Large Intestine Structure and Function

Question 1

Which muscle layer is incomplete?

Answer 1

Longitudinal muscle layer - found in strips

•circular muscle layer extends out inbetween these strips

Question 2

How many bands of teniae coli span the entire length of the colon?

Answer 2

3

Question 3

What is formed as a result of contractions of teniae coli?

Answer 3

Pouches / haustra are formed - making the puckered appearance

Question 4

What is the mucosa of the large intestine composed of?

Answer 4

Simple columnar epithelium - flat

Large straight crypts are lined with a number of goblet cells

Question 5

Describe the location of the rectum

Answer 5

•Straight, muscular tube (between end of sigmoid colon and anal canal)

Question 6

What is the epithelium of the rectum?

Answer 6

Simple columnar

Question 7

How would you describe the muscularis externa of the alimentary canal?

Answer 7

•thick compared to other regions of alimentary canal

Question 8

Where does the anal canal lie?

Answer 8

In between the distal rectum and the anus

Question 9

How does the muscularis externa compare between the anal canal and the rectum?

Answer 9

Muscularis is thicker than the rectum - internal anal sphincter

Question 10

What kind of muscle composes the external anal spincter?

Answer 10

Skeletal muscle

Question 11

What is the epithelium of the anal canal?

Answer 11

Simple columnar - stratified squamous

Question 12

What does the large intestine absorb and what does it absorb?

Answer 12

No absorptive role of nutrients in humans

Actively transports sodium from lumen into the blood allowing for the osmotic absorption of water - dehydration of chyme - solid faecal pellets

Question 13

What happens to undigested carbohydrate (cellulose) in the large intestine?

Answer 13

Bacterial fermentation of undigested carbohydrate

Question 14

What is formed as a result of bacterial fermentation?

Answer 14

Makes:

Short chain fatty acids

Vitamin K

Gas (flatus) - nitrogen, CO2, Hydrogen, methane, hydrogen sulphide

Question 15

What happens as a result of mass movement contraction from colon to rectum?

Answer 15

Rectal wall becomes distended - mechanoreceptors initiate defaecation reflex - urge to defaecate

Question 16

What is the nervous control of the defaecation reflex?

Answer 16

Parasympathetic control by the pelvic splanchnic nerves

Question 17

What do these pelvic splanchnic nerves influence?

Answer 17

Contraction of rectum

Relaxation of internal and contraction of external anal sphincters

Increased peristaltic activity in colon

These act to increase pressure on the external anal sphincter

Question 18

What is controls the voluntary delay of defaecation?

Answer 18

Descending pathways, appear after about 2 years of life

Question 19

Will toxins eventually be absorbed following long periods of retention (constipation)?

Answer 19

NO

Question 20

What are symptoms associated with constipation?

Answer 20

Headaches

Nausea

Loss of appetite

Abdominal distension

Question 21

What is diarrhoea defined as?

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

Give examples of enterotoxigenic bacteria

Answer 23

Vibrio cholerae, Escherichia coli

Question 24

How do enterotoxigenic bacteria cause diarrhoea?

Answer 24

Protein enterotoxins maximally turn on intestinal chloride secretion from crypt cells.

Increases H2O secretion

Swamps absorptive capacity of villus.

Flat surface of the colon means that it can’t absorb this vast quantity of water

Question 25

What secondary messengers do protein enterotoxins utilise?

Answer 25

cAMP

cGMP

calcium

Question 26

How does sodium glucose solution used to treat diarrhoea?

Answer 26

Sodium is the driving factor for water absorption – rehydrates patient