Large intestine anatomy and histology Flashcards
As a reminder, study the blood supply origins of different portions of the GIT
State the functions of the large intestine
- Absorption of water, and electrolytles compaction of stool
- storage of stool
- propulsion of GI contents
- defecation
The large intestine extends from the ileocecal junctinon to the anus. What is the opening called that connects the ileum to the cecum? What is the valve that guards the opening?
Ileal orifice is the opneing
Illeal papilla is the valve - formed by two lips of semilunar shape (superior and inferior lip).
State the key macroscopic components of the large intestine
- omental appendices
- Teniae coli - the tonic contraction of these muscles, causes shortening of the wall they are with, giving the haustrated appearance
- haustrations - sacculations of the wall of the colon
The appnedix is a lymphoid pouch, and arises from the caecum. What is the short triangular mesentery called, that attaches the appendix to the terminal illeum and caecum?
Meso-appendix
What vessel supplies the caecum?
Superior mesenteric Artery (the ileocolic artery - terminal branch of superior mesenteric)
Superior mesenteric vein - (ilecolic vein)
State the position of peritoneum for each segment of the colon
When the ascneding colon meets the right lobe of the liver, it turns 90 degrees to move horizontally. What are the two names for this?
- Hepatic flexure (right colic flexure)
The transverse colon extends from the ??????? to the ?????. Here, it turns 90 degreees to point inferiorly. This turn is called the ????
At the flexure, the colon is attached to the diaphragm by the phrenicocolic ligament.
- Hepatocolic flexure spleen
- Splenic flexure
What is the blood supply for the ascending colon and first 2/3rds of the transverse colon?
- Superior mesenteric artery
-
Ascending
- ileocolic arteries
- right colic artery
- middle colic artery
-
Transverse
- middle colic artery
- To a lesser extend, right and middle colic via the anastamoses
-
Ascending
-
Superior mesenteric vein
-
Ascending
- right colic
- ileocolic
- transverse:
- Middle colic
-
Ascending
What periotneal mesentery attaches to the posterior wall of the abdomen?
- Mesocolon
After the left colic flexure, the colon moves inferiorly towards the pelvis - the descending colon. When it turns medially, it becomes the?????
- Sigmoid colon.
What is the name of the space between the descending colon and the abdominal wall?
Left paracolic gutter
The sigmoid colon is in the left lower quadrant of the abdomen, extending from the left iliac fossa to the level of ??? vertebra.
What mesentery attaches the colon to the posterior wall?
S3
Sigmoid mesocolon The long length of the mesentery permits this part of the colon to be particularly mobile.
What is the blood supply for the posterior 1/3 of the transverse colon, descending colon and sigmod colon?
- Inferior mesenteric artery
- marginal artery
- left colic artery
- superior sigmoid artery
- sigmoid arteries
- inferior mesenteric vein
- left colic veins
- sigmoid and recto-sigmoid veins
What vessel supplies collateral supply to the colon?
The rectum has two major flexures - what are they? WHat direction do they travel?
- sacral flexure -also known as the dorsal flexure
- anorectal flexure - also known as the ventral flexure
- Anteroposterior
The anorectal flexure of the anal canal is at how many degrees? What is it’s function?
- 80 degrees
- important role in fecal contience - maintained during resting state by puborectalis muscle.
There are 3 lateral flexures of the rectum. name them
Superior transverse fold
Middle transverse fold
Inferior transverse fold
The anal canal is a continuation of the rectum. It’s opening is controlled by two muscles - what are they?
What are the major vessels that supply the rectum?
What are the major veins for the rectum and anal canal?
- inferior mesenteric vein (superior rectal vein)
- internal iliac vein (left and right middle rectal veins)
- internal iliac vein (the left and right inferior rectal veins, which branch of the left and right internal pudendal vein)
Superior empties into portal circulation, whilst middle and inferior empties into the systemic circulation. Thus the rectum is a site of portocaval anastomosis.
- inside the anal canal, there are presence of special longitudinal folds called what? These are jointed together by what structures?
- The anal valves form a irregular cicrcle called what?
Pectinate line (denate line)
The regions above and below the pectinate line differ in structure and neurovascular supply. This is a result of their different embryological origins. The superior aspctect of the anal canal (down to the anal valves, is what kind of epithelium? also, what kind of epithelium is found below the pectinate line?
Simple columnar
Non-keratinised stratified squamous.
At what point does the does the anal canal epithelium transition to skin?
Inter-sphincter groove
Arterial supply for above and below pectinate line?
- Above - Inferior mesenteric artery - The superior rectal artery and middle rectal artery
- Below… - Inferior rectal artery - from internal pudendal arter which is from internal iliac artery
What features (structures and cells) are absent in the large colon histologically that would be found in the small bowel.
Conversley, what structures would you expect to see?
- plicae circularies
- no villi
- Paneth cells
You would expect to find:
- the normal GI layers
- Crypts of lieberkuhn, but deeper than in smalll bowel
- Absorptive cells and lots and lots of goblet cells line the epithelium
- Crypts of lieberkuhn, but deeper than in smalll bowel
