small intestine function

Question 1

how long is the small intestine ?

Answer 1

6 metres (ranges from 4.5-9 metres)

Question 2

how long is the duodenum and what is its function ?

Answer 2

25cm long
gastric acid neutralisation, digestion, iron absorption

Question 3

how long is the jejunum and what is its function ?

Answer 3

2.5m long
nutrient absorption 95%

Question 4

how long is the ileum and what is its function ?

Answer 4

3.5 m
NaCl/H2O absorption causing chyme dehydration

Question 5

what increases the absorbative surface area of the small intestine ?

Answer 5

pilcae folds (3x 1m2)
villi (10 x 10m2)
microvilli (600x 200m2)

Question 6

what do villus cells absorb in the small intestine ?

Answer 6

NaCl
monosaccharides
amino acids
peptides
fats
vitamines
minerals
water

Question 7

what do crypt cells secrete ?

Answer 7

secretes Cl and water

Question 8

how much fluid does the small intestine secrete every day ?

Answer 8

1500ml

Question 9

where does small intestine H2O secretion come from ?

Answer 9

crypt cells

Question 10

why is H2O important for digestion ?

Answer 10

maintains lumenal contents in liquid state
promotes mixing of digestive enzymes
aids nutrient presentation to absorping surface
dilutes and washes away potentially injurious substances

Question 11

how do crypt cells secrete chlorine ?

Answer 11

1- Cl- pumped into the cell by NakCl cotransporter (Na,K pumped out and Cl- pumped in)
2- cell already highly negative so drives Cl- out through the CFTR channel and water follows through tight junctions due to osmolarity gradient

Question 12

how is chlorine secretion by crypt cells controlled ?

Answer 12

adenylate cycles converts ATP to cAMP which phosphorylates PkA

this activates the CFTR channel and allows Cl- through

Question 13

what condition is caused when CFTR channel is broken ?

Answer 13

cystic fibrosis

Question 14

what are the two modes of motility in the small intestine ?

Answer 14

segmentation
peristalsis

Question 15

when does segmentation occur and how does it work ?

Answer 15

after/during a meal

continuous contraction and relaxation of short intestinal segments which mixes chyme with digestive enzymes

it also brings chyme into contact with absorbing surfaces

Question 16

what cells initiate segmentation ?

Answer 16

pacemaker cells in the lontidudinal muscle layer

and creates basic electric rhythm (BER)

Question 17

what is the frequency of segmentation determined by ?

Answer 17

basic electric rhythm (BER)
which is unaffacted by the autonomic nervous system

Question 18

when does peristalsis occur ?

Answer 18

following absorption of nutrients (once stomach and intestines are empty)

Question 19

what is the MMC migrating motility complex ?

Answer 19

pattern of peristaltic activity travelling down small intestine

as one ends in the ileum another begins until food is detected in the stomach

1- moves undigested material into large intestine
2- limit bacteria colonisation of the small intestine

Question 20

what hormone regulates the MMC peristalsis ?

Answer 20

motilin

Question 21

what neurons mediate peristalsis ?

Answer 21

myenteric plexus neurons

Question 22

describe the gastro ileal reflex ?

Answer 22

gastric emptying causes increased segmentation activity in the ileum

opening of ileocecal valve

entry of chyme into large intestine

distension of colon

reflex contraction of ileocecal sphincter (prevents backflux into small intestine)

Question 23

what is the law of intestine ?

Answer 23

that a bolus moves from oral side to anal side towards area of relaxation