Large intestine structure and function Flashcards
How long is the colon?
1.5 - 1.8 m
Whats the order of sections of the large intestine
Caecum (+ appendix)
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
Rectum
Anal canal & Anus
What is the purpose of the appendix?
Absolutely fuck all
Has lots of lymph nodes near it though
How is the muscle in the large intestine different from the small intestine?
In the large intestine, the longitudinal muscle layer is incomplete
Instead, it runs in three strips called teniae coli along the entire colon
The large intestine has a segmented, quilted appearance.
Why is this?
Contraction of the Teniae coli forces the circular muscle layer out the gaps
This is what produces the Haustra (pouches)
How is the mucosa in the large intestine different from that of the small intestine?
Both have simple columnar epithelium, but the large intestine has no villi
What are the crypts like in the large intestine?
Larger, straight and lined with a large number of goblet cells
What is the rectum?
Straight muscular tube between end of sigmoid colon and anal canal
What type of epithelium is found in the rectum?
Simple columnar epithelium
What is the muscularis externa like in the rectum?
Thicc
(Only in anal canal is it thicker)
How long is the anal canal?
2-3cm
Between the distal rectum and anus
What is the specific role of the muscularis externa in the anal canal?
Muscularis externa forms the internal anal sphincter
What type of muscle is the external anal sphincter?
Skeletal
What type of epithelium is found in the anal canal?
Proximal = Simple columnar
Distal = Stratified squamous
What is the main role of the colon?
Actively uptakes sodium in order to absorb water through osmosis
Why is there a large amount of colonic bacteria (1014)?
Long residence time in the colon
What benefits do we get from colonic bacteria?
- Breakdown of undigested to SC fatty acids
- Produce Vitamin K which we need for blood clotting
What gasses are there in the colon?
Nitrogen
CO2
Hydrogen
Methane
Hydrogen sulphide
What happens to our large intestine following a meal?
Mass movement contraction from colon to rectum:
- Mass moving into rectum causes distension
- Distension activates mechanoreceptors
- Mechanoreceptors stimulate defaecation reflex casuing defaecation urge
What controls the defaecation reflex?
Parasympathetic NS via the Pelvic splanchnic nerves
What is the effect of the defaecation reflex?
- Contraction of the Rectum
- Relaxation of Internal (smooth) sphincter
- Contraction of External (skeletal) sphincter
- Increased peristaltic activity in colon
(leaves you prepped for a dump)
After the defaecation reflex, what is needed before you release your faeces?
External anal sphincter must be relaxed voluntarily
Descending pathways prevent this from happening before youre ready
What are the symptoms of constipation and what causes these to happen?
The build up of material causes rectum distension which can cause:
- Headaches
- Nausea
- Loss of Appetite
- Abdominal Distension
What are the main causes of diarhhoea?
Pathogenic bacteria
Protozoans
Viruses
Toxins
Certain foods in certain people
What is an enterotoxin?
A toxin produced in or affecting the intestines
Give examples of enterotoxigenic bacteria
Vibrio cholerae
Escherichia coli
Describe how enterotoxigenic bacteria cause diarrhoea
- Bacteria produces protein enterotoxins
- Enterotoxins elevate intracellular second messangers like cAMP, cGMP, calcium
- Increased Cl- secretion from crypt cells
- This causes increased water secretion
- Water secretion > water absorption by villi
How is diarrhoea treated?
By giving a Sodium/glucose solution (Oral rehydration therapy)
This drives H2O absorption so absorption > secretion
