Large intestine structure and function Flashcards
How does the ileum ultimately connect to the colon?
ileum - ileocaecal valve - caecum - vermiform appendix
How long is the colon?
1.5-1.8m
Name the 4 parts of the colon
ascending, transverse, descending and sigmoid
Is the circular or longitudinal muscle layer incomplete in the colon?
longitudinal
What are teniae coli?
3 bands spanning the entire length of the colon which is why the longitudinal muscle is disrupted
What are haustra and how are they formed?
pouches of the large intestine due to the contractions of the teniae coli
What epithelium is found in the mucosa of the large intestine?
simple columnar
Describe the crypts of the large intestine
large and straight
large amount of goblet cells to secrete mucus to help with lubrication for the movement of faeces
Where is the rectum anatomically?
Between the sigmoid colon and the anal canal
Describe the rectum
straight muscular tube with simple columnar epithelium and a thick muscularis externa
Where is the anal canal anatomically?
2-3cm between the distal rectum and anus
What epithelium makes up the anal canal?
stratified squamous epithelium
How many anal sphincters are there?
2 - internal and external which is comprised of skeletal muscle
What is the primary role of the colon?
dehydrate chyme
How does the colon dehydrate the chyme?
active transport of sodium and the water follows
What are the 2 reasons for the transmit time of the colon being relatively long?
bacterial colonisation
ferment undigested carbohydrate
What are the 3 products after fermentation of undigested carbohydrates
vitamin K
short chain fatty acids
Gas
Explain the difference in muscle between the internal and external anal sphincters
internal - smooth under autonomic control
external - skeletal under voluntary control
Explain how the defaecation reflex comes about
following a meal the faeces travels from the colon to the rectum which distends the wall of the rectum which is sensed by mechanoreceptors
How is the defaecation reflex controlled by the nervous system?
parasympathetically by pelvic splanchnic nerve
After the defaecation reflex has begun explain how this leads to faces being expelled
MMC in colon increases pressure on external sphincter which you voluntarily relax and pass faeces
How can you put off the expulsion of faeces?
descending neural pathways
Is there absorption of toxins from faecal material due to long retention times in the colon in constipation?
NO
What are the symptoms of constipation and what are these due to?
headache, nausea, abdominal distension and loss of appetite caused by distension of rectum
How can constipation be treated?
laxatives
What is the definition of diarrhoea?
Too frequent passage of faeces which are too liquid
What are some causes of diarrhoea?
pathogenic bacteria, toxins, viruses, food, nerves, protozoans
What do enterotoxigenic bacteria do? plus examples
vibrio cholera, E coli
Produce protein enterotoxins to turn on chloride secretion and therefore promote extreme water loss
What do enterotoxigenic bacteria do to intracellular 2nd messengers?
turn them on eg cAMP, cGMP and calcium
How is diarrhoea by enterotoxigenic bacteria now treated in developing countries to prevent children dying?
sodium-glucose solution as the villi are not damaged so this will promote rehydration and the washing away of bacteria
