Large Intestine Structure and Function Flashcards
What muscular layer of the large intestine is complete?
The circular muscle layer
What muscle layer of the large intestine is incomplete and how does it appear on the large intestine?
The longitudinal muscle layer - 3 strips of longitudinal muscle run along the entire length of the outside of the colon
What are the 3 strips of longitudinal muscle running along the outside of the large intestine known as?
Teniae coli
The contractions of the teniae coli cause
the haustra - puckered appearance of the colon
What epithelium is the mucosa of the large intestine composed of?
Simple columnar epithelium
What cells provide the lubrication needed in the large intestine for the movement of faeces?
Goblet cells
What nerve is the main innervation from the parasympathetic system to the GI tract?
Vagus nerve
What nerve is the main innervation from the sympathetic system to the GI tract?
Splanchnic nerve
What effect do the parasympathetic and sympathetic systems have on the GI tract, respectively?
Parasympathetic - stimulatory
Sympathetic - inhibitory
What functions does the pancreas have?
Exocrine and endocrine
What are the functions of the large intestine?
It actively transports sodium from the lumen into the blood causing the osmotic absorption of water and dehydration of the chyme to produce solid faeces
What are the main components of the large intestine?
Caecum Ascending colon Transvers colon Descending colon Sigmoid colon
What is the ileocaecal valve?
Where the ileum and the large intestine join
What essential vitamin is obtained from the bacterial fermentation of undigested carbohydrates in the intestines?
Vitamin K
Why is vitamin K essential?
It is essential for the clotting of blood
What can be obtained from the bacterial flora in the intestines that acts as an energy source?
Short chain fatty acids
The bacterial flora in the colon protects against
pathogenic bacteria in the colon
What is the rectum?
Straight, muscular tube between the end of the sigmoid colon and the anal canal
What is the epithelium type of the mucosa of the rectum?
Simple columnar epithelium
How does the muscularis externa of the rectum compare to elsewhere in the alimental canal?
It is thicker in the rectum
Is the muscularis externa of the anal canal thicker or thinner than that of the rectum?
Thicker
What muscle type is the external anal sphincter formed from?
Skeletal muscle
How does the epithelium of the anal canal change as you move down the canal?
Epithelium changes from simple columnar to stratified squamous
Normally the anus is closed by the
internal anal sphincter
What muscle type is the internal anal sphincter formed from?
Smooth muscle
Which anal sphincter is under autonomic control and which is under voluntary control?
Autonomic - internal
Voluntary - external
The rectal wall distends as a result of
the mass movement of faecal material into the rectum
The distension of the rectal wall triggers the
mechanoreceptors responsible for the defaecation reflex which stimulates the urge to defaecate
Is the defaecation reflex under sympathetic or parasympathetic control?
Parasympathetic via the pelvic splanchnic nerves
What is caused by the defaecation reflex?
Contraction of rectum
Relaxation of internal anal sphincter
Contraction of external anal sphincter
What is the defaecation reflex?
Increased peristaltic activity in the colon increasing the pressure on the external anal sphincter which relaxes under voluntary control and allows the expulsion of faeces
What is diarrhoea?
The too-frequent passage of faeces which are too liquid
What are the common causes of diarrhoea?
Pathogenic bacteria Protozoans Viruses Toxins Food
Enterotoxigenic bacteria produce protein enterotoxins which
maximally turn on intestinal chloride secretion from the crypt cells, causing increased water secretion
Increased water secretion swamps the
absorptive capacity of the villi
What solutions can be given to drive water reabsorption and cause rehydration?
Sodium or glucose solutions
