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Practical class 2
ACCESSORY DIGESTIVE ORGANSACCESSORY DIGESTIVE ORGANSACCESSORY DIGESTIVE ORGANS ACCESSORY DIGESTIVE ORGANSACCESSORY DIGESTIVE ORGANS
OBJECTIVES
By the end of the practical session you should be able to:
- Outline the gross structure, relations, neurovascular supply and lymph drainage of the liver.
- Define the anatomical features, relations, function and clinical considerations of the extra- hepatic biliary system.
- Describe the anatomical relations, development, vascular supply and functions of the pan- creas.
- Describe the origin, course, distribution and relations of the arteries supplying the gastrointestinal tract.
- Describe the portal venous system and explain its role in nutrition, and the nature and location of portosystemic anastomoses.
Background readingBackground readingBackground readingBackground readingBackground reading
Rogers: chapter 32: The liver, biliary system and pancreas 40: (Arterial supply to the gut, The hepatic portal venous system) 27: (Nerve supply to the gastrointestinal tract)
Label these four ligaments on the following diagram, and complete the labelling.
What are the major functions of the liver?
GALL BLADDER AND BILIARY APPARATUS
The gall bladder is embedded in the inferior surface of the right lobe of the liver, its function is to store and concentrate bile.
The gall bladder does NOT synthesise bile.
Where is bile synthesised, and how does it reach the gall bladder?
Sketch the gall bladder in the space below to indicate its fundus, body and pylorus.
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The fundus of the gall bladder is related to the tip of the right 9th costal cartilage.
Identify the gall bladder under the lower free border of the liver. Trace its drainage duct (the cysticcysticcysticcysticcystic ductductductductduct) to the junction with the hepatic ducthepatic ducthepatic ducthepatic ducthepatic duct where it forms the common bile ductcommon bile ductcommon bile ductcommon bile ductcommon bile duct which can be followed down to the second part of the duodenum.
Complete the labelling of the extrahepatic biliary apparatus on the following diagram.
On a prosected specimen review the biliary apparatus.
Lift the head of the pancreas to locate the lower part of the common bile duct and trace it down to its junction with the major pancreatic ductmajor pancreatic ductmajor pancreatic ductmajor pancreatic ductmajor pancreatic duct and their joint entry into the medial aspect of the 2nd part of the duodenum.
Look into the duodenum again to view the major duodenal papilla which marks the internal orifice of entry of the hepatopancreatic duct.
Is this the only drainage point into the gut for the exocrine secretion of the pancreas?
PANCREAS
The pancreas is a diffuse gland, extending approximately horizontally across the upper abdomen from the curve of the duodenum to the hilum of the spleen
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VESSELS AND NERVES OF THE GASTROINTESTINAL
TRACT
Arterial supply
Three unpaired arterial branches leave the front of the abdominal aorta to supply the gastrointestinal tract. The most proximal (coeliac trunkcoeliac trunkcoeliac trunkcoeliac trunkcoeliac trunk) supplies the foregut and its three derivatives (liver, pancreas and spleen). The second (superior mesentericsuperior mesentericsuperior mesentericsuperior mesentericsuperior mesenteric) passes through the mesentery to supply the midgut. The most distal (inferior mesentericinferior mesentericinferior mesentericinferior mesentericinferior mesenteric) supplies the hindgut.
You should know what the boundaries of the fore-, mid- and hind-gut are, as it will greatly simplify your understanding of the blood supply of the gastrointestinal tract. Ask one of the demonstrators if you are unsure.
COELIAC TRUNK
This divides into three branches to supply the foregut as far as the opening of the common bile duct into the duodenum, as well as the liver, spleen and pancreas.
Identify the coeliac trunk as it arises from the aorta at the upper border of the pancreas.
At which vertebral level does the coeliac trunk arise?
Note the site of potential arterial anastomosis at the greater curvature of the stomach.
What vessels contribute to this anastomotic site?
What is the function of these anastomotic sites?
On suitable prosections trace the major arterial branches of the coeliac trunk.
Left gastricLeft gastricLeft gastric Left gastricLeft gastric Common hepaticCommon hepaticCommon hepaticCommon hepaticCommon hepatic SplenicSplenicSplenicSplenicSplenic
Label these and the other vessels on the following diagram.
SUPERIOR MESENTERIC ARTERY
This supplies the midgut from the second part of the duodenum to the end of the second third of the transverse colon. Find the superior mesenteric vessels in the mesentery and note the pattern of the arterial arcades at the proximal and distal ends. Try to find the following major branches:
IleocolicIleocolicIleocolic IleocolicIleocolic Right colicRight colicRight colicRight colicRight colic Middle colicMiddle colicMiddle colicMiddle colicMiddle colic
INFERIOR MESENTERIC ARTERY
This supplies the hind-gut from the distal third of the transverse colon to the rectum. Locate the inferior mesenteric artery on the prosections available, and try to find the following major arterial branches to the hindgut.
Left colicLeft colicLeft colic Left colicLeft colic SigmoidalSigmoidalSigmoidalSigmoidalSigmoidal Superior rectalSuperior rectalSuperior rectalSuperior rectalSuperior rectal
On the following diagram, label the major branches of the inferior mesenteric artery. Make sure that you know the distribution of these vessels.
At which vertebral level does the inferior mesenteric artery arise?
Does the inferior mesenteric artery pass above or below the duodenum.
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What is the marginal artery, and what vessels contribute to it?
Venous return
The venous drainage of the gut essentially mirrors the arterial supply but with several important differences. It is critical to appreciate that ALL nutrient-laden blood from the gut, passes via the portal veinportal veinportal veinportal veinportal vein to the liver (the hepatic portal system), before returning to the systemic system.
What is a portal system?
Locate the hepatic portal vein on the prosections available.
It is important to understand the arrangement of the major vessels which contribute to the portal vein; these are the splenicsplenicsplenicsplenicsplenic, superiorsuperiorsuperiorsuperiorsuperior and inferior mesenteric veinsinferior mesenteric veinsinferior mesenteric veinsinferior mesenteric veinsinferior mesenteric veins. Note that there is no “coeliac vein”.
The venous drainage of the foregut is fairly complex and ultimately drains into the splenic, superior mesenteric and portal veins. That of the midgut is quite regular. Each branch of the superior mesenteric artery is accompanied by a vein, all of which ultimately drain into the superior mesenteric vein, a large trunk which lies to the right of the artery. Locate this vessel on the prosections. Confirm that it receives the splenic vein behind the neck of the pancreas. Here, it 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. The inferior mesenteric vein drains the hind-gut in a similarly regular fashion and enters the splenic vein part way along its length.
Sketch the arrangement of the major vessels which contribute to the portal vein in the space below.
Should flow in the portal vein become compromised, pressure in the vessel will be increased resulting in portal hypertension. This results in blood from the gut ‘short-circuiting’ the portal vein and returning directly to the heart via the systemic system. This occurs by way of porto-systemicporto-systemicporto-systemicporto-systemicporto-systemic anastomosesanastomosesanastomosesanastomosesanastomoses. (Revise the meaning of the term 'anastomosis'.) Essentially there are 3 major sites at which capillaries of the portal and systemic systems are in close apposition, and when portal blood pressure is raised above a certain level, blood will flow into the systemic veins from the portal veins.
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What are the clinical consequences of portal hypertension, and how might it be detected?
Nerve supply
All parts of the gut and its derivatives are innervated by parasympathetic and sympathetic nerves. Most come from the coeliac plexuscoeliac plexuscoeliac plexuscoeliac plexuscoeliac plexus but the inferior hypogastric (pelvic) plexusinferior hypogastric (pelvic) plexusinferior hypogastric (pelvic) plexusinferior hypogastric (pelvic) plexusinferior hypogastric (pelvic) plexus contributes parasympathetic fibres to the hindgut.
The coeliac plexus receives its parasympathetic input from the two vagivagivagivagivagi. What effect do these nerves have on the motility and sphincter tone of the stomach?
a) Parasympathetic activation.
b) Sympathetic activation.
The parasympathetic activity of the vagus is opposed by the sympathetic fibres reaching the abdo- men by 3 major pairs of splanchnic nervessplanchnic nervessplanchnic nervessplanchnic nervessplanchnic nerves.
Which parts of the stomach secrete acid and pepsin and which secrete gastrin?
What and where is a myenteric plexus of Auerbach and what and where is the plexus of Meissner?
4.Lightly mark a horizontal line on the anterior abdominal wall joining the levels of the (^) costalcostalcostalcostalcostal marginsmarginsmarginsmarginsmargins in the mid-clavicular line (the subcostal planesubcostal planesubcostal planesubcostal planesubcostal plane).
5.Palpate the iliac crestiliac crestiliac crestiliac crestiliac crest between the mid-axillary line and the anterior superior iliac spineanterior superior iliac spineanterior superior iliac spineanterior superior iliac spineanterior superior iliac spine to find the projecting lip called the iliac tubercleiliac tubercleiliac tubercleiliac tubercleiliac tubercle. Draw a horizontal line connecting the two iliac tubercles (the intertubercular planeintertubercular planeintertubercular planeintertubercular planeintertubercular plane).
You have now subdivided the anterior abdominal wall into nine regions which are used to aid navigation in the otherwise rather featureless area. The most commonly used names for these regions are given below:
R.R.R.R.R. HYPOCHONDRIACHYPOCHONDRIACHYPOCHONDRIACHYPOCHONDRIACHYPOCHONDRIAC EPIGASTRICEPIGASTRICEPIGASTRICEPIGASTRICEPIGASTRIC L.L.L.L.L. HYPOCHONDRIACHYPOCHONDRIACHYPOCHONDRIACHYPOCHONDRIACHYPOCHONDRIAC
R.R.R.R.R. LUMBARLUMBARLUMBARLUMBARLUMBAR UMBILICALUMBILICALUMBILICALUMBILICALUMBILICAL L.L.L.L.L. LUMBARLUMBARLUMBARLUMBARLUMBAR
R.R.R.R.R. ILIACILIACILIACILIACILIAC HYPOGASTRICHYPOGASTRICHYPOGASTRICHYPOGASTRICHYPOGASTRIC L.L.L.L.L. ILIACILIACILIACILIACILIAC
(pubic)(pubic)(pubic)(pubic)(pubic)
Sketch the abdomen in the space below and indicate these regions.
Positions of the visceral organs
Many of the visceral organs of the abdomen are highly variable in position, depending on individual build, body position, state of filling of the organ, etc. Nonetheless a reasonable estimate may be made in most cases.
- The liver:liver:liver:liver:liver: occupies most of the right hypochondrium and epigastrium. Its upper border (in mid-respiration) is marked by a line from the right 5th rib and costal cartilage across the lower end of the sternum to the left 5th intercostal space in the mid-clavicular line to the costal margin in the right mid-axillary line.
- The (^) gall bladdergall bladdergall bladdergall bladdergall bladder: lies at the tip of the 9th costal cartilage; this is best recognised as the point at which the lateral border of the right rectus muscle crosses the costal margin.
- StomachStomachStomachStomachStomach: the most consistently placed part is the pylorus. In the supine subject this lies on a plane crossing both costal margins at the mid-clavicular line (i.e. where the lateral border of rectus
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abdominis crosses the costal margin), about 1-2cm to the right of the midline. However, the pylorus descends several cms on standing up. Most of the rest of the stomach lies above and to the left of the pyloric position, and the fundus may lie as high as the fifth rib in the left mid-clavicular line.
- The (^) appendixappendixappendixappendixappendix: the most constant part of the appendix is its base, this point lies 2/3 of the way down a line joining the umbilicus to the right anterior superior iliac spine, and the surface marking is termed McBurneys pointMcBurneys pointMcBurneys pointMcBurneys pointMcBurneys point.
- The coloncoloncoloncoloncolon: the ascending colon rises from McBurney’s pointMcBurney’s pointMcBurney’s pointMcBurney’s pointMcBurney’s point to the transpyloric plane; the transverse colon hangs down to umbilical level then rises to the left lumbar regions; the sigmoid colon crosses to the centre of the hypogastric area.
Why is the pylorus the most consistentely located part of the stomach?
Palpation of abdominal organs
The ease with which intra-abdominal structures can be felt depends on the physique of the subject and the experience of the examiner. You should however be able to do the following. Note that the abdomen is most relaxed (and palpation therefore easiest) if the subject lies supine with hips and knees flexed.
- Abdominal aortaAbdominal aortaAbdominal aortaAbdominal aortaAbdominal aorta: can be felt pulsing powerfully by lumbar vertebral bodies just to the left of the midline. Note: a ruler with one end placed on the mid-abdomen and held down firmly can often be seen to flick in response to aortic pulsations.
- Descending colonDescending colonDescending colonDescending colonDescending colon: may often be felt in the left lumbar region because of the relative solidity of its contents.
Radiographs
Look at the display of radiographs to appreciate the ways in which contrast media can be used to visualise abdominal viscera.
What evidence of visceral position can be seen in a plain film?
Auscultation and percussion of the abdominal viscera
- Ask a demonstrator to show you how to listen to the bowel sound with the help of a stethoscope.
- The demonstrator will also show you the method for percussion of the liver.
