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HOM > Down the duodenum > Flashcards

Down the duodenum Flashcards

1
Q

what glands produce a mixed mucous/serous secretion

A

submandiubular and sublingual

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2
Q

what gland produces a serous secretion only

A

parotid glands

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3
Q

what are the 4 major functions of saliva

A

lubrication, defence, buffering, digestion

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4
Q

describe the lubrication function

A

glycoproteins called mucins produced. solution of food products facilitates taste, speech, swallowing

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5
Q

what are the defence molecules found in saliva

A

lysozyme, lactoferrin and antibodies, proline rich proteins bind to and neutralise tannins

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6
Q

what is the buffering effect

A

bicarbonate ions raise the ph of saliva from acidic during basal secretion to ph8 during active secretion

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7
Q

what enzyme is responsible for the digestive function of saliva

A

salivary amylase breaks down starch to oligosaccharides but is inhibited by low ph in the stomach. it is protected by bolus of food

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8
Q

what cells produce primary secretion of saliva

A

acinar cells

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9
Q

what is the primary secretion composition

A

isotonic to plasma and high in nacl

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10
Q

what does the high conc of nacl in primary secretion do

A

draws water into the acinar lumen

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11
Q

what is the other function of acinar cells

A

secrete salivary enxymes and other proteins by exocytosis

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12
Q

what do myoepithelial cells do

A

contract to empty saliva into the ducts

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13
Q

what happens to the saliva as it proceeds through the ducts

A

becomes more hypotonic

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14
Q

what promotes ion exchange in the salivary ducts

A

aldosterone

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15
Q

salivation is controlled by the

A

ANS

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16
Q

what type of response is there to the prospect of food in the cephalic phase of digestion

A

anticipatory response

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17
Q

what do PS fibres do

A

secrete ach and VIP to promote vasodilation therefore increase blood supply, metabolism and growth

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18
Q

what does PS stimulation also do

A

cause contraction of myoepithelial cells and via ach open more of the acinar cell channels increasing vol of saliva secreted

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19
Q

what do sympathetic fibres do

A

promote vasoconstriction, myoepithelial cell contraction and via cAMP exocytosis

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20
Q

describe the swallowing process

A

bolus pushed back to mouth > touch receptors in the pharynx > initiate the swallowing reflex

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21
Q

where is the swallowing reflex coordinated

A

swallowing centre in the medulla and lower pons

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22
Q

what is the swallowing reflux called

A

deglutition

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23
Q

what is deglutition apnoea

A

the respiratory centre of the medulla is directly inhibited by the swallowing centre for a brief term.

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24
Q

how is inhalation of the food prevented

A

fine control of multiple striated muscles in the pharyngeal region

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25
Q

what is the upper oesophageal sphincter

A

consists of the striated cricopharyngeus muscle.

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26
Q

describe the layers of muscle in the human oesophagus

A

upper third: longituindal and circular layers of muscle are striated, middle third contains smooth and striated, lower third contains ENITRELY SMOOTH

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27
Q

where does the primary peristaltic wave begin

A

begins just below the UOS and sweeps the bolus downwards. if bolus fails to be moved all the way down the stomach&raquo_space; secondary peristaltic wave is initiated

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28
Q

how is a secondary peristaltic wave initiated

A

persistent distension of the oesophagus

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29
Q

how is the secondary peristaltic wave also initiated

A

local reflex and part of vagovagal reflex

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30
Q

what is the lower oesophageal sphincter

A

region of specialized circular smooth muscle at the bottom of the oeseophagus

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31
Q

what controls the LOS

A

ENS fibres which receive input from the ANS

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32
Q

describe the action of the LOS

A

normally tonically contracted but relaxes due to NO before food has arrived

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33
Q

why does the LOS relax before food has arrived

A

feed forward vagal reflex

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34
Q

what is the gastro-oesophageal reflux

A

acidic contents of the stomach enter the oesophagus leading to heart burn

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35
Q

what is barretts oesphagus

A

when epithelium of oesophagus changes to that of the stomach

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36
Q

what happens in the achalasia

A

reflex relaxation of the spinchter is compromised therefore there is difficulty swallowing

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37
Q

how much mucus is secreted by the oesophagus and why

A

small amount to lubricate food during swallowing

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38
Q

what is emesis

A

vomiting coordinated in the vomiting centre of the medulla oblongata

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39
Q

what is the chemoreceptor trigger zone

A

receptors on the floor of the fourth ventricle of the brain, stim of this zone leads to vomiting

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40
Q

why can emetics stimulate vomiting

A

can interact with the chemoreceptor trigger zone as it lies outside the blood brain barrier

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41
Q

what is the 1st stage of vomitting

A

increased salivation,

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42
Q

what is the 2nd stage of vomitting

A

retroperistalsis (sweep contents up the digestive tract into small through pyloric sphincter)

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43
Q

3rd stage of vomitting

A

lowering of intrathroacic pressure coupled with an increase in abdominal pressure as the abdominal muscles contract. propels stomach contents into the oesophagus without retroperistalsis

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44
Q

4th stage of vomitting

A

upper oesophageal sphincter remains contracted, the person retches: the contents drain back into the stomach, eventually the spinchter may relax and allow vomiting

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45
Q

what can happen with bile?

A

bile can enter the vomit due to duodenal contraction in severe cases

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46
Q

what are the 4 main functions of the stomach

A

act as reservoir, facilitate digestion, destroy ingested microbes, regulate appetite through feedback effects on the brain aswell as feedforward mechanisms

47
Q

what is the vagovagal reflex responsive to

A

oesophageal or stomach stretch which causes the fundus and body of the stomach to relax

48
Q

what is a receptive relaxation

A

fundus and body of the stomach relax so food can be accommodated with little increase in pressure

49
Q

what is the antrum

A

thicker muscular walls of the stomach and performs forceful contractions, leads into the pylorus

50
Q

what is the pyloric sphincter

A

circular muscle, narrowly opening therefore limiting the rate of stomach emptying.

51
Q

why do slow waves generated by ICCs in the stomach body stop at the pylorus

A

pyloric sphincter region lacks ICCs

52
Q

What increases the duration and amplitude of the plateau and the increase of aps and contractions occuring?

A

ach and gastrin

53
Q

what happens when the wave of contraction reaches the pylorus

A

the pyloric sphincter contracts to prevent passage of ingesta

54
Q

what happens after the pyloric sphincter contracts

A

stomach contents are forced backwards towards the middle of the stomach in retropulsion

55
Q

what is chyme

A

food mixed with gastric secretions

56
Q

what happens to the pylorus between contractions

A

it relaxes then under the influence of tonic gastric pressure allowing contents to pass into the duodenum. large or tougher food particles tend to remain in the stomach for longer

57
Q

what is the migrating myoelectric complex

A

the wave of contractile activity that sweep remaining food towards relaxed pylorus, into the duodenum and this continues down into the terminal ileum

58
Q

what initiates the myoelectric complex

A

the hormone motilin

59
Q

name the gastric glands

A

cardiac, oxyntic, pyloric

60
Q

cardiac secretes

A

mucus

61
Q

pyloric secretes

A

mucus and gastrin

62
Q

oxyntic glands secrete

A

hcl, pepsiongens, chymosin, other enzymes, intrinsic factors, mucus

63
Q

where are the cardiac glands

A

near entrance of oesophagus

64
Q

where are oxyntic glands and what cell types are contained here 3

A

in the funus and body containing parietal, chief and mucus secreting cells

65
Q

where are the pyloric glands and what cell types 2

A

antrum, contains mucus secreting and G cells which secrete gastrin

66
Q

what do chief cells secrete

A

pepsinogens

67
Q

how are chief cells stimulated

A

by vagal ACh and a cholinergic reflex in response to acidity

68
Q

what does acidity do

A

cleavage of pepsinogens to form pepsins, cleavage of prochymosin to form chymosin/rennin

69
Q

what does vitamin b12 first bind to

A

haptocorrin secreted in saliva protecting it from stomach acidity

70
Q

what does vitb12 bind to in the small intestine

A

an intrinsic factor secreted by the stomach parietal cells to resist digestion by proteases.

71
Q

role of gastric acid 6

A

delay gastric emptying, improve absorption of calcium + iron and release vit b12, activate pepsinogens, destroy ingested microbes

72
Q

describe the composition of gastric juice

A

between meals = more nacl, low hcl. at stimulation = parietal cells active, isotonic solution of hcl.

73
Q

what does acid secretion involve

A

proton pumps on luminal membranes of pariteal cells, stimulated by intracellular reaction of co2 with water, hco3- and cl0 exchanger

74
Q

what is alkaline tide

A

gastric venous blood becomes more alkaline due hco3- added to plasma

75
Q

name the 3 forms of control on acid secretion

A

endocrine, paracrine and neurocrine transmitter release

76
Q

what is role of gastrin

A

role is to promote histamine production and release from ecl cells

77
Q

what promotes release of gastrin

A

local stretch reflexes, bagal stimulation via GRP, peptides, AA and Ca2+ in the stomach lumen

78
Q

what is the role of histamine

A

agonist of hcl secretion, released from enterochromaffin like cells, a paracrine transmitter

79
Q

role of ach

A

promotes release of acid, histamine and gastrin and inhibits somatostatin release

80
Q

what do ach and gastrin both do

A

increase free caclium within the parietal cell.

81
Q

maximum secretion of hcl requires ….

A

activation of both ca2+ and camp pathways resulting in potentiation

82
Q

how does histamine act

A

acts on h2 receptors to increase camp as a secondary messenger

83
Q

what is the inhibition of acid secretion mediated by….. 3, give details

A
  1. somatostatin - paracrine released from D cells. prevents excessive acid secretion
  2. secretin - released from S cells, inhibits acid secretion by stim vagal afferent fibres, reduce gastrin release
  3. prostaglandins - paracrines promote bicarb and mucus prod
84
Q

what is the first phase of acid secretion

A

cephalic phase - mediated by feedforward ach, acid secretion increases but negative feedback through somatostatin release limitis ph change

85
Q

what is the second phase of acid secretion

A

gastric phase - due to presence of food, protons buffered by proteins in food, ph rises, secretory mechanisms from inhibition reduces changes in ph, stretch of stomach wall = vagovagal and local reflexes which increase gastrin/acid release, peptides and aa stim g cells to increase gastrin secretion

86
Q

what is the third phase of acid secretion

A

intestinal phase - chyme enters duodenum. duodenal stretch triggers vagovagal reflexes increasing acid secretion and gastrin release. decrease in ph = decrease in acid secretion

87
Q

what is the protection from acid and ulcer formation

A

stomach mucosa is protected by mucus and bicarb by epithelial lining of stomach and gastric glands (gastric mucosal barrier)

88
Q

what is the gastric mucosal barrier

A

mucus and bicarb secreted by mucous cells forming epithelial lining of stomach and gastric glands = alkaline lining

89
Q

describe how epithelial mucous cells are lost

A

they are lost from the stomach surface and replaced by mucous cells from the necks of the gastric glands which migrate upwards and over the surface

90
Q

how are neck mucous cells replaced

A

replaced as stem cells deeper within the glands which divide and differentiate

91
Q

if the gastric mucosal barrier is compromised what happens

A

gastric ulcer, treated with drugs to suppress acid secretion including h2-receptor antagonists and h+/k+ atpase proton pump inhibitors

92
Q

what are predispositions to gastric ulcers

A

NSAID drugs e.g. asprin and gram negative helicobacter pylori (bacterium)

93
Q

what is the control of gastric emptying

A

level of tone of the pyloric sphincter is carefully controlled by the body. ENS, ANS and hormones. Relaxation promoted by inhibitory fibres which release NO

94
Q

what are neural and hormonal reflexes often involved in

A

slowing the emptying of stomach contents generally by inhibiting gastric motility/tightening the pyloric sphincter

95
Q

what are enterogastric reflexes

A

slow gastric emptying when the distal gut is stretched

96
Q

what are enterogastric reflexes in response to

A

excess acid, fat digestion products, peptides and amino acids

97
Q

what substances are absorbed across the stomach wall

A

alcohol, ketamine and aspirin

98
Q

what part of the pancreas is bicarbonate rich

A

exocrine section

99
Q

pancreatic acinar cells secrete what

A

enzymes by exocytosis, the proteases as inactive zymogens

100
Q

pancreatic secretory trypsin inhibitor is packaged in……. which helps to……

A

same zymogen granules as trypsinogen, helps protect acinar cells from activation of trypsin inappropriately

101
Q

what do acinar cells secrete a small amount of

A

nacl rich solution into the lumen

102
Q

what do pancreatic duct cells secrete a lot of

A

aqueous component of the pancreatic juice, bicarb solution

103
Q

what nerves stimulate pancreatic secretion

A

parasympathetic

104
Q

what does sympathetic stimulation do

A

vasoconstriction, decreasing secretion

105
Q

enteric neurons pass where

A

from stomach and duodenum to pancreas

106
Q

what is the main stimulus for CCK release

A

fat digestion products in duodenum

107
Q

what does cck stimulate in the pancreas

A

enzyme secretion from acinar cells and potentiates the effect of secretin on duct cells

108
Q

what do ach and cck increase in pancreatic cells

A

intracellular calcium

109
Q

what do secretin and vip increase

A

intracellular [camp]

110
Q

what does camp do in the acinar and duct cells

A

open the luminal chloride channels, increasing secretion

111
Q

what is the luminal chloride channel in duct cells

A

cystic fibrosis transmembrane conductance regulator

112
Q

what is the most common form of cystic fibrosis

A

impaired electrolyte and water secretion into the duct system > clogged ducts > maldigestion and nutrient deficiency

113
Q

what is cholera toxin

A

results in high levels of camp > excessive secretion by the CFTR of cl-, na+ and water > diarrhoea

HOM (8 decks)

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