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PHSL 233 > L28 > Flashcards

L28 Flashcards

1
Q

what are the components of gastric secretions

A

acid

pepsin

intrinsic factor

mucus

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2
Q

what are the functions of the acid in gastric secretion

A

 protective role (kills bacteria)

 denature proteins (chemical digestion)

 optimum pH for many digestive enzymes (pepsin requires a low pH to be activated)

 render fluid isosmotic (150 mM HCl - HCO3-
-neutralised part)

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3
Q

what is the osmolarity of the gastric secretions. why

A

200mOsmol

This is because of the bicarbonate in the stomach (this is here fore protection of the epithelial lining of the stomach)

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4
Q

what is the pH of the stomach

A

1

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5
Q

what is the main digestive enzyme in the stomach

A

pepsin

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6
Q

why do we need intrinsic factor

A

for absorption of vitamin B12

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7
Q

what is B12 important for

A

(DNA, red blood cells, pernicious anaemia)

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8
Q

what os pernicious anaemia

A

B12 effects the production of RBC

therefore if you are severally lacing in intrinsic factor it causes anemia

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9
Q

why is mucus an important gastric secretion

A

protects against acid and mechanical forces

makes the lining elastic

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10
Q

what are the 3 different functions anatomical regions of the stomach and what do they secrete

A

Lower esophageal sphincter and cardia = mucus and HCO3-

fundus and body = H+, intrinsic factor, mucus, HCO3-, pepsinogen, lipase

antrum and pylorus = mucus and HCO3-

NOTE: fundus and body secret lipase but there is no fat digestion until the intestine

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11
Q

where is gastrin secreted from and what is it secreted into

A

gastrin is secreted by the late part of the stomach (antrum and pylorus) into the BLOOD (its a hormone) which then causes acid secretion in the upper parts of the stomach (fundus and body)

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12
Q

what are the structures of the stomach

lumonal to interstitial

A

laminar propria (contains gastric glands)

muscularis mucosa

sub mucosa

muscularis externa

serosa

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13
Q

where are the gastric glands located

A

in the body of the stomach (in the lamina propria)

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14
Q

describe the structure of the gastric glands

A

gastric pit = opening

surface cells

mucus secreting cells

oxyntic/parietal cells

chief cells

enterochromaffin like cells (ECL cells)

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15
Q

what do surface cells secrete. why is that important

A

The surface cells produce bicarbonate which is important for protecting the epithelial lining from the acid

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16
Q

what do mucus cells secrete. why is that important

A

Mucus cells are important for making it elastic and to withstand the mechanical factors. They also protect againsted the acids

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17
Q

what do parietal cells secrete

A

acid and intrinsic factor

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18
Q

what do chief cells secrete

A

enzymes such as pepsinogen

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19
Q

what do ECL cells secrete

A

ECL cells release histomine which is important in the control of gastric acids secretion

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20
Q

Parietal cells and chef and ecl cells are in close proximity

why is this

A

for control of the parietal cells

21
Q

what is the volume and composition of gastric secretions

A

 2 - 3 litres per day

 composition varies depending on eating or fasting

22
Q

between meals what is the rate of gastric secretion

A

15-30 mL/hour

23
Q

isosmotic fluid is secreted by surface cells. what is the composition of this

A

 isosmotic solution with similar [Na+] as plasma but higher [HCO3-]
 also mucus

about 200mOsmol

24
Q

what happens to the volume of gastric secretion when we are eating

A

it is superimposed on basal secretion are much larger volumes of
secretion

 produced at 150 mL/hour (5-10x higher)

25
Q

how are gastric secretions isosmotic

A

 isosmotic (150 mM) solution of HCl produced by parietal cells
 remember surface cells secrete HCO3- (H+ + HCO3 –> H2CO3 –> H2O + CO2)
 therefore final gastric secretion has an osmolality of ≈ 200 mOsmol/L

26
Q

what happens to the composition of gastric secretions while eating

A

more…
isosmotic fluid (HCl)
 pepsinogen - secreted by chief cells
 intrinsic factor - oxyntic (parietal) cells
 more mucus (There is a lot of mechanical force in the stomach therefore we need lots of mucus to keep them alive)

27
Q

as the rate of secretion increases what happen to Cl-

A

it slightly increases (linear)

28
Q

as the rate of secretion increases what happen to H+

A

it parabolically increase (HUGE increase) and then tappers off towards the end

29
Q

as the rate of secretion increases what happen to Na+

A

it decreases parabolically (but not as much as H+ increases)

30
Q

as the rate of secretion increases what happen to K+

A

says the same (slight increase but negalable)

31
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.

E. increase upon stimulation by a factor of 100.

A

A. from liver and don’t get until duodenum

B. 15-30mL/hour

D. chief cells = enzymes, parietal cells = intrinsic factor

E. 5-10x

C is correct

32
Q

what needs to happen to the parietal cells in order for acid to be secreted

A

they undergo a number of structural changes

33
Q

describe a non secreting parietal cell

A

 small intracellular canaliculi
 short stubby microvilli at apical pole
 extensive tubulovesicular system (these hold the components for acid secretion, but they are quiescent)

there are also few mitochondria

34
Q

describe a secreting parietal cell

A

 disappearance of
tubulovesicular system
 development of extensive intracellular canaliculi
 appearance of large apical microvilli
 increase surface area of apical membrane by 50-100-fold

you also get a Huge increase in mitochondria because you need to produce the enzyme we need to feed which requires a H/K ATPase which requires energy (more H/K ATPases get inserted into the membrane)

35
Q

what is the main change in a secreting parietal cell

A

the addition of more H/K ATPases into the apical membrane

36
Q

describe H/K ATPase in the secreting parietal cell

A

 is responsible for acid secretion
 primary active transporter
 utilises ATP to actively transport H+ out of cell in exchange for K+ into the cell. (primary active transport)

 80% of the protein in the tubulovesicular membrane is the H+/K+ ATPase

37
Q

what % of the proteins in the tubulovesicular membrane is the H+/K+ ATPase

A

80%

38
Q

H/K ATPase is sitting in vesicles under the membrane when it is inserted into the membrane the driving force is K and the conc of K is maintained with another K channel in the apical membrane

A

j

39
Q

describe the events of the parietal cell at the apical membrane

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

this causes the secretion of HCl and water follows passively

40
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.

E. requires a secondary active apical transport system.

A

B and C aren’t involved in HCl secretion

D. should say small instead of large

E. primary active transport

A is correct

41
Q

Function of basolateral transporters –

basal (unstimulated) conditions

A

Na+/K+ ATPase maintains K+ in cell above equilibrium

K+ channel recycles K+ and generates membrane potential

Na+/H+ and Cl-/HCO3- exchanger maintain pH homeostasis and maintenance of Cl above
equilibrium

42
Q

describe both membranes in the unstimulated state of the parietal cell

A

the basolateral membrane is always set up and the H/K ATPase is in vesicles under the apical membrane

43
Q

when the parental cell is stimulated the H/K ATPases are inserted into the apical membrane

you also produce more H+ which causes more HCO3- to be formed

A

s

44
Q

what is omeprazole

A

Drug given to people with gastric ulcers/reflux (people that make too much acid) it is very specific in the fact that it only targets the H/K ATPase

45
Q

describe apical transporters in stimulated conditions of the parietal cell

A

on stimulation fusion of tubulovesicular membrane inserts H+/K+ ATPase in apical membrane

activation of apical K+ and Cl- channel therefore K+ and Cl- diffuse into the lumen

presence of K+ in the lumen stimulates the H+/K+ ATPase to exchange H+ for K+

H+ obtained from hydration of CO2 by carbonic anhydrase

water driven out of cells by the efflux of ions

result is a secretion of HCl plus some KCl into the lumen

46
Q

describe basolateral transporters stimulated conditions of the parietal cell

A

 Na+/K+ ATPase maintains K+ above equilibrium
 K+ channel contributes to membrane potential
 Na+/H+ exchanger plays a minimal role
 Cl-/HCO3 exchanger means that 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)
 the exchanger is what provides the Cl- ion that is secreted with H+

47
Q

describe pepsins

A

 proteolytic enzymes (cleaves proteins)
 secreted as inactive precursor pepsinogen by chief cells
 converted to active pepsins by acidic pH and pepsins

48
Q

describe the mucus and HCO3- secretions

A

 mucus secreted by mucus neck cells in glands and surface cells
 HCO3- rich solution secreted by surface cells
 get a layer of alkaline mucus that protects the stomach from
 abrasion
 acid pH

49
Q

the stomach secretes bicarbonate for protection

what is another way the stomach can get this bicarbonate

A

This bicarbonate is also coming from the blood because it is alkaline tide (from basolateral membrane) therefore the bicarbonate released into the blood through the anhydrase reaction is recycled and secreted out into the mucus of the stomach

PHSL 233 (31 decks)

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