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Physiology > lecture 27 - the gut 1: saliva and stomach > Flashcards

lecture 27 - the gut 1: saliva and stomach Flashcards

1
Q

processing of food

A
  • motility
  • secretion
  • digestion
  • absorption
  • excretion
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2
Q

motility

A

mechanical breakdown

controlled movement along gut

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3
Q

secretion

A

addition of enzymes and electrolytes

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4
Q

digestion

A

chemical breakdown

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5
Q

absorption

A

transport proteins

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6
Q

excretion

A

secretion of metabolic waste production and xenobiotics

elimination of faeces

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7
Q

structure of the gut tube

A
  • plica
  • mucosa
  • submucosa
  • circular mucosa
  • longitudinal mucosa
  • submucosal glands
  • villi
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8
Q

regulation of gut function

A
  • neural
  • hormonal
  • local
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9
Q

neural regulation of gut function

A

ANS
• vagus nerves

enteric nervous system - in the gut wall

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10
Q

hormonal regulation of gut function

A

endocrine

dispersed enters-endocrine cells

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11
Q

local regulation of gut function

A

paracrine

eg. histamine

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12
Q

3 key stages of regulation

A

cephalic

gastric

intestinal

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13
Q

functions of saliva

A
  • lubrication - fluid and mucus
  • digestion - amylase & R proteins
  • solution
  • moistness
  • protection - fluid and bicarbonate keeps pH up so amylase will work, lysozyme and immunoglobulins
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14
Q

salivary glands

A

3 pairs of glands account for 90% of saliva

parotid glands
• serous (watery)
• amylase

sublingual & submandibular glands
• mixed secretion

10% from minor glands
• mucous
• mucins

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15
Q

total secretion from salivary glands

A

1.5 litres a day

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16
Q

salivary gland structure

A

acinus leads to duct

secrete K+ and HCO3-

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17
Q

salivary fluid secretion

A

primary fluid from acinar epithelial cells
• isotonic - plasma like

secondary ductal modification
• Na+ & K+ reabsorption
• K+ & HCO3- secretion
• ducts impermeable to water

hypotonic saliva - HCO3- rich

18
Q

control of salivation

A

in cephalic phase
• sight, smell, taste and thought of food

parasympathetic - cholinergic
• cranial nerves VII and IX
• large volume

sympathetic - noradrenergic
• smaller volume
• rich in enzymes and mucus

19
Q

gastric functions

A
  • reservoir
  • mixing food with gastric secretions
  • digestion
  • controlled gastric tempting - food to duodenum
  • protection
20
Q

2 types of digestion

A

mechanical

chemical

21
Q

structure of stomach

A

starts at oesophagus and enters body of stomach

contains rugae - surface folding increases area

leaves via Antrum by pyloric valve

22
Q

what do gastric pits do?

A

increase SA

23
Q

composition of gastric juice

A
  • HCl - parietal cells
  • pepsinogen to pepsin - chief cells
  • mucus and bicarbonate - mucus neck and surface epithelial cells
  • intrinsic factor - parietal cells
24
Q

how much gastric juice a day?

A

2 litres

25
Q

what are parietal cells stimulate by?

A

ACh

gastrin

histamine

26
Q

what happens in parietal cells?

A

H2O & CO2 converted to H+ and HCO3- by carbonic anhydrase

H+ is exchanged for K+ by K+/H+ ATPase into lumen of the stomach

Na+/K+ ATPase on basolateral membrane

potassium leaky channels allow K+ recycling

HCO3- exchanged for Cl-

H+ and Cl- combine to make HCl

27
Q

what do proton pump inhibitors (PPIs) do?

A

they block the K+/H+ ATPase so H+ cannot be pumped into the lumen of the stomach to make it more acidic

28
Q

what happens on the apical membrane of parietal cells?

A

H+/K+ ATPase - primary proton pump

K+ channels - supplies K+ for recycling through proton pump

Cl- channels - supplies anion for HCl

29
Q

what happens on the basolateral membrane of parietal cells?

A

Na+/K+ ATPase

Cl-/HCO3- exchange

30
Q

what do chief cells do?

A

secrete pepsin and gastric lipase

digest proteins and fats

stimulated by:
• ACh
• acid
• secretin

31
Q

what is pepsin inactivated and denatured?

A

inactivated > pH 3.5

denatured > pH 7.2

32
Q

what do mucous neck cells and surface cells do?

A

secrete mucus and HCO3-

mucus provides physical barrier between lumen and epithelium

HCO3- buffers gastric acid to prevent damage of epithelium

33
Q

how does the stomach stop auto digestion?

A

gastric mucosal protection

mucus-HCO3- barrier

34
Q

control of parietal cell function

A 
direct and indirect chemical regulators 
• histamine from ECL cells 
• somatostatin from D cells 
• gastrin from G cells 
• Ach from vagus and enteric neurones
35
Q

what do ECL cells do?

A

in body only

secrete histamine

stimulate gastric acid secretion

36
Q

what do D cells do?

A

in body and antrum

secrete somatostatin

inhibition of gastric acid

37
Q

what do G cells do?

A

in antrum only

secrete gastrin

stimulate gastric acid secretion

38
Q

how does histamine act?

A

binds to H2 receptors on parietal cells in the body

increases cAMP

leads to HCl secretion

39
Q

what is cimetidine?

A

a H2 antagonist

40
Q

what are G cells activated by?

A

ACh
peptides
amino acids

Physiology (29 decks)

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