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Human Physiology - Hormones and Health > Upper Digestive Tract Secretion > Flashcards

Upper Digestive Tract Secretion Flashcards

1
Q

How much saliva is produced each day?

A

1-1.5L

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2
Q

What does decreased function of the salivary glands lead to?

A
  • dry mouth
  • dental caries
  • infections of buccal mucosa
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3
Q

What are amylases?

A

enzymes in the saliva that are active between pH 4-11

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4
Q

How does the parasympathetic NS mediate salivary secretion?

A

by the release of ACh which binds to muscarinic receptors which cause watery saliva to be secreted

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5
Q

How does the sympathetic NS mediate salivary secretion?

A

by the release of noradrenaline that binds to alpha and beta adrenergic receptors which cause thicker saliva to be secreted

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6
Q

What are the 7 organic constituents of saliva?

A
  • mucin
  • alpha-amylase
  • RNAse and DNAase
  • lingual lipase
  • lactoferrin
  • secretory IgA
  • lysozyme
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7
Q

What is HCl produced by?

A

parietal cells

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8
Q

What does HCl do?

A
  • kill most ingested
    bacteria
  • cleave pepsinogens to pepsins
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9
Q

What are pepsinogens produced by?

A

chief cells in the stomach

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10
Q

What are intrinsic factors?

A

proteins that help the intestines absorb vitamin B12, which is the only gastric secretion required for life

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11
Q

What is gastrin released by?

A

G cells in the stomach and duodenum

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12
Q

What happens to gastrin?

A

it is secreted straight into the blood and does not enter the lumen

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13
Q

What does mucus do?

A

protect gastric mucosa from mechanical and chemical destruction

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14
Q

What is mucus?

A

a thin layer of fluid that covers the luminal surface of the airway

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15
Q

What is the composition of gastric juice?

A

99.5% water and 0.5% solids

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16
Q

What are the inorganic substances of gastric juice?

A
  • HCl
  • electrolytes
  • bicarbonate
  • sulphate
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17
Q

Where is rennin found and what does it do?

A

in infants to help with milk protein digestion

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18
Q

How does the rate of gastric secretion affect the ionic composition of gastric juice?

A
  • higher rate = higher [H+]
  • lower rate = lower [H+]
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19
Q

What can prolonged vomiting lead to?

A

hypokalaemia since [K+] is higher in gastric juice than plasma

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20
Q

What is the basal and max rate of gastric acid secretion?

A
  • basal = 1-5 mM/h
  • max = 6-40 mM/h
21
Q

What condition will lead to a higher gastric rate than normal?

A

duodenal ulcer

22
Q

What conditions will lead to a lower gastric rate than normal?

A

gastric ulcer and pernicious anaemia

23
Q

What are the 3 stimulants of gastric acid secretion?

A

ACh, gastrin and histamine

24
Q

What are the functions of gastrin?

A
  • stimulate HCl secretion
  • increase gastric and intestinal motility
  • increase pancreatic secretion
  • help with proper growth of GI mucosa
25
Q

What is the pH at which pepsins have the highest activity?

A

anything less than 3

26
Q

What do pepsins do?

A

digest 10-20% of total dietary protein

27
Q

When are pepsins irreversibly inactivated?

A

at duodenum pH

28
Q

What is intrinsic factor secreted by?

A

parietal cells in the fundus

29
Q

Where is the IF-B12 complex completely absorbed?

A

at the terminal ileum

30
Q

How is intrinsic factor stimulated?

A

by the same stimuli that evoke HCl secretion (ACh)

31
Q

What are mucins?

A

the main component of gastric mucus; large molecules with CHO side chains that are insoluble in acid pH and can be destroyed by pepsin

32
Q

What is the function of mucins?

A

to coat and lubricate the mucosal surface

33
Q

How are mucins regulated?

A

by the same mechanism that enhances HCl secretion (ACh) and mechanically stimulated by food

34
Q

What are the paracrine effects of prostaglandins?

A
  • directly inhibit parietal cell secretion
  • mediate mucosal defence
35
Q

What are the 3 components of mucosal defence?

A
  • stimulation of mucus, phospholipid and HCO3- secretion
  • enhancement of mucosal blood flow
  • stimulation of mucosal cell turnover
36
Q

What does prostaglandin deficiency predispose to?

A

gastric mucosal injury

37
Q

What does the gastric mucosal barrier do?

A

protect against abrasion, HCl and pepsin

38
Q

What is the gastric mucosal barrier?

A

a thick mucus layer (1mm) made up of mucins and HCO3-

39
Q

What does the unstirred layer of the gastric mucosal barrier do?

A

slow the inward diffusion of H+ and outward diffusion of HCO3-

40
Q

What is the pH of the gastric mucosal barrier at the cell surface and gastric juice in the lumen respectively?

A
  • cell surface = 7
  • lumen = 2
41
Q

What does the gastric mucosal barrier depend on?

A
  • Ca2+ and cholinergic agonists to stimulate HCO3- secretion
  • adrenergic agonists to decrease HCO3- secretion
  • aspirin and NSAIDs to inhibit mucous and HCO3- secretion
42
Q

What does the rate of repair of the gastric mucosal barrier depend on?

A

the extent of the injury; can be between 48 hours to 3-5 months

43
Q

Give examples of ulcer therapy

A
  • neutralising HCl (antacids)
  • prevent acid release (omeprazole or cimetidine)
  • helicobacter pylori bacillus (antibiotic)
  • prostaglandin agonist (misoprostol)
44
Q

What does carbohydrate gastric digestion depend on?

A

the action of salivary alpha-amylase (halts at low pH)

45
Q

Why is fat gastric digestion minimal?

A

high acidity inhibits fats from forming emulsions

46
Q

What are the only substances absorbed during gastric absorption?

A

highly lipid-soluble substances e.g. ethanol

47
Q

What is gastritis?

A

a painful or burning sensation in the chest due to an increase in gastric acid secretion or a backflush of acidic chyme into the oesophagus

48
Q

What factors cause gastritis?

A
  • overeating
  • smoking
  • fatty foods, coffee, alcohol
  • lying down immediately after meal
  • tight clothing

Human Physiology - Hormones and Health (14 decks)

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