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Physio > Regulation Of GI Function > Flashcards

Regulation Of GI Function Flashcards

1
Q

GI functions

A

. Provides body w/ water, electrolytes, and nutrients
. Secrete digestive and buffering juices
. Move food down the GI tract
. Digest food into components that can be absorbed into circulatory or lymph systems
. Circulate blood through GI organs to carry away absorbed nutrients

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2
Q

Phasic contractions

A

Contract and relax in seconds
. Single unit smooth muscle
. Rhythmic contractions

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3
Q

Tonic contractions

A

. Sustained contractions lasting from minutes to hours
. Multi-unit smooth muscle
. Sphincters

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4
Q

The kind of smooth muscle contraction that occurs depends on ____

A

. Myogenic properties of the smooth muscle

. Does NOT depend in neural or hormonal input, that can only inc. or dec. intensity of contractions

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5
Q

Percentage of CO to splanchnic circulation

A

25%

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6
Q

Postprandial hyperemia

A

. After eating, the GI tract receives an even greater volume of blood
. Due to vasodilation of mesenteric arterioles
. Local vasodilator substances are inc. as result of enhanced metabolic activity of cells

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7
Q

Mobilization of blood in GI

A

. Splanchnic circulation has the largest reservoir function of any vascular bed
. When blood is mobilized from all body regions, 70% comes from vascular reserves of splanchnic circulation

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8
Q

Regulation of GI by sympathetic nerves

A

. Postganglionic sympathetic nn. Directly innervate smooth m. Of splanchnic resistance arterioles
. Blood flow in splanchnic circulation is dec. by SNS but will slowly return to normal due to accumulation of metabolic vasodilators
. Call autoregulatory escape

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9
Q

Functional hyperemia

A

. There is no direct innervation of blood vessels by PNS
. Since PNS stimulation inc. GI motility and secretions, the resulting elevation in metabolism indirectly causes inc. in blood flow

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10
Q

Parallel component of splanchnic circulation

A

. Composed of celiac, sup. And inf. Mesenteric aa.

. Allows for indecent regulation of blood flow to individual GI segments or accessory organs

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11
Q

Series component of splanchnic circulation

A

. Composed of portal vein
. Venous drainage from GI abdominal organs empties into portal vein that goes to the liver
. Requires that all venous blood from gut is delivered to liver before entering the general systemic circulation

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12
Q

Characteristics of mucosal capillaries

A

. Higher capillary density in comparison to other organs
. Larger surface area for small intestinal nutrient absorption
. Efficient delivery of O2 to metabolically active cells
. Fenestrated capillaries in SI provide an enormous pore area for H2O and solute exchange
. Highly permeable to small solutes, but are impermeable to macromolecules

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13
Q

Visceral smooth muscle (muscularis externa)

A

. Circular muscle: determine radial dimensions of tube (circumference)
. Longitudinal muscle: determine AP dimensions of tube (length)

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14
Q

Mucosa and submucosa of GI system

A

. Enterocytes absorb and secrete electrolytes
. Cells replaced every 48-72 hrs
. Endocrine cells secrete hormone and/or paracrine
. Lamina propria: basement membrane for enterocytes/endocrine cels
. Muscularis mucosa: thin smooth mm. That affects mucosal folding
. Mucosal capillaries provide cells w/ O2 and take away absorbed nutrients and CO2
. Lymph vessels absorb some nutrients

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15
Q

Enteric nerve plexuses (intramural plexuses)

A

. Myenteric plexus (auerbach’s) nerve plexus that control motility of visceral smooth mm.
. Submucosa plexus (Meissner’s plexus: n. Plexus that controls secretionof some peptides by endocrine cells and secretion and absorption of electrolytes by enterocytes

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16
Q

GI sympathetic Postganglionic efferent nerves originate in _____

A

. Sup. Cervical ganglia
. Celiac ganglia
. Sup. And inf. Mesenteric ganglia

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17
Q

GI Postganglionic sympathetic nn. Terminate in/on ____

A

. Salivary glands: inc. salivary secretion
. Visceral smooth m. Sphincters: constriction
. Enteric neurons: inhibit neuronal activity
. Smooth m. Of splanchnic resistance arterioles: constriction
. Mucosa: inhibit secretions

18
Q

Parasympathetic efferent nerves originate in ___

A

. Brainstem nuclei: CN VII, XI, and X

. Sacral parasympathetic nucleus of spinal cord: pelvic n.

19
Q

Parasympathetic efferent nn. Terminate in/on _____

A

. Submandibular and otic ganglia that contain postganglionic nn. That innervate salivary glands to inc. salivary secretion
. Striated mm. Of pharynx, UES, and upper 1/3 esophageal body: swallowing reflex
. Postganglionic parasympathetic neurons innervating abdominal accessory organs: inc. secretion of digestive and buffering juices into intestinal lumen
. Enteric neurons: modulate neuronal activity (function as postganglionic parasympathetic neurons

20
Q

Afferent fibers of GI system

A

. Present w/in sympathetic and parasympathetic nn.
. N. Fibers project from GI back to brain, spinal cord, and/or vertebral ganglia
. Afferent sensory input from GI can alter efferent autonomic output tot he GI tract

21
Q

Enteric neurons cell body location

A

Within the wall of the esophagus, stomach, SI, and LI and may project outside gut to peripheral ganglia or accessory organs

22
Q

Enteric neurons originate in ___

A

. Myenteric plexus: control motility and secretions from accessory organs
. Submucosa plexus: control enterocytes secretion and absorption, endocrine cell secretion of some hormones and paracrines

23
Q

Enteric neurons terminate in/on ___

A

. Other enteric neurons
. Visceral smooth m. for contraction/relaxation
. Smooth m. Sphincters
. Enterocytes: secretion or absorption of electrolytes
. Endocrine cells (inc./dec. release of some hormone and. Paracrines
. Prevertebral sympathetic neurons: modulate sympathetic efferent n. Activity to GI

24
Q

Intrinsic primary afferent neurons (IPANS)

A

. Sensory neurons of ENS
. Chemosensitive: sense nutrient content in lumen (pH, osmolality, specific food components)
. Mechanosensitive: sense tension of smooth mm.

25
Q

Motor neurons in enteric system

A

. Excitatory: ACh, neurokinins (substance P, substance K)

. Inhibitory: NO, VIP, ATP

26
Q

NANC neurons

A

. No adrenergic, noncholinergic neurons that use NTs other than NE and ACh (neurokinins, NO, VIP, ATP)
. NANC neurons may be excitatory or inhibitory motor neurons

27
Q

GI motor neurons innervate ____

A

. Visceral smooth m.
. Smooth m. Sphincters
. Enterocytes and endocrine cells: secretion or absorption of electrolytes and modulation of release of hormones and/or paracrines

28
Q

Intestinofugal afferent neurons (IFANs)

A

. Cell body in the myenteric plexus w/ neural projections to prevertebral sympathetic ganglia
. Modulate sympathetic efferent n. Activity to GI

29
Q

Short neural reflexes

A

. Only neurons involved in this reflex are enteric neurons

. Short neural reflexes may be localized w/in segment or may coordinate the activity of adjacent segments

30
Q

Long (CNS) neural reflexes

A

. Neural reflex must involve extrinsic autonomic nn.
. Involve both afferent and efferent parasympathetic and/or sympathetic nn. And/or IFANs
. Override short neural reflexes to modulate GI function
. Produce rapid, coordinate activity among many segments and accessory organs of GI tract or btw segments that are not adjacent to each other

31
Q

Vagal preganglionic neurons of excitatory GI pathway

A

. Originate in rostral dorsal motor nucleus (DMN) and synapse on excitatory motor neurons in myenteric plexus
. When activated, ACh is released from myenteric neurons, smooth m. Is depolarized to threshold, and an AP occurs resulting in contraction of smooth m.

32
Q

Vagal preganglionic neurons of inhibitory pathway

A

. Originate in caudal DMN
. Synapse on NANC motor neurons in myenteric plexus
. Activation causes generation of NO in myenteric neurons resulting in immediate hyperpolarization of smooth m.
. Once activation ceases, there is an “off” depolarization of the smooth m.

33
Q

“Off” depolarization when smooth muscle does not have intrinsic tone

A

. Force production will not change during hyperpolarization but it will increase during off depolarization
. Referred to as “off contraction”

34
Q

Off depolarization reaction is smooth m. Has intrinsic tone

A

. Force production will dec. during hyperpolarization (relaxation) then inc. during off depolarization

35
Q

Gastrin and cholecystokinin (CCK)

A

. Second messenger mechanism is to inc. intracellular Ca

36
Q

Secretin-like peptides

A

. Secretin, VIP, GIP, GLP-1 and 2

. Second messenger mechanism is to stimulate cAMP synthesis

37
Q

GI peptides that function as hormones

A

. Gastrin, CCK, motilin, GLP-1, GIP
. Released from GI mucosal endocrine cells into portal circulation
. Reach measurable quantities in systemic circulation
. Global actions only limited by location of receptors
. May also have paracrine actions

38
Q

GI peptides that function as paracrines

A

. Somatostatin and histamine (not peptide)
. Released from GI mucosal endocrine cells to bind to receptors located on nearby cells
. Do not circulate in plasma
. Local action limited by its diffusion, reuptake, and degradation and by location of its receptors

39
Q

GI peptides that function as neurocrines

A

. Substance P, VIP, and gastrin-releasing peptide (GRP)
. Released from n. Terminals to bind to receptors located on nearby cells
. Do not circulate in plasma
. Local action limited by diffusion, reuptake, and degradation of neurocrine, and by location of its receptors

40
Q

Other hormones released from endocrine cells not located in the GI tract that can also have effects on GI functions

A

. Aldosterone
. Thyroid hormone
. Vitamin D

Physio (62 decks)

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