Dissection 11.2 explores the peritoneal cavity.
DISSECTION 11.2 Exploration of the peritoneal cavity Objectives
I. To identify and study the location of the stomach, liver, gallbladder, lesser omentum, epiploic foramen, greater omentum, and falciform ligament in the supracolic com-partment. II. To identify and study the location of the duodenum, jejunum, ileum, mesentery, caecum, vermi-form appendix, ascending, transverse, descending, and sigmoid colon, transverse mesocolon, and sigmoid meso colon in the infracolic compartment.
Instructions
The following brief description gives only the general arrangement of the abdominal viscera which may be examined without dissection. It is important to confirm the location of the abdominal organs without damage to the structures which will be dissected later. The posi-tions given for the various structures are approximate because the abdominal viscera move with respiration and alter their position with the age and bodily habitus of the individual. The relative position of organs is also changed by distension and movement of the hollow viscera, particularly those which are free to move on a mesentery.
1. Identify the greater omentum and note its conti-nuity with the stomach. Identify the transverse co-lon fused with the posterior surface of the greater omentum, a short distance inferior to the stomach.
2. The supracolic compartment of the peritoneal cavity lies superior to the greater omentum and transverse mesocolon. It contains the liver, stomach, spleen, and superior part of the duodenum. It lies anterior to the pancreas, duodenum, kidneys, and suprarenal glands.
3. The liver fills the greater part of the right hypochon-drium, and is mainly under cover of the ribs and dia-phragm. Most of the liver surface is covered with the peritoneum, and it is divided into a large right and small left lobes by the falciform ligament.
4. Examine the falciform ligament. It is attached to the anterior surface of the liver, a little to the right of the
median plane. It extends to the supraumbilical part of the anterior abdominal wall.
5. The sharp inferior margin of the right lobe lies ap-proximately along the right costal margin. Close to the tip of the ninth right costal cartilage, the round-ed fundus of the gallbladder protrudes below the inferior margin of the liver. The right lobe then ap-pears from behind the costal cartilages and almost immediately joins the left lobe between the right and left costal margins. The inferior margin of the left lobe continues in the same direction up to the eighth left costal cartilage. Here it turns more sharp-ly upwards to meet the superior surface of the liver, posterior to the fifth left costochondral junction [Fig. 11.3].
6. The superior surface of the right lobe fits into the right dome of the diaphragm. It reaches the level of the upper border of the fifth rib in the right mid-clavicular plane. Posteriorly, it lies on the posterior part of the diaphragm, the right suprarenal gland, and the superior part of the right kidney.
7. The stomach lies obliquely across the supracolic compartment from upper left to lower right in a J- or C-shaped curve. The greater part is hidden by the liver, diaphragm, and ribs, but part of its anterior surface is in contact with the anterior abdominal wall, inferior to the left lobe of the liver [Fig. 11.3].
Pass a hand upwards over the anterior surface of the stomach and identify its superior rounded fun-dus and the oesophagus entering the right border inferior to the fundus and posterior to the liver. Lift up the inferior margin of the liver and trace the right concave border of the stomach—the lesser curvature—downwards. The lesser curvature runs from the entry of the oesophagus into the stomach, to a thickening—the pyloric sphincter—in the wall of the stomach where it meets the duodenum. Note a sharp angulation of the lesser curvature (incisura angularis) which marks the junction of the body of the stomach with the pyloric part [Fig. 11.10].
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General arrangement of the abdominal viscera
8. Identify the thin sheet of the peritoneum (the lesser omentum) which passes from the lesser curvature of the stomach to the liver. It is short where the ab-dominal oesophagus abuts on the liver but length-ens towards the pylorus. The lesser omentum ends in a thickened free edge on the right side. This thick margin contains the portal vein, the proper hepat-ic artery, and the bile duct, all of whhepat-ich run from the superior part of the duodenum to the liver [Fig.
11.11]. The small area on the liver to which the edge of the lesser omentum is attached superiorly is the porta hepatis.
9. Pass a finger to the left, posterior to the free edge of the lesser omentum. The finger passes through the epiploic foramen into the lesser sac, pos-terior to the lesser omentum and stomach. If the finger is directed upwards in the foramen, it enters a narrow extension of the lesser sac—the superior recess between the liver and the dia-phragm [see Fig. 11.13]. A finger in the thorax pushed inferiorly between the descending aorta and the diaphragm lies posterior to the finger in the superior recess but is separated from it by the diaphragm.
10. Trace the left convex border of the stomach from the fundus to the pylorus. The fold of peritoneum which passes from this curvature is the dorsal mes-entery of the stomach. Superiorly, it passes to the diaphragm (gastrophrenic ligament). Inferior to this, it extends to the spleen (gastrosplenic liga-ment). Inferiorly it forms the greater omentum.
This greater omentum ends where the first part of the duodenum becomes adherent to the posterior abdominal wall.
11. Pull the upper part of the greater curvature of the stomach to the right and expose the spleen deep in the left hypochondrium. It lies posterior to the stomach and anterior to the upper part of the left kidney. Posterolaterally, the spleen lies against the diaphragm which separates it from the pleural cavity. Confirm this with a finger in the left pleu-ral cavity. Note that the long axis of the spleen lies parallel to the tenth rib, and that the spleen lies between the ninth and eleventh ribs, pos-terior to the mid-axillary line. The gastrosplenic and lienorenal ligaments are attached to a narrow strip on the medial aspect of the spleen. This is the hilus of the spleen. Other than the hilus, the
spleen is completely covered by the peritoneum [Fig. 11.6].
12. Follow the first part of the duodenum pos-terosuperiorly to the right till it turns abruptly downwards. It continues vertically as the second part, which is adherent to the posterior abdomi-nal wall. It passes posterior to the attachment of the mesentery of the transverse colon [Fig. 11.12]
and connects the parts of the intestine in the su-pracolic and infracolic compartments. The head of the pancreas lies medial to this part of the duodenum.
13. Infracolic compartment: turn the greater omen-tum up and find the transverse colon adherent to its posterior surface. The colon can be differen-tiated from the small intestine by: (i) its position;
(ii) the sacculation of its wall; (iii) the thickened bands of longitudinal muscle on the wall—taeniae coli; and (iv) the small projecting sacs of perito-neum filled with fat—appendices epiploicae [Fig. 11.12]. Trace the transverse colon and its mesentery—the transverse mesocolon—in both directions. The transverse mesocolon is mainly fused to the greater omentum and is attached to the front of the pancreas and the second part of the duodenum [Fig. 11.13].
14. The transverse colon is continuous through the right and left colic flexures with the ascending and descending colon [Fig. 11.12]. The ascending and descending colon are adherent to the posterior ab-dominal wall in the right and left paravertebral gut-ters, respectively. The part of these gutters lateral to the colon are the paracolic gutters. They form a route of communication between the infracolic and supracolic compartments.
15. The right colic flexure lies anterior to the inferior part of the right kidney, close to the inferior mar-gin of the liver. The left colic flexure lies at a much higher level [see Fig. 11.23] in contact with the ant-erior (colic) surface of the spleen.
16. The caecum is a blind-ended sac in the right iliac fossa. It is continuous superiorly with the ascend-ing colon and medially with the terminal ileum and vermiform appendix [Fig. 11.14]. The taeniae coli pass over the surface of the caecum and converge on the base of the vermiform appendix. A blind extension of the peritoneal cavity passes upwards,
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The abdominal cavity
posterior to the caecum. This is the retrocaecal re-cess [Fig. 11.15]. Attempt to explore it.
17. At the left iliac fossa, the descending colon becomes continuous with the sigmoid colon. The sigmoid colon loops postero-inferiorly into the lesser pelvis to continue as the rectum on the pelvic surface of the third piece of the sacrum. Here the taeniae coli of the sigmoid colon spread out into the more uni-form longitudinal muscle layer of the rectum. The short mesentery of the sigmoid colon is attached across the margin of the superior aperture of the lesser pelvis [Figs. 11.12, 11.13] and on the pelvic surface of the sacrum.
18. The inferior half of the duodenum, jejunum, and ileum constitute the infracolic part of the small intestine. They are centrally placed within a bound-ary formed by the caecum and colon [Fig. 11.12].
Between the caecum on the right and the sigmoid colon on the left, the boundary is incomplete and coils of small intestine lie in the lesser pelvis. The infracolic part of the duodenum completes this C-shaped structure. It consists of the lower half of the second part, the third part which crosses the verte-bral column immediately anterior to the inferior vena cava and aorta on the third lumbar vertebra, and the short fourth part which joins the jejunum on the left side of the second lumbar vertebra [Fig. 11.12].
19. The jejunum and ileum lie in the free edge of the mesentery. The root of the mesentery runs oblique-ly from the duodenojejunal junction to the ileocae-cal junction. It partly divides the infracolic part of the peritoneal cavity into right superior and left inferior regions. The left inferior region is continuous with the pelvic peritoneal cavity. Both regions are filled with coils of the small intestine. The vermiform ap-pendix lies at the right extremity of the left inferior region [Figs. 11.12, 11.13].
20. Pick up the mesentery. Note the short attachment to the posterior abdominal wall and the long, complexly folded free margin containing the je-junum and ileum. The jeje-junum and ileum can-not be differentiated from each other clearly. The wall of the jejunum is thicker than the wall of the ileum. There is usually less fat in the mesentery of the jejunum so that the vessels and the spaces between them are more clearly visible than in the ileal mesentery. The jejunum is approximately two-fifths of the 6 m this part of the intestine is said to measure.
21. A number of variable accessory peritoneal folds are found in relation to the duodenum and caecum [Figs. 11.14, 11.15]. Each of these produces a peri-toneal recess. These folds and recesses should be noted where present.
Fig. 11.10 A diagram of the anterior surface of the stomach to show its parts.
Incisura angularis
Pyloric canal Oesophagus
Fundus
Body
Pyloric antrum
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General arrangement of the abdominal viscera
Gastrosplenic ligament
Lienorenal ligament Stomach Liver (left lobe)
Lesser sac Epiploic foramen
Spleen
Left kidney Pleural cavity Liver (right lobe)
Falciform ligament
Gallbladder Bile duct Hepatic artery Portal vein
Inferior vena cava
Right kidney Aorta (thoracic) Peritoneal cavity
A
P L R
Diaphragm
Fig. 11.11 A horizontal section through the abdomen at the level of the epiploic foramen. Blue = peritoneal cavity. Red = lesser sac.
A = anterior; P = posterior; R = right; L = left.
Xiphoid process
Stomach Ligamentum teres
Gallbladder
Ninth costal cartilage
Liver Right colic flexure
Duodenum Taeniae coli Ascending colon
Right superior part of infracolic compartment
Caecum
Terminal ileum Vermiform
appendix
Transverse colon
Beginning of jejunum
Left kidney
Descending colon Appendices epiploicae
Root of the mesentery
Bifurcation of aorta Left inferior part of infracolic compartment
Sigmoid colon
Urinary bladder
Fig. 11.12 The abdominal viscera after removal of the jejunum, ileum, and greater omentum.
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The abdominal cavity
Oesophagus
Left triangular ligament
Left gastric A.
Left suprarenal gland Superior gastropancreatic fold
Pancreas (body and tail) Duodenum, fourth part Duodenum, third part Splenic A. in lienorenal ligament
Diaphragm
Aorta
Ureter
Sigmoid mesocolon Retrocaecal recess
Attachment of ascending colon Root of the mesentery Root of transverse
mesocolon Pancreas (head) Duodenum, first
part
Duodenum, second part Portal V. in lesser
omentum Layers of coronary
ligament Inferior gastropancreatic fold
Inferior vena cava
Falciform ligament
Superior recess of omental bursa
Fig. 11.13 Diagram of the posterior abdominal wall to show the attachments of the mesenteries and peritoneal ligaments. The oesophagus, duodenum, and rectum are the only parts of the gut tube left in situ.
Fig. 11.14 The anterior surface of the ileocaecal region.
Vascular fold of caecum Sup. ileo-caecal recess Ant.
taenia
Caecum
Vermiform appendix
Mesentery Terminal ileum Inf. ileocaecal recess Ileocaecal fold Mesentery of appendix
Caecum
Vermiform appendix
Terminal ileum
Retrocaecal recess
Fig. 11.15 The inferior surface of the ileocaecal region. The caecum has been turned forwards to show the retrocaecal recess in which the vermiform appendix commonly lies.
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General arrangement of the abdominal viscera
of the duodenum, behind the superior and in-ferior duodenal folds of the peritoneum. The inferior mesenteric vein lies behind the superior duodenal fold. The opening of the superior recess faces down; and that of the inferior recess faces up.
The superior and inferior ileocaecal recess-es lie behind the fold of the caecum and the ileo caecal fold [Fig. 11.14]. The fold of the caecum contains the anterior caecal artery. The retro -caecal recess lies behind the caecum and may contain the vermiform appendix [Fig. 11.15].