Large intestine: structure and function Flashcards
where does the large intestine start?
ileocaecal valve
what are the 4 parts of the large intestine?
ascending
transverse
descending
sigmoid
what’s different about the muscularis externa of the large intestine compared with S.I?
The large intestine has a complete circular muscle layer but the longitudinal layer is in 3 separate strips throughout the length of the large intestine
what gives the large intestine it’s puckered appearance?
contracted haustra
Main function of goblet cells in the lining of crypts in large intestine
Goblet cells are interspersed between simple columnar epithelium producing mucus that provides lubrication for movement of faeces
describe rectum structure:
mucosa, and muscula externa
The rectum is a straight, muscular tube
mucosa - simple columnar epithelium
muscularis externa - thicker to hold onto faeces
what is the mucosa of L.I comprised of?
simple columnar epithelium
what are teniae coli?
the ribbon-like parts of longitudinal smooth muscle - entire length of colon
where is the anal canal found?
between distal rectum and anus
is the muscularis thicker in the rectum or anal canal?
anal canal due to the internal anal sphincter
which type of muscle is found in:-
External anal sphincter
Internal anal sphincter
external - skeletal muscle
internal - ring of smooth muscle
what type of control is the anal canal under?
voluntary - you can hold a poo in if you can’t find a toilet
what is the outermost layer of the large intestine?
Ascending and descending colon - adventitia
Transverse colon - serosa
main functions of the colon
actively transports Na+ from lumen into blood which in turn pulls H20 across with it - dehydrates chyme and makes solid faecal pellets
bacterial fermentation of undigested carbohydrate
what products are made from bacterial fermentation of undigested carbohydrate?
short chain fatty acids
vitamin K
gas - nitrogen, CO2, H2, CH4 etc
What is Vitamin K important for?
blood clotting
in a normal state, how is the anus kept closed?
internal anal sphincter (s.m under automatic control) and external anal sphincter (skeletal muscle under voluntary control)
what is the wave of intense contraction called that follows eating a meal
mass movement contraction
Describe the defaecation reflex?
reflex that gives us the urge to go for a poo
it is initiated by the contraction of the rectum. The internal anal sphincter relaxes whilst the external contracts. Increased peristaltic activity moves material along and increases pressure on ext anal sphincter. This then relaxes under voluntary control and expels faeces
when this reflex is triggered you can either choose to delay or defecate
What control is there over the defaecation reflex?
parasympathetic control via pelvic splanchnic nerves (no sympathetic influence)
however, there is a voluntary delay of defaecation - descending pathways
symptoms associated with constipation? (4) and main reason for these?
headaches
nausea
loss of appetite
abdominal distension
due to distension of rectum
Causes of diarrhoea (5)
pathogenic bacteria protozoans viruses toxins food
give 2 types of enterotoxigenic bacteria that commonly cause diarrhoea
vibrio cholerae
excherichia coli
how do enterotoxigenic bacteria work?
These toxins turn on intestinal Cl- secretion from crypts - they elevate intracellular second messengers like cAMP, cGMP etc and ensure the CFTR channel is always open so therefore the crypts secrete H20 all the time as H20 moves with Cl- => profuse watery diarrhoea
treatment of secretory diarrhoea
Give sodium/glucose solution
oral rehydration therapy - drives H20 absorption
must let diarrhoea run but keep hydrating them
