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Intro to GI physiology
Terms in this set (41)
mouth, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine, and anus
what is the linear sequence of the GI tract?
salivary glands, pancreas, liver, and gallbladder
what are the secretory structures/organs of the GI tract?
epithelial cells, lamina propia, and muscularis mucosae
what does the mucosal layer of the GI tract contain?
collagen, elastin, glands, blood vessels
what does the submucosal layer of the GI tract contain?
circular (dense innervation) and longitudinal (scant innervation) muscle
what kind of muscle is found in the GI tract?
(lumen face) mucosa, submucosa, submucosal/meissner's plexus, circular muscle, myenteric plexus, longitudinal muscle, serosa (blood face)
what are the layers of the GI tract from lumenal face to blood face?
vagus nerve (CN 10; upper GI tract) and the pelvic nerve (lower GI tract)
what nerves are responsible for the parasympathetic innervation of the GI tract?
upper GI tract: upper third of esophageal striated muscle, stomach wall, small intestine, and ascending colon
what organs does the vagus nerve innervate in the GI tract?
lower GI tract; external anal canal striated muscle, and the walls of the transverse, descending, and sigmoid colons
what organs does the pelvic nerve innervate in the GI tract?
preganglionic fibers synapse on ganglia that are found within the myenteric and submucosal/meissner's plexuses of the walls of GI tract organs
where are the ganglia of the parasympathetic nervous system for the GI tract found?
the vagus nerve is mixed, it carries 75% afferent (sensory) fibers and 25% efferent (motor/reflex) fibers; vasovagal reflexes refer to vagal afferent information stimulating vagal efferent response
what do vasovagal reflexes refer to?
celiac, superior mesenteric, inferior mesenteric, and hypogastric sympathetic ganglia
what sympathetic ganglia serve the GI tract?
sympathetic postganglionic fibers synapse on the myenteric and submucosal/meissner's plexuses (vs parasympathetic ganglia in these structures)
in regards to sympathetic innervation, do pre or postganglionic nerve fibers synapse on GI tract organs?
parasympthetic and sympathetic innervation of the GI tract
what does the extrinsic portion of GI tract innervation refer to?
the enteric/intrinsic nervous system is found in the ganglia of the myenteric and submucosal/meissner's plexuses; it communicates directly with the parasympathetic and sympathetic nervous system; contains ~100,000,000 neurons
what is the enteric nervous system?
peptides released from endocrine cells; portal circulation -> liver -> systemic circulation -> target cell; gastrin, CCK, secretin, ghrelin, motilin, GLP-1, and GIP
what are 7 examples of GI hormones, and what is the route they must take to act on target cells?
gastrin is secreted by G cells of pylorus portion of the stomach; stimulates gastric H+ secretion and stimulates growth of gastric mucosa
what cells secrete gastrin, and what are its effects?
CCK is secreted by I cells of the duodenum and the jejunum; stimulates pancreatic enzymes and bicarb secretion
what cells secrete CCK, and what are its effects?
secretin is secreted by S cells of the duodenum; stimulates pancreatic bicarb secretion, inhibits gastric H+ secretion
what cells secrete secretin, and what are its effects?
glucose-dependent insulinotropic peptide (GIP) is secreted by the duodenum and jejunuml; stimulates insulin secretion from pancreatic β-cells before food is eaten, and inhibits gastric H+ secretion
what are the effects of glucose-dependent insulinotropic peptide (GIP)?
glucagon-like peptide-1 (GLP-1) is secreted by intestinal L cells; stimulates secretion of insulin before food is eaten
what are the effects of glucagon-like peptide-1 (GLP-1)?
albumin, alkaline phosphatase, ALT, and AST
in a standard metabolic panel, what are indicators of liver function?
indicators of liver function
albumin, alkaline phosphatase, ALT, and AST are all found in a standard metabolic panel. what organ do they give us information about?
BUN, calcium, chloride, bicarb, and creatinine
in a standard metabolic panel, what are indicators of renal function?
indicators of renal function
BUN, calcium, chloride, bicarb, and creatinine are all found in a standard metabolic panel. what organ do they give us information about?
HLA DQ2 and HLA DQ8 (alleles for celiac disease); anti-endomysial antibody, tTG antibody, and anti-gladian antibody
what are the standard markers used in a serology test for celiac disease?
crohn's disease; autoimmune attack of the GI tract; note the lack of normal upper GI tissue
diverticulitis; inflammation of pouches (diverticula) in the colon (primarily) or small intestine (occasionally); note the circled diverticuli
celiac disease; autoimmune disorder of the small intestine in reaction to gliadin (found in gluten); note the segmentation of the small intestine
the 2 GI effectors are: 1. epitheleal absorption and secretion; 2. motility via smooth muscle (able to handle higher preloads)
what are the 2 GI effectors in the minds of physiologists?
smooth muscle does not require troponin for contractions; Ca influx -> Ca binds calmodulin -> Ca/calmodulin stimulates MLCK -> MLCK phosphorylates myosin light chains -> myosin-phosphate forms cross bridges with actin leading to contraction; note the as long as Ca is present, muscle contraction will occur
what are the general steps in smooth muscle contraction?
The GI system demonstrates slow waves, or spontaneous oscillations in membrane potential beginning in the distal stomach; if the peak of a slow wave depolarizes past a threshold potential, then spike potentials will occur, leading to increased Ca entry and resulting in muscle contaction; local rate of slow wave generation determines the maximum rhythmic contraction frequency; NOTE: interstitial cells of cajal are responsible for slow wave propagation
how are GI smooth muscle contractions regulated using slow waves, spike potentials, and Ca?
the interstitial cells of cajal are responsible for slow wave propagation
what cells are responsible for propagation of slow waves?
the enteric nervous system is composed of the submucosal/meissner's and myenteric plexuses; the submucosal plexus controls absorption and secretion via acting on epithelial cells; the myenteric plexus controls motility via acting on longitudinal and circular muscle
what are the two divisions of the enteric nervous system, and what are they responsible for controlling?
paracrine factors exert their effects on cells in close proximity, while endocrine factors exert their effects on systems far away; seratonin, somatostatin, and histamine are examples of paracrine effectors
what is the difference between a paracrine and an endocrine factor?
serotonin (released in response to stomach distention, and acts to produce peristalsis; EC cell), histamine (stimulate secretion of gastric acid; EC-L cells), and somatostatin (inhibit acid secretion by the fundus and body of the stomach, and cause vasoconstriction; d cells) are all examples of paracrine factors in the GI tract
what are three examples of paracrine factors in the GI tract?
serotonin is a paracrine factor secreted by enterochromaffin (EC) cells in response to stomach distention and act on the myenteric plexuses of the enteric nervous system to stimulate peristalsis
what cells secrete serotonin, what is it secreted in response to, and what is its effect in the GI tract?
histamine is a paracrine factor secreted by gastric enterochromaffin-like (EC-L) cells, and acts to stimulate secretion of HCl from parietal cells in fundus and body of the stomach
what cells secrete histamine, what is its effect in the GI tract?
somatostatin is a paracrine factor secreted by d cells in the pancreas, and acts to inhibit secretion of HCl by the fundus and body of the stomach
what cells secrete somatostatin, what is its effect in the GI tract?
there are 4 phases of GI events: 1. interdigestive phase, occurs between meals; 2. cephalic phase, occurs when we see, smell, and taste food; 3. gastric phase, occurs as food moves down the stomach; 4. intestinal phase, occurs as food moves through the intestines; 3 and 4 overlap
what are the 4 phases of gastrointestinal response?
gastric secretion is stimulated during the cephalic and gastric phases, and is inhibited during the intestinal phase
during the gastrointestinal response, when is gastric secretion stimulated and when is it inhibited?
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