digestion - lecture 5

Question 1

describe enterogastric reflex

Answer 1

factors in duo also control rate of gastric emptying /antral peristalsis

Question 2

what is vomiting

Answer 2

emptying of the contents of upper git

Question 2

what does vomiting result from

Answer 2

increase in intraabdominal pressure due to action of diaphragm and abdominal pressures - git is mostly passive - not reverse peristalsis

Question 3

describe vomiting steps

Answer 3

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

Question 4

describe regulation of vomiting - afferent

Answer 4

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

Question 5

what precedes and accompanies vomiting

Answer 5

Imbalance between parasymp and symp
sweating, vasoconstriction, salivation, alternating bradychardia, tachycardia

Question 6

describe regulation of vomiting - efferent

Answer 6

widespread autonomic discharge
nausea
retching
emesis
need vomitting center to vomit

Question 7

what helps emesis

Answer 7

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

Question 8

where do afferent impulses to vomiting center come from

Answer 8

can arise from many places

Question 9

what is ctz

Answer 9

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

Question 10

name the 3 stages of vomiting

Answer 10

nausea
retching
emesis

Question 11

describe nausea - stages of vomiting

Answer 11

pyschic experience

Question 12

describe retching - stages of vomiting

Answer 12

abrupt
uncoordinated respiratory movements with glottis closed

Question 13

describe emesis - stages of vomiting

Answer 13

actual expulsion of contents of upper git

Question 14

what happens during emesis

Answer 14

person takes deep breath, glottis closes, abdominal muscles contract and exert pressure on gastric contents

Question 15

when is emesis completed

Answer 15

with the reversal of thoracic pressures from neg to pos
as diaphragm displaced upwards = forces eso contents to be expelled through the mouth

Question 16

describe small intestine - function

Answer 16

most digestion and ALL absorption of nutrients occur in si

Question 17

describe small intestine - regions

Answer 17

duodenum - mostly digest and absorb
jejunum
Ileum - some things can only be absorbed here

Question 18

what are functions of upper si

Answer 18

neutralization
osmotic equilibration
digestion
absorption

Question 19

describe neutralization

Answer 19

chyme from stomach is v acidic
must be rapidly neutralized
stomach mucosa protected from acid but si mucosa isnt

Question 20

describe osmotic equilibrium

Answer 20

chyme will be isotonic by time it leaves duodenum

Question 21

what are motor activities of si

Answer 21

effective mixing = bring stuff to absorptive cells
slow propulsion = 2-6 hrs needs times

Question 22

describe intestinal contractions - gen

Answer 22

governed by electrical characteristics of sm

Question 23

describe intestinal contractions - frequency

Answer 23

governed by ber

Question 24

describe intestinal contractions - spikes

Answer 24

phase locked to ber
initiated by stretch or ach

Question 25

describe intestinal contractions - amplitude of contraction

Answer 25

related to number of spikes/burst of era (spikes)

Question 26

describe intestinal ber - eca

Answer 26

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

Question 27

describe proximal vs distal stomach

Answer 27

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

Question 28

describe mechanism regulating intestinal mobility

Answer 28

ber generated by muscle fibers in si show aborally declining freq gradient - highest duo and lowest terminal illuem

Question 29

what is frequency gradient determined by

Answer 29

series of pacemaker regions along intestine - each with slightly lower freq than preceding one

Question 30

what does distribution of ber in time and space long intestine establish

Answer 30

distribution of spikes and contractions = thus the proximal portions of intestine show more activity than distal ones

Question 31

describe maximal contractile activity in si

Answer 31

cannot exceed ber freq of that gut segment

Question 32

what is most common type of contractile activity in si after meal

Answer 32

segmentation

Question 33

what is segmentation initiated by

Answer 33

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

Question 34

what is function of segmentation

Answer 34

mixing and propulsion

Question 35

describe slow propulsion of segmentation of si

Answer 35

more contraction and stronger proximally = slow net aboral propulsion of contents

Question 36

describe proximal and distal segmentation

Answer 36

prox = more and stronger contractions
dist = fewer and weaker contractions
net aboral movement

Question 37

describe peristalsis in small intestine

Answer 37

Infrequent and irregular
weak, shallow
travels for short distances only a few cm = not over whole length

Question 38

describe intestinal peristalsis

Answer 38

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

Question 39

describe the law of the intestine

Answer 39

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

Question 40

describe colon

Answer 40

ileocecal sphincter mostly closed 1500ml/d enters
cecum –> ascending colon –> transverse colon –> descending colon –> sigmoid colon
200ml/d = expelled from rectum, rest absorbed

Question 41

describe colon contractile activity

Answer 41

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

Question 42

describe functions of colon

Answer 42

mixing = promotes absorption of water and ions
propulsion = slow 50-60h for conversion of chyme to feces
Storage= stored while absorbing

Question 43

describe motor activity of colon

Answer 43

segmentation and peristalsis governed by irregular ber

Question 44

how and when does li empty contents

Answer 44

2-3 times a day
Corresponding to intake of new meal
increase activity in colon and distal si

Question 45

name reflexes after intake of meal

Answer 45

gastroileal
gastrocolic
ileocolic

Question 46

describe gastroileal reflex

Answer 46

activate gastric region of stomach = increase activity in ileum
opening of illeocecal sphincter

Question 47

describe gastrocolic reflex

Answer 47

as stomach has new meal = stretch and increase activity of sigmoid colon if enough pressure = activate defacation reflex

Question 48

describe ileocolic reflex

Answer 48

small
increase activity in ileum = increase activity at distal end of colon

Question 49

describe interdigestive period

Answer 49

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

Question 50

what happens if have diarrhea

Answer 50

peristalsis in si to move contents along