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Alimentary System > [Physiology] Small Intestine > Flashcards

[Physiology] Small Intestine Flashcards

1
Q

what is the total legnth of the small intestine

A

~6 metres (range 4.5 - 9 metres)

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2
Q

duodenum legnth

A

25 cm long

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3
Q

duodenum function

A

Gastric acid neutralisation; Digestion; Iron absorption

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4
Q

jejunum legnth

A

2.5 m long (2/5 total length)

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5
Q

jejunum function

A

Nutrient absorption - 95%

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6
Q

ileum function

A

NaCl/H2O absorption ⇒ chyme dehydration

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7
Q

ileum legnth

A

3.5 m long (3/5 total length)

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8
Q

what are absorptive surfaces enhanced by

A

folds, villi, microvilli

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9
Q

what 8 things does the villus cell absorb

A

NaCl
Monosaccharides
Amino acids
Peptides
Fats
Vitamins
Minerals
Water

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10
Q

what is the function of a crypt cell

A

Secretes Cl & Water

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11
Q

how much fluid does the small intestine secrete per day

A

~1500ml H2O per day

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12
Q

where does the secretion of H2O come from

A

epithelial cells lining crypts of Lieberkuhn

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13
Q

how is H2O secreted, by what means of diffusion

A

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

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14
Q

why is H2O secretion important

A

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

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15
Q

what normally happens after H2O is secreted from crypt cells

A

they are reabsorped by villi

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16
Q

what are the two types of intestinal movement

A

Segmentation
Peristalsis

17
Q

when is segmentation most common

A

during a meal

18
Q

what occurs when contraction happens by segmentation

A

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

Relaxed areas then contract and push chyme back

19
Q

what does segmentation do successfully

A

Provides thorough mixing of contents with digestive enzymes

Brings chyme into contact with absorbing surface

20
Q

how are segmentation contractions initiated

A

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

21
Q

what produces oscillation in membrane potential

A

Intestinal basic electrical rhythm (BER)

22
Q

when oscillations reach a certain threshold what occurs

A

action potential, producing a contraction

23
Q

what does action potential frequency determine

A

stregnth of contraction

24
Q

what happens to BER as you move further down the intestine

A

decreases as move down intestine → rectum

25
Q

parasympathetic nervous system causes

A

increase in contraction

26
Q

sympathetic nervous system

A

decrease in contraction

27
Q

what effect does autonomic nervous system have on BER

A

no effect

28
Q

what occurs follwing apsorbtion of nutrients

A

segmentation stops and peristalsis starts

29
Q

migrating motility complex

A

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

30
Q

what happens as one MMC ends

A

another begins

31
Q

what does arrival of food in stomach do to MMC

A

stops MMC and initiaes segmentation

32
Q

what does MMC aim to do

A

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

33
Q

what is motilin

A

(hormone) involved in initiation of MMC

34
Q

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

A

Muscle on oral side of bolus contracts

Muscle on anal side of bolus relaxes

Bolus is moved into area of relaxation towards colon

35
Q

what is the law of the intestine mediated by

A

neurones in myenteric plexus

36
Q

Gastric emptying ⇒ ↑ segmentation activity in ileum

A

Opening of ileocaecal valve (sphincter)

Entry of chyme into large intestine

Distension of colon

Reflex contraction of ileocaecal sphincter (prevents backflux into small intestine)

Alimentary System (44 decks)

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