digestion - lecture 3 Flashcards by Misha Gandhi

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

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name and describe
2 esophageal forces

gravity = minor importance- small effect for liquid
peristalsis = esophageal contents carried towards stomach = most of force

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what is peristalsis

wave of contraction moving over wall of organ
narrows lumen
sets up gradient of pressure favoring aboral movement

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describe peristalsis

each time we swallow = one single primary peristaltic wave generated
takes 8-10 seconds to be propagated length of eso

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what is primary peristalsis part of

deglutition reflexes

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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

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describe deglutition center - somatic

Sequential proximal to distal wave of activity of striated muscle
smooth wave
activated based on location first

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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

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what is latency

time between onset of stimulation and response

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describe musculature of esophagus

proximal third of eso striated
distal third smooth
peristaltic wave moves over entire eso as smoothly propagated wave

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describe musculature of esophagus - striated portion

peristalsis results from sequential firing of vagal motor neurons
activating progressively more distal regions of musculature

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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

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what happens when cut vagal nerve - high up

high up in neck = no primary peristalsis

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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

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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

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what happens when bolus gets stuck in eso

secondary peristalsis

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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

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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

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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