Intestines Flashcards
What does small intestine consist of?
-Duodenum
-Jejenum
-Ileum
-Extends from pylorus of stomach to ileocaecol junction
What does large intestine consist of?
-Begins with caecum
-Also consists of appendix, ascending, transverse, descending and sigmoid colon
-Ends with rectum and anal canal
Duodenum
-Duodenum runs a C-shaped course around the head of the pancreas
-Starts from the pylorus and ends at the duodenojejunal flexure (junction). -Flexure is roughly at the level of L2 vertebra, 2-3cm to the left of the midline and takes the form of an acute angle
-Most of the duodenum is retroperitoneal except for a short portion of the first part (covered by the hepatoduodenal ligament)
Which part of the duodenum is intraperitoneal?
-Superior part
-Because hepato-duodenal ligament wraps around it
-Rest are retroperitoneal
4 parts of the duodenum
1) Superior
2) Descending
3) Horizontal/inferior
4) Ascending
Duodenum (internal)
-Internally, the mucosa of the duodenal wall is the same as the stomach (rugae)
-Major duodenal papilla is where bile and pancreatic juice are released into the duodenum to aid digestion of chyme that is passed down from the stomach
-The level of the major duodenal papilla also indicates the junction between foregut and midgut
Blood supply of the duodenum
-Arterial supply of the duodenum arises from the coeliac trunk and superior mesenteric arteries much like the pancreas
-Proximal to level of the major duodenal papilla, it is supplied by the superior pancreaticoduodenal artery (SPDA) via the gastroduodenal artery. -Distally, it is supplied by the inferior pancreaticoduodenal artery (IPDA)
-Veins drain either directly into the hepatic portal vein or through the superior mesenteric and splenic veins
Jejenum and ileum
-Jejunum begins at the duodenojejunal flexure where the GI tract resumes an intraperitoneal course
-Ileum ends at the ileocaecal junction
-Jejenum is 40% of length
-Ileum is 60% of the length
Differences between jejenum and ileum
The mesentery and SMA (superior mesenteric artery)
-The mesentery is a fan-shaped fold of peritoneum that attaches the jejunum and ileum to the posterior abdominal wall
-Between two the layers of the peritoneum are the superior mesenteric vessels and autonomic nerves
-Jejunal and ileal branches of the SMA supply the jejunum and ileum
-The SMA arises from the abdominal aorta at the level of L1, 1cm inferior to the coeliac trunk
Large intestine function
In the large intestine, water is absorbed from the indigestible residues of the liquid chyme, converting it into semisolid stool or faeces.
Main features of large intestine
-Omental (epiploic) appendages: small, fatty projections of the peritoneum
-Teniae coli: longitudinal bands of smooth muscle
-Haustra: sacculations of the wall of the colon
Caecum
-Caecum is the first part of the large intestine and is continuous with the ascending colon distally
-The caecum is a blind ended pouch with the ileal orifice opening into the caecum (the ileocaecal junction).
-Both caecum and appendix are intraperitoneal organs.
-The caecum is supplied by the ileocolic artery, a branch of SMA. The appendicular artery is a branch of the ileocolic artery.
Appendix
-The appendix is a blind intestinal diverticulum that contains masses of lymphoid tissue. It arises from the posteromedial aspect of the caecum inferior to the ileocaecal junction.
-Both caecum and appendix are intraperitoneal organs.
Separations of the colon
-Ascending colon - from caecum to the right colic flexure (retroperitoneal)
-Transverse colon - from right to left colic flexure (intraperitoneal)
-Descending colon - from left colic flexure to sigmoid colon (retroperitoneal)
-Sigmoid colon - S-shaped loop linking descending colon to rectum (intraperitoneal)
Blood supply of colon
-Main arterial supply to the colon derives from the SMA (midgut portion) and IMA (hindgut portion)
-Branches of the colic arteries and sigmoid arteries form a marginal artery that runs along the colon
-Midgut portion drains into the superior mesenteric vein
-Hindgut portion drains into the inferior mesenteric vein
-The IMA arises at the level of L3
Positions of the appendix
-Retrocaecal appendix is the most common position.
-Base of the appendix typically is one third of the way along the oblique line joining the right ASIS to the umbilicus, the McBurney point.
-Appendicitis can cause severe acute abdominal pain over the McBurney point
-Such pain usually commences as a vague pain in the periumbilical region (T10 level) as it stretched the visceral peritoneum
-Subsequent severe pain over the lower right quadrant is a result of irritation of the parietal peritoneum
Blood supply of the foregut structures
Blood supply of the midgut structures
Blood supply of the hindgut structures
Venous drainage of GI tract
