Large intestine structure and function

Question 1

How long is the colon?

Answer 1

1.5 - 1.8 m

Question 2

Whats the order of sections of the large intestine

Answer 2

Caecum (+ appendix)

Ascending colon

Transverse colon

Descending colon

Sigmoid colon

Rectum

Anal canal & Anus

Question 3

What is the purpose of the appendix?

Answer 3

Absolutely fuck all

Has lots of lymph nodes near it though

Question 4

How is the muscle in the large intestine different from the small intestine?

Answer 4

In the large intestine, the longitudinal muscle layer is incomplete

Instead, it runs in three strips called teniae coli along the entire colon

Question 5

The large intestine has a segmented, quilted appearance.

Why is this?

Answer 5

Contraction of the Teniae coli forces the circular muscle layer out the gaps

This is what produces the Haustra (pouches)

Question 6

How is the mucosa in the large intestine different from that of the small intestine?

Answer 6

Both have simple columnar epithelium, but the large intestine has no villi

Question 7

What are the crypts like in the large intestine?

Answer 7

Larger, straight and lined with a large number of goblet cells

Question 8

What is the rectum?

Answer 8

Straight muscular tube between end of sigmoid colon and anal canal

Question 9

What type of epithelium is found in the rectum?

Answer 9

Simple columnar epithelium

Question 10

What is the muscularis externa like in the rectum?

Answer 10

Thicc

(Only in anal canal is it thicker)

Question 11

How long is the anal canal?

Answer 11

2-3cm

Between the distal rectum and anus

Question 12

What is the specific role of the muscularis externa in the anal canal?

Answer 12

Muscularis externa forms the internal anal sphincter

Question 13

What type of muscle is the external anal sphincter?

Answer 13

Skeletal

Question 14

What type of epithelium is found in the anal canal?

Answer 14

Proximal = Simple columnar

Distal = Stratified squamous

Question 15

What is the main role of the colon?

Answer 15

Actively uptakes sodium in order to absorb water through osmosis

Question 16

Why is there a large amount of colonic bacteria (10¹⁴)?

Answer 16

Long residence time in the colon

Question 17

What benefits do we get from colonic bacteria?

Answer 17

• Breakdown of undigested to SC fatty acids
• Produce Vitamin K which we need for blood clotting

Question 18

What gasses are there in the colon?

Answer 18

Nitrogen

CO2

Hydrogen

Methane

Hydrogen sulphide

Question 19

What happens to our large intestine following a meal?

Answer 19

Mass movement contraction from colon to rectum:

1. Mass moving into rectum causes distension
2. Distension activates mechanoreceptors
3. Mechanoreceptors stimulate defaecation reflex casuing defaecation urge

Question 20

What controls the defaecation reflex?

Answer 20

Parasympathetic NS via the Pelvic splanchnic nerves

Question 21

What is the effect of the defaecation reflex?

Answer 21

• Contraction of the Rectum
• Relaxation of Internal (smooth) sphincter
• Contraction of External (skeletal) sphincter
• Increased peristaltic activity in colon

(leaves you prepped for a dump)

Question 22

After the defaecation reflex, what is needed before you release your faeces?

Answer 22

External anal sphincter must be relaxed voluntarily

Descending pathways prevent this from happening before youre ready

Question 23

What are the symptoms of constipation and what causes these to happen?

Answer 23

The build up of material causes rectum distension which can cause:

• Headaches
• Nausea
• Loss of Appetite
• Abdominal Distension

Question 24

What are the main causes of diarhhoea?

Answer 24

Pathogenic bacteria

Protozoans

Viruses

Toxins

Certain foods in certain people

Question 25

What is an enterotoxin?

Answer 25

A toxin produced in or affecting the intestines

Question 26

Give examples of enterotoxigenic bacteria

Answer 26

Vibrio cholerae

Escherichia coli

Question 27

Describe how enterotoxigenic bacteria cause diarrhoea

Answer 27

1. Bacteria produces protein enterotoxins
2. Enterotoxins elevate intracellular second messangers like cAMP, cGMP, calcium
3. Increased Cl- secretion from crypt cells
4. This causes increased water secretion
5. Water secretion > water absorption by villi

Question 28

How is diarrhoea treated?

Answer 28

By giving a Sodium/glucose solution (Oral rehydration therapy)

This drives H2O absorption so absorption > secretion