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Physiology 2 > 2. GI Part 7 > Flashcards

2. GI Part 7 Flashcards

1
Q

GI tract functions (5)

A
  1. secretion
  2. digestion
  3. absorption
  4. motility
  5. storage
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2
Q

what does the GI tract supply the body with (3)

A
  1. nutrients
  2. electrolytes
  3. water
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3
Q

how does the GI tract coordinate its functions (2)

A
  1. intrinsic control system

2. extrinsic control system

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4
Q

what is the intrinsic control system

A

located in wall of GI tract

enteric nervous system, GI hormones

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5
Q

what is the extrinsic control system

A

located outside the GI tract

vagus and splanchnic nerves, non-GI hormones

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6
Q

describe the enteric nervous system

A

a component of the autonomic nervous system

located within the GI wall

enables autonomic regulation of GI functions

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7
Q

describe plexus submucosa (Meissner)

A

located between submucosa and circular musculature

regulates mucus secretion and food absorption

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8
Q

describe plexus myenteric (Auerbach)

A

located in muscularis external, between longitudinal and circular musculature

control of the muscular activity (tone and contractions rhythm)

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9
Q

how are cells arranges in the enteric nervous system

how are cells connected

how do cells work together

A

cells are arranged in bundles of as many as 1000 parallel fibers (longitudinal or circular arrangement)

within each bundle, msucle fibers are electrically connected with one another through gap junctions

each bundle of smooth msucle fibers is partially separated from the next by loose connective tissue, but the bundles fuse with one another at many points and works as a syncytium

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10
Q

how are enteric neurons different from typical neurons

A

unlike typical neurons, enteric neurons secrete their neurotransmitter from varicosities or bulge like structures on often lengthy axonal collaterals or branches

the effect of an enteric neuron is spread to affect a wide area

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11
Q

what do sensory nerve cells do in ENS

A

detect changes and stimuli and regulate function

axons go to other enteric nerve cells and to the CNS

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12
Q

mechanosensitive cells (mechanoreceptors) in the ENS

A

recognize stretching of intestinal wall or volume changes (intraluminal pressure)

induce a response – gastric phase of gastric acid secretion

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13
Q

chemo sensitive cells (chemoreceptors) in the ENS

A

detect presence of nutrients in the GI lumen, changes in osmolarity, changes in pH

induce a response – sensibilization of enteroendocrine cells

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14
Q

interneurons in the ENS

A

process signals coming from other nerve cells or form the CNS and propagate them to other neurons

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15
Q

motor neurons of the ENS

A

induce a change in the GI tract in response to a stimulus

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16
Q

types of motor neurons in the ENS and their locations

A

muscle motor neurons – primarily located in myenteric plexus

secreto motor neurons – primarily located in submucosa plexus

vaso motor neurons – located in both plexuses

17
Q

what does NANC mean

A

non-adrenergic, non-cholinergic neurotransmitters secreted by enteric neurons

18
Q

examples of NANC (3)

A

nitric oxide – inhibitory substance that reduces motility of GI tract

VIP – inhibits gastric secretion and causes vasodilation and relaxation of smooth muscle sphincters

Substance P – excitatory substance, increases secretion and motility of the GI tract

19
Q

interaction of CNS and ENS – outer (extrinsic) innervation comprises (3)

A

parasympathetic fibers
sympathetic fibers
visceral afferent fibers

20
Q

ENS – parasympathetic neurotransmitter and what it does

A

uses Ach which stimulates many GI functions

21
Q

ENS – sympathetic neurotransmitter and what is does

A

uses noradrenaline which has an inhibitory effect on the GI tract

22
Q

neurons with origin in medulla oblongata through the vagus nerve go where

A 
oesophagus
stomach
small intestine
ascending colon
pancreas
gallbladder
liver
23
Q

neurons with origin in the sacral spinal cord through the pelvic nerve go where

A

descending colon

distal parts of the GI tract

24
Q

ENS parasympathetic postganglionic neurotransmitters

A

excitatory – acetylcholine

inhibitory – NANC substances, VIP, NO

25
Q

where do sympathetic nerve fibers of the ENS exit

A

thoracal and lumbar segments of the spinal cord

26
Q

length of sympathetic pre and post ganglionic axons of the ENS

A

preganglionic neurons have short axons

postganglionic neurons have long axons extending to target organs

27
Q

what is the sympathetic ganglion chain

A

on either side of the spinal cord, many sympathetic ganglia are arranged like a string

28
Q

what is the sympathetic postganglionic neurotransmitter

A

noradrenaline – inhibitory

29
Q

what are the 2 types of electrical waves and which one produces contractions

A

slow waves – don’t produce contractions

spikes – produce contractions

30
Q

describe slow waves

A

not action potentials

slow undulating changes in the resting membrane potential

frequency – 3-12 per minute (depending on location)

31
Q

where do slow waves originate

A

specialized smooth msucle cells – interstitial cells of Cajal (ICC)

32
Q

what as ICC considered to be

A

electrical pacemakers for smooth msucle cells

similar to Purkinje cells in the heart

33
Q

what do ICC form

A

networks with each other and are interposed between the smooth msucle cells

34
Q

what is the origin of the slow wave

A

ICC undergo cyclic changes in membrane potential due to unique ion channels that periodically open and produce currents

35
Q

what are spike potentials and when do they occur

A

true action potentials

occur automatically when the resting membrane potential of the GI smooth msucle becomes more positive than -40 mV

36
Q

when do slow waves induce an action potential

A

only when they reach smooth muscle cells that are (or were previously) sensitized

37
Q

when do spike potentials appear

A

each time the peaks of the slow waves become more positive than -40 mV

38
Q

what makes the frequency of the spike waves greater, how does this affect contractions

A

the higher the slow wave potential rises, the greater the frequency of the spike potentials and the higher the contractions

Physiology 2 (11 decks)

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