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RUSVM Physiology 2 > Gastrointestinal Physiology 11-14 > Flashcards

Gastrointestinal Physiology 11-14 Flashcards

1
Q

Characteristics of smooth muscle cells in the GI tract

A
  • function as a synctitium
  • cells are arranged in bundles of fibers
  • muscle fibers are electrically connected to eachother by gap junctions
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2
Q

Components of extrinsic and intrinsic control systems that regulate GI tract functions

A
  • systems located in the wall of the GI tract (intrinsic systems)
    • nerves- enteric nervous system
    • endocrine secretions- secretin, gastrin, CCK, GIP, and motilin
  • systems located outside the wall of the GI tract (extrinsic systems)
    • nerves- vagus and splanchnic nerves
    • endocrine secretions- aldosterone
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3
Q

Functions of the enteric nervous system (ENS)

A

a component of the autonomic nervous system, located within the GI wall–> autonomic regulation of GI elementary functions

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4
Q

Plexus Myentericus

A

in the muscularis externa, between longitudinal and circular muscle–> control of the muscular activity, muscle tone and contraction rhythm

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5
Q

Plexus submucosus

A

between submucosa and circular muscle–> mucus secretion and reabsorption

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6
Q

enteric neurons

A

secrete their neurotransmitter from varicosities or bulge-like structures located on often lengthy axonal collaterals or branches. the effect of an enteric neuron is spread to affect a wide area

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7
Q

dogiel type 1 enteric neuron

A

small cell body with short dendrites. motor neurons

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8
Q

dogiel type 2 enteric neuron

A

large cell bodies with one or 2 long dendrites. sensory neurons

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9
Q

dogiel type 3 enteric neuron

A

multiple shapes and functions

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10
Q

sensory nerve cells

A

detect changes or stimulus and regulates function

axons go to other enteric nerve cells and to the CNS

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11
Q

mechanoreceptors

A

recognize stretching of intestinal wall or volume changes by intraluminal pressure

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12
Q

chemoreceptors

A

detect nutrients, osmolarity, pH

neurites–> decodification of the stimulus–> sensibilization of the endocrine cell

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13
Q

interneuron

A

process signals coming from other nerve cells or from the CNS

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14
Q

muscle motor neurons

A

primarily located in the plexus myentericus

stimulatory: Ach–> M3–> increase motility
inhibitory: NO, ATP, VIP, NANC

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15
Q

secretomotor neurons

A

primarily located in the plexus submucosus

stimulatory: Ach, Substance P and VIP–> increase secretion
inhibitory: SOMA and NPY

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16
Q

vasomotor neurons

A

in both plexuses

ach and VIP–> increase vasodilation

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17
Q

under physiological conditions, is the GI tract under inhibition or stimulation?

A

inhibition

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18
Q

GI motility disorders

A

hypoganglionosis

hirschsprung’s disease (congenital megacolon)

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19
Q

ATP

A

non-peptide, in postganglionic sympathetic neurons, function is to contract muscle cells

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20
Q

NO

A

non-peptide, in gastric nerves, function is to reduce motility

21
Q

vasoactive intestinal polypeptde

A

peptide, in parasympathetic ganglia, function is vasodilation, relaxation of smooth muscle and sphincters

22
Q

substance P

A

peptide, in sympathetic ganglia, function is to increase secretion and motility

23
Q

neuropeptide Y

A

peptide, in postganglionic sympathetic neurons, function is to inhibit secretion

24
Q

slow wave

A

rhythm of GI contraction frequency controlled by these slow waves of smooth muscle membrane potential
not action potentials, slow, undulating changes in the resting membrane potential
origin not completely understood, may come from interstitial cells of Cajal

25
Q

spike potentials

A

true action potentials
occur automatically when the resting membrane potential of the GI smooth muscle becomes more positive than about 40mV
the higher the slow wave potential rises, the greater the frequency of the spike potentials

26
Q

three types of GI reflexes essential to GI control

A
  1. reflexes integrated entirely within the gut wall enteric nervous system–> control GI secretion, peristalsis, mixing contractions, local inhibitory effects
  2. reflexes form the gut to the prevertebral sympathetic ganglia and then back to the GI tract–> transmit signals long distances to other areas of the GI tract
    - —gastrocolic reflex: signal form the stomach that causes evacuation of the colon
    - —enterogastric reflex: signal from the colon and small intestine to inhibit stomach motility and secretion
    - —colonoileal reflex: signal from the colon to inhibit emptying of ileal contents into the colon
  3. reflexes from the gut to the spinal cord or brain stem and then back to the GI tract
    - —reflexes from the stomach and duodenum to the brain stem and back to the stomach to control gastric motor and secretory activity
    - —pain reflexes that cause general inhibition of the entire GI tract
    - —defecation reflexes that travel from the colon and rectum to the spinal cord and back again to produce the colonic, rectal, and abdominal contractions required for defecation
27
Q

peristaltic reflex

A

stretching of the intestinal wall during the passage of a bolus triggers a reflex that constricts the lumen behind the bolus and dilated the lumen ahead of it–> coordination of longitudinal and circular musculature–> propulsive movement of the GI content

a property of many syncytial smooth muscle cells

proximal to the site of distention: excitatory motor neurons are stimulated–> Ach and Sp–> smooth muscle contraction

distal to the site of distention: inhibitory motor neurons are stimulated–> NO, ATP, VIP–> smooth muscle relaxation

28
Q

vagovagal reflex

A

afferent and efferent fibers of the vagus nerve coordinate responses to gut stimuli via the dorsal vagal complex in the brain

stimulation of mechanical receptors located in the gastric mucosa stimulates vagus afferents

controls contraction of the GI muscle layers in response to distention of the tract by the chymus

active during the receptive relaxation of the stomach in response to swallowing food

when food enters the stomach, this reflex goes from the stomach to the brain, then back again to the stomach causing active relaxation of the smooth muscle in the stomach wall

29
Q

motility of the stomach

A
  1. the gastric store- tonic relaxation and tonic contraction
  2. the gastric pump- strong peristaltic wave in the antrum
  3. passage into the grinder and then into the pylorus
  4. emptying of fluid and pre-digested particles into the duodenum

increased pressure after stomach filling induces a reflectory relaxation of the stomach

  1. receptive relaxation– vagovagal reflexes
  2. adaptive relaxation– gastro-gastric reflexes
  3. feedback relaxation
30
Q

intestinal motility functions

A
  • mixing of food with digestive juices
  • enhancing contact between intestinal wall and food
  • peristalsis, the propulsive movement of the chymus distally
31
Q

digestive period of intestinal motiility

A

propulsive pattern: peristaltic wave–> fast aboral migrating contractions
nonpropulsive pattern: segmentation–> localized contractions of circular muscle, small segments of the intestine contract tightly, dividing the gut into 2 segments of constricted and dilated lumen

32
Q

interdigestive period of intestinal motility

A

time in which stomach and small intestine are empty
between meals–> migrating motoric complex, typically lasts 80-120 minutes
phase 1: motoric rest, no contractions
phase 2: intermittent and irregular contractions, sometimes isolated stronger ones
phase 3: strong peristaltic contractions starting from the stomach and migrating distally to reach the colon

33
Q

migrating motoric complex

A

helps push indigested material out of the intestine

control of the bacterial population

34
Q

motility of the large intestine

A

mixing activity is prominent
in horses and pigs, colonic segmentation is more pronounced and results in the formation of sacculations or haustra
antiperistaltic waves: oral migrating contractions that impeded the movement of ingesta, causing a more intense mixing activity

35
Q

pathologic contractions

A

giant contractions with high amplitude and long lasting contraction
oral migrating: vomitting
aboral migrating: diarrhea

36
Q

vomitting

A

defense mechanism and important clinical sign activated in order to eliminate GI content

complex reflex involving many striated muscle groups and other structures outside the GI tract

coordinated in the brainstem

37
Q

vomiting stimuli

A

before food intake

after food intake–> visceral afferents to vomiting center

after absorption–> stimulate chemoreceptor trigger zone in the area postrema

38
Q

vomiting sequence of events

A

antiperistaltic wave originates in duodenum

propulsion of ingesta toward stomach

contraction of abdominal musculature increasing intra-abdominal pressure

expansion of chest cavity while glottis remains closed in order to lower intrathoracic pressure

relaxation of lower esophageal sphincter

opening of upper esophageal sphincter

39
Q

Concerning GI smooth muscle cells, which one is true?

A. their contraction cannot be extrinsically influenced

B. spike potentials do not conduce to a contraction

C. they show spontaneous undulations in the membrane potential

A

C

40
Q

Which kinds of sensory neurons will be stimulated during the peristaltic reflex?

A. chemosensitive neurons

B. mechanosensitive neurons

A

B

41
Q

Inhibitory muscle motor neurons use:

A. acetylcholine
B. substance P
C. NO, ATP, VIP

A

C

42
Q

The proximal stomach serves a storage function in retaining food

A. True
B. False

A

A

43
Q

Vomiting contains only ingesta of gastric origin

A. True
B. False

A

B

44
Q

Diarrhea

A

increase in frequency of defecation or fecal volume

volume increase is often due to increased water content

water in the gut results from ingested water, water secreted by glands of the GI tract, or water secreted or lost directly through mucosal epithelium

diarrhea occurs when there is a mismatch between secretion and absorption

45
Q

malabsorptive diarrhea

A

absorption is inadequate to recover all secreted water

viral, bacterial, protozoan infections

destruction of the villi and reduced length

shortened villi cause a loss of absorptive intestinal surface area

more affected are mature enterocytes that possess the enzymes of the brush border and transport proteins

46
Q

secretory diarrhea

A

rate of intestinal secretion increases and overwhelms the absorptive capacity

some pathogenic bacteria produce enterotoxins which bind to enterocytes and stimulate the adenylyl cyclase activity and the production of cAMP–> opening of chloride channels, water and other electrolytes follow

47
Q

defectation

A

internal and external anal sphincters

internal is normally tonically contracted–> anal continence

internal is parasympathetically innervated by the sacral spinal segment and sympathetically innervated by the lumbar segment

in most species: sympathetic stimulation–> constriction of the sphincter; parasympathetic stimulation–> relaxation

voluntary constriction of the external anal sphincter will block the reflector activation of defecation

48
Q

retrosphincteric reflex

A

feces accumulates in the rectum

peristaltic movement of feces into the rectum and relaxation of internal sphincter

urge to defecate

RUSVM Physiology 2 (3 decks)

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