GIT physiology 1 Flashcards
mechanical digestion
mixing waves - gentle, rippling peristaltic movements - creates chyme
chemical digestion
different enzymes require different environments
many molecules require stepwise digestion
all require specific conditions
3 types of chemical digestion
secreted enzymes
brush border enzymes
cytosolic enzymes
carbohydrases
chemically digest carbohydrates
- pancreatic amylase
- a-dextrinase, sucrase, lactase, maltase in brush border
- ends with monosaccharides which can be absorbed
proteases
chemically digest proteins
- trypsin, chymotryp[sin, carboxypeptidase, and elastase from pancreas
lipases
chemically digest lipids
- pancreatic lipase most important in triglyceride digestion
- emulsification by bile salts increases surface area
nucleases
chemically digest nucleic acids
- ribonuclease and deoxyribonuclease in pancreatic juice
- nucleosides and phosphates in brush border
3 types of movement in the GI tract
- interdigestive clearing
- squishing
- peristalsis
interdigestive clearing
driven by a pacemaker
rhythm that sweeps the gut clean
squishing
stretch driven rhythmic contraction
for mechanically breaking up food
peristalsis
local stretch driven propulsion
mechanical aspects of digestion are modulated by
ANS/hormones/paracrines
basal electrical rhythm
cells opening and closing channels constantly
enteric smooth muscle
tonic/phasic
bundles electrically connected via gap junctions contraction stimulated by Ca
tonic/phasic
on/off or oscillating
bundles of enteric smooth muscle is connected via
gap junctions
contraction of enteric smooth muscle is stimulated by
calcium
Ca2+ channels in enteric smooth muscle are
slow to open/close
long AP duration/contraction
excitation of smooth muscle
lots of things can open smooth muscle Ca channels
- ANS activity - acetyl choline
- enteric nervous system activity
- local chemistry
- autorhythmicity - some GIT smooth muscle cells are pacemakers
- hormones, lumocrines
- stretch
how does stretch excite enteric smooth muscle
stretching smooth muscle opens mechanically gated channels;s and causes it tp contract
stretch triggering enteric smooth muscle is called
myogenic stretch response
how does ANS open Ca channel;s
acetylcholine stimulates Gi tract smooth muscle
autorhymicity
some GIT smooth muscle cells are pacemakers
when there is no food to digest
phasic pacemaker dominates - continual slow intrinsic electrical activity - basal electrical rhythm