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1

small intestine

The small intestine consists of the duodenum, jejunum and ileum. It extends from the pyloric sphincter to the ileocecal junction where it opens into the large intestine. It is the main site of digestion and absorption. A number of structural adaptations are present in the small intestine to increase the surface area for absorption.

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plicae circulares

circular folds in the mucosa that can be seen. It increases the surface area and helps slow food for more absorption time. its not present in the large intestine. mainly in the jejunum.

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microvilli

microscopic protrusions from the luminal surface of the intestinal cells

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villi

finger like projections of the mucosa

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mesentery

Most of the small intestine is suspended from the posterior abdominal wall by the mesentery. This arrangement ensures that the coils of the jejunum and ileum are freely mobile. The root of the mesentery is approximately 15cm long. Blood vessels, lymphatics and nerves enter at the root of the mesentery and pass through it to supply the small intestine. This arrangement prevents tangling and trapping of the neurovascular structures.

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The root of the mesentery is attached to the posterior wall along a line that extends from the left side of the second lumbar vertebra to the region of which joint?

sacroiliac

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duodenum

The duodenum is the first part of the small intestine and the main site of digestion. It is a C-shaped tube that is approximately 25cm long (12 finger breadths) that extends from the pyloric sphincter to the jejunum. The duodenum is divided into four parts

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four parts of the duodenum

first part is the superior. second is the descending, third is the horizontal and fourth is the ascending. the first part is the forgut, 2,3,4 midgut. minor and major papillae open into D2, this is also the last part of the forgut.

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relations of the duodenum

the head of the pancreas sits in the Cshape of the duodenum, and the common bile duct opens into D2. It lies inferior to the superior part medial to the descending part and sup to the inf part.

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Anterior relations of the duodenum

superior part: Quadrate lobe of liver and gallbladder
Descending part: fundus of gallbladder, right lobe of liver, transverse colon, coils of small intestine.
Horizontal part: root mesentery, coils of jejunum.
Ascending part: beginning of root of mesentery and coils of jejunum

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posterior relations of the duodenum

Superior part: lesser sac, GDA, bile duct, portal vein, IVC
Descending part: hilus of right kidney
Horizontal part: right ureter, IVC, aorta
Ascending part: left margin aorta

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Which part of the duodenum has part of the lesser omentum attached to its superior border and part of the greater omentum attached to its inferior border?

superior

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Which part of the duodenum is supported by the suspensory muscle of the duodenum (ligament of Treitz)?

ascending

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Which part of the duodenum has an intraperitoneal section?

ascending

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blood supply to the duodenum

The first two parts of the duodenum are foregut structures and the third and fourth parts are midgut structures therefore the duodenum receives arterial blood from both the coeliac trunk and the superior mesenteric artery.

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The parts of the duodenum proximal to the major duodenal papilla are supplied by a branch of the gastroduodenal artery which arises from the coeliac trunk. What is the name of this branch?

superior pancreatoduodenal artery

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The parts of the duodenum distal to the major duodenal papilla are supplied by a branch of the superior mesenteric artery. What is the name given to this branch?

inferior pancreatoduodenal artery

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jejunum and ileum

The jejunum extends from the duodenojejunal junction; it is approximately 2.5m long. The ileum extends from the distal end of the jejunum to the ileocaecal junction; it is approximately 3.6m long.

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Most absorption occurs in the jejunum but the terminal ileum is the only site of absorption for which substance?

vitamin b12

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blood supply to the jejunum and ileum

The jejunum and ileum are supplied by the superior mesenteric artery. The superior mesenteric artery enters the mesentery at the root of the mesentery and divides into about 15-18 branches. The arteries unite to form loops termed arcades. The arcades give rise to straight vessels, vasa recta, which project to the intestinal wall.

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structural differences between the jejunum and ileum

Jejunum: in left upper quadrant of infracolic compartment. less fat in mesentery. redder. Fewer large arcades. More vascular.
Ileum: mostly in the right lower quadrant of infracolic compartment. Short vasa recta. narrower. paler. Mainly short and looped arcades. More fat in mesentery. Thinner walled.

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Histologically the duodenum can be differentiated from other parts of the small intestine by the presence of

brunners glands

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Histologically the ileum can be differentiated from other parts of the small intestine by the presence of

peyers patches

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The region of the small intestine with the highest abundance of plicae circulares is the

proximal jejunum

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brunners glands

Brunner's glands (or duodenal glands) are compound tubular submucosal glands found in that portion of the duodenum which is above the hepatopancreatic sphincter (aka sphincter of Oddi). The main function of these glands is to produce a mucus-rich alkaline secretion (containing bicarbonate) which protects the duodenum from acidic chyme. alkaline for enzymes and lubricates.

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peyers patches

lymphoid nodules

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functions of the large intestine

Functions of the colon include water absorption, synthesis of vitamins, storage of undigested food and the formation and excretion of faeces.

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large intestine

The large intestine is shorter than the small intestine, but much larger in diameter. It is divided into the caecum, ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, sigmoid colon, rectum and anal canal.

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teniae coli

Three distinct strips of muscle formed from the longitudinal fibres of the muscularis externa.

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epiploic appendages

Small fat-filled sacs that project from the outer wall of the intestine.

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haustra

Sacculations in the wall of the large intestine.

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semilunar folds

Folds on the internal wall of the intestine between the haustra.

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blood supply of the large intestine

The regions proximal to the distal third of the transverse colon are midgut structures and therefore supplied by the superior mesenteric artery. Those distal to this point are hindgut structures and therefore supplied by the inferior mesenteric artery.

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branches of the superior mesenteric to the large intestine

appendicular, caecal, ileicolic, right colic, middle colic, marginal

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branches of the inferior mesenteric to the large intestine

sigmoidal, superior rectal, left colic,

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caecum

blind ended pouch at the start of the colon. Its in the right lower quadrant. right iliac fossa. the psoas major lies posterior. supplied by the ant and post caecal arteries.
Two orifices open into the posteromedial wall of the caecum. One is the ileal orifice and the other is the orifice of the appendix. The ileal orifice opens into the caecum at the ileocaecal valve. The ileocaecal valve consists of two horizontal folds of mucous membrane, one above and one below the ileal orifice. It is debatable whether the ileocaecal valve prevents reflux of caecal contents into the ileum but it may control the flow of the contents from the ileum into the colon.

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appendix

The appendix represents the tip of the caecum that fails to enlarge during development. It presents the 4 basic layers of the gastrointestinal tract and a lumen of variable diameter. The lumen is wide in young children, obliterated by middle age and narrow in adolescence. Asolescents are more prone to appendicitis.
The length of the appendix varies between individuals (ranging from 6-13cm) and the position of the tip is also variable. It may coil up behind the caecum, hang down into the pelvis, project up lateral to the caecum or project up anterior or posterior to the ileum. This can make it difficult to find during appendicectomy. However the appendix may be located by following the three bands of the teniae coli as they descend over the caecum and converge at the base of the appendix. In relation to surface anatomy the base of the appendix is located at McBurney's point.

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McBurneys's point is located two-thirds of the way along an imaginary line that extends laterally from the umbilicus to which structure?

anterior superior iliac spine

39

The appendix has a short mesentery which is suspended from the mesentery of the small intestine. What is the name given to this mesentery?

mesoappendix

40

The appendicular vein drains via the ileocolic vein into which vein?

superior mesenteric vein

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ascending colon

The ascending colon is approximately 13cm long; it extends upwards through the right lower quadrant and turns as it reaches the liver forming the hepatic flexure. Its retroperitoneal. The anterior relations of the ascending colon are the greater omentum, coils of the small intestine and the anterior abdominal wall.

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Transverse colon

The transverse colon forms the longest portion of the colon being approximately 38cm long. It extends from the hepatic flexure, hangs down and crosses the abdomen and then ascends towards the spleen. It turns at the splenic flexure where it leads into the descending colon. intraperitoneal. The anterior relations of the transverse colon are the greater omentum and the anterior abdominal wall.

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descending colon

The descending colon is approximately 25cm long. It descends from the splenic flexure, passes through the left upper and left lower quadrants and becomes continuous with the sigmoid colon. Retroperitoneal. he anterior relations of the descending colon are the greater omentum, coils of the small intestine and the anterior abdominal wall.

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sigmoid colon

forms an S shaped loop as it extends between the descending and rectum.

45

At which vertebral level does the sigmoid colon meet the rectum?

S3

46

Which structure attaches the sigmoid colon to the posterior pelvic wall?

sigmoid mesocolon

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rectum

The junction between the sigmoid colon and the rectum (rectosigmoid junction) is marked by changes in the muscle layer. The teniae coli disappear and are replaced by a complete layer of longitudinal muscle. The rectum is not straight like its name suggests, a number of flexures are apparent.The rectum is partially retroperitoneal and partially below the level of the peritoneum (subperitoneal).

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sacral flexure of the rectum

his flexure follows the curve of the sacrum and coccyx.

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anorectal flexure

The sharp postero-inferior angle where the rectum pierces the pelvic diaphragm. Important in maintaining faecal continence.

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superior and inf lateral flexures

Located on the left side of the rectum.

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intermediate lateral flexure

Located on the right side of the rectum.

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relations of the rectum

Anterior: vagina, seminal vesicles, coils of intestine, prostate, base bladder
Posterior: sacrum, median sacral artery, coccyx

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anal canal

4cm long, extends down and back from rectal ampulla.

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upper half of the anal canal

anal columns present. Superior rectal vein drains to portal system via IMV and splenic. Nerve fibres from hypogastric plexus. columnar epithelium. ANS. Hindgut dirivative. Sensitive to stretch. Suppled superior rectal branch of IMA.

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lower half of the anal canal

stratified squamous epithelium. No anal columns present. Supplied by inferior rectal branch of pudendal artery. Innervated by the inferior rectal branch of pudendal nerve. Sensitive to pain temp touch and pressure. Inf rectal vein drains to internal iliac via pudendal vein. Lymph drains to superficial inguinal nodes. derived from protodeum.