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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
Motor neurons in enteric system
. Excitatory: ACh, neurokinins (substance P, substance K) | . Inhibitory: NO, VIP, ATP
26
NANC neurons
. 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
GI motor neurons innervate ____
. 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
Intestinofugal afferent neurons (IFANs)
. Cell body in the myenteric plexus w/ neural projections to prevertebral sympathetic ganglia . Modulate sympathetic efferent n. Activity to GI
29
Short neural reflexes
. 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
Long (CNS) neural reflexes
. 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
Vagal preganglionic neurons of excitatory GI pathway
. 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
Vagal preganglionic neurons of inhibitory pathway
. 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
“Off” depolarization when smooth muscle does not have intrinsic tone
. Force production will not change during hyperpolarization but it will increase during off depolarization . Referred to as “off contraction”
34
Off depolarization reaction is smooth m. Has intrinsic tone
. Force production will dec. during hyperpolarization (relaxation) then inc. during off depolarization
35
Gastrin and cholecystokinin (CCK)
. Second messenger mechanism is to inc. intracellular Ca
36
Secretin-like peptides
. Secretin, VIP, GIP, GLP-1 and 2 | . Second messenger mechanism is to stimulate cAMP synthesis
37
GI peptides that function as hormones
. 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
GI peptides that function as paracrines
. 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
GI peptides that function as neurocrines
. 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
Other hormones released from endocrine cells not located in the GI tract that can also have effects on GI functions
. Aldosterone . Thyroid hormone . Vitamin D

Physio (62 decks)

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