digestion - lecture 7

Question 1

name and describe what each cell type in gastric glands in fundus and corpus secrete

Answer 1

parietal = intrinsic factor and hcl
chief cells = pepsinogen
mucous neck cell = mucin
surface epi cell = bicarb mucus

Question 2

does mucin protect git mucosa from acid damage

Answer 2

huge layer of mucous

Question 3

what is gmb

Answer 3

gastric mucosal barrier
apical surfaces and tjs = impermeable to hydrogen ions

Question 4

what is muci bicarb layer

Answer 4

bicarb secreted and mucin
absorbed into mucous layers
h+ neutralized = bc bicarb also added to layer
protects acidic ph from getting to cells = like surface epi cells

Question 5

describe gastric mucosa protection

Answer 5

muci bicarb layer
gmb
rapid cell turnover = reepithelization ~ 1 mil new cells = stomach and si

Question 6

how do ulcers form

Answer 6

normal hcl output but weak barrie = aspirin and nsaids and helicobacter pylori contribute to weak barrier
or
normal barrier but excessive hcl output = gastrin producing tumours

Question 7

describe neural regulation of secretion - cephalic phase

Answer 7

ens
excitatory
acts on secretory cells = hcl, mucin, pepsin
when stretch vagal inputs (cephalic)
vagally mediated
also vasodilation = parasym
symp = inhibits secretion and vasoconstricts

Question 8

describe neural regulation of secretion - gastric phase

Answer 8

distension - stretch receptors
reinforced by vagal vagal reflex
affected by secretagogues
gastrin goes to heart and increase hcl output from parietal cells

Question 9

what are secretagogues

Answer 9

aas or partially digested proteins which act on gastrin releasing cells = g cells = leads to release of gastrin

Question 10

what is gastrin

Answer 10

peptide hormone
released by endocrine cells in antrum - g cells

Question 11

what is gastrin released in response to

Answer 11

secretagogues - products of protein digestion
local enteric reflexed = distension in antrum
vagally mediated reflexes = vagovagal

Question 12

what also happens during cephalic phase

Answer 12

vagally mediated release of gastrin also released during cephalic phase
want to be prepared before meal arrives

Question 13

describe gastrin release

Answer 13

self regulating
secretagogues (products of protein breakdown) = act on g cell and inhibit acid release from parietal - somatostatin - neg = g cell stops gastrin = goes to heart = parietal cells (give hcl which activates pepsinogen to pepsin optimal ph)
when ph <2 = g cells sense when stop gastrin
so then ph rise = neg feedback loop

Question 14

what does low ph do

Answer 14

Low pH causes the release of Somatostatin which inhibits the G-cell and the Parietal Cell

Question 15

describe physiological roles of gastrin

Answer 15

stimulates hcl secretion
trophic effect = growth, stimulates production of more parietal cells = increase number

Question 16

what does gastrin stimulate

Answer 16

hcl secretion from parietal cell

Question 17

when is gastrin released

Answer 17

Precedes and accompanies meal
occurs as part of cephalic phase

Question 18

describe pos feedback of gastric secretion

Answer 18

release stimulated by stretch in stomach and presence of secretagogues in stomach

Question 19

describe neg feedback of gastric secretion

Answer 19

release inhibited by low ph in stomach and by somatostatin

Question 20

describe somatostatin

Answer 20

release occurs in presence of low ph in stomach
inhibits gastrin release from g cells
inhibits hcl secretion from parietal cells

Question 21

What Role does Histamine Play in HCl Secretion?

Answer 21

lots of histamine present in gastric mucosa
histamine administration elicits large vols of gastric juice with lots of hcl

Question 22

what is common mediator hypothesis

Answer 22

gastrin and ach cause histamine release
histamine is final local common chemostimulator of parietal cell
WRONGGGGGGGG

Question 23

describe Regulation of Parietal Cell HCl Secretion

Answer 23

PARIETAL cells have receptors for all 3 on surface = ach, gastrin and histamine

Question 24

describe receptor interaction hypothesis

Answer 24

separate receptors
interaction among 3 receptors
blockade or stimulation of one receptor, changes properties of one or both of the other 2 receptors
cooperative effect = histamine sensitive to ach and gastrin

Question 25

describe permissive hypothesis

Answer 25

histamine constantly released in gastric mucosa and presented to parietal cells as a tonic background = sensitize them to other stimuli
blocking tonic background release of histamine or using h2 receptor antagonists inhibits acid secretion in response to ach and gastrin

Question 26

describe intestinal phase

Answer 26

secretagogues to heart –> enterooxyntin –> gastrin —> acts on parietal cell and secretes hcl
also inhibits gastric secretion
neg feedback on secretions = secretin, cck, gip, vip, neurotensin

Question 27

describe motor and secretory activities of stomach

Answer 27

at any moment in time reflect balance between excite and inhibitory influences on muscular and glandular cells in gastric wall

Question 28

describe optimal secretory activity

Answer 28

result of interplay between neural and hormonal mechanisms
gastric secretions at any moment in time reflects balance between excite and inhibit

Question 29

describe pre intestinal changes

Answer 29

meal reduced to semi liquid consistency = chyme
acidified, osmotic pressure unchanged
limited digestion

Question 30

describe pre intestinal changes - enzymes

Answer 30

some polysacc –some salivary amylase pytalin (inactivated in acidic ph of stomach)–> disacc
some proteins –gastric pepsin–> polypep
lipid –> di and monoglycerides, fatty acids - active at stomach only

Question 31

describe upper intesine functions

Answer 31

chyme neutralization = alkaline secretions
osmotic equilibration = will be isotonic by time reaches colon = want nutrients to flow back to systems
Digestion continues
absorption begins

Question 32

name accessory organs which secrete stuff into si

Answer 32

liver
gallbladder
pancrease
all into duo via common pathway = ampulla of water (sphincter of oddi)

Question 33

describe liver and biliary system

Answer 33

right and left hepatic ducts
cystic duct
common bile duct
ampulla of water
pancreatic duct w/ sphincter of oddi

Question 34

describe pancreas

Answer 34

endo and exocrine components

Question 35

describe pancreatic juice - composition

Answer 35

0.5-1.5l/day
isotonic
main electrolytes = sodium, potassium, chloride, BICARB
ph = 7.2-8.2

Question 36

describe pancreatic juice - enzymes

Answer 36

pancreas produces largest and most powerful digestive enzymes
enzymes = 3% protein, only breast milk has more proteins than this
= amylases, proteases, lipases

Question 37

what is important for absorption

Answer 37

dissac must be converted to monosacc
right now = amylase converts poly to disacc

Question 38

describe pancreatic proteases - trypsin

Answer 38

proenzyme – enteropeptidase - enterokinase –> enzyme
trypsinogen –> trypsin by enterokinase in SMALL INTESTINE

Question 39

describe pancreatic proteases

Answer 39

chymotrypsinogen –> chymotrypsin
proelastase –> elastase
procarboxypeptidase –> carboxypeptidase
all BY TRYPSIN ENZYME
trypsin inhibitor = also secreted by pancreas = to prevent activation in pancreas

Question 40

where is gastrin released

Answer 40

by g cells in stomach and duo

Question 41

what does proton pump inhibitor do

Answer 41

blocks 90-95% of release of acid from parietal cells

Question 42

what happens if block h2 receptor

Answer 42

ulcer diseases treatment = bc blocks 70% of acid release from parietal
used to decrease hcl secretion
also h+/k+ atpase blockers