Large Intestine - Structure and Function

Question 1

What are the 4 parts of the large intestine?

Answer 1

Ascending
Transverse
Descending
Sigmoid

Question 2

What are the bands in the large intestine called and how many are there?

Answer 2

Teniae coli

3 that run along the entire length of colon

Question 3

What does contraction of teniae coli do?

Answer 3

Forms haustra (pouches)

Question 4

What is the mucosa layer of the large intestine made of?

Answer 4

Simple columnar epithelium - flat

Question 5

What are the crypts in the large intestine like?

Answer 5

Large, straight with a lot of goblet cells so there is plenty lubrication for the movement of faeces

Question 6

What is the mucosa of the rectum made of?

Answer 6

Simple columnar epithelium

Question 7

How does the muscularis externa in the rectum differ from the rest of the alimentary canal?

Answer 7

Thicker

Question 8

What is the rectum?

Answer 8

Straight, muscular tube between the sigmoid colon and the anal canal

Question 9

Where is the anal canal?

Answer 9

2-3cm between distal rectum and anus

Question 10

How does the muscularis externa of the anal canal differ from the rectum?

Answer 10

Thicker than the rectum because of the internal anal sphincter

Question 11

What is the external anal sphincter made of?

Answer 11

Skeletal muscle

Question 12

How does the epithelium change in the anal canal?

Answer 12

Simple columnar -> stratified squamous

Question 13

What is the role of the colon in absorption?

Answer 13

No nutrient absorption

Actively transports Na from lumen to blood = absorption of water = dehydration of chyme = solid faecal pellets

Question 14

What is the role of microflora in the colon?

Answer 14

Supplies vitamin K

Question 15

How is the anus kept closed?

Answer 15

By internal anal sphincter (smooth muscle under automatic control) and external anal sphincter (skeletal muscle under voluntary control)

Question 16

What happens following a meal to lead towards defaecation?

Answer 16

Wave of intense contraction (MMC) moves through the colon to the rectum
Distension of the rectal wall is produced by mass movement of faecal material into rectum which is picked up by mechanoreceptors leading to defaecation reflex

Question 17

How is the defaecation reflex controlled?

Answer 17

Under parasympathetic control via pelvic splanchnic nerves

NO sympathetic influence

Question 18

What makes up the defaecation reflex?

Answer 18

Contraction of rectum
Relaxation of internal anal sphincter
Contraction of external anal sphincter
Increased peristaltic activity in colon - causes increased pressure on external anal sphincter = relaxes it

Question 19

What happens in constipation?

Answer 19

No absorption of toxins from faecal material following long periods of retention

Question 20

What are the symptoms associated with constipation?

Answer 20

Headaches
Nausea
Loss of appetite
Abdominal distension

Question 21

What is diarrhoea?

Answer 21

Too frequent passage of faeces which are too liquid

Question 22

What are the causes of diarrhoea?

Answer 22

Pathogenic bacteria
Protozoans
Viruses
Toxins
Food
Stress

Question 23

What does enterotoxigenic bacteria do?

Answer 23

Produces protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells causing an increase in water secretion

Question 24

How does enterotoxins increase Cl secretion and hence water secretion?

Answer 24

Elevate intracellular second messengers:
cAMP
cGMP
calcium

Question 25

How is secretory diarrhoea treated?

Answer 25

Sodium/glucose solution which drives water absorption = rehydration