digestion - lecture 2 Flashcards
what are target cells for excitatory and inhibitory enteric neurons
smooth muscle cell or secretory cell
describe ans modulation of ens
cns = parasym (excitatory - vagal nerve ach onto nicotinic receptors) and symp (inhibitory release noradrenaline)
sensory afferent fibers to cns = send info to cns to activate and ans = feedback on system
describe activation of ans
Sensory afferents –> parasym = medulla pregang and ans efferents have effect
sensory afferents –> sympa = spinal chord postgang - sympathetic chain of ganglia
efferent sends through vagal nerve
describe things that effect cns
afferent neurons with info from chemoreceptors, osomoreceptors and mechanoreceptors
sight, smell and taste of foods = activates directly salivation and also secretion in stomach
emotional state = if anxious = not induce saliva as usual
also cortical pathways
happens outside gut wall = efferent autonomic neuron’s synapse on enteric neurons
what doe ans modulation of ens allow for
integrated activity over longer distances along git
long extrinsic reflexes
ps = excites - can excite inhibitory neurons
s = inhibits - can inhibit inhibitory neurons
what is neural control of integration by
ens and ans
what are non git hormones
may influence growth and development of git
what are git hormones
may influence activities outside git
what do git hormones do
regulates activities inside git
describe hypothalamic feeding center - stimulates hunger
increase appetite
ghrelin released by glands in stomach during fasting
describe hypothalamic feeding center - induces satiety
decrease appetite
leptin released by fat cells with overeating
what is des
diffuse endocrine system
scattered among other cells in mucosa
largest most diverse endocrine system in body
name 5 most important gi hormones
gastrin
cck
secretin
gip
vip
name 3 modes of hormonal reg and describe briefly
autocrine = own cell
paracrine = on nearby cell
endocrine = through blood stream capillary and the effects target tissues
what type of hormones are git regulatory hormones
mostly peptides
describe how git hormones get to target cell
released from mucosa inton portal blood (hepatic portal vein) and goes to liver then to heart then to systemic circ and then to target tissues (tissues of gut)
do git hormone have only one target
nooooooooo
multiple targets = diff effects like inhibitory or excitatory
what do git hormones interact with
each other and with neurotransmitters
synergistically = potentiate each other so net effect larger then alone
antagonistically = inhibits
what does propulsion - flow - in git rely on
gradients of pressure deltaP
Variations in resistance 1/R
describe pressure - propulsion in git
muscles produce coordinated contractions of muscular elements in git wall = creates gradient of pressure
circular muscles activated in diff parts = segmentation
activate in each region = peristalsis
describe resistance - propulsion in git
normally little to no resistance
sphincters closed at rest
= prevents movement, high resistance but open at right time
stomach acid moves up lower esophageal sphincter = heart burn and damage
describe normal flow in git
aboral - away from mouth
meets little to no resistance
what are the phases of deglutition - swallowing
oral - voluntary
Pharyngeal
esophageal
gastric
Describe pharynx
conveys food from mouth to eso through process known as deglutition = swallowing
connected to nasal passages and to mouth and eso and trachea
describe esophagus
transports food into stomach
requires relaxation of 2 sphincters = ues and les
describe oral phase - mouth–> pharynx
voluntary control
can chew or spit out
lips closed and use tongue
bolus = food in mouth, one sticky mass
once choose to swallow = involuntary
describe oral phase - anterior mouth –> pharynx
push food up against hard palate
bolus moves to back of tongue and soft palate comes up and closes off nose
bolus moves to pharynx and epiglottis closes off trachea
describe cortical vs medullary centers
Cortical = voluntary, ability to initiate
deglutition center = involuntary reflexes driven by coordinate movements- as soon as make decision to swallow - in medulla
oral phase definition
transport of bolus (masticated insalivated mass of food) from anterior to posterior of mouth
define deglutition center
series of reflexes coordinated in deglutition center in medulla oblongata
name and describe 2 important aspects of oral phase
ability to initiate = voluntary –> cortex
coordinated movements = reflex involuntary –> medulla
describe pharyngeal phase - gen
stretch of pharyngeal receptors once food at back of throat
larynx moves close to glottis to protect airways
what is pharynx and describe
region where respiratory and digestive tracks cross
must be controlled by reflexes if not = food moves into airways and bacteria can lead to infections in lungs, ppl who have stroke have trouble swallowing
name and describe 4 important aspects of pharyngeal involuntary phase
1 - passages to nose, mouth and trachea blocked
2 - apnea = stop breathing to decrease chance you pull in air when you swallow
3 - ues relaxes
4 - pharynx muscles contract and push bolus into eso
must happen in correct order
describe path of air and food
respiratory tract for air going into trachea and git for bolus going to eso both tracts cross in pharynx
describe deglutition reflexes - gen
a series of protective reflexes
initiated by stimulation of afferent fibers in pharnyx
Organized in deglutition center
closing off nasal, oral and laryngeal cavities = prevents misdirection of bolus
respiration briefly inhibited
what is deglutition
swallowing of food
describe deglutition reflexes - specific
Pharyngeal receptors send afferents to cns –> deglutition center in medulla - send efferents to do =
protective reactions
Deglutition apnea
relax ues
contract pharyngeal constrictor muscles
describe upper esophageal sphincter - closure
impulses originate in cns
mediated by vagus nerve
releases ach (consTANTly) causing muscle contraction
striated muscle uper 1/3 eso and smooth muscle lower 2/3 eso
describe upper esophageal sphincter - during deglutition
relaxation = impulses stop and muscles relax no ach
cricopharyngeus = striated muscle = where ues is
describe pharyngeal phase - 4 aspects
involuntary
rapid = 1/5th of sec
stereotyped = reflex driven same sequence each time
temporospatial coordination = same sequence so wont choke, at right time and order
describe esophageal phase
gradient of pressure moves down eso
vagus somatic = synapses on striated muscle
vagus autonomic = synapses on ens then smooth muscle
body of eso = in thoracic cavity
recall neg pressure in thoracic cavity = -5mmhg - -10mmhg
sphincters must be closed all the time
describe whole of pharyngeal phase
bolus in pharnyx = reflexes cause it to move downwards
as moves down = presses on epiglottis and covers the glottis = secondary effect
reflexive contraction of vocal chords = larynx moves upwards and forwards to fit under base of tongue
glottis closes and protects lower airways = epiglottis and movement of larynx = deglutition reflex
ues relaxes and pharyngeal muscle contracts = push bolus across the released ues into eso
