[Physiology] Small Intestine

Question 1

what is the total legnth of the small intestine

Answer 1

~6 metres (range 4.5 - 9 metres)

Question 2

duodenum legnth

Answer 2

25 cm long

Question 3

duodenum function

Answer 3

Gastric acid neutralisation; Digestion; Iron absorption

Question 4

jejunum legnth

Answer 4

2.5 m long (2/5 total length)

Question 5

jejunum function

Answer 5

Nutrient absorption - 95%

Question 6

ileum function

Answer 6

NaCl/H2O absorption ⇒ chyme dehydration

Question 7

ileum legnth

Answer 7

3.5 m long (3/5 total length)

Question 8

what are absorptive surfaces enhanced by

Answer 8

folds, villi, microvilli

Question 9

what 8 things does the villus cell absorb

Answer 9

NaCl
Monosaccharides
Amino acids
Peptides
Fats
Vitamins
Minerals
Water

Question 10

what is the function of a crypt cell

Answer 10

Secretes Cl & Water

Question 11

how much fluid does the small intestine secrete per day

Answer 11

~1500ml H2O per day

Question 12

where does the secretion of H2O come from

Answer 12

epithelial cells lining crypts of Lieberkuhn

Question 13

how is H2O secreted, by what means of diffusion

Answer 13

passively (osmotically) as a consequence of active secretion of chloride into intestinal lumen

Question 14

why is H2O secretion important

Answer 14

Maintains lumenal contents in liquid state

Promotes mixing of nutrients with digestive enzymes

Aids nutrient presentation to absorbing surface

Dilutes and washes away potentially injurious substances

Question 15

what normally happens after H2O is secreted from crypt cells

Answer 15

they are reabsorped by villi

Question 16

what are the two types of intestinal movement

Answer 16

Segmentation
Peristalsis

Question 17

when is segmentation most common

Answer 17

during a meal

Question 18

what occurs when contraction happens by segmentation

Answer 18

Contraction (few seconds) moves chyme (up & down) into adjacent areas of relaxation

Relaxed areas then contract and push chyme back

Question 19

what does segmentation do successfully

Answer 19

Provides thorough mixing of contents with digestive enzymes

Brings chyme into contact with absorbing surface

Question 20

how are segmentation contractions initiated

Answer 20

depolarisation generated by pacemaker cells in longitudinal muscle layer (cf gastric motility)

Question 21

what produces oscillation in membrane potential

Answer 21

Intestinal basic electrical rhythm (BER)

Question 22

when oscillations reach a certain threshold what occurs

Answer 22

action potential, producing a contraction

Question 23

what does action potential frequency determine

Answer 23

stregnth of contraction

Question 24

what happens to BER as you move further down the intestine

Answer 24

decreases as move down intestine → rectum

Question 25

parasympathetic nervous system causes

Answer 25

increase in contraction

Question 26

sympathetic nervous system

Answer 26

decrease in contraction

Question 27

what effect does autonomic nervous system have on BER

Answer 27

no effect

Question 28

what occurs follwing apsorbtion of nutrients

Answer 28

segmentation stops and peristalsis starts

Question 29

migrating motility complex

Answer 29

Pattern of peristaltic activity travelling down small intestine (starts in gastric antrum)

Question 30

what happens as one MMC ends

Answer 30

another begins

Question 31

what does arrival of food in stomach do to MMC

Answer 31

stops MMC and initiaes segmentation

Question 32

what does MMC aim to do

Answer 32

Move undigested material into large intestine Limit bacterial colonisation of small intestine

Question 33

what is motilin

Answer 33

(hormone) involved in initiation of MMC

Question 34

If intestinal smooth muscle is distended (eg by bolus of chyme): [law of the intestine]

Answer 34

Muscle on oral side of bolus contracts Muscle on anal side of bolus relaxes Bolus is moved into area of relaxation towards colon

Question 35

what is the law of the intestine mediated by

Answer 35

neurones in myenteric plexus

Question 36

Gastric emptying ⇒ ↑ segmentation activity in ileum

Answer 36

Opening of ileocaecal valve (sphincter) Entry of chyme into large intestine Distension of colon Reflex contraction of ileocaecal sphincter (prevents backflux into small intestine)