GI 2 - Gastric Function Flashcards
(99 cards)
1
Q
what are the gastric functions
A
-temporary storage of ingested material
-production of chyme
-meter delivery of chyme to duodenum
- partially sterilize meal
-initiates protein digestion
- produces specialized secretions
2
Q
what specialized secretions does the stomach produce
A
-HCl acid
-pepsinogen
- intrinsic factor
- mucus
- hormones/paracrines
3
Q
what is the function in the fundus and body
A
secretion and resevoir
4
Q
what is the function in the antrum
A
mixing and grinding
5
Q
what are the 4 ways of gastric motility
A
-receptive relaxation
-peristalsis
- emptying
- migrating motility complex (MMC)
6
Q
what is the function of receptive relaxation
A
-accommodate the volume of the meal
- reduce pressure prevents gastric reflux and premature gastric emptying
7
Q
what is the function of peristalsis
A
- chyme production
-trituration
8
Q
what is trituration
A
mix ingested nutrients with gastric secretions, breakdown large particles and increase SA for digestion
9
Q
how much is emptied into the small intestine per hour
A
200 kcal/hour
10
Q
what is function of MMC
A
sweep ingested solids that cannot be digested out of stomach and through intestinal tract
11
Q
when does MMC occur
A
during fasting
12
Q
how long does MMC take
A
90 mins to get from stomach to colon
13
Q
what is gastric receptive relaxation initiated by
A
-stretch of gastric or duodenal wall
- protein or fat in duodenum
14
Q
what hormone mediates receptive relaxation
A
CCK
15
Q
describe the pathway of gastric receptive relaxation
A
- stretch, fat, or protein causes CCK release which either does long vaso vagal reflex to the DVC or short ENS reflex using NO and VIP to relax
16
Q
what is the function of gastric receptive relaxation
A
accommodate increased volume of food and slows emptying
17
Q
what is gastric peristalsis/trituration generated by
A
pacemaker cells (interstitial cells of cajal) located in GI smooth muscle
18
Q
describe how peristalsis happens
A
smooth muscle cells undergo spontaneous phases of deploarizations and repolarizations called basic electrical rhythm (BER) of the stomach
19
Q
what is the frequency of peristalsis/trituration
A
3 times per minute
20
Q
what are the functions of peristalsis/trituration
A
- acts to mix and break down gastric contents
-regulate gastric emptying
-peristaltic wave forces chyme through pyloric sphincter - causes pyloric sphincter to contract reducing volume released to small intestine
21
Q
what is the rate of gastric emptying influenced by
A
- solid vs liquid
- nutrient content
- force of gastric contractions
22
Q
how often is 50% of the stomach contents emptied
A
2.5-3 hours
23
Q
how long does total emptying of the stomach take? small intestine?
A
stomach: 4-5 hours
small intestine: 3-5 hours
24
Q
how long is transit through the colon
A
8-15 hours
25
what are factors that increase force of antral contractions which increase gastric empyting
-gastrin
- distension of stomach
26
what are factors that decrease force of antral contractions and decrease gastric empyting
- contents of duodenum
27
what are enterogastrones
hormones secreted by duodenum in response to nutrients and acid in chyme
28
what are the enterogastrones and what do they each respond to
- CCK: fat and protein
- secretin: acid
- GIP: carbohydrate
29
what is the pathway of how enterogastrones affect gastric emptying
- high acidity, high fat, high AAs, hypertonicity, distension all increase secretion of enterogastrones and stimulate neural receptors
- enterogastrones directly decrease gastric emptying
- neural receptors decrease gastric emptying directly though enteric neurons OR long reflexes by increasing SNS efferents and decreasing PNS efferents to decrease gastric emptying
30
what is the MMC and when does it occur
-intervals of strong propulsive contractions that sweep the stomach and small intestine of indigestible material
-occurs in between meals (fasting state)
31
what hormone is involved in the MMC and what does it work through
intrinsic to ENS and involved motilin
32
when does the MMC stop
when meal is ingested
33
describe gastric glands
- exocrine glands
- produce gastric juice
-variety of cell types and secretions
34
what type of cell is the parietal cell, what does it secrete and what is its function
- exocrine
- HCl; activation of pepsinogen and sterilization of meal
- intrinsic factor; vitamin B12 absorption
35
what type of cell is a chief cell, what does it secrete and what is its function
-exocrine
- pepsinogen; protein digestion
36
what type of cell is a surface mucous cell, what does it secrete and what is its function
- exocrine
- mucus and HCO3-; gastroprotection
- trefoil factors; gastroprotection
37
what type of cell is an ECL cell, what does it secrete and what is its function
-paracrine
- histamine
- regulation of gastric secretion
38
what type of cell is a G cell, what does it secrete and what is its function
- endocrine
- gastrin
- regulation of gastric secretion
39
what do nerves release and what is its function
-gastrin releasing peptide; regulation of gastric secretion
- Ach; regulation of gastric secretion
40
what type of cell is a D cell, what does it release and what is its function
-paracrine
- somatostatin
- regulation of gastric secretion
41
what type of cell is a Gr cell, what does it release and what is its function
- endocrine
- ghrelin
- stimulates hunger
42
what type of cells are found in corpus gastric glands
- surface mucous cells
- mucous neck cells
- parietal cells
- D cells
- ECL cells
- chief cells
43
what is another name for corpus gastric glands
oxyntic gland
44
what differentiates oxyntic glands and pyloric glands
-oxyntic glands have abundant amounts of parietal and chief cells
- pyloric glands have abundant mucus secreting cells and secrete hormones that regulate gastric function
45
where are oxyntic glands found? pyloric glands?
-oxyntic: fundus
-pyloric: antral
46
what is the mechanism of acid secretion by a cell
- CO2 + H2O-> H2CO3 by carbonic anhydrase
-carbonic acid splits and the HCO3- is transported across the basolateral membrane by the HCO3-/Cl- antiporter into the capillary and creates the alkaline tide
- the H+ is transported across the apical membrane via the K+ H+ primary active antiporter
- H+ combines with Cl- in the gastric gland lumen to form HCl
47
what do oxyntic cells have receptors for and what do each hormone do
activate: gastrin, histamine, acetylcholine,
inhibit: somatostatin
48
cells secrete up to ____ of HCl and
2 L/day; intrinsic factor
49
where are proton pumps located in the oxyntic cell
apical membrane
50
what is an example of synergism in the stomach
hormones that stimulate oxyntic cell function
51
what does high levels of HCl negatively inhibit
gastrin secretion
52
what does gastrin secretion stimulate
acid secretion by parietal cells and histamine secretion
53
what does histamine secretion stimulate
acid secretion from parietal cells
54
what is an example of an H2 receptor antagonist
ranitidine
55
what is the stimulus for neural control of oxyntic cell function
stretch of gastric wall
56
describe neural control mechanism of oxyntic cell function
- stimulus causes short reflex using Ach to stimulate parietal cells and chief cells to release gastrin and acid in the oxyntic gland
- stimulus causes long reflex of vaso vagal reflex to DVC which uses AcH to stimualte oxyntic gland and uses GRP to cause G cells to secrete gastrin
57
what does somatostatin inhibit
parietal cells, ECL cells, and G cells
58
what is the pathway of acid release by parietal cells
- G cells release gastrin
- gastric causes direct release of acid by parietal cells and acts on ECL cell to release histamine which causes acid secretion from parietal cell
59
what are the phases of GI activation
-cephalic phase
- gastric phase
- intestinal phase
60
what controls the cephalic phase and when does it occur
- the vagus nerve
- occurs before contents enter GI tract via vagus nerve
61
what controls the gastric phase
-local nervous secretory reflexes
- vagal reflexes
- gastrin histamine stimulation
62
what controls the intestinal phase
- nervous mechanisms
- hormonal mechanisms
63
what are the stimulants for the cephalic phase of acid secretion
sight, smell, taste, thoughts of food
64
what is the mechanism of the cephalic phase
-cephalic phase stimuli -> PNS preganglionic neurons -> enteric neurons -> AcH -> parietal cell acid release and stimulates G cell and ECL cell
65
what is the mechanism of the gastric phase
- food in the stomach causes peptides -> G cell -> gastrin -> ECL cell -> histamine -> acid release from parietal cell
- distenstion from food in the stomach activates neural reflexes -> enteric neurons -> ACh release -> parietal cell acid release and stimulates G cell and ECL cell
66
what is the mechanism of the intestinal phase
- increased H+, distension, osmolarity, fats in duodenum causes release of enterogastrones which inhibit acid release from parietal cell and inhibit G cells
- increased H+, distension, osmolarity, fats in duodenum -> neural reflex -> ENS -> AcH -> increased acid release from parietal cell
67
what happens during the interdigestive period (fasting)
- acid is secreted at low levels
- lack of buffer causes low pH in stomach
- basal secretions stimulated by histamine and Ach
- gastrin low due to low pH in gastric lumen
68
what is the function of the events in the interdigestive period
possibly to sterilize gastric lumen
69
what is the basal secretion rate
0-11 mEq/hr
70
what is the stimulated secretion rate
10-63 mEq/hr
71
what is the function of acid
-facilitates digestion of proteins
- protects against some pathogens
- increases absorption of B12, iron and calcium
72
what are PPIs and what do they do
- proton pump inhibitor
- binds to and inhibits H+ K+ pump
- nearly 100% inhibition
- may have side effects related to functions of acid
-prescribed to people with severe GERD
73
what is intrinsic factor and what is it secreted by
glycoprotein secreted by oxyntic cells
74
how is intrinsic factor secreted
- exocytosis
- secretion activated by same secretagogues that activate HCl secretion
-mechanism unknown but different than acid secretion
75
how do inhibitors of proton pump affect intrinsic factor
does not inhibit it but reduces its function
76
what is intrinsic factor required for
vitamin B12 absorption
77
what is vitamin B12 important in and what would a deficiency cause
RBC production
-pernicious anemia
78
what is the function of chief cells
secretes pepsinogen by exocytosis to initiate digestion of protein
79
what is pepsinogen activated to pepsin by
low pH
80
what is pepsinogen activation to pepsin inactivated by
pH greater than 5
81
what does pepsin do
protein digestion (not a significant amount)
82
what is the main activation of chief cell function mediated through
local and vagal reflexes that release AcH
83
describe the neural control of chief cell function
same as oxyntic cell function
84
describe the pathway of activation of pepsinogen in the gastric lumen
chief cells secrete pepsinogen
- parietal cell secretes HCl and IF
- Pepsinogen is converted into Pepsin by HCl
- pepsin breaks down protein into peptides
85
what are the stimuli for ghrelin
fasting and low body fat
86
what does ghrelin secretion cause
-CNS to increase hunger and eating
- tissues to decrease metabolism
87
what is ghrelin produced by
endocrine cells located in oxyntic glands
88
what does ghrelin stimulate in the brain
hypothalamic NT neuropeptide Y
89
when does ghrelin spike
before meal times
90
compare ghrelin levels in someone who lost weight compared to someone who got gastric bypass
- ghrelin levels are higher in someone who has lost weight
91
why doesnt the stomach digest itself
gastric mucosal barrier
92
what is the gastric mucosal barrier
two hydrophilic layers separated by hydrophobic barrier
- mucus is secreted by mucous cells onto surface of epithelium
- contains long chains of oligosachharides that expand and retain water
- viscoelastic substance that coats surface of gastric epithelial cells
- high pH produced by surface cell secretion of HCO3
93
how does the gastric mucosal barrier limit diffusion of acid through the plane off the gel
via viscous fingering
94
what is mucus secretion in the gastric mucosal barrier stimulated by
prostaglandins (NSAIDS)
95
what helps stabilize the barrier in the gastric mucosal barrier
trefoil proteins
96
where can ulcers be found in the GI tract
gastric and duodenal
97
what are the 2 causes of ulcers and what do they do to cause the ulcer
- helicobacter pylori- bacterial infection destroys the gastric diffusion barrier
- zollinger-ellison syndrome- g cell tumor
98
what is mucosal destruction
gastritis causing an ulcer
- mostly oxyntic gland mucosa
99
what are the issues with emptying in gastric disfunction
-obstruction
- gastroparesis
- dumping
