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Phgy 210 > Digestive system lecture 3 > Flashcards

Digestive system lecture 3 Flashcards

1
Q

What is the pressure of the stomach, where is it located?
What is the pressure of the body of the esophagus?

A

stomach is in abdominal cavity and has +5 pressure
-stomach has positive P, thus the contents will be sucked in
-it is -5mmhg (inthoracic is negative)

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2
Q

What are the esophageal forces?

A
  1. Gravity minor importance; small effect for liquids
  2. Peristalsis esophageal contents carried toward stomach
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3
Q

What is perisistalsis?
What happens each time we swallow?

A

-Peristalsis - a wave of contraction moving over the wall of the organ, narrowing the lumen and setting up a gradient of pressure favoring
aboral movement
-Each time we swallow, a single Primary Peristaltic Wave is generated

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4
Q

How long does it take for the wave to propagated?
What is primary peristalsis apart of?

A

-It takes 8-10 seconds to be propagated the length of the esophagus
-Primary peristalsis is part of the deglutition reflexes

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5
Q

What type of activation does the vagus somatic fibers do vs the vagus autonomic fibers?
What is latency?

A

-vagus somatic fibers activate the deglutition center sequentially (one after the other), proximal to distal activation (wave of activity in the striated muscle)
-the vagus autonomic fibers do synchronus activation, with increased latency of the activation in the esophagus
-latency=time between activation and response, time increases a bit after each one, allowing for smooth activation

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6
Q

How does the peristaltic wave move over the enitire esophagus?
What is the musculature of the proximal third vs the distal third of the esophagus?

A

-peristaltic wave moves over the entire
esophagus as a smoothly propagated contraction
-the musculature of the proximal third
of the esophagus is striated, while that of the distal third is smooth

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7
Q

How does peristalsis occur in the striated portion (proximal third of esophagus)

A

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

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8
Q

How does peristalsis occur in the smooth muscle portion (distal third of esophagus)
What is critical for the propgation?

A

-once some of the enteric neurons have been activated, they are capable of relaying and activating other enteric neurons (in an orderly
fashion), evoking and propagating muscular contraction in the
aboral direction, independently of the extrinsic nerves.
-the integrity of the enteric innervation is critical to the
propagation of the peristaltic wave in the distal esophagus

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9
Q

What happens if we cut the vagus nerve in peristalsis?

A

-if the cut is high up in the neck there is no primary peristalsis (no swallowing

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10
Q

What happens if we cut the vagus nerve transthoraically?
-What part allows propagation?

A

-primary peristalsis continues
-the vagal somatic fibers still wotk and more proximal part of the LES is active so we can still have propgation

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11
Q

In primary peristalsis what is the vagus nerve and the intact ENS for?

A

-Vagus Nerve - essential for initiating peristalsis in the proximal esophagus
Intact ENS - essential for continuing and propagating peristalsis in the distal esophagus

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12
Q

What is secondary peristalsis initiated by?
What are the 2 things that mediates is?

A

-nitiated by local distension
- mediated by enteric reflexes short, local reflexes
-or long reflexes Vagal Sensory Afferents to CNS which stimulates Efferent Vagal input = “VAGAL-VAGAL REFLEXES

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13
Q

How mnay secondary peristaltic waves can be generated?
What can further strengthen the response in deglutition center?

A

-Several secondary peristaltic waves may be generated, until the bolus has been displaced
-afferent (vagus) response

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14
Q

How long is the LES?
How much of the LES is above and below the diaphragm?
What is the pH above the diaphgram, and below?

A

-LES is the bottom 4 cm of the esophagus
-Half above (2cm above diphragm) and half below (2cm below diaphragm) the diaphragm
-above=pH 7
-below=pH 2

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15
Q

How does the vagus nerve affect the LES?
WHat is important about the LES

A

-it has excitatory inputs which leads to inhibtory neuron activation of NANC which relaxes the muscle
-Its ability to act as a sphincter is a property of the musculature. It has residual resistance in absence of ENS or Autonomic Innervation

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16
Q

What is the closure and the relaxation called in the LES?
What is LES relxation part of?

A

-closure is myogenic (contracted at rest)
-relaxation is neurogenic, Local ENS release of NANC (-) or vagal stimulation to activate inhibitory ENS neurons
-is part of the deglutition reflex

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17
Q

What do vagal somatic vs vagal autonomic fibers lead to?

A

-vagal somatic=skeletal muscle (upper esophagus)
-vagal autonomic= ENS lower esophagus, then to smooth muscle lower esophagus, then to LES relaxation

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18
Q

What is the LES?
-what happens in the absense of swallowing?
-What is the LES tone?

A

LES – bottom 4 cm of the esophagus, straddles the diaphragm
-In the absence of swallowing, the sphincter is in a state of
tone, and its walls are in firm apposition.
-LES tone is myogenic, but subject to neural and hormonal influences

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19
Q

What is the relaxation of the LES, what initiates and mediates it? What does this lead to release of
How do these actions affect muscle tone?

A

Relaxation of the LES is a reflex.
It is initiated during swallowing and mediated by vagal efferent fibers releasing ACh onto inhibitory enteric neurons which release NANC transmitters.
This causes decreased muscle tone

20
Q

What is the pressure in the thoracic cavity and the abominal cavity of the LES?
What happens when intrabdominal pressure increases?

A

-thoracic cavity is -5mmhg
-abominal cavity is +5mmhg
-Increases in intraabdominal pressure increase pressure equally on the stomach and the intraabdominal LES

21
Q

What happens when there is a 100mmhg increase in intrabdomial pressure in the LES?

A

-there is an equal increase in pressure in the abdominal cavity

22
Q

What happens when you have a hiatus hernia?

A

-the whole 4cm of the LES is above the diaphragm, which means the intraabdominal pressure no longer increases the LES pressure

23
Q

What are the 2 different segments of the LES, what pressure is each subject to?
what do these pressure vary with?

A

-the LES has an intrathoracic segment (subject to negative pressure) and an intraabdominal segment (subject to positive pressure)
-the pressures within these segments vary with phases of respiration

24
Q

WHat does the presence of the intraabdominal segment allow in the LES?

A

-allows the sphincter to maintain an effective barrier between the stomach and esophagus

25
Q

What happens when intraabdominal pressure is raised?
What does this cause to the pressure gradient?

A

-the pressure in the terminal segment of the LES and the intragastric compartment are raised equally,
-so that there is no effective change in the gradient of pressure between the
stomach and the esophagus

26
Q

What are the 2 LES characterisitics?

A

-Intrinsic Physiologic Sphincter (Myogenic) tonically contracted in the absence of swallowing
-Anti-reflux mechanism assisted by the presence of an Intraabdominal Segment

27
Q

What is an incompetent LES?
What is heartburn (pyrosis)

A

-Incompetent LES - Sphincter fails to close
-Heartburn” (Pyrosis): burning sensation, radiating upwards in the chest towards the neck, due to acid reflux into the esophagus

28
Q

What does progesterone do in the LES?
What does gastrin do?

A

progesterone lowers resistance in the LES
-it travels in the bloodstream and increases acid

29
Q

What are the 3 main functions of the stomach?

A

1.Temporary Storage: 1 – 2 L
2. Physical Disruption and Mixing of Contents:
Bolus → semi-liquid consistency = CHYME
3. Propulsion into Duodenum: Regulated Propulsion

30
Q

Why is propulsion in the duodenum slow?

A

-it is slow to allow food to absorb, and to not cause damage to the duodenum

31
Q

What are the main regions of the stomach?
What is the boundary between SI and stomach?
What is the proximal vs distal part of the stomach for?

A

fundus, body and antrum
-pyloric spincter
-proximal (upper portion) is thin walled to allow for increased storage capacity
-the distal (lower portion) is thick walled to allow for mixing and propulsion

32
Q

What is the stomach wall composed of?

A

-Composed of same four basic layers as the rest of the GI tract, with some modifications

33
Q

What does the gastric mucosa consist of and what types of cells does it contain, what are they arranged in?

A

-Gastric Mucosa: Consists of folds called rugae
-Contains many different cell types
-Arranged in pits and glands
-All epithelial in origin

34
Q

WHat does the muscularis externa contain?

A

-Contains an extra layer of smooth muscle
-Oblique muscle

35
Q

What is the volume of an empty stomach?
What happens during a meal, and what can the stomach volume increase to?

A

empty stomach volume is 50ml
-receptive relaxation occurs which is restricted to the proximal stomach
-the volume can increase to around 1500mL

36
Q

What is receptive relaxation?

A

-it is an increase in volume without signifcan tincrease in intraluminal pressure
-it is also one of the deglutition reflexes

37
Q

What receptor allows for receptive relxation?
WHat type of activation is occruing?

A

-the vagal efferents from the deglutition centre come and activate the sensory NANC neurons for further relaxation
-receptive relaxation

38
Q

What are the 4 things that occur when a meal arrives?

A

-ENS Sensory neurons sense distension
Send sensory Afferent to Deglutiiton Center
Vagal Efferents activate
ENS inhibitory neurons

39
Q

What happens if vagi to proximal stomach are cut (what is limited/increased)?

A

-If the vagi to the proximal stomach are cut, receptive relaxation is limited, resulting in great increase in intragastric pressure

40
Q

What are the 4 phases of deglutition?
What happens with the intake of a meal and deglutition center stimulation?

A

oral, pharyngeal, esophageal, and gastric
-you have a wave of activation and relaxation appropriate for carrying the bolus along the upper GIT and allowing it to be accommodated in the stomach

41
Q

What reflex is receptive relaxation due to?
What is it initiated by, and what does it result in an inhibition and increase of?

A

-largely to a vagally-mediated reflex, initiated by swallowing, and results in the inhibition of stomach muscle tone, and the consequent increase in intragastric pressure

42
Q

WHat is the transmitter released by the inhibitory enteric neurons activated by?
What does the local distension created by the entering meal activate?

A

-activated by the vagus is NANC
-created by the entering meal activates
local (enteric) and long (vago-vagal) reflexes which sustain receptive relaxation

43
Q

What are the first 4 activities in the upper GIT when a meal enters?

A
  1. generate pressure to tranport pharynx
    2.reflexes protecting airways
  2. relax UES
  3. contract pharyngeal constrictors
44
Q

What are the last 3 waves of activity in the upper GIT?

A
  1. primary peristalsis propagated along esophagus
    6.relax LES
  2. accomadate through gastric receptive relaxation
45
Q

What is the activity of proximal and distal stomach for?

A

-proximal is for storage
-distal is for physical disruption and regulated propulasion

Phgy 210 (24 decks)

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