Lecture 12 Large Intestine Structure and Function Flashcards
What connects the ileum with the cecum
Ileocaecal valve
What are the four parts of the colon
Ascending colon, Transverse colon, Descending Colon and Sigmoid colon
Describe the muscular layer of the colon
Circular muscle layer complete but longitudinal muscle layer incomplete
What are the 3 bands that run the full course of the large intestine
Teniae coli
Contractions of the Teniae coli form
Haustra
What cells are the mucosa of the large intestine made of
Simple columnar flat epithelial cells
What and where is the rectum
Straight, muscular tube (between end of sigmoid colon and anal canal)
What type of cells make up the lining of the rectum
Simple columnar epithelium
Describe the muscular externa of the rectum
Thick compared to other regions of the alimentary canal
Where is the anal canal located
2-3cm between distal rectum and anus
Describe the Internal and external anal sphincter
Muscularis thicker than rectum internal anal sphincter
External anal sphincter = skeletal muscle
What type of cells line the anal canal
Transitions from simple columnar to stratified squamous
Does nutrient absorption occur in the colon
No
How does colon absorb water from chyme to produce faeces
• Actively transports sodium from lumen into blood this causes osmotic absorption of water and dehydration of chyme into solid faecal pellets
What does the long residence time in the con cause
Bacterial colonisation
What is Gas (flatus) made up of
nitrogen, CO2, hydrogen, methane, hydrogen sulphide
Describe the normal physiology of the anal sphincter muscles
• Normally, anus closed by internal anal sphincter (smooth muscle under automatic control) and external anal sphincter (skeletal muscle under voluntary control)
What happens at the rectum following a meal
• Wave of intense contraction (Mass Movement Contraction) travels from the colon to rectum
Mechanoreceptors detect this causing a deflection reflex and an urge to defaecate
Describe the defection reflex
Under parasympathetic control – via pelvic splanchnic nerves (no sympathetic influence)
A Contraction of rectum
B Relaxation of internal and contraction of external anal sphincters
C Increased peristaltic activity in colon
Pressure on external anal sphincter - relaxes under voluntary control expulsion of faeces
When does constipation occur
• No absorption of toxins from faecal material following long periods of retention
Symptoms of constipation
Headaches
Nausea
Loss of appetite
Abdominal distension
Causes of diarrhoea
pathogenic bacteria protozoans
viruses
toxins
food
Give examples of Enterotoxigenic Bacteria
Vibrio cholerae,
Escherichia coli
How do enterotoxigenic bacteria increase water secretion
• Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells
increase H2O secretion which swamps the capacity of the villus leading to watery diarrhoea
• Act by elevating intracellular second messengers:
cAMP
cGMP
calcium
