Stomach

Question 1

3 major functions of the stomach

Answer 1

1. temporal storage
2. absorption of water soluble and lipid soluble substances (like alcohol and some drugs)
3. preparation of the chyme for digestion in the SI

Question 2

most of the protein components of food are what? in the stomach

Answer 2

broken down into smaller constituents

uses pepsin (acidic environment needed)

Question 3

surface mucus cells in stomach

Answer 3

located at opening of gastric glands

secrete mucus

Question 4

mucus neck cells in stomach

Answer 4

neck of gastric gland and secrete less viscous mucus than those located at the opening

also secrete HCO3-, and water to protect the lining of the stomach against acid

Question 5

parietal (Oxyntic) cells

Answer 5

secrete HCL and intrinsic factor for B12 absorption

Question 6

chief (zymogen) cells

Answer 6

basal region of glands

secrete pepsinogen via exocytosis

Question 7

D cells in stomach

Answer 7

found in the antrum

secrete somatostatin –> inhibits acid secretion therefore gastrin release

Question 8

enterochromaffin-like cells (ECLs)

Answer 8

scattered throughout the mucus

secrete histamine –> which stimulates acid secretion by the parietal cells

also increases blood flow locally

Question 9

G cells in stomach

Answer 9

enteroendocrine cells that secrete gastrin

found mostly in the pyloric region

secreted into blood (not lumen of stomach) and stimulates gastric juice secretion and gastric/intestinal motility

Question 10

EtOH and aspirin

Answer 10

can break down mucus…which is the protective glycocalyx for the stomach

so excessive uses of these can cause ulcers

Question 11

pepsin

Answer 11

secreted by chief as pepsinogen and activated by acid (HCl)

pepsin = endopeptidase

Question 12

gastric lipase

Answer 12

lipid breakdown

78% homologous to lingual lipase

Question 13

intrinsic factor

Answer 13

vitamin B12-binding protein and considered a ‘essential factor’

loss = achlorhydria –> pernicious anemia

Question 14

relationships between the concentration of these ions as the rate of secretion increases..

HCl
Na
K

Answer 14

H+ = increases rapidly

Cl- = increases but not as much as H+ … but also has a higher absolute value

Na+ = decreases

K+ = low absolute amount, but still see slight increase

Question 15

maximal acid secretion is when after a meal

Answer 15

one hour after

lowest pH = 3 hours after

during this process the food acts a buffer to raise pH

Question 16

parietal cell

Answer 16

distinctive characteristics:

1. intracellular canalculi
2. abundance of mitochondria
3. extensive SER (tubulovesicular membranes)

Question 17

parietal cell in the resting state

Answer 17

the tubulovesicles (containing transporters responsible for H+ and Cl- secretion) –> located underneath the plasma membrane

Question 18

tubulovesicular membranes

Answer 18

in apical portion of the parietal cell and contain the H/K-ATPase

Question 19

stimulation of parietal cells

Answer 19

cyctoskeletal rearrangement occurs leading to the fusion of the tubulovesicles membrane into the canalicular membrane

this increases surface area of apical membrane and the appearance of microvilli

as a consequence –> greatly increases number of H/K-ATPase and K+ and Cl- channels into the plasma membrane and O2 consumption to support acid secretion

Question 20

carbonic anhydrase in parietal cell

Answer 20

secreted protons by these cells mostly are derived from the dissociation of water and the CA reaction

water –> H + OH

OH + CO2 –> HCO3- via CA –> goes out blood side membrane

H –> goes out into lumen via K/H-ATPase

Question 21

apical membrane transporters of parietal cells

Answer 21

1. H/K-ATPase –> how H+ is secreted into lumen
2. K+ channel –> how you secrete (recycle) the K+ back into lumen to continue to use #1
3. Cl- channel –> Cl - enters cell from blood side –> goes into lumen via this channel down gradient

Question 22

basolateral membrane transporters of parietal cells

Answer 22

1. Na/K-ATPase –> pumps in K+ from blood so can secrete K+ out apical membrane to supply fuel for H/K ATPase
2. K+ channel
3. Cl-/HCO3- exchanger –> pumps HCO3- out into blood … and Cl- into cell which will eventually go into lumen

Question 23

receptor for gastrin on parietal cell

Answer 23

gastrin-cholecystokinin, CCK-B

Question 24

receptor for Ach on parietal cell

Answer 24

muscarinic receptor, M3

Question 25

receptor for histamine on parietal cell

Answer 25

H2

Question 26

stimulation of CCK-B and M3 receptors on parietal cell -->

Answer 26

increases intracellular Ca2+, which stimulates HCl secretion gastrin --> CCK-B (secreted by D cells into the blood vessels) Ach --> M3 (from vagus nerve)

Question 27

stimulation of H2 receptors on parietal cell -->

Answer 27

increases intracellular cAMP --> HCl secretion | histamine from ECL cell

Question 28

'potentiation effect'

Answer 28

the effect of 2+ stimulants is greater than just 1 Ex: gastrin + Ach --> larger increase in intracellular Ca2+

Question 29

major humoral effectors (secretagogues) for gastric secretion

Answer 29

Gastrin (G) Histamine (H) ACh

Question 30

neural effectors for gastric secretion

Answer 30

a. distention of stomach --> (+) mechanoreceptors --> (+) parietal cells directly through a short local reflex and by long-vagal reflexes

Question 31

direct and indirect mechanisms for stimulating gastric secretion

Answer 31

Direct: - ACh, H, and G all bind to their respective receptor on the parietal cell Indirect: - ACh and gastrin indirectly induce acid gastric secretion as a result of their stimulation of histamine release from ECL cells and possibly from mast cells in the lamina propria

Question 32

H2 receptor blockers

Answer 32

block the H2 receptors on parietal cells but also inhibit the acid secretion stimulated by ACh and gastrin

Question 33

where else are CCK-B and M3 receptors found - besides the parietal cell (most important for gastric secretion regulation)

Answer 33

ECL cells activation of these receptors --> (+) Histamine release --> (+) HCl secretion

Question 34

phases of gastric secretion of acid (general)

Answer 34

1. basal 2. cephalic 3. gastric 4. intestinal

Question 35

basal phase of gastric acid secretion

Answer 35

inter-digestive period...

Question 36

cephalic phase of gastric acid secretion

Answer 36

shortest period takes place before food enters the stomach initiated by though, sight, smell and taste (no mental shit...why called cephalic) A. Neurogenic influence = parasympathetic vagus nerve causes release of ACh --> (+) parietal cells, G cells, and ECL cells ** also stimulates chief cells --> pepsinogen B. Endocrine influence = vagal stimulation also causes gastrin release which acts like ACh mostly

Question 37

gastric phase of gastric acid secretion

Answer 37

longest phase....triggered by the presence of food in the stomach due to distension and chemical nature A. Neurogenic influence = stomach distension stimulates mechanoreceptors leading to secretion of ACh due to parasympathetic reflexes B. Endocrine influence = amino acids and peptides activate G-cells in the antrum ...gastrin therefore released into blood to stimulate further acid secretion and Histamine release ...gastrin secretion falls as pH of stomach falls between 2-3 and somatotstatin is released from D cells

Question 38

intestinal phase of gastric acid secretion

Answer 38

presence of chyme in duodenum --> enterogastric reflex in order to (-) gastric secretion acid in duodenum --> secretin released --> (-) G cells and reduces parietal response to gastrin also...FAs in the duodenum and jejunum cause release of gastric inhibitory peptide (GIP) and CCK --> inhibit acid secretion and gastrin release