Flashcards in Anatomy Of The Intestines Deck (67)
Microscopic structure of the small intestine?
Mucosa folded into villi
Villi separated by crypts
What happens when the cells of the small intestine epithelium reproduce and where do they do it?
Reproduce in the villi
Migrate towards the tips, maturing as they go
-acquire capacity to absorb
What do the microvilli do?
Massively increase the surface area to form a brush border
What does the brush border form?
An unstirred layer where nutrients meet and react with enzymes secreted by enterocytes (epithelial cells), completing digestion prior to absorption.
What are the main layers of the small intestine?
-with blood vessels, lymphatics and submucosal plexus
-2 smooth muscle layers, longitudinal and circular.
-Myenteric plexus lies between them
-loosely arranged fibroblasts
-vessels and nerves pass through it
Covered by mesothelium, commonly called serosa
What are enterocytes?
Columnar cells which contain brush border enzymes for digestion
What are goblet cells?
Exocrine glands which secrete mucin
What cells do the crypts of Lieberkuhn contain?
Stem cells - produce new cells
Enteroendocrine cells - synthesise and secrete hormones
Paneth cells - secrete protective agents
Peyer's patches (only in ileum)
Brunner's glands - secrete alkaline fluid to neutralise chyme
What protective agents do Paneth cells secrete?
Defensins and lysosyme
What do Peyer's patches do?
Contain MALT which house white blood cells and lymphocytes
Produce antibodies to protect from infection
Over all function of the large intestine?
Receives digested food from small intestine, from which it absorbs water and sodium to form faeces
Tell me about the cecum
First part of the colon
Blind ended sac
Slightly inferior to ileocecal junction
Can be palpated in right iliac fossa if enlarged due to poo/gas
Where is the appendix?
Attached to the posteriomedial end of caecum
Contains lymphoid tissue
What is the blood supply to the cecum?
Arterial: SMA -> ileocolic artery
Venous: ileocolic vein -> IMA
Where does the ascending colon extend from and to?
Cecum to right lobe of liver
Right colic flexure/hepatic flexure
Where does the transverse colon extend from and to?
Right colic flexure -> left colic flexure/splenic flexure
Where does the descending colon extend from and to?
Left colic flexure to the sigmoid colon
Where in relation to the left kidney is the descending colon?
Passes anteriorly to it over its lateral border
What marks the beginning of the sigmoid colon?
Where the descending colon turns medially
What structures are just posterior to the sigmoid colon?
Left common iliac artery
What is lateral to the ascending and descending colon? Function?
Left and right paracolic gutters
Drain any fluid that leaks from the colon
Clinical relevance of the paracolic gutters?
Allow any potentially infectious material to circulate around the peritoneal cavity which can cause further infection
This is how a ruptured appendix can cause peritonitis
Arterial and venous supplies to the ascending colon?
Arterial - ileocolic and right colic branches of SMA
Venous - ileocolic and right colic tributaries of SMV
Blood supply of the transverse colon?
Arterial - middle colic of SMA
Venous - SMV
Blood supply of descending colon?
Arterial: Left colic and superior sigmoid - branches of IMA
Venous - IMV
Blood supply of sigmoidal colon?
Arterial: sigmoid arteries - branches of IMA
Which artery forms an anastamosis between the superior and inferior mesenteric arteries?
Clinical relevance of the colonic blood supply?
It is collateral, so maintains blood supply in case of occlusion/stenosis of one of the major arteries.
Where is the rectus located?
Begins at S3
Immediately anterior to sacrum
How does the extension of the peritoneal cavity in the pelvis differ between men and women?
Women: formed between posterior wall of uterus and colon - recto-uterine pouch / pouch of Douglas
Men: between posterior wall of bladder and the colon - retro-vesicle pouch
What can an ulcer in the duodenal cap/ampulla erode into?
Gastroduodenal artery, causing massive blood loss
What sections is the duodenum divided into? At which vertebral level is each?
Superior - L1
Descending - L1-L3
Inferior - L3
Ascending - L3-2
Which part of the duodenum is connected to the liver and by what?
What are the first 2cm of the duodenum called?
The duodenal cap or ampulla
Which part of the duodenum curves around the head of the pancreas?
What structures does the inferior portion of the duodenum cross over?
Aorta and IVC
Posterior to SMA and SMV
Which part of the duodenum is most susceptible to duodenal ulcers?
Where does the duodenum join the jejunum and what happens here?
Suspensory muscle of the duodenum contracts which can widen the flexure
What does the ileocecal valve do?
Prevents reflux of contents back into the ileum
Features of the jejunum?
Mainly in upper left quadrant
Thick intestinal wall
Longer vasa recta than ileum
Red in colour
What are arcades?
What is between the layers of the mesentery of the small intestine?
Superior mesenteric vessels
Features of the ileum?
Mainly in lower right quadrant
Thin intestinal wall
Shorter vasa recta
Pink in colour
Arterial blood supply to the small intestine?
Before the duodenal papilla
-gastroduodenal artery - branch of the celiac trunk
Distal to duodenal papilla
-inferior pancreaticoduodenal artery, branch of SMA
What do the veins of the small intestine drain into?
Hepatic portal vein
(they follow the major arteries)
At what level does the SMA arise from the abdominal aorta?
Blood supply of the jejunum and the ileum?
Jejunal and ileal arteries which are branches of the SMA
(Split into many branches and form arcades, vasa recta arise from them)
Venous drainage of the jejunum and ileum?
Superior mesenteric vein
Which two veins anastamose and where to form the hepatic portal vein?
Superior mesenteric vein and splenic vein
At the neck of the pancreas
Which parts of the duodenum are retroperitoneal and intraperitoneal?
First segment is intra-peritoneal
Rest is secondarily peritoneal so jejunum and ileum are mobile
Which has lumen is larger in diameter, small or large intestine?
Large has a larger diameter
What lymphoid tissue the small and large intestines have?
Small - Peyer's patches
Large - none
What is the appendix? How long is it?
A blind intestinal diverticulum
Blood supply to the appendix?
Abdominal aorta -> ileocolic -> appendicular
Ileocolic -> SMV
Arterial supply of the rectum?
IMA -> superior rectal -> right and left branches
Common iliac -> R and L internal iliac
-right and left middle rectal
-inferior pudendal -> right and left inferior rectal
Venous drainage of the rectum?
Superior rectal vein -> IMV -> splenic -> portal
Middle and inferior rectal veins -> systemic system
How do you know where the anal canal begins?
Where the rental ampulla narrows at the level of U-shaped sling formed by the puborectalis muscle
How does the anal canal descend?
Between anococcygeal ligament and perineal body
What is the superior half of the mucous membrane of the anus characterised by?
Describe the anal columns
In the superior half of mucous membranes
Contain terminal branches of superior rectal artery and vein
Inferior ends are joined by anal valves
Superior to valves are anal sinuses
What does passing faeces compressed when passing through the anal canal and what is the point?
Aids in evacuation of faeces
What forms the pectinate line?
Inferior comb-like shape of anal valves
Vasculature of the anal canal above the pectinate line?
IMA -> superior rectal
Arterial supply of the anal canal below the pectinate line?
Inferior rectal arteries and middle rectal arteries
Middle anastomose with superior and inferior arteries
What is the inferior part of the anal canal derived from?
Innervation of the anal canal?
Above pectinate line
-visceral afferents travel with the parasympathetic nervous system to spinal sensory ganglia S2-S4 (referred pain)
Below pectinate line
-inferior anal nerves
-branches of pudendal nerve