Regulation Of GI Function Flashcards
GI functions
. 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
Phasic contractions
Contract and relax in seconds
. Single unit smooth muscle
. Rhythmic contractions
Tonic contractions
. Sustained contractions lasting from minutes to hours
. Multi-unit smooth muscle
. Sphincters
The kind of smooth muscle contraction that occurs depends on ____
. Myogenic properties of the smooth muscle
. Does NOT depend in neural or hormonal input, that can only inc. or dec. intensity of contractions
Percentage of CO to splanchnic circulation
25%
Postprandial hyperemia
. 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
Mobilization of blood in GI
. 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
Regulation of GI by sympathetic nerves
. 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
Functional hyperemia
. 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
Parallel component of splanchnic circulation
. Composed of celiac, sup. And inf. Mesenteric aa.
. Allows for indecent regulation of blood flow to individual GI segments or accessory organs
Series component of splanchnic circulation
. 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
Characteristics of mucosal capillaries
. 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
Visceral smooth muscle (muscularis externa)
. Circular muscle: determine radial dimensions of tube (circumference)
. Longitudinal muscle: determine AP dimensions of tube (length)
Mucosa and submucosa of GI system
. 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
Enteric nerve plexuses (intramural plexuses)
. 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
GI sympathetic Postganglionic efferent nerves originate in _____
. Sup. Cervical ganglia
. Celiac ganglia
. Sup. And inf. Mesenteric ganglia
GI Postganglionic sympathetic nn. Terminate in/on ____
. 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
Parasympathetic efferent nerves originate in ___
. Brainstem nuclei: CN VII, XI, and X
. Sacral parasympathetic nucleus of spinal cord: pelvic n.
Parasympathetic efferent nn. Terminate in/on _____
. 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
Afferent fibers of GI system
. 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
Enteric neurons cell body location
Within the wall of the esophagus, stomach, SI, and LI and may project outside gut to peripheral ganglia or accessory organs
Enteric neurons originate in ___
. Myenteric plexus: control motility and secretions from accessory organs
. Submucosa plexus: control enterocytes secretion and absorption, endocrine cell secretion of some hormones and paracrines
Enteric neurons terminate in/on ___
. 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
Intrinsic primary afferent neurons (IPANS)
. Sensory neurons of ENS
. Chemosensitive: sense nutrient content in lumen (pH, osmolality, specific food components)
. Mechanosensitive: sense tension of smooth mm.