Large Intestine Structure and Function

Question 1

What components make up the large intestine?

Answer 1

Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon

Question 2

Where is the vermiform appendix located?

Answer 2

Attached to the caecum beside the ileocaecal valve

Question 3

What muscle layer is complete and which is incomplete?

Answer 3

Circular is complete

Longitudinal is incomplete

Question 4

What is the name of the three bands that span the length of the colon?

Answer 4

Teniae coli

Question 5

What does the contraction of the Teniae coli form?

Answer 5

Pouches (Haustra) being formed giving the colon a puckered appearance

Question 6

What is the mucosa of the large intestine made of?

Answer 6

Simple columnar epitelium with large, straight crypts lined with goblet cells
Mucus will aid faeces passing

Question 7

What is the function of the colon?

Answer 7

No nutrient absorption but actively transports sodium from the lumen into the blood
Due to osmotic absorption and water following sodium this will dehydrate the chyme and make solid faecal pellets

Question 8

What is needed to breakdown cellulose?

Answer 8

Cellulase but not made in the human body, must come from bacteria

Question 9

What products are digested in the colon?

Answer 9

Short chain fatty acids
Vitamin K - Blood clotting
Gas

Question 10

How is the rectum designed histologically?

Answer 10

Straight, muscular tube lined with simple columnar epithelium
Muscularis externa is thicker compared to other regions of the alimentary canal

Question 11

What is the design of the anal canal?

Answer 11

2-3cm long

Muscularis externa is thicker than that of the rectum

Question 12

How many rectal sphincters are there and how are they controlled?

Answer 12

Internal anal sphincter - Under autonomic control as it is made of smooth muscle with a thick muscularis externa
External anal sphincter - Under voluntary control as it is made of skeletal muscle

Question 13

How does the epithelium differ at the external anal sphincter?

Answer 13

It is stratified squamous as it is the same as the skin on the outer body

Question 14

How does the urge to defaecate come about?

Answer 14

Distension of the rectal wall produced by mass movement of faecal material into the rectum innervates mechanoreceptors leading to the defaecation reflex being signalled and thus the urge

Question 15

What effect does parasympathetic control have on the urge to defaecate and what nerves innervate this?

Answer 15

Contraction of the rectum
Relaxation of anal sphincters
Increased peristaltic activity in the colon so there is an increase of pressure on the external anal sphincter and when it relaxes you defaecate
Happens via the pelvic splanchnic nerves

Question 16

What are the associated symptoms of constipation?

Answer 16

Headaches
Nausea
Vomiting
Abdominal distension

Question 17

What are all the associated symptoms of constipation due to?

Answer 17

Distension of the rectum

Question 18

What is secretory diarrhoea?

Answer 18

Too frequent passage of faeces which are too liquid

Question 19

What are the causes of diarrhoea?

Answer 19

Pathogenic bacteria
Protozoans
Viruses
Toxins
Food

Question 20

What do enterotoxigenic bacteria do?

Answer 20

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells resulting in increased water secretion

Question 21

What three intracellular messengers elevate to allow enterotoxigenic bacteria to work?

Answer 21

cAMP
cGMP
Calcium ions

Question 22

What does water secretion swamp?

Answer 22

The absorptive capacity of villous cells leading to profuse watery diarrhoea

Question 23

What volume of diarrhoea is excreted daily by someone who has cholera?

Answer 23

25litres

Question 24

What happens if water transport is increased so much it has risen above the maximum absorptive capacity?

Answer 24

The lack of surface of area will cause the water to be excreted

Question 25

Do enterotoxins damage villus cells?

Answer 25

No

Question 26

How do you drive water absorption and help rehydration?

Answer 26

Give a sodium/glucose solution

Question 27

Is secretion necessary in diarrhoea?

Answer 27

Yes, it is needed to wash away the infection but not on the levels of dehydration

Question 28

If dehydrated what type of therapy can be done?

Answer 28

Oral rehydration