26: Stomach Flashcards
Parietal cell function: the players
HCL dissociate in to hydrogen and bicarb
- proton pump (hydrogen potassium)
- potassium and chloride channles
- carbonic anhydrase
- bicarb/chloride antiporter
Parietal cell function
hydrogen out, sodium in
potassium goes out and recycles continuously
so we get rid of H ions
Parietal cell function 2
Bicarb/cholride antiporter:
chloride comes in, and exits. like K
bicarb stays and diffuses into blood vessle
stomach is like a
washing machiene/grinder
to produce chyme and finish what mouth didn’t
mechanical digestion
gentle waves in stomach to mix bolus with juices
more vigours from body to stomach to pyloric region to move chyme
intense near pyloriys to opening of pyloric sphincter to squirt out teaspoons (1-2 per wave)
protein digestion
starts in stomach
HCl denatures protein molecs
HCl activates pesinogen to pepsin to break peptide bonds to A.As
Fat digestion
continues in stomach
gastric lipase splits triglycercides (but most effective at pH 5-6) (infant stomach)
HCl also
kills microbes
Mucous
keeps stomach walls from being digested
Things stomach absorbs
water
electrolytes
drugs (asprin)
fat (to slow passage of alcohol to intestine where it is quicker)
alcohol (more slowly if fat taken in too)
Cephalic Phase
anticipation prepare mouth and stomach sight, smell, memories, thoughts of food salivation (facial and Glossopharyngeal) gastic glands secrete gastric juices (Vagus)
Gastric Phase
breakdown of material
Intestinal Phase
controlled release of chyme
entry into duodenoum slows gastic activity, inc intestinal activity
Neural influence on Gastric Phase
strech receptors and chemoreceptors–> signal bolus entry
vigorous peristalsis and gastric gland secretions
chyme periodically released into duodenum
Endocrine influences on Gastric Phase
distention and pressure of food= G cells secrete gastrin
gastrin
inc gastric gland secretions and motillity
causes pyloric sphincter relaxation
Neural influence on Intesinal Phase
distension of duodenum and chem contents of chyme= activated symp nerves
this slows gastric activity
Endocrine influnce on Intesinal Phase
distension of duodenum and contents of chyme= hormonal release from dnteroendocrine cells here
secretin
cholecystokinin (CCK)
secretin
dec stomach secretions
CCK
dec stomach emptying
gatric emptying
inc as bolus enters stomach
distension of stomach and presence of food in it causes
secretion of gastric and vagaal nerve impulses
secretion of gastric and vagaal nerve impulses stimulates
contraction of lower esophogeal spincter and stomach
relaxation of pylorc sphincter for emptying
Enterogastric reflex regulates
regulate amount of chyme released into duodenum
CCK and secretin relases
CCK and secretic both
stim symp impulses and inhibit gastric emptying
Enterogastric reflex initiated by
distension of duodenum and contents of chyme
sensory impulses sent to medulla to inhibit parasymp stim of stomach
2 types of influence for intestinal and gastric phases
neural
endocrine
smooth muscle control
involuntary
mostly ANS
ACH and norepi
membrane potential -50 to -60
smooth muscle types
single/unitary
multiunit
categorized by manner of excitation
unitary SM
walls of GI tract
gall baldder walls
walls of urinary bladder
may not be in contact with motor neuron
Unitar SM is
autorythmic
connect via gap junction: transmit APs from one fiber to another
adhering to eachother=transmission of force
slow synched graded contraction
conexons
entire unit and channels between cells
conexens
the individual cells that make up the unit
genotypes and phenotypes
want conexons that have same numbers so that channels work most efficiently
function syncytium
a group of cells that get one nervous system input. react as a group!
how smooth and skeletal muscle differ (smooth described)
SR poorly developed (SM)
thick filaments of SM have actin grabbing heads entire lengthen
thick and thin filaments arranged diagonally within cell for twisting motion
circular muscle
contracting at right angles to each other
smooth muscle varicosities
little bumps
release neurotransmitters into diffuse junctons of SM fiber
special features of SM (about contraction)
can sustain contraction for a long time without tiring at small NRG cost
maintains low level of tone even w/o APs
stress relaxation response
Stress relaxation in SM
stretch causes inc in tension
tension decs w/in 1-2 minutes
allows SM to change length but maintain ability to contract (important for storage organs)
never goes down to zero!
Length-tension relationship
SM operate over wider range of resting lengths
generally broader length-tension relationships in SM compared to skeletal muscle
proton pump of parietal cell
pushes H out of cell
H+/K+ ATPase
antiporter
Cl-/HCO3-
why do we cross parietal cell?
to get into blood stream
where do CO2 and H2O come from
CO2: metabolism
H2O just in cell
carbonic anhydrase in parietal cell
major in disposing of cellular waste
Goal of parietal cell
to secrete HCl!
what makes CA?
H2O and CO2 make carbonic anhydrase
CA dissociates into
bicarb and H… we need to get rid of this
