Large Bowel Flashcards
What is the main function of the large bowel?
Reabsorption of electrolytes and water and elimination of undigested food and waste
What is the length and diameter of the large bowel?
1.5m long
6cm diameter
What are the parts of the large bowel?
Consists of:
- Appendix
- Caecum
- Colon(large intestine) -Ascending colon, Transverse colon, descending colon and sigmoid colon
- Rectum
- Anal canal
Starts from the ileoceacal valve/Caecum following on from the end of the small intestine(ilium) part of the small bowel
What is the appendix?
Thin finger like projection from the caecum that is not clinically relevant in humans
Where do each parts of the colon run to and from?
Ascending Colon-right side of the abdomen up from Caecum to hepatic flexture (the turn of the colon near the liver)
Transverse Colon-runs from the hepatic flexure to splenic flexure(turn of the colon near the spleen)
Descending Colon- runs from splenic flexure to the sigmoid colon
Sigmoid colon(s-shaped)-runs fromthe descending colon to the rectum
Describe the blood supply of the bowel?
- Then proximal transverse colon is supplied with blood form the middle COLIC ARTERY(branch of the superior mensenteric artery)
- The distal third of the transverse colon is supplied by the INFERIOR MENSENTERIC ARTERY and supplies the rest of the colon
The region between the midgut and the hindgut is snesitive to Ischemia as there is less blood supply here
What does the foregut, midgut and hindgut consist of?
Foregut -gives rise to the esophagus, stomach, liver, gallbladder, bile ducts, pancreas and proximal duodenum
Midgut-distal half of the duodenum, jejunum, ileum, cecum, ascending colon, and the proximal half of the transverse colon
Hindgut-distal 1/3 of the transverse colon, descending colon, sigmoid colon and the upper anal canal.
What is the peritoneum and its structure and functions?
Serous membrane forming the lining of the abdominal cavity and covers most of the organs in the abdominal cavity including the colon
- Has FATTY TAGS (appendices epiploicae) -function unknown thought to be protective
- has muscle coat has 3 thick LONGITUDINAL BANDS( taeniae coli)-necessary for large intestine mobility
- These cause a pouched a ppearence of the cut wall(HAUSTRA)
-Lymphoid tissue nodulaes are common in small intestine(Peyers Patches) and large intestine(Solitary noduales)
What are the main functions of the colon?
- absorbs electrolytes and water
- Most things done in the proximal colon
- Na+ and Cl- absorbed by exchandge mechanisms and ion channels
- water follows by osmosis
- K+ moves passively into the lumen
How much water can the large intestine absorb?
4.5 L but normallly 1.5L is reabsorbed
What is the difference between the rectum and the rest of the colon?
- Has TRANSVERSE RECTAL FOLDS in its SUBMUCOSA
- absence of TAENIA COLI in its muscular exterior
What are the key structures of the Anal Canal?
-surrounded by internal circular muscle and external striated muscle
Describe the mucosal structure of the Large Bowel?
From Lumen to ouside:
MUCOSA-Epithelium, lamina propria, Muscularis Mucosae
SUBMUCOSA- submucosa space which has mucous secreting glands, Submucosal Plexus (MEISSNERS PLEXUS) nerves that sit on top of the submuscosal layer
MUSCULARIS- longitudinal muscel and circular muscle, Myentric Plexus (AUERBACH’S PLEXUS)
SEROSA- secures everything beneath it and has the vein and arteries going through it
What are the intestinal glands in the large intestine made up of and what are there functions?
- Enterocytes have lots of microvilli to absorb water
- Crypts dominated by Goblet cells and increase of goblet cells towards the rectum(as more mucus needed to help flow of increasingly solid contents)
- Stem cells are found in the crypts