Large Intestine Structure and Function

Question 1

what is the caecum?

Answer 1

a blind sac at the start of the large intestine (large in herbivores)

Question 2

name the four parts of the large intestine

Answer 2

> ascending
transverse
descending
sigmoid

Question 3

what layer of muscle is complete throughout the large intestine?

Answer 3

the circular layer

Question 4

what do contractions of teniae coli produce in the large intestine?

Answer 4

pouches - haustra

Question 5

how many bands of teniae coli are there in the large intestine?

Answer 5

three

Question 6

what type of epithelium makes up the mucosa in the large intestine?

Answer 6

simple columnar

Question 7

describe the crypts in the large intestine

Answer 7

they are large and straight with a large number of goblet cells

Question 8

describe the anatomy of the rectum

Answer 8

it is a straight, muscular tube between the end of the sigmoid colon and the anal canal

Question 9

what epithelium is found in the rectum?

Answer 9

simple columnar epithelium

Question 10

is the muscularis externa thicker or thinner compared to other regions of the alimentary canal?

Answer 10

thicker

Question 11

what type of muscle comprises the external anal sphincter?

Answer 11

skeletal muscle

Question 12

how does the epithelium change in the anal canal?

Answer 12

from simple columnar to stratified squamous

Question 13

what absorption takes place in the colon?

Answer 13

active transport of sodium into the blood leads to the osmotic absorption of water

Question 14

what can long residence time in the colon lead to?

Answer 14

bacterial colonisation

Question 15

how much colonic microflora is there in the human gut?

Answer 15

1kg

Question 16

what does bacterial fermentation of undigested carbohydrate lead to?

Answer 16

> short chain fatty acids
vitamin k
gas

Question 17

name the gases produced in the colon

Answer 17

> nitrogen
> methane
> co2
> hydrogen
> hydrogen sulphide

Question 18

describe the events in the rectum following a meal

Answer 18

> mass movement contraction from colon to rectum = distension of faecal material into rectum
mechanoreceptors triggered
defaecation reflex stimulated
creates urge to defecate

Question 19

what is the nerve innervation of the defaecation reflex?

Answer 19

parasympathetic control via pelvic splanchnic nerves

Question 20

describe the defaecation reflex

Answer 20

> contraction of rectum
relaxation of internal sphincter
contraction of external sphincters
increased peristaltic activity in colon

Question 21

what symptoms are associated with constipation?

Answer 21

> headaches
nausea
loss of appetite
abdominal distension

Question 22

what can cause diarrhoea?

Answer 22

> pathogenic bacteria
> protozoans
> viruses
> toxins
> food
> stress

Question 23

what are the effects of protein enterotoxins produced by enterotoxigenic bacteria?

Answer 23

the maximally turn on intestinal chloride secretion from crypt cells creating an increase in h2o secretion

Question 24

how to protein enterotoxins turn on intestinal chloride secretion?

Answer 24

They elevate intracellular secondary messengers:
> cAMP
> cGMP
> calcium

Question 25

why does increased h2o secretion create watery diarrhoea?

Answer 25

it swamps the absorptive capacity of villus cells

Question 26

what is the treatment for enterotoxins?

Answer 26

oral rehydration therapy: sodium glucose solution

Question 27

how does sodium/glucose solution help treat diarrhoea?

Answer 27

it drives h2o absorption allowing for rehydration, and since secretion is ongoing the infection is washed away.