digestion - lecture 5 Flashcards
describe enterogastric reflex
factors in duo also control rate of gastric emptying /antral peristalsis
what is vomiting
emptying of the contents of upper git
what does vomiting result from
increase in intraabdominal pressure due to action of diaphragm and abdominal pressures - git is mostly passive - not reverse peristalsis
describe vomiting steps
oral direction - to mouth
proximal stomach and above relax
upper duo and distal stomach contract
gradient of pressure due to concerted contraction of abdominal muscles = diagram lowers (decreases barrier of les) and abdominal muscles contract
intraabdominal pressure increases bc muscles contract and overcomes les resistance
describe regulation of vomiting - afferent
pharyngeal stimulation - gag reflex
git or urogenital distension - contents go too quickly to duo
pain, cardiac ischemia - childbirth
biochemical diseq
vestibular signals
psychogenic factors = site or smell of something
what precedes and accompanies vomiting
Imbalance between parasymp and symp
sweating, vasoconstriction, salivation, alternating bradychardia, tachycardia
describe regulation of vomiting - efferent
widespread autonomic discharge
nausea
retching
emesis
need vomitting center to vomit
what helps emesis
high resistance at distal end of stomach = relaxation of upper gi tract and spasm of plyoric antrum and duodenum
contraction of abdominal muscles and diaphragm
where do afferent impulses to vomiting center come from
can arise from many places
what is ctz
chemoreceptor trigger zone = in medulla, outside blood brain barrier
agents in bloodstream can act on this = toxins or emetic substances
distinct from vomiting center
sends signals to vomiting center
chemotherapy drugs activate ctz
name the 3 stages of vomiting
nausea
retching
emesis
describe nausea - stages of vomiting
pyschic experience
describe retching - stages of vomiting
abrupt
uncoordinated respiratory movements with glottis closed
describe emesis - stages of vomiting
actual expulsion of contents of upper git
what happens during emesis
person takes deep breath, glottis closes, abdominal muscles contract and exert pressure on gastric contents
when is emesis completed
with the reversal of thoracic pressures from neg to pos
as diaphragm displaced upwards = forces eso contents to be expelled through the mouth
describe small intestine - function
most digestion and ALL absorption of nutrients occur in si
describe small intestine - regions
duodenum - mostly digest and absorb
jejunum
Ileum - some things can only be absorbed here
what are functions of upper si
neutralization
osmotic equilibration
digestion
absorption
describe neutralization
chyme from stomach is v acidic
must be rapidly neutralized
stomach mucosa protected from acid but si mucosa isnt
describe osmotic equilibrium
chyme will be isotonic by time it leaves duodenum
what are motor activities of si
effective mixing = bring stuff to absorptive cells
slow propulsion = 2-6 hrs needs times
describe intestinal contractions - gen
governed by electrical characteristics of sm
describe intestinal contractions - frequency
governed by ber
describe intestinal contractions - spikes
phase locked to ber
initiated by stretch or ach
describe intestinal contractions - amplitude of contraction
related to number of spikes/burst of era (spikes)
describe intestinal ber - eca
intrinsic f of ber varies in diff cells of si = declines from prox to distal intestine
duo f = 12
jejunum f = 10
Ileum f = 8/min
pacemakers present along entire lenght of si, each group of pacemaker cells drives ~1000 cells
describe proximal vs distal stomach
f ber is greater
excitability of sm greater=easier to excite, need less ach
thickness of smooth muscle greater
both frequ and amplitude of muscle contractions greater in proximal si
describe mechanism regulating intestinal mobility
ber generated by muscle fibers in si show aborally declining freq gradient - highest duo and lowest terminal illuem
what is frequency gradient determined by
series of pacemaker regions along intestine - each with slightly lower freq than preceding one
what does distribution of ber in time and space long intestine establish
distribution of spikes and contractions = thus the proximal portions of intestine show more activity than distal ones
describe maximal contractile activity in si
cannot exceed ber freq of that gut segment
what is most common type of contractile activity in si after meal
segmentation
what is segmentation initiated by
Initiated by myogenic response to distension = response of circular muscle for effective mixing
ens organizes = coordinates and organizes contraction over length of si
ans and hormones modulate = parasymp increases and symp decreases
what is function of segmentation
mixing and propulsion
describe slow propulsion of segmentation of si
more contraction and stronger proximally = slow net aboral propulsion of contents
describe proximal and distal segmentation
prox = more and stronger contractions
dist = fewer and weaker contractions
net aboral movement
describe peristalsis in small intestine
Infrequent and irregular
weak, shallow
travels for short distances only a few cm = not over whole length
describe intestinal peristalsis
mediated by series of local reflexes
involves interaction of longitudinal and circular muscles = max f cannot exceed f of ber
integrity of ens needed
modulated by ans and hormones
describe the law of the intestine
radial stretch –> receptors –> neurally mediated =
ahead of bolus = contraction of longitudinal muscle and relaxation of circular muscle ahead of bolus - shorten the tube, low resistance
behind bolus = contraction of circular muscle and relaxation of longitudinal muscle behind bolus
describe colon
ileocecal sphincter mostly closed 1500ml/d enters
cecum –> ascending colon –> transverse colon –> descending colon –> sigmoid colon
200ml/d = expelled from rectum, rest absorbed
describe colon contractile activity
similar to si but slower, more sluggish and irregular
digestion and absorption of nutrients completed by SI
but some water and ions absorbed by COLON
describe functions of colon
mixing = promotes absorption of water and ions
propulsion = slow 50-60h for conversion of chyme to feces
Storage= stored while absorbing
describe motor activity of colon
segmentation and peristalsis governed by irregular ber
how and when does li empty contents
2-3 times a day
Corresponding to intake of new meal
increase activity in colon and distal si
name reflexes after intake of meal
gastroileal
gastrocolic
ileocolic
describe gastroileal reflex
activate gastric region of stomach = increase activity in ileum
opening of illeocecal sphincter
describe gastrocolic reflex
as stomach has new meal = stretch and increase activity of sigmoid colon if enough pressure = activate defacation reflex
describe ileocolic reflex
small
increase activity in ileum = increase activity at distal end of colon
describe interdigestive period
gi motility organized into intense pattern of cyclic myoelectric motor activity
reccuring at regular intervals = 90 mins
moving sequentially over distal stomach and si up to distal ileum = 2-10cm/min
MMC = migrating myoelectric (motor) complex
what happens if have diarrhea
peristalsis in si to move contents along
