Large Intestine Structure and Function Flashcards
Which muscle layer is incomplete?
Longitudinal muscle layer - found in strips
•circular muscle layer extends out inbetween these strips
How many bands of teniae coli span the entire length of the colon?
3
What is formed as a result of contractions of teniae coli?
Pouches / haustra are formed - making the puckered appearance
What is the mucosa of the large intestine composed of?
Simple columnar epithelium - flat
Large straight crypts are lined with a number of goblet cells
Describe the location of the rectum
•Straight, muscular tube (between end of sigmoid colon and anal canal)
What is the epithelium of the rectum?
Simple columnar
How would you describe the muscularis externa of the alimentary canal?
•thick compared to other regions of alimentary canal
Where does the anal canal lie?
In between the distal rectum and the anus
How does the muscularis externa compare between the anal canal and the rectum?
Muscularis is thicker than the rectum - internal anal sphincter
What kind of muscle composes the external anal spincter?
Skeletal muscle
What is the epithelium of the anal canal?
Simple columnar - stratified squamous
What does the large intestine absorb and what does it absorb?
No absorptive role of nutrients in humans
Actively transports sodium from lumen into the blood allowing for the osmotic absorption of water - dehydration of chyme - solid faecal pellets
What happens to undigested carbohydrate (cellulose) in the large intestine?
Bacterial fermentation of undigested carbohydrate
What is formed as a result of bacterial fermentation?
Makes:
Short chain fatty acids
Vitamin K
Gas (flatus) - nitrogen, CO2, Hydrogen, methane, hydrogen sulphide
What happens as a result of mass movement contraction from colon to rectum?
Rectal wall becomes distended - mechanoreceptors initiate defaecation reflex - urge to defaecate
What is the nervous control of the defaecation reflex?
Parasympathetic control by the pelvic splanchnic nerves
What do these pelvic splanchnic nerves influence?
Contraction of rectum
Relaxation of internal and contraction of external anal sphincters
Increased peristaltic activity in colon
These act to increase pressure on the external anal sphincter
What is controls the voluntary delay of defaecation?
Descending pathways, appear after about 2 years of life
Will toxins eventually be absorbed following long periods of retention (constipation)?
NO
What are symptoms associated with constipation?
Headaches
Nausea
Loss of appetite
Abdominal distension
What is diarrhoea defined as?
•Too frequent passage of faeces which are too liquid
What are the causes of diarrhoea?
pathogenic bacteria
protozoans
viruses
toxins
food
Stress
Give examples of enterotoxigenic bacteria
Vibrio cholerae, Escherichia coli
How do enterotoxigenic bacteria cause diarrhoea?
Protein enterotoxins maximally turn on intestinal chloride secretion from crypt cells.
Increases H2O secretion
Swamps absorptive capacity of villus.
Flat surface of the colon means that it can’t absorb this vast quantity of water
What secondary messengers do protein enterotoxins utilise?
cAMP
cGMP
calcium
How does sodium glucose solution used to treat diarrhoea?
Sodium is the driving factor for water absorption – rehydrates patient
