Large Intestine Structure and Function

Question 1

how long is the colon?

Answer 1

1.5-1.8m

Question 2

what are the four parts of large colon?

Answer 2

ascending, transverse, descending, sigmoid

Question 3

what is involved in the large intestine?

Answer 3

Ileum  
ileocaecal valve 
 caecum (blind sac) 
 vermiform (worm-like) 
appendix –
 lymph nodes

Question 4

which layers or the large intestine are complete and incomplete?

Answer 4

circular muscle is complete

longitudinal muscle is incomplete

Question 5

what type of epithelium is the mucosa of large intestine

Answer 5

simple columnar

Question 6

what function does goblet cells have that are attached to crypts

Answer 6

lubrication of faeces

Question 7

what type of tube is the rectum?

Answer 7

straight, muscular

between sigmoid colon and anal canal

Question 8

what type of epithelium is mucosa of the rectum?

Answer 8

simple columnar

Question 9

where is the anal canal?

Answer 9

2-3 cm between distal rectum and anus

Question 10

what type of muscle is the external anal sphincter?

Answer 10

skeletal muscle

Question 11

what type of epithelium is the anal canal?

Answer 11

simple columnar to stratified squamous

Question 12

what is the tenia coli?

Answer 12

The taeniae coli (also teniae coli or tenia coli) are three separate longitudinal ribbons (taeniae meaning ribbon in latin) of smooth muscle on the outside of the ascending, transverse, descending and sigmoid colons

Question 13

what is the function of the colon?

Answer 13

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

Question 14

what is the colonic microflora?

Answer 14

10^14 bacteria

Question 15

what is a result of long residence time in the colon?

Answer 15

bacterial colonisation

Question 16

what nervous system control defaecation reflex?

Answer 16

parasympathetic via splanchnic nerves

Question 17

what happens in the defaecation reflex

Answer 17

Contraction of rectum
Relaxation of internal and contraction of external anal sphincters
Increased peristaltic activity in colon
 Pressure on external anal sphincter - relaxes under voluntary control  expulsion of faeces

Voluntary delay of defaecation - descending pathways

Question 18

what is constipation?

Answer 18

No absorption of toxins from faecal material following long periods of retention

Question 19

what are symptoms associated with constipation?

Answer 19

Headaches
Nausea
Loss of appetite
Abdominal distension

due to distension of rectm

Question 20

what is diarrhoea?

Answer 20

Too frequent passage of faeces which are too liquid

Question 21

what are causes of diarrhoea?

Answer 21

pathogenic bacteria
protozoans
viruses
toxins
food
first year medical exams…

Question 22

what are examples of enterotoxigenic bacteria?

Answer 22

Vibrio cholerae, Escherichia coli

Question 23

what is the result if enteroxoigenic bacteria?

Answer 23

Produce protein enterotoxins which maximally turn on intestinal chloride secretion from crypt cells
H2O secretion
Act by elevating intracellular second messengers:
cAMP
cGMP
calcium
H2O secretion swamps absorptive capacity of villus cells  profuse watery diarrhoea (25 litres per day for cholera)

Question 24

what is the treatment of secretory diarrhoea?

Answer 24

Enterotoxins don’t damage villus cells

Give sodium/glucose solution

Drive H2O absorption rehydration

Secretion still going wash away infection

Oral rehydration therapy