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PHSL233 > Lecture 28 - Gastric Acid Secretion > Flashcards

Lecture 28 - Gastric Acid Secretion Flashcards

1
Q

What are the components of gastric secretions?

A

Acid
Pepsin
Intrinsic factor
Mucus

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2
Q

What is the function of acid in gastric secretions?

A

Protective role
Denature proteins
Optimum pH for many digestive enzymes
Render fluid isosmotic
- (150 mM HCl - (HCO3-) - neutralised part)

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3
Q

What is the function of pepsin?

A

Protein digestion

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4
Q

What is the role of intrinsic factor in gastric secretions?

A

Vitamin B12 absorption (DNA, red blood cells, pernicious anaemia)

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5
Q

What is the role of mucus in gastric secretions?

A

Protects against acid and mechanical forces

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6
Q

What luminal secretion occurs at the LES and cardia?

A

Mucus
HCO3-

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7
Q

What luminal secretion occurs at the fundus and body?

A

H+
Intrinsic factor
Mucus
HCO3-
Pepsinogens
Lipase

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8
Q

What luminal secretion occurs at the antrum and pylorus?

A

Mucus
HCO3-

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9
Q

What is the apical HCO3-/Cl- exchanger in salivary duct cells driven by?

A

Cl- via CFTR

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10
Q

Where does the HCO3- come from in salivary duct cells?

A

Either carboanhydrase reaction or from basolateral side

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11
Q

What cells make up the gastric glands in body of stomach?

A

Surface cells
Mucus secreting cells
Oxyntic (parietal) cells
Chief cells
Enterochromaffin like (ECL) cells

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12
Q

What do the surface cells in gastric glands secrete?

A

HCO3-

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13
Q

What do the parietal cells in gastric glands secrete?

A

Acid
Intrinsic factor

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14
Q

What do the chief cells in gastric glands secrete?

A

Pepsinogen

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15
Q

What do ECL cells in gastric glands secrete?

A

Histamine

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16
Q

How much is secreted by the gastric glands per day?

A

2-3 L per day

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17
Q

When do gastric secretion composition change?

A

Eating or fasting phase

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18
Q

What do ECL cells sit in close proximity to?

A

Oxyntic (parietal) cells

19
Q

What is the rate of gastric secretion between meals?

A

15-30ml/h

20
Q

What is gastric secretion between meals secreted by?

A

Surface cells

21
Q

What is the gastric secretion composition between meals?

A

Isosmotic solution with similar [Na+] as plasma but higher [HCO3-]
Also mucus

22
Q

What is the rate of gastric secretion while eating?

A

150ml/hr (5-10x higher)

23
Q

What is the composition of gastric secretion while eating?

A

Isosmotic (150 mM) solution of HCl produced by parietal cells
Pepsinogen
Intrinsic factor
More mucus

24
Q

What is the final gastric secretion osmolality and why?

A

Remember surface cells secrete HCO3-
H+ + HCO3 <=> H2CO3 <=> H2O + CO2
Therefore final gastric secretion has an osmolality of ≈ 200 mOsmol/L

25
Q

What does final composition of gastric secretion depend on?

A

Rate of secretion

26
Q

Gastric secretions
A. consist of bile acids.
B. between meals have a rate of 3 mL/min.
C. of surface epithelium are mucus and bicarbonate.
D. of chief cells contain intrinsic factor.

A

C. of surface epithelium are mucus and bicarbonate.

A - Does not
B - 15-30ml/hr
D - Chief cells have pepsinogen, Parietal cells have intrinsic factor

27
Q

What is associated with the stimulation of acid secretion in gastric glands?

A

A number of structural changes in parietal cell

28
Q

What is the structure of non secreting parietal cell?

A

Small intracellular canaliculi
Short stubby microvilli at apical pole
Extensive tubulovesicular system

29
Q

What does the tubulovesicular system hold in non-secreting parietal cells?

A

Holds the components for acid secretion, but they are quiescent

30
Q

What is the structure of secreting parietal cell?

A

Extensive canaliculi
Large apical microvilli
Mitochondria located around basolateral membrane

31
Q

What are the changes in parietal cells from nonsecreting to secreting?

A

Disappearance of
tubulovesicular system
Development of extensive intracellular canaliculi
Appearance of large apical microvilli
Increase surface area of apical membrane 50-100-fold

32
Q

What is the function of structural changes in parietal cells?

A

To insert H/K-ATPase into apical membrane
- 80% of the protein in the tubulovesicular membrane is the H+,K+ -ATPase
H+,K+ -ATPase is responsible for acid secretion
- primary active transporter (potassium driven opposed to sodium driven)

33
Q

What are the events at the apical membrane of secreting parietal cell?

A

K+ and Cl- diffuse down their electrochemical gradients into the lumen via channels
K+ is recycled back across the apical membrane via H+,K+ -ATPase
Secretion of HCl
Water follows passively

34
Q

The secretion of hydrochloric acid (HCl)
A. is dependent on an apical (luminal) K+ gradient.
B. requires an apical bicarbonate gradient.
C. requires an apical Na+ gradient.
D. requires the change of the parietal cells from large intracellular canaliculi to an extensive tubulovesicular system

A

A. is dependent on an apical (luminal) K+ gradient.

B & C - K+ gradient
D - Opposite

35
Q

What is the source of H+ ions that are secreted in parietal cells?

A

Carboanhydrase reaction

36
Q

What is the function of Na/K+ ATPase in unstimulated parietal cells?

A

Maintains K+ in cell above equilibrium

37
Q

What is the function of basolateral K+ channels in unstimulated parietal cells?

A

Recycles K+ and generates membrane potential

38
Q

What is the role of basolateral NHE and Cl/HCO3 exchanger in unstimulated parietal cells?

A

pH homeostasis and maintenance of Cl- above equilibrium

39
Q

What is omeprazole?

A

Drug that is used to treat gastric ulcers or reflux.
Targets Hydrogen/Potasium ATPase which is found only in stomach (one type in kidney but not important).
- Drug is very specific

40
Q

What is the function of the basolateral Cl/HCO3 exchanger in stimulated parietal cells?

A

For each mole of H+ ion secreted an equivalent amount of base is produced
This is extruded across the basolateral membrane by the Cl-/HCO3- exchanger (alkaline tide after a meal)
This provides the Cl- ion that is secreted with H+

41
Q

Where is mucus secreted from in gastric glands?

A

Mucus secreted by mucus neck cells in glands and surface cells

42
Q

What do the surface cells in mucus glands secrete?

A

Mucus and HCO3 rich solution

43
Q

Why do we have mucus and HCO3 in gastric secretions?

A

To provide a layer of alkaline mucus that protects stomach from abrasion and acidic pH

PHSL233 (32 decks)

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