Large Intestine Structure and Function

Question 1

How long is the colon?

Answer 1

1.5-1.8m

Question 2

What are the 4 parts of the colon?

Answer 2

• Ascending
• Transverse
• Descending
• Sigmoid

Question 3

How do the longitudinal and circular muscle layers differ?

Answer 3

Circular muscle layers is complete by longitudinal muscle layer is incomplete

Question 4

What are the 3 bands of the colon called?

Answer 4

Teniae coli

Question 5

What does contraction of the teniae coli result in?

Answer 5

Pouches (haustra) resulting in a puckered appearance

Question 6

What is the mucosa of the large intestine composed of?

Answer 6

Simple columnar epithelium

Question 7

What provides lubrication for movement of faeces?

Answer 7

Large straight crypts lined with large numbers 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 is the mucosa of the rectum?

Answer 9

Simple columnar epithelium

Question 10

How does the muscularis externa of the rectum compare to that of other regions of the alimentary canal?

Answer 10

Thicker

Question 11

What is the anal canal?

Answer 11

2-3cm between distal rectum and anus

Question 12

How does the muscularis of the anal canal compare to that of the rectum?

Answer 12

Thicker, contains internal anal sphincter

Question 13

What is the external anal sphincter?

Answer 13

Skeletal muscle

Question 14

How does the epithelium of the anal canal transition?

Answer 14

Simple columnar to stratified squamous

Question 15

What nutrient absorption role does the colon play?

Answer 15

No important role

Question 16

What is the result of the active transport of sodium from the lumen into the blood?

Answer 16

• Osmotic absorption of water
• Dehydration of chyme
• Production of solid faecal pellets

Question 17

What does the long residence time in the colon lead to?

Answer 17

Bacterial colonisation

Question 18

How much colonic microflora is there?

Answer 18

10^14 bacteria (~1kg)

Question 19

What does the bacterial fermentation of undigested carbohydrate lead to?

Answer 19

• Short chain fatty acids
• Vitamin K
• Gas

Question 20

What are the components of flatulence?

Answer 20

• Nitrogen
• CO2
• Hydrogen
• Methane
• Hydrogen sulphide

Question 21

Why is the anus normally closed?

Answer 21

Closed by internal anal sphincter and external anal sphincter

Question 22

What is the control of the internal anal sphincter?

Answer 22

Smooth muscle under autonomic control

Question 23

What is the control of the external anal sphincter?

Answer 23

Skeletal muscle under voluntary control

Question 24

Describe the production of the urge to defecate.

Answer 24

• Following meal wave of intense contraction (MMC) from colon through to rectum
• Distension of rectal wall produced by mass movement of faecal matter into rectum
• Stimulates mechanoreceptors
• Defaecation reflex
• Urge

Question 25

What is the control of the defecation reflex?

Answer 25

Under parasympathetic control via pelvic splanchnic nerves

Question 26

What influence does the sympathetic system have on the defecation reflex?

Answer 26

No influence

Question 27

What are the components defecation reflex?

Answer 27

- Contraction of rectum - Relaxation of internal and contraction of external anal sphincters - Increased peristaltic activity in colon

Question 28

What is the result of the defecation reflex?

Answer 28

- Increased pressure on external anal sphincter - Relaxes under voluntary control - Expulsion of faeces

Question 29

What is voluntary delay of defecation due to?

Answer 29

Descending pathways

Question 30

Describe the frequency of bowel movements?

Answer 30

Varies considerably from person to person

Question 31

What is the absorption of toxins from faecal material following long periods of retention?

Answer 31

No absorption

Question 32

What are the symptoms associated with constipation?

Answer 32

- Headaches - Nausea - Loss of appetite - Abdominal distension

Question 33

What is constipation due to?

Answer 33

Distension of rectum

Question 34

What is diarrhoea?

Answer 34

Too frequent passage of faeces which are too liquidy

Question 35

What are the causes of diarrhoea?

Answer 35

- Pathogenic bacteria - Protozoans - Viruses - Toxins - Food

Question 36

How many deaths a year is diarrhoea responsible for?

Answer 36

2.5 million of the 1,500 million cases a year

Question 37

Give 2 examples of enterotoxigenic bacteria.

Answer 37

- Vibrio cholerae | - Escherichia coli

Question 38

What doe enterotoxigenic bacteria produce?

Answer 38

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells which leads to increased H2O secretion

Question 39

How do enterotoxigenic bacteria act?

Answer 39

Elevate intracellular second messengers: - cAMP - cGMP - Calcium

Question 40

How does H2O secretion lead to profuse watery diarrhoea?

Answer 40

H2O secretion swamps absorptive capacity of villus cells

Question 41

What damage do enterotoxins do to villus cells?

Answer 41

No damage

Question 42

What is the treatment for secretory diarrhoea?

Answer 42

- Give sodium/glucose solution | - Oral rehydration therapy

Question 43

What does sodium/glucose solution do?

Answer 43

Drives H2O absorption leading to rehydration