digestion - lecture 6 Flashcards
what is mcc
migrating myoelectric (motor) complex
describe phase 1 of mcc
60 mins
no spike potentials on ber
no contractions
describe phase 2 of mcc
20 mins irregular spike potentials and contractions
describe phase 3 of mcc
10 mins
regular spike potentials and contractions
at its max force
describe myogenic properties of distal stomach - gen
each activates after the first - as go down more distally
interrupted by meal
phase 3 earlier and then later
where is mcc
distal stomach
si
describe initiation of mcc
not cns or ans
sometimes gut peptides can effect
needs ens - periodic activation of pattern generating circuitry
describe propagation of mcc
via ens with modulation via ans and gut peptides
describe interruption of mcc
intake of new meal
what is mcc function
housekeeping
gastric emptying of large nondigestible particles
mmc moves tings fowards - even in absence of meal = large turnover of cells in mucosa
describe secretion = exo vs endo
exo = into git, external lumen environment
endo = hormones into blood stream - intneral environment
what is process of digestion
sequence of interdependent steps
Enzymes = proteins = need to recycle eventually
duplication of enzyme activity
medium requirements = ph and ions for enzymes to function
what is digestion - secretion
chemical breakdown of food to progressively smaller molecules
results from secretory activity of large number of exocrine glands found in/with association with git
secretions released into lumen of digestive tract
describe secretion
active
depends on energy and blood flow
results in release of fluids containing ions and many enzymes
secretory cells near capillaries since need raw materials
name and describe 3 types of enzyme
amylases = breakdown starches/carbs
proteases = proteins
lipases = fats
describe pattern of regulation of secretion
nervous - ans = max control at mouth and lessens as go down git
Hormonal - gut peptides = important at bottom of git and not at top at alls
name mouth salivary glands
parotid
submandibular
sublingual
what do secretions in mouth do
protect and lubricate
Chemical digestion
describe a secretion that protects and lubricates
mucin - mucous
describe secretions that allow for chemical digestion
salivary amylase = can work at neutral ph, begins carb digestion
lingual lipase = only active at acidic ph = starts working in stomach only - produce by tongue for lipid digestion
describe the salivary glands
parotid = cheek, serous fluid
sublingual = mucin rich fluid to lubricate
submandibular gland = mixed fluid
descrive saliva - components
0.5-1.5 liters/dat
Na+, K+, Cl-, HCO3-
hypotonic
ph 6.5-7.0
descrive saliva - enzymes
amylase = ptylin ph ~7 breaksdown starch polysacch to maltose dissach
mucin
lipase
Lysozyme = break down bacteria cell walls
describe gland regulation
ans =
parasymp mostly = mainly excitatory, blocked by atropine, ach on muscarinic = secretion and vasodilation
sympathetic = not much, vasoconstriction
describe regulation of salivary secretion
simple conditioned reflexes
happens at cephalic phase = related to level of head
eyes nose –> higher centers in cortex
sensory receptors in mouth –> afferents
both act on salivary centers in medulla
efferents sent via parasymp = to salivary glands
describe phases of secretion
psychic - conditioned reflex, thinking/seeing food and gustatory - taste = CEPHALIC
GASTRIC
INTESTINAL
describe mixed gastric juice - components
15-2 liters/day
isotonic fluid = Na+, K+, Cl- **H+
ph 1-2 = v low
describe mixed gastric juice - enzymes and stuff
hcl
pepsinogen (zymogen, inactive precursor)
intrinsic factor (need for vit b12 at illeum)
mucin (alkaline secretions)
name and describe enzymes involved in protein digestion
proteins to smaller peptides = pepsin, trypsin, chymotrypsin, elastase
smaller peptides to aas = aminopeptidase and carboxypeptidase
describe surface epithelial cells throughout git
secrete mucous alkaline fluid = protect and lubricate
describe secretions of upper stomach
cardiac and pyloric tubular glands secrete akaline mucin rich fluid
describe secretions of lower stomach
fundus and body tubular glands secrete acid, enzymes and intrinsic factor
describe gastric glands in fundus and corpus
tubular gland = invagination, increases sa of secretion at level of stomach
Explain what gastric glands in fundus and corpus secrete
mucous neck cell = goblet cell, secretes mucin
parietal cell secrets hcl into lumen of gland and enters stomach
chief cells secrete pepsinogen = broken down to pepsin in presence of acid, secretes zymogen granules
describe structure of parietal cell
apical part
intracellualr canaliculi= invaginations increase sa for cells to release hcl
capillary at basolateral side =need lots of raw materials
lots of mito since need lots of energy
describe parietal cell - carbonic anhydrase
alkalinzation of blood
takes co2 from blood and produces bicard
for every hcl molecular moving into lumen = 1 molecule bicarb moves into capillary
describe parietal cell - h+/k+ atpase
Important pump
acidify lumen
only on apical side in parietal cells ONLY
usually h+ = 4x1o^-5 in cap = v small, huge gradient, pumping against = much energy needed
hclm isotonic, 150meq h+ and 150 meq cl-
proton pump = when inhibit = treatment for ulcers/lower stomach acids
describe parietal cell - na+/k+ atpase
keeps ionic balance
not specific for parietal cells
describe postprandial urinary alkaline tide
can measure in urine sample
water moves into lumen passively
describe cl- and h+
cl- entering cell =actively transported across canalicular membrane
h+ = available from dissociation of intracellular water, actively pumped into canaliculi in exchange for k+
describe secretion of h+
leaves excess of oh- in cell
results in increase of intracellular ph
Causes more co2 to diffuse in from plasma (together with metabolic co2) combines with water in presence of carbonic anhydrase = produces h2co3
h2co3 reacts with excess oh- to give h20 and hc03-
hco3 - diffuses into circ restoring intracellular status quo and gives rise to INCREASED ALKALINITY IN THE VENOUS BLOOD
where does water move
into canaliculi pasively
describe parietal cell secretion
pure hcl fluid
constant composition, ph ~0.8
secretion independent of type, magnitude of stimulus
mixed gastric juice, ph1-2 = modified by non parietal alkaline gastric secretions = depends on number of parietal cells active
and and describe the 3 functions of hcl
1 - precipitates soluble proteins = allows proteins to remain longer in stomach, curds = bigger so more time to breakdown
2 - denatures proteins more readily digested = easier for peptidases to work
3 - activates pepsin and provides optimal ph for pepsin to work (acidic)
what does hcl do
converts pepsinogen to pepsin
pepsin = can cleave pepsinogn to pepsin = autocatalysis
what does pepsin do
converts proteins to polypeptides
what is intrinsic factor and explain
secretion of stomach essential to life
glycoprotein
secreted by parietal cells
required for absorption of vit b12
in distal si = ileum
what happens if deficient in vit b12
pernicious anemia
intrinsic factor-B12, must form complex
where is mucin secreted from - 3
1 - all surface epithelial cells
2 - cardiac and pyloric tubular glands - lots here
3 - mucous neck cells (fundus and corpus)
what is point of mcc ex
like with cherry pit
can force through with these contractions - pyloric sphincter - objects big so takes time
