digestion - lecture 3 Flashcards
describe upper git pressures
pharynx = continuous with mouth at atm
ues = very positive
body of eso = intrathoracic - so neg -5mmhg, so if not closed then contents of stomach will be sucked into eso and air from mouth
les = positive but way less then ues
intragastric pressure = slight positive
name and describe
2 esophageal forces
gravity = minor importance- small effect for liquid
peristalsis = esophageal contents carried towards stomach = most of force
what is peristalsis
wave of contraction moving over wall of organ
narrows lumen
sets up gradient of pressure favoring aboral movement
describe peristalsis
each time we swallow = one single primary peristaltic wave generated
takes 8-10 seconds to be propagated length of eso
what is primary peristalsis part of
deglutition reflexes
describe deglutition center - somatic and autonomic
driven by diff inputs depending on if started or smooth muscle
sends vagus somatic (striated) and autonomic (smooth) fibers
both excitatory = activates ens - not directly on muscle then ens activates muscle
describe deglutition center - somatic
Sequential proximal to distal wave of activity of striated muscle
smooth wave
activated based on location first
describe deglutition center - autonomic
synchronous activation
increased latency of activation in distal eso
wave of activity in smooth muscle
each activates = slightly longer than others = gradient
what is latency
time between onset of stimulation and response
describe musculature of esophagus
proximal third of eso striated
distal third smooth
peristaltic wave moves over entire eso as smoothly propagated wave
describe musculature of esophagus - striated portion
peristalsis results from sequential firing of vagal motor neurons
activating progressively more distal regions of musculature
describe musculature of esophagus - smooth muscle portion
once some of enteric neurons have been activated = capable of relaying and activating other enteric neurons = orderly fashion
evokes and propagtes muscular contraction in aboral direction - independent of extrinsic nerves
integrity of enteric innervation critical to propagation of peristaltic wave in distal esophagus
what happens when cut vagal nerve - high up
high up in neck = no primary peristalsis
what happens when cut vagal nerve - lower down
cut transthoracically = primary peristalsis continues
since propagates through ens and leads to contraction of next spot too
need one autonomic fiber intact
distal eso has enteric circuitry needed for propagation of peristaltic wave
what regulates primary peristalsis
vagus nerve = essential for imitating peristalsis in proximal eso
intact ens = essential for continuing and propagating peristalsis in distal eso
vagal somatic = skeletal muscle of upper eso
vagal autonomic = ens of lower eso
wave of contraction
what happens when bolus gets stuck in eso
secondary peristalsis
describe secondary peristalsis
Initiated by local distension
mediated by enteric reflexes (short, local) or long reflexes
(vagal sensory afferents to cns = reinforce efferent vagal input = VAGAL-VAGAL reflexes)
activates ens
several secondary peristaltic waves must be generated until bolus displaced
describe les - anatomically
terminal 4 cm of eso = smooth muscle
thickening of muscle of sphincter (no visible enlargement of circular muscles) NOT SEEN IN LES
half above - 2cm and half below - 2cm diaphragm
describe les - ability and function
Anatomically insignificant = property of muscle itself
ability to act as sphincter is property of musculature
has residual resistance in absence of ens or autonomic innervation
functionally important
constant tone = no input from cns
describe les closure and relaxation
closure is myogenic = contracted at rest
relaxation is neurogenic = local ens release of NACN (-) or v agal stimulation to activate inhibitory ens neurons
comes from deglutition center = excitatory inputs (parasymp) activates inhibitory ens neurons
is les relaxation part of deglutition reflexes
YES YOU KNOW IT IS LOSER
describe les - definition
lowest 4 cm of eso
straddles diaphragm
in absence of swallowing sphincter in state of tone = walls in firm apposition
les tone is myogenic but can subject to neural and hormonal influences
describe relaxation of les - generally
Reflex
Initiated during swallowing
mediated by vagal efferent fibers releasing ach = activate inhibitory enteric neurons which release nanc transmitters = causes decreased muscle tone
describe normal les
2cm above diaphragm and 2 cm below
thoracic cavity = -5mmhg
abdominal cavity = +5mmhg
intragastric pressure of les = 20mmhg
Increases when bend over or pregnant
describe what happens if intraabdominal pressure increases
increases pressure equally on stomach and intraabdominal les
describe les if 100mmhg increase
pressure now = 120mmhg = preserves barrier
Thoracic = -5mmhg
abdominal = 105mmhg
describe hiatus hernia
if les displaced into thorax = intraabdominal pressure increases and does not increase les pressure
all pushed above = wont prevent flow of contents now
describe les - segments
intrathoracic segment - subject to neg pressure
intraabdominal segment - subject to positive pressure = allows sphincter to maintain effective barrier
pressures within these segments vary with phases of respiration
intraabdominal pressure raised = pressure in terminal segment of les and intragastric compartment raised equally
so that there is no effective change in gradient of pressure between stomach and eso
describe 2 characteristics of les
1 = intrinsic - property of thing itself - physiological sphincter = tonically contracted in absence of swallowing
2 = anti reflux mechanism assisted by presence of an intraabdominal segment
what happens of incompetent les
sphincter fails to close
what is pyrosis
heart burn
burning sensation
radiates upwards in chest towards neck
due to acid reflux into esophagus
eso cannot protect itsself from stomach acids
describe progesterone effect on les
lowers resistance in les
many women in last trimester = have heartburn
also increase pressure intraabdominal since have fetus in abdomen
describe gastrin effect on les
if increase = closes les
gastrin also increases acidity
does not effect at physiological levels of gastrin = have to be hella high
name and describe the 3 motor functions of stomach
1 - temporary storage = 1-2L of food/drink
2 - physical disruption and mixing of contents = bolus –> semi liquid consistency = chyme
3 - propulsion into duodenum= regulated propulsion = need to give time for si to absorb
describe stomach anatomically
parts = fundus, body, antrum, pylorus
proximal = storage, thin walled, relaxation of upper part to accommodate meal
distal = mixing and propulsion, thick walled, need strong muscle
describe stomach wall
same 4 basic layers as rest of git but some modifications
describe gastric mucosa
folds called rugae
many diff cell types = arranged in pits and glands, all epithelial in origin
describe musculares externa of stomach
contains extra layer of sm
= oblique muscle
grinding - movement of stomach
what is intragastric pressure
empty stomach has small vol = 50ml
pressure inside increases greatly if put much food in it
how does stomach accommodate the meal
receptive relaxation
increase in vol without significant increase in intraluminal pressure
restricted to proximal stomach
too high of pressure = contents move into si more rapidly
expands capacity
what is receptive relaxation
ens inhibitory neurons - local
Excitatory vagel efferents activate ens inhibitory neurons
leads to relaxation of musculature in proximal stomach
larger and less pressure
happens before meal arrives
is receptive relaxation a deglutition reflex
yes
describe vago vagal reflex in stomach
most of stretch happens when meal arrives
need more relaxation
vagal afferents sense distension and leads to vagal vagal feedback
Further activates inhibitory neurons
need before meal, ens, and vagal vagal to stretch stomach
what happens if vagi to proximal stomach cut
receptive relaxation limited = great increase in intragastric pressure
describe whole phases of deglutition - summary
reflexes controlled in deglutition center
oral–>pharnygeal–>esophageal–>gastric
with intake of meal and stimulation of deglutition center= have a wave of activation and relaxation that carries bolus along upper git and allows it to be accomodated in stomach
