GI Physiology Flashcards
Refers to movement of food from stomach to duodenum
Gastric emptying
Basic GI layers
Mucosa, Submucosa, Muscularis, Serosa
Function of the GI tract for secretion and absorption
Mucosa - Epithelium
Part of the mucosa innervated by the Meissner’s plexus
Muscularis mucosa - smooth muscle cells controlling the eptihelium
GI tract structure: composed of collagen, elastin, glands and blood vessels
Submucosa - composed of connective tissue
GI tract structure: composed of muscle layer
Muscularis
Muscle layer that causes decreases diameter of the lumen
Inner Circular Muscle layer
GI muscle layer: shortens segment of the GI tract
Outer Longitudinal Muscle layer
Muscle layer of the GI tract: refers to the actual peristalsis
Outer longitudinal muscle layer
Serosa layer of the GI tract is also known as?
Adventitia or mesothelium
GI plexus located between submucosal and inner circular muscle layer
Meissner’s plexus - also known as Submucosal plexus, for secretion, absorption and contraction of muscularis mucosae.
GI plexus between inner circular and outer longitudinal muscle layer.
Auerbach’s plexus - also known as Myenteric plexus. For motility
GI layer not seen in esophagus
Serosa
Strongest layer of the Esophagus
Submucosa
Muscle layer of the Stomach
Inner oblique, middle circular and outer longitudinal layer
Myenteric plexus is mainly excitatory except in what region?
Pyloric sphincter and ileocecal valve - relaxation
Extrinsic innervation of GI tract: excitatory of esophagus to upper large intestine
Vagus nerve
Excitatory extrinsic innervation of Gi tract from lower large intestine to Anus
Pelvic nerves
Refers to the alternate movement of inner circular and outer longitudinal muscle layers
Reciprocal innervation
Three main function of VIP: Vasointestinal peptide
- Relaxation of pyloric sphincter and ileocecal valves
- Receptive relaxation of LES
- Receptive relaxation of Stomach
GI hormone: stimulated by gastric distention causes increase gastric H+ secretion and stimulates growth of gastric mucosa
Gastrin
Main inhibitory of Gastrin
H+ and somatostatin
GI hormone: stimulated during fasting.
Motilin
From M cells, causes activation of migrating myoelectric complex or interdigestive myoelectric complex
Motilin
GI hormone: increases pancreatic and biliary HCO3- secretion. And decreases effect of gastrin on gastric mucosa
Secretin - from S cells
Protective hormone for the duodenum against the acid of the stomach
Secretin
GI hormone: main trigger of release is Glucose. Increases insulin secretion and inhibits gastric emptying
Glucose dependent insulinotropic peptide - from K cells
Different Incretin hormones
GIP from K cells
GLP from L cells
Glucagon
GI hormone: produced by I cells in respond to all foods (FA: main trigger)
Cholecystokinin - CCK
Function of CCK
Gallbladder relaxation
Sphincter of Oddi Relaxation
Increaes pancreatic enzyme and HCO3- secretion
Inhibits gastric emptying
Motilin has an action on GI tract except on what region?
Motilin act only on stomach and small intestine and not on Large intestine
Most potent stimuli for gastrin secretion
Protein - phenylalanine, tryptophan and methionine
Neurocrine from vagus nerve to G cells
GRP/ Bombesin
GI hormone: secreted in response to hypoglycemia thus resulting to glycogenolysis and gluconeogenesis
Enteroglucagon
Incretin hormone secreted by L cells of small intestines that stimulates insulin secretion
Glucagon like peptide 1 ( GLP-1)
GI hormone: that inhibits release of all GI hormones and gastric H+ secretion
Somatostatin
GI hormone: secreted by mast cells of gastric mucosa that increased H+ secretion, potentiates gastrin and Ach action
Histamine
GI hormone: that inhibits appetite, found at the ventromedial hypothalamus
Satiety center
Location of the Appetite/hunger center
Lateral hypothalamus - stimulates appetite
It sends signals to Satiety and Hunger Center
Arcuate nucleus pathway
It releases POMC to decrease appetite
Anorexigenic neurons
It releases Neuropeptide Y to increase appetite
Orexigenic neurons
It stimulates anorexigenic neurons and inhibits orexigenic neurons
Leptin (fat cells), insulin and GLP-1
It inhibits anorexigenic neurons
Ghrelin (gastric cells)
Inhibits Ghrelin
Peptide YY
It refers to constant level of contraction or tone without regular periods of relaxation
Tonic contractions - orad stomach, lower esophageal, ileocecal and internal anal sphincters
Tonic contractions are due to _ waves
Subthreshold slow waves - not true action potential but capable of irregular contractions
It refers to periodic contractions followed by relaxation for mixing and propulsion purposes.
Phasic contractions - in esophagus, gastric antrum and small intestines
Phasic contractions are due to?
Spike potentials - true action potentials
Refers to GI pacemaker
Interstitial cells of Cajal
Depolarization during slow wave is due to?
Sodium influx
With slowest frequency
Stomach - 3waves/min
Fastest frequency
Duodenum - 12 waves/min
Spike potentials are due to?
Calcium influx - threshold of -40mV
What is the most common stimulus for Gi peristalsis?
Distention
It refers to muscles upstream contract, muscles downstream exhibit receptive relaxation
Myenteric reflex
What is the Law of the Gut?
Myenteric reflex + anal direction of peristalsis
How long does it take to transfer material from pylorus to ileocecal valve?
3-5 hours
How long does it take to transfer material from ileocecal valve to colon?
8-15 hours
Swallowing center?
Medulla
Three phases of swallowing?
Oral phase
Pharyngeal phase
Esophageal phase
Phase of swallowing that prevents aspiration of food contents
Pharyngeal phase - soft palate pulled upward, glottis covered, upper esophageal sphincter relaxes
Peristalsis that creates high pressure behind bolus of food propelling it towards the stomach
Primary peristaltic contraction - accelerated by Gravity
Relxation of the lower esophageal sphincter is vagally-mediated using?
VIP or vasoinstestinal peptide
Peristalsis that clears the esophagus of remaining food?
Secondary Peristaltic Contraction
Three muscle layers of the stomach
Inner oblique layer
Middle circular layer
Outer longitudinal layer
Three anatomic division of the stomach
Fundus, body and antrum
Two functional division of the stomach
Orad stomach ( thin-walled) and Caudad stomach ( thick-walled)
Refers to food propelled back to stomach for further reduction in particle size and mixing with gastric juice
Retropulsion - due to inner oblique muscle layer
Propelling of food from stomach to duodenum
Gastric emptying - 3 hours
Gastric emptying is inhibited by what?
Fat ( due to CCK)
H+ in duodenum (due to direct neural reflex)
Refers to the back-forth movement with no net forward motion.
Segmentation contraction - mixes chyme with pancreatic enzymes
It propels chyme towards the large intestines
Peristaltic contraction - actual peristalsis
What is reciprocally innervated means?
When one is contracted, the other is relaxed, and vice-versa. Prevent opposing each other
Sac-like segments due to segmental contractions of the large intestines
Haustra
It function merely for water absorption, to dry up feces
Proximal colon - 1.5L of water
Function as storage for feces
Distal colon
Refers to movement of colonic contents over long distances (from transverse colon to sigmoid colon)
Mass movement - occur 1-3x a day
Maneuver against closed glottis that assist defecation
Valsalva maneuver
Odor of the stool is due to what bacterial products?
Mercaptan, indole, skatole and hydrogen sulfide
Refers to increase peristalsis in ileum and relaxation of the ileocecal sphincter due to presence of food in the stomach
Gastroileal reflex
Food in the stomach increases peristalsis in the colon and frequency of mass movements
Gastrocolic reflex - mediated by parasympathetic NS, CCK and Gastrin
Refers to a reverse wave peristalsis that begins from the small intestines
Vomiting - preceded by Nausea
Vomiting center
Medulla
Incomplete vomiting
Retching
Gland with serous secretion only
Parotid gland
Gland with mixed secretion of mucus and serous
Submandibular and sublingual glands
Innervation of parotid gland
Cranial nerve 9
Innervation for submandibular and sublingual glands?
CN 9
Effect of sympathetic NS on salivation
Decreases salivation
Effect of parasympathetic NS on salivation
Increases salivation
Initial saliva is high in?
Sodium and Chloride ions
Final saliva is high in?
Bicarbonate and potassium ions