Week 3.10 - Large Intestine Structure and Function

Question 1

Why is appendicitis common?

Answer 1

vermiform appendix has many lymph nodes surrounding

Question 2

what is the length of the large intestine?

Answer 2

1.5-1.8 metres

Question 3

What does the muscularis externa layer of the large intestine consist of?

Answer 3

circular muscle and longitudinal muscle not complete around whole intestine - only 3 teniae coli.

Question 4

What do the tenia coli create?

Answer 4

haustra

Question 5

What is the mucosa layer of the large intestine?

Answer 5

smooth - no folds or villi - but has crypts. simple columnar

Question 6

What are the large intestine crypts function?

Answer 6

• contain large amount of goblet cells for lubrication
• stem cells for epithelial regeneration

Question 7

What is the rectum and its structure?

Answer 7

straight muscular tube between sigmoid and anal canal. muscularis externa is thicker than other parts of GIT. needs to hold faeces for hours and push it out.

Question 8

What is anal canal and its structure?

Answer 8

2-3cm long between distal rectum and anus. muscularis is thicker than rectum and has internal and external anal sphincter. stratified squamous

Question 9

What controls the anal sphincters?

Answer 9

internal is involuntary smooth muscle controlled by autonomic.
external is voluntary skeletal muscle

Question 10

which parts of the GIT have stratified squamous epithelium?

Answer 10

mouth, oesophagus and anal canal

Question 11

What are the anal sphyincters made of?

Answer 11

muscularis external of rectal canal

Question 12

What is the main mechanism of the large intestine?

Answer 12

moves water out into blood using sodium to dehydrate chyme so faeces are solid

Question 13

How long does food stay in the large intestine and why?

Answer 13

long time. 1kg of bacteria fermenting it. helps form vitamin K which is important for blood clotting and prevents haemorrhage

Question 14

what gives us the urge to defecate?

Answer 14

When food reaches rectum, it causes distention of rectal wall. once moves in, mechanoreceptors send a defection reflex, giving us urge to defecate.

Question 15

what nerves control defecation?

Answer 15

parasympathetic control - sympathetic not involved. from pelvic splanchnic nerves

Question 16

What parasympathetic innervations are not controlled by vagal nerve?

Answer 16

defacation reflex - pelvic splanchnic, glossopharyngeal and facial nevres are exceptions

Question 17

What happens after contraction of the rectum?

Answer 17

internal sphincter relaxes. increases peristaltic activity in colon, increasing pressure of external sphincter. then when we are ready , we relax the external sphincter

Question 18

What are symptoms of constipation?

Answer 18

• headache,
• nausea,
• loss of appetite,
• abdominal distention

Question 19

How do you manage constipation?

Answer 19

• eat more fibre,
• change diet,
• drink water,
• exercise,
• medication if needed

Question 20

What causes diarrhoea?

Answer 20

• pathogenic bacteria,
• protozoa,
• virus,
• toxins,
• food

Question 21

How does enterotoxogenic bacteria cause diarrhoea?

Answer 21

secretes toxins in small intestine which turn on chloride secretion from crypt cells and cause water to enter - 25L from 1.5L.
- activates cAMP, cGMP and calcium.

Question 22

How do you treat diarrhoea?

Answer 22

hydration therapy - sodium/glucose solution which helps absorb water. takes 3 days ish. enterotoxins dont destroy villi so still function.