List the main branches arising from these three arteries and make sure you know their course and distribution.

Look at the general disposition of these structures. Displace the greater omentum and transverse colon superiorly so that the small bowel can be examined. Starting from the duodeno-jejunal junction follow the jejunum and the ileum to the start of the large bowel. Note that there is no macroscopic demarcation between jejunum and ileum. The bowel does, however, change its character from above downwards. With the help of the diagram below name five points that will enable a surgeon to determine the level of a loop of small intestine during an operation.

What is Meckel's diverticulum?

Next study the large bowel. it can easily be distinguished from small bowel by:

What is diverticulosis?

What is diverticulitis?

Now concentrate on the area of the ileocaecal junction and appendix. Make sure you know this region well. The frequency of appendicitis demands it! Bear in mind that the first operation you will probably perform might be an appendectomy.

Find the caecum. It is the blind pouch of large bowel that projects downwards from the beginning of the ascending colon, below the ileocaecal junction. Its posterior wall may be firmly attached to the posterior wall of the right iliac fossa or, more commonly, separated from it by a retrocaecal fossa which can extend as far up as the liver.

The vermiform appendix is attached to the posteromedial wall of the caecum, below the ileocaecal junction. Its length and position varies considerably. Compare the appendices of the cadavers on all the neighbouring tables.

Identify the mesoappendix. This is the mesentery of the appendix; the appendicular artery runs in it. Where does this artery originate?

Why is appendicitis more common in children?

ACUTE APPENDICITIS

A common abdominal condition. Pain usually begins as para-umbilical discomfort, accompanied by malaise, and diarrhoea or constipation. (It is dangerous to use laxatives in cases of suspected appendicitis: vigorous contraction of the gut wall often ruptures the inflamed appendix, precipitating peritonitis). The temperature is usually raised. Within 2448 hours the pain refers to the right iliac fossa. The site of maximum tenderness (which is pain elicited by the probings of the examiner) is at McBurney's point. This lies at the junction of the lateral one-third with the medial two-thirds of a line joining the anterior superior iliac spine to the umbilicus. In 65% of adults the appendix is retro-caecal; in 25% it hangs over the pelvic brim. A pelvic location for an inflamed appendix may be anticipated before surgery by digital examination through the anal canal.

Pus from an appendix abscess can track upwards in the right paracolic gutter to reach the subphrenic space (between the thoracic diaphragm and liver). Referred pain in the right shoulder ensues.

The appendix is removed through a McBurney grid-iron incision (refer back to practical 1). The caecum is delivered through the incision and the root of the appendix found by tracing the taeniae coli. A long retro-caecal appendix may also be retro-colic (retroperitoneal behind the ascending colon) and a second incision may be required to gain proper access so as to mobilise the colon to remove the appendix intact. The colon is most easily freed from its lateral side. Why?

Examine the ascending colon. It runs from the right iliac fossa to the hepatic flexure under the right lobe of the liver. From the hepatic flexure, it runs almost horizontally to the splenic flexure, invested in its mesentery, the transverse mesocolon. The descending colon, extends from the splenic flexure to the pelvic brim, where it acquires a mesentery (the sigmoid mesocolon) and becomes the sigmoid colon. The rectum will be studied together with the other structures in the pelvis.

The artery of the midgut is the superior mesenteric artery which supplies the gut from the entrance of the bile duct into the duodenum to a level just short of the splenic flexure of the colon. It arises from the front of the aorta about one centimetre below the origin of the coeliac trunk.

At what vertebral level is the superior mesenteric given off.

Locate the superior mesenteric artery as it descends over the third part of the duodenum. Its first branch is the inferior pancreatico-duodenal artery. Where does the superior pancreatico-duodenal artery come from?

Trace the following branches of the superior mesenteric artery:

• jejunal;
• ileal;
• ileocolic;
• right colic;
• middle colic.

Make sure you know the course and distribution of these important vessels. What is the blood supply of the appendix? How does it reach the appendix?

Complete the labelling of the following diagram:

The artery of the hindgut is the inferior mesenteric artery. It supplies the gut from the splenic flexure up to and including the rectum. At what vertebral level is the inferior mesenteric artery given off?

Name the main branches of the inferior mesenteric artery. Make sure you know their course and distribution.

What is the marginal artery?

It is convenient to study the venous return with the arterial supply as the two are essentially similar. The vessels draining the foregut and its derivatives ultimately drain into the portal vein. They roughly correspond to the arteries of the foregut. Locate the portal vein on the dissection.

The oesophageal veins are important. Why?

The venous drainage of the midgut is quite regular. Each branch of the superior mesenteric artery is accompanied by a vein. All these veins ultimately flow into the superior mesenteric vein, a large trunk which lies to the right of the artery. Locate this vessel on the dissection. Confirm that it receives the splenic vein behind the neck of the pancreas. Here, the superior mesenteric vein acquires a new name, the portal vein. Note that it is named portal vein above and superior mesenteric vein below the level of entry of the splenic vein, but the two represent a single continuous trunk.

What is the destination of the portal vein?

What is the purpose of the portal circulation?

What anastomoses exist between the portal and systemic venous systems?

In the diagram below, colour the systemic venous system blue and the portal system purple. Label the regions of porto-systemic anastomosis (1 - 3), which are liable to become varicosed in portal hypertension.

The inferior mesenteric vein receives tributaries identical to the branches of the inferior mesenteric artery. The vein runs vertically upwards and joins the splenic vein, behind the body of the pancreas. Confirm this on the dissection.

Why is knowledge of the lymphatic drainage of the gastrointestinal tract important?

From virtually the whole length of the gastrointestinal tract the lymph vessels pass back along the course of the arteries to lymph nodes that lie in front of the aorta at the origins of the coeliac, superior and inferior mesenteric arteries. These are called the coeliac, superior and inferior mesenteric groups of lymph nodes. Hence if you know the arterial supply to the gastrointestinal tract and its associated glands, you almost always know its lymphatic drainage. The exception to this general rule is the rectum. Although the major artery of the rectum is the superior rectal branch of the inferior mesenteric artery, lymph also follows the middle rectal artery to the internal iliac lymph nodes. (You will consider this further when you study pelvis & perineum).

The coeliac, superior mesenteric and inferior mesenteric lymph nodes are also termed preaortic nodes. They drain into each other from below upwards, the coeliac group itself draining into the cisterna chyli.

Which lymphatic channel originates from the cisterna chyli?

The pre-aortic nodes are, however, the last in a series of lymph node "filters" that lie between the mucous membrane of the gut and the cisterna chyli.

The first filtering mechanism consists of isolated lymphatic follicles which lie in the mucous membrane of the alimentary canal. What are Peyer's patches?

From the follicles lymph drains to nodes that lie in the peritoneal attachments at the margins of the intestine and from there to nodes that are found halfway between the gut and the aorta. Finally lymph will drain into the pre-aortic nodes.

All parts of the gut and its derivatives are innervated by parasympathetic and sympathetic nerves. Most come from the coeliac plexus but the inferior hypogastric (pelvic) plexus

contributes parasympathetic fibres to the hindgut.

The coeliac plexus receives its parasympathetic input from the two vagus nerves. What is their function?

What is the myenteric plexus of Auerbach?

What is the plexus of Meissner?

The sympathetic contribution to the coeliac plexus is from the splanchnic nerves. What is their function?

Where do they arise? How do they reach the abdomen?

By now you should be absolutely clear what is meant by the term "referred pain" and you should know where pain from the appendix is referred. Discuss this with a colleague and/or demonstrator if you are unsure.

Objectives

By the end of this practical and any further necessary study you should be able to describe the gross anatomy, understand the function and outline the relations of the following structures:

• Liver
• Gall bladder and biliary system
• Duodenum
• Pancreas
• Spleen

Background reading - read the sections in your textbooks on:

• liver and biliary tree
• duodenum
• pancreas
• spleen

Consider the relations of the liver and complete the labelling on the following diagram of the posterior aspect of the liver:

Look at the liver and revise its peritoneal reflections. Define the following:

• Falciform ligament
• Coronary ligament
• Bare area of the liver
• Left and right triangular ligaments (these are little more than the left and right extremities of the coronary ligaments).

What structure is found in the free edge of the falciform ligament?

Locate the porta hepatis and name the structures going through it.

On the posterior surface of the liver identify the inferior vena cava. Venous blood leaves the liver through the three (usually) hepatic veins. These veins provide partial support (anchoring) to the liver.

Name two other factors that will contribute to the support of the liver.

Identify the left and right lobes. The right is the larger of the two. The left is smaller and incorporates the quadrate and caudate lobes. Identify these lobes. Discuss with a demonstrator the segmentation of the liver, according to its arterial supply. It is of great surgical importance. You will hear more about this in the clinical symposium on liver surgery.

Diagram showing the segmentation of the liver:

What proportion of the liver tissue can be sacrificed in the event of surgery to eliminate carcinoma of the liver?

Which lobe is usually preserved and why?

Examine the gall bladder. It is usually firmly attached to the underside of the liver. Identify the fundus, body and neck. The narrow neck gives way to the cystic duct. What is the function of the gall bladder?

What is biliary colic?

What is Murphy's sign?

Bile is manufactured by the liver cells. It is collected into microscopic canaliculi. These will eventually drain into the left and right hepatic ducts. These join (usually at the porta hepatis) to form the common hepatic duct. This in turn is joined by the cystic duct to form the common bile duct. At this stage, remind yourself of the structures that run in the free edge of the lesser omentum. What is their relationship one to another?

What and where is the sphincter of Oddi?

Complete the labelling on the following diagram:

If a gallstone became lodged at the sphincter of Oddi, which other organ would be affected?

What is the blood supply of the gall bladder? Where does it come from?

Learn the blood supply, venous drainage, lymphatic drainage and innervation of the liver and gall bladder.

Write a short account of the peritoneal reflections of the liver:

List the relations of the liver:

Examine the duodenum. The initial 2.5cm lies within peritoneum, the rest is completely retroperitoneal. It consists of four parts. Appreciation of the directions of the four parts is important. Identify and describe the various parts. Make a note of their direction.

Label the diagram below:

The duodenum terminates at the duodeno-jejunal flexure. There is no distinction between the duodenum and jejunum apart from the peritoneal arrangement: the duodenum is retroperitoneal, the jejunum has a mesentery.

Identify the common bile duct and main pancreatic duct where they enter the second part of the duodenum at the duodenal papilla.

Complete the labelling of the diagram:

THE BILIARY DUCTS

The accessory pancreatic duct opens about 2 cm proximal to the papilla.

Discuss the relations of the duodenum. Name as many as possible.

Learn the blood supply and lymph drainage of the duodenum.

The pancreas is a soft, lobulated gland lying immediately behind the peritoneum of the posterior abdominal wall. The transverse mesocolon is attached to its anterior surface, just above the inferior border. It consists of a head, neck, body and tail. The lower part of the head is prolonged to the left, behind the superior mesenteric artery and vein, in front of the aorta. This is the uncinate process. Identify these parts on you dissection.

The pancreas has both endocrine and exocrine components. The exocrine component is responsible for the secretion of various digestive enzymes. These are collected into a series of ducts which, in turn, open into a principal pancreatic duct. The pancreatic duct joins the common bile duct to form the ampulla of Vater. The ampulla opens in the duodenum, at the duodenal papilla. The accessory pancreatic duct (draining the uncinate process) also opens in the duodenum, about 2cm proximal to the duodenal papilla.

What is the blood supply of the pancreas?

What are the important relations of the pancreas?

What effects might you expect from a carcinoma of the head of the pancreas?

Examine the spleen. It lies beneath the costal margin, in the left hypochondrium. To which ribs is it related?

Try to orientate the spleen. Its antero-superior border is notched. It has an outer convexity which lies against the diaphragm and a hilum that lies in the angle between the stomach and the left kidney. The splenic artery reaches the hilum where it divides into four or five branches before entering the spleen. Branches from the splenic artery supply the stomach. Which ones?

Name the important relations of the spleen and revise its peritoneal attachments.

Finally, replace all the abdominal viscera in situ. Make a "mental picture" of all the organs, their relations and peritoneal reflections. Revise the major vessels and their branches. Learn the microscopic anatomy of the gastrointestinal tract and its derivatives.

After completing this practical, you should be able to carry out the following on a living subject:

Work in pairs, taking it in turns to repeat the observations on each other. Subjects should strip to display the abdominal wall.

For descriptive purposes, the abdomen is divided into four quadrants or nine regions, usually projected onto the anterior abdominal wall. These are used in clinical practice to describe the sites of abnormal features such as masses, tenderness, reported pains etc. It is important not only to have some knowledge of the regions, but also what organs can be expected to occupy them - a mass in the right upper quadrant, for example, cannot arise from the bladder.

The quadrants are centred on the umbilicus. They and their contents are illustrated on the adjacent page. Unfortunately the position of the umbilicus is variable, and depends greatly on the condition of the anterior abdominal wall. Nevertheless, in modem clinical practice, the abdomen is normally divided into quadrants.

The nine regions are created by intersections between two horizontal and two vertical planes. Strictly these are:

Horizontal: the transpyloric plane

the intertubercular plane

Vertical: the left and right lateral lines

The transpyloric plane (so called because it cuts through the pylorus) lies midway between the sternal notch and the upper border of the pubic symphysis. The intertubercular plane passes through the iliac tubercles (tuberosities).

The lateral lines are in fact the midclavicular planes, each of which also passes through the ipsilateral mid-inguinal point.

In fact, in clinical practice, the nine abdominal regions are defined imprecisely. For example, a clinician would not bother to run a tape measure from sternal notch to pubis to define the transpyloric plane. Instead, the subcostal plane is often substituted.

Is the liver palpable in a normal subject?

Is the spleen palpable in a normal subject?

The gastrointestinal tract is normally impalpable, although parts of the colon can often be palpated if only mildly pathological e.g. the sigmoid colon in chronic constipation. Other retroperitoneal structures (kidney, pancreas, great vessels) are impalpable unless enlarged, although kidneys and the abdominal aortic pulse may be felt in very thin people.

Follow these instructions to subdivide your colleague's abdomen into the nine regions:

1. Identify the costal margin, iliac crest and anterior superior iliac spine.
2. Identify the pubic tubercle, which can be palpated through clothing on the superior border of the pubis 2-3cm from the midline. Bisect the line joining this to the anterior superior iliac spine to find the mid-inguinal point.
3. Lightly mark a horizontal line on the anterior abdominal wall joining the levels of the costal margins in the mid-axillary line (the subcostal plane).
4. Palpate the iliac crest between the mid-axillary line and the anterior superior iliac spine to find the projecting lip called the iliac tubercle. Draw a horizontal line connecting the two iliac tubercles (the intertubercular plane).
5. On each side draw a vertical line on the abdomen which if extended both ways would cross the mid-clavicular and mid-inguinal points.

The most commonly used names for these abdominal regions are:

Draw the dividing lines on the diagram of the anterior abdominal wall below and label each region. The contents of the nine abdominal regions are shown below

THE ABDOMINAL REGIONS

1. The umbilicus is found (unsurprisingly) in the umbilical region of the anterior abdominal wall, though its level is rather variable.

2. The anterior abdominal muscles as a whole can be tensed by attempting to breathe out against a closed glottis. Palpate them under these conditions and during normal breathing.

Is rectus abdominis wider at the top or the bottom?

Note that its most lateral part lies on the mid-clavicular/mid-inguinal line; in well muscled subjects this is the simplest way of locating this line.

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