small intestine structure and function

Question 1

what is the function of the duodenum?

Answer 1

gastric acid neutralisation
digestion
iron absorption

Question 2

what is the function of the jejunum?

Answer 2

nutrient absorption

Question 3

what is the function of the ileum?

Answer 3

NaCl and water absorption for chyme dehydration

Question 4

how many fluid do we lose in our GI tract?

Answer 4

200ml

Question 5

how does the ileum restore some of the water lost from the GI tract?

Answer 5

it absorbs Na/Cl which causes water to follow

Question 6

how is the absorptive surface area of the small intestine enhanced?

Answer 6

the intestine has lots of folds, villi and microvilli which increase the surface area for absorption

Question 7

what are the secretory cells and where are they found?

Answer 7

goblet cells found in the intestinal crypt

Question 8

how is water secreted from the crypts?

Answer 8

crypt cells actively secrete Cl into the intestinal lumen which builds an osmotic gradient for water to follow

Question 9

what is the main function of the villi?

Answer 9

absorption

Question 10

why is water secreted in the small intestine?

Answer 10

maintains luminal contents in a liquid state
promotes mixing of nutrients with digestive enzymes
helps in absorption of nutrients
dilutes and washes away any potentially harmful substances

Question 11

crypt cells secrete Cl to drive water out of the cell into the lumen, but how does villi absorb water?

Answer 11

villi absorb NaCl which builds the osmotic gradient for H20 to follow and enter the cell

Question 12

how do patients with cystic fibrosis suffer from malabsorption?

Answer 12

there is a gene defect in CFTR chanel protein which allows Cl to exit the cell.
the defect prevents Cl from leaving the cell thus an osmotic gradient isn’t build up so water cannot be secreted.
water secretion is required to aid in absorption of nutrients

Question 13

what are the 2 types of intestinal motility?

Answer 13

peristalsis

segmentation

Question 14

what is responsible for the production of segmentation?

Answer 14

depolarisation from pacemaker cells in the longitudinal muscle layer produces the BER
however these signals don’t reach the membrane potential
if Ach is released from the parasympathetic system it reaches threshold firing an action potential = contraction

Question 15

what is the nerve supply for segmentation and what are their effects?

Answer 15

sympathetic - splanchnic nerves - decrease strength of contraction
parasympathetic - vagus - increases strength of contraction

Question 16

what effect does the autonomic nervous system have on the basic electrical rhythm?

Answer 16

no effect
they may increase or decrease the strength of contraction but it doesn’t affect the BER which determines the speed of contractions

Question 17

migrating motility complex is used to describe what process?

Answer 17

peristalsis

Question 18

what does the migrating motility complex aim to do?

Answer 18

moves undigested material into the large intestine

limits bacterial colonisation of small intestine

Question 19

what hormone is involved in the initiation of the MMC?

Answer 19

motilin hormone

Question 20

what nerve supply is responsible for the movement of material through the intestine?

Answer 20

the myenteric plexus (aucherbach plexus)

Question 21

what prevents the back flow of material from the caecum into the ileum?

Answer 21

reflex contraction of the ileocaecal sphincter

Question 22

what is the length of the duodenum?

Answer 22

25cm

Question 23

what is the length of the jejunum?

Answer 23

2.5m

Question 24

what is the length of the ileum?

Answer 24

3.5m

Question 25

what part of the small intestine absorbed nutrients?

Answer 25

jejunum

Question 26

what part of the small intestine does the final chymal dehydration occur and how does this happen?

Answer 26

ileum

absorption of Na, Cl and H20

Question 27

whats the function of the crypt cells?

Answer 27

secretion of 1500ml of H20 per day

driven by the active secretion of Cl into the lumen

Question 28

what is the gastroileal reflex?

Answer 28

as faecal material moves from the small intestine into large intestine, the ileocaecal valve relaxes and the caecum dilates.
when material is in the large intestine the ileocaecal valve contracts to prevent backflow of material.