DSA: Intro To GI Physiology Flashcards
What are the 2 surfaces of the GI tract wall?
Mucosal Surface - Faces GI Lumen
Serosal Surface - Faces Blood
What are the layers of the GI tract wall from LUMEN to BLOOD?
Mucosal - Epithelial Cells - Lamina Propria - Muscularis Mucosae Submucosal Submucosal Plexus Circular Muscle Myenteric Plexus Longitudinal Muscle Serosal Layer
What are the functions of the 3 Mucosal Layer components?
Epithelial Cells - Absorb/Secrete
Lamina Propria - Connective tissue
Muscularis Mucosae - SMOOTH muscle cells that change shape/surface area of epithelial cell layer
Which 2 layers provide motility of the GI Tract? What are their defining characteristics?
- Circular Muscle - Thick layer and more densely innervated.
- Longitudinal Muscle - Thin layer and few nerve fibers.
Which 2 plexuses contain the nervous system of the GI Tract?
- Submucosal Plexus (Meissner)
Between Submucosal and Circ. M. - Myenteric Plexus
Between Circ. And Longitudinal M.
Which components make up the Muscularis Propria?
- Circular Muscle
- Myenteric Plexus
- Longitudinal M.
Which 2 nerves supply PARASYMPATHETIC innervation of the GI Tract?
Vagus N. (CN X) and Pelvic N.
Which areas are innervated by the Vagus N?
Upper GI
Striated Muscle - upper 1/3 esophagus Stomach Wall Small Intestine Ascending Colon Portion of Transverse Colon
Which areas are innervated by the Pelvic nerve?
Lower GI
Walls of Transverse, Sigmoid, and Descending Colon
Where are the PARASYMPATHETIC ganglia located in the GI Tract? SYMPATHETIC Ganglia?
Parasympathetic - IN WALLS of organs within Submucosal and Myenteric Plexuses
Sympathetic - OUTSIDE GI Tract Walls
What percent of the Vagus N. Is AFFERENT? EFFERENT?
Afferent - 75 Percent
Efferent - 25 Percent
Allows for Vagovagal Reflex
Which 4 SYMPATHETIC ganglia serve the GI Tract?
Celiac
Superior Mesenteric
Inferior Mesenteric
Hypogastric
What are the 2 components of the ENTERIC NS?
Submucosal Plexus
Myenteric Plexus
Can exert all functions WITHOUT CNS
Which 3 functions are controlled by the ENTERIC NS?
Contraction
Secretion
Endocrine
What is the path for HORMONE regulation in the GI Tract?
Endrocrine Cell —> Secrete Hormone —> Enter Portal Circ. —> Liver —> Systemic Circ. —> Target Cell
Which 4 GI peptides are classified as HORMONES?
Gastrin
Cholecystokinin (CCK)
Secretin
Glucose Dependent Insulinotropic Peptide (GIP)
What is the path for PARACRINE regulation in the GI Tract?
Endrocrine Cell —> Secrete Hormone —> Act on local target
Which GI peptide acts via a PARACRINE method?
Somatostatin
What is the path of NEUROCRINES within the GI Tract?
Neuron of GI Tract —> Action Pot. —> Release of neurocrine on target
Which substances act as NEUROCRINES within the GI Tract?
ACh NE VIP NO GRP Enkephalins Neuropeptide Y Substance P
What are the 2 forms of Gastrin? When are they secreted?
G17 (Little Gastrin) - Secreted in response to a MEAL.
G34 (Big Gastrin) - Secreted during INTERDIGESTIVE period.
Note: Only the C-terminal TETRAPEPTIDE is necessary for biological activity.
Which cells secrete Gastrin?
G Cells in antrum of the stomach
Which stimuli initiate Gastrin secretion?
- Products of protein digestion - small peptides and AA; especially phenylalanine and tryptophan
- Distention of stomach by food
- Vagal Stimulation - such as local vagal response with Gastrin Releasing Peptide (GRP)
Which 2 conditions INHIBIT Gastrin secretion?
- Low pH of gastric content
2. Somatostatin
What are 2 major actions of Gastrin?
- Stimulate increased H+ secretion
2. Stimulate growth of gastric mucosa
What is the cause of Zollinger-Ellison Syndrome? Signs/Symptoms? Treatment?
Cause: Gastrin secreting tumor usually in the non B-cell pancreas
Sign/Symptom: Increased H+ secretion by parietal cells; hypertrophy gastric mucosa; duodenal ulcers; acidification of intestinal lumen —> deactivated pancreatic lipase —> decreased fat digestion/increased fat excretion (steatorrhea)
Treat: H2 Blocker; Inhibitor of H+ Pump; Remove tumor
What are the 2 receptors for CCK? What is their sensitivity for CCK and Gastrin?
CCKa - ONLY CCK
CCKb - Equally CCK and Gastrin
Note: C-Terminal Heptapeptide necessary for CCK activity.
Which cells secrete CCK?
J Cells of the duodenal and jejunal mucosa
What are the 2 main stimuli for CCK secretion?
- Monoglycerides / FA (Not Triglyc.)
2. Small peptides / AA
What is the OVERALL function of CCK?
Ensure pancreatic enzymes & bile salts secreted to aid in digestion/absorption.
What are the 5 ACTIONS of CCK?
- Stimulate contraction of gallbladder & relax Sphincter of Oddi —> bile enters lumen —> emulsify/solubilize dietary lipids.
- INCREASE Pancreatic enzyme release
- Lipase, Amylase, Protease - INCREASE Pancreatic HCO3- secretion
- Potentiate effect of Secretin - Growth of exocrine pancreas and gallbladder
- Inhibition of gastric emptying
Which cells secrete Secretin?
S Cells of Duodenum
What stimulates secretion of Secretin?
H+ and Fatty Acid in lumen of Small Intestine
What are the 2 main functions of Secretin?
- INCREASE Pancreatic and Biliary HCO3-
2. DECREASE Gastric H+ secretion and inhibit trophic effects of Gastrin on gastric mucosa
Which HORMONE is the only one secreted in response to ALL 3 NUTRIENTS?
Glucose Dependent Insulinotropic Peptide (GIP)
Which cells secrete GIP?
K Cells of the Duodenal and Jejunal mucosa
What are the 3 stimuli for GIP secretion?
Fatty Acids
Amino Acids
ORAL Glucose
What are the 3 main actions of GIP?
- INCREASED Insulin secretion from pancreatic B-cells (Incretin Effect)
- DECREASED Gastric H+ Secretion
- DECREASED Gastric Emptying
What defines a Candidate GI Hormone?
Failure to meet one or more of the following criteria:
- Function independent of neural activity
- Isolated, purified, chemically identified and synthesized
- Secreted in response to physiological stimulus —> Carried in blood —> Produce physiologic action at site
What are the 4 candidate GI Hormones?
Motilin
Pancreatic Polypeptide
Enteroglucagon
Glucagon-like Peptide 1 (GLP-1)
Where is Motilin secreted? What is the function of Motilin?
Secretion: Upper duodenum during FASTING state
Function: INCREASE gastrointestinal motility; initiate interdigestive myoelectric complexes that occur at 90 min interval
What stimulates secretion and is the function of Pancreatic Polypeptide?
Stimulation: Secreted by Pancreas in response to ingestion of Carbs, Protein, and Lipids
Function: INHIBIT Pancreatic HCO3- secretion; Not fully understood.
What stimulates and is the function of GLP-1?
Stimulation: Synthesized/secreted by L Cells of Small Intestine
Function: Incretin - binds to pancreatic Beta cell receptors & stimulates insulin secretion; Inhibits glucagon secretion; inhibits appetite
Somatostation:
Secreted By?
Stimuli?
Function?
Secreted by D Cells (both endocrine/paracrine) of GI Mucosa; Hypothalamus; Delta Cells of Endocrine Pancreas
Stimuli: DECREASED luminal pH
Function: Inhibit secretion of GI hormones; Inhibit gastric H+ secretion
Histamine:
Secreted by?
Function?
Secreted by Enterochromaffin-like (ECL) cells in gastric glands
Function: Along with Gastrin and ACh, Histamine stimulates H+ secretion
Where are the centers located that control appetite & feeding behavior?
Hypothalamus
Satiety Center - Ventral Posterior Nucleus (VPN)
Feeding Center - Lateral Hypothalamic Area (LHA)
What are the 2 types of neurons within the Arcuate Nucleus that impact satiety and feeding centers?
- Anorexigenic Neurons
- Release pro-opiomelanocortin (POMC)
- Cause DECREASED appetite - Orexigenic Neurons
- Release Neuropeptide Y
- Cause INCREASED appetite
Which 5 substances affect satiety/feeding centers by influencing anorexigenic and orexigenic neurons?
Leptin, Insulin, GLP-1, Ghrelin, and Peptide YY (PYY)
What effect does Leptin have on satiety/feeding centers?
Stimulate Anorexigenic Neurons
Inhibit Orexigenic Neurons
DECREASE APPETITE (Long Term) - Secreted by fat cells in proportion to body fat.
What effect does Insulin have on satiety/feeding centers?
Stimulate Anorexigenic Neurons
Inhibit Orexigenic Neurons
DECREASE APPETITE - Short Term
What effect does GLP-1 have one satiety/feeding centers?
Synthesized/secreted by Intestinal L Cells
DECREASE APPETITE
What effect does Ghrelin have on feeding/satiety centers?
Secreted by Gastric Cells BEFORE meal ingestion.
Stimulate Orexigenic Neurons
Inhibit Anorexigenic Neurons
INCREASE APPETITE
What effect does Peptide YY (PYY) have on feeding/satiety centers?
Secreted by L Cells following meal
DECREASE APPETITE
- Directly act on hypothalamus
- Inhibit Ghrelin secretion
