PHGY216-FINAL > Module 6: Section 3 > Flashcards

Module 6: Section 3 Flashcards

(51 cards)

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1
Q

3 areas of the stomach

A

1) fundus
2) body
3) antrum

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2
Q

Fundus

A

part of the stomach that lies above the esophageal opening

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3
Q

body of stomach

A

main part of stomach

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4
Q

antrum

A
  • very muscular
  • lower section
  • has the pyloric sphincter
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5
Q

pyloric sphincter

A

barrier between stomach and S intestine

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6
Q

functions of stomach

A

1) store ingested food until it’s ready to be released into S intestine
2) secrete HCl and enzymes needed for protein digestion
3) mechanically mix food w/ gastric secretions to produce chyme (thick fluid)

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7
Q

4 aspects of gastric motility

A

1) gastric filling
2) gastric storage
3) gastric mixing
4) gastric emptying

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8
Q

what is volume of empty stomach

A

50mL

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9
Q

max volume of stomach

A

abt 1000mL- 4000mL

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10
Q

what do pacemaker cells do in the fundus

A

generate slow wave potentials that travel down length of stomach
- 3/min

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11
Q

what is the pyloric sphincter normally?

A
  • almost closed
    – only fluid can flow through
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12
Q

retropulstion

A

when peristaltic wave pushes chyme to pyloric sphincter and it cannot pass through it, the chyme folds back on itself only to be propelled forward and folded back over and over

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13
Q

volume of chyme in antrum

A

30 mL

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14
Q

what’s the main factor influencing strength of contractions in stomach

A

amount of chyme in stomach and its fluidity
- more chyme, more distention and therefore more contractions

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15
Q

how will chyme reach pyloric sphincter faster?

A

the faster it becomes a liquid

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16
Q

what also influences the rate of gastric emptying?

A

duodenum

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17
Q

what happens if duodenum is not ready to receive chyme

A

it will send signals to reduce gastric emptying
- neuronal responses (mediated by intrinsic nerve plexus and autonomic nerves) called the enterogastric reflex
- also hormonal responses
– Hormones can be released from duodenal mucosa

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18
Q

2 most important hormone secretions from duodenal mucosa

A

secretin and cholecystokinin (CCK)

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19
Q

4 duodenum stimuli that affect gastric emptying

A
  • fat
  • acid
  • hypertonicity
  • distention
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20
Q

duodenum stimuli that affect gastric emptying: FAT

A
  • most potent stimulus for gastric emptying
  • takes a long time for fat digestion and absorbed into lumen of S intestine
  • presence of fat reduces gastric emptying to allow more time for processing
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21
Q

how long can high fat meals stay in the stomach vs proteins and carbs

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A

6 hours
- high protein and carb can be 3 hours

22
Q

duodenum stimuli that affect gastric emptying: ACID

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A
  • duodenum much neutralize stomach acid to prevent tissue damage and to digestive enzymes
  • does this by secreting (mainly from pancreas) NaHCO3
  • high acid levels will reduce gastric emptying
23
Q

duodenum stimuli that affect gastric emptying: HYPERTONICITY

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A
  • breakdown of carbs and proteins can increase osmolarity
  • water moves freely across duodenal wall so it moves into lumen by osmosis
  • if digestion is faster than absorption, increased osmolarity will bring enough water to distend duodenum and decrease plasma volume
  • increased osmolarity in duodenum will inhibit gastric emptying
24
Q

duodenum stimuli that affect gastric emptying: DISTENTION

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A

the more the duodenum is distended the slower gastric emptying rate is

25
situations that could induce vomiting
- touch stimulation at back of throat - irritation or distentioon of stomach or duodenum - elevated intracranial pressure (throwing up after head injury) - rotation or acceleration of head (motion sickness) - chemical agents or drugs that interact w/ chemoreceptor trigger zone next to vomiting center - psychogenic vomiting
26
oxyntic muscosa
oxyntic muscosa - line fundus and body and pyloric gland area (which lines antrum)
27
3 types of secretory cells in oxyntic muscosa
1) mucous cell 2) chief cell 3) parietal cell
28
what are the secretions of the three secretory cells of the oxyntic muscosa collectively known as?
gastric dig juice
29
mucous cell
cells that line pits and the entrance to glands secrete watery mucous
30
chief cells
-more numerous - in gastric glands - secrete pepsinogen
31
parietal cells
- also in gastric glands - secrete HCl and intrinsic factor
32
what is the mucosa in gastric pits covered in?
surface epithelial cells that secrete viscous alkaline mucous that makes a thick cover (a few mm) over mucosa
33
HCl functions in stomach
1) activates pepsinogen to active form of pepsin 2) helps breakdown CT and muscle fibers 3) denature proteins 4) kills microorganisms ingested w/ food
34
mechanism of HCl secretions
1) in parietal cells, H2O is broken down into H+ and OH- - H+ secreted into lumen by H+-K+ATPase (active transport) - HCO3- that's brought into parietal cells passively leaks back into lumen 2) OH- combines w/ H+ to make H2CO3 to remake H2O - parietal cells have lots of carbonic anhydrase so H2O combines w/ CO2 (either metabolic activity or plasma) to make H2CO3 - it partially dissociates into H+ and HCO3- regenerating the H+ secreted 3) HCO3- moved into plasma by Cl- HCO3- exchanger - exchanger makes buildup of Cl- within parietal cells which will move thru channels down electrochem gradient into gastric lumen
34
how pepsinogen is converted to (active) pepsin
1) once released, HCl cleaves off small part of protein to release pepsin 2) the pepsin can then cleave more pepsinogen to make more of itself 3) active pepsin starts protein digestion by splitting AA linkages to release smaller AA chains - this is dependent on acidic environment of stomach
35
why is pepson stored in chief cells as pepsinogen
must be stored in inactive form since the active form can digest proteins - avoids the digestion of the proteins in the chief cells
36
what does mucus help w/
1) acts as lubricant and protects gastric mucosa from mechanical injury 2) protects stomach wall from acidic env. - mucus = alkaline to neutralize 3) protects stomach from self digestion - since it's alkaline it will neutralize pepsin that comes near wall
37
what is intrinsic factor sec by and why?
parietal cells - important for B12 absorption
38
what is B12 essential for?
normal function of RBCs
39
when can B12 be absorbed?
ONLY when combined with intrinsic factor
40
what does B12-intrinsic factor complex interact w/?
receptor in latter part of S intestine causing receptor mediated endocytosis
41
other secretory cells
- G-cells - enterochromaffin-like cells - D-cells
42
G-cells
- endocrine cells - in pyloric gland area - secrete gastrin hormone - release is stim by protein in stomach and ACh from intrinsic nerve plexus - once in blood it travels to stomach body and fundus to stim chief and parietal cells to increase their secretions
43
enterochromaffin-like cells
found among chief and parietal cells in ocyntic mucosa - secrete histamine which acts as a paracrine to increase HCl secretion
44
what is histamine release stim by?
gastrin and ACh
45
D-cells
- found near pylorus and in duodenum - in response to acid they secrete somatostatin which acts as a paracrine to inhibit secretions of parietal cells, G cells and ECL cells
46
protein digestion in stomach
- food here isn't mixed with gastric juices so little protein dig occurs until food moves into antrum which it is thoroughly mixed with gastric juices
47
carb digestion in stomach
food is mixed with salivary amylase - even tho acid inhibits amylase activity, the interior food mass isn't exposed to acid
48
is water and food absorbed into blood from stomach wall?
NO - 2 categories of substances that can cross stomach wall
49
2 subatnces that can cross stomach wall
1) alcohol - ethanol is somewhat lipid soluble 2) aspirin - weak acids like acetylsalicylic acid are unionized in acidic env like stomach - in unionized form, they are lipid soluble
50
where is alcohol absorbed faster?
across intestinal wall
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