GIT Physiology Flashcards
For secretion, absorption & contraction of muscularis mucosae; Between submucosal and inner circular muscle layer
Submucosal Plexus/Meissner’s Plexus
For motility; Between inner circular & outer longitudinal muscle layers
Myenteric Plexus/Auerbach’s Plexus
Which layer is NOT seen in the esophagus?
Serosa
Strongest layer of the esophagus?
Submucosa
3 muscle layers are found in the stomach instead of two. What are theses muscle layers?
Inner obliqueMiddle circularOuter longitudinal
The myenteric plexus is mainly excitatory except for which regions?
Pyloric sphincter and Ileocecal valve
From G cells in the Antrum of Stomach; Increases Gastric H+ secretion
Gastrin
From S cells in the duodenum; Increases Pancreatic HCO3 secretions
Secretin
From I cells in the Duodenum & Jejunum; Stimulates GB contraction, sphincter of Oddi relaxation
Cholecystokinin (CCK)
From K cells in the Duodenum; Increases insulin secretion
Glucose-dependent Insulinotropic Peptide (GIP)
From M cells in the Duodenum & Jejunum; Stimulates in times of fasting
Motilin
Form of Gastrin is secreted in response to a meal
Little Gastrin (17 AA)
Form of Gastrin is secreted in the interdigestive period
Big Gastrin (34 AA)
Most potent stimuli for gastrin secretion
Phenylalanine, Tryptophan, Methionine
Neurocrine from vagus nerve to G cells
GRP/Bombesin
GI hormone classified as an Incretin
GIP, GLP-1
GI hormone responsible for interdigestive myoelectric complex
Motilin
Secreted by pancreas in response to CHO, CHON, lipids; Inhibits pancreatic HCO3 & enzymes
Pancreatic polypeptide
Secreted by intestinal cells in response to Hypoglycemia; Stimulates glycogenolysis and gluconeogenesis
Enteroglucagon
Secreted by cells throughout the GI tract in response to H; Inhibits release of ALL GI hormones, gastric H secretion
Somatostatin
Secreted by mast cells of gastric mucosa; Increases H secretion; potentiates gastrin and Ach action
Histamine
Inhibits appetite; Found on the Ventromedial Hypothalamus
Satiety Center
Stimulates appetite; Found at the Lateral Hypothalamic area
Appetite/Hunger Center
Sends signals to satiety & hunger center
Arcuate nucleus
Releases POMC to decrease appetite
Anorexigenic Neurons
Releases Neuropeptide Y to increase appetite
Orexigenic Neurons
Stimulates Anorexigenic Neurons, Inhibits Orexigenic Neurons
Lepton (Fat Cells), Insulin, GLP-1
Inhibits Anorexigenic Neurons
Ghrelin (Gastric Cells)
Inhibits Ghrelin
Peptide YY (PYY)
GI pacemaker
Interstitial Cells of Cajal
What is the most common stimulus for GI Peristalsis?
Distention
What is the Myenteric Reflex?
Muscles upstream contract, Muscles downstream exhibit Receptive Relaxation
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
Triggers reflex when food is at the pharynx
Oral Phase
Soft palate pulled upward (closes nasopharynx), glottis covered (prevents aspiration), Upper Esophageal sphincter (UES) relaxes
Pharyngeal Phase
UES closes, Primary and Secondary Esophageal Peristalsis occurs
Esophageal Phase
Creates high pressure behind bolus of food propelling it towards the stomach; Accelerated by gravity
Primary Peristaltic Contraction
Clears Esophagus of remaining food
Secondary Peristaltic Contraction
Capacity of Stomach
1.5L
Increases distensibility of orad stomach
CCK
Contraction of caudad stomach and pyloric sphincter
Retropulsion
Propelling food from stomach to duodenum
Gastric Emptying
Duration of Gastric Emptying
3 hours
Back-and-forth movement with no net forward motion; Mixes chyme with pancreatic enzymes
Segmentation Contraction
Propels chyme towards large intestines
Peristaltic Contraction
Saclike segments due to segmental contractions of the large intestines
Haustra
Colon: For absorption of water
Proximal Colon
Colon: For storage of Feces
Distal Colon
Food in the stomach increases peristalsis in the ileum and relaxation of the ileocecal sphincter
Gastroileal Reflex
Food in the stomach increases peristalsis in the colon and frequency of mass movements
Gastrocolic Reflex
Wave of reverse peristalsis that begins from the small intestines
Vomiting
Vomiting Center
Medulla
Incomplete vomiting; Closed UES
Retching
Daily volume of Saliva
1000ml
Daily volume of Gastric Secretion
1500ml
Daily volume of Pancreatic Secretion
1000ml
Daily volume of Bile
1000ml
Daily volume of S.I. Secretion
1800ml
Daily volume of Brunner’s Gland Secretion
200ml
Daily volume of L.I. Secretion
200ml
pH of Gastric Secretion
1.0-3.5
pH of Saliva
6.0-7.0
pH of Pancreatic Secretion
8.0-8.3
pH of Bile
7.8
pH of S.I. Secretion
7.5-8.0
pH of Brunner’s Gland Secretion
8.0-8.9
pH of L.I. Secretion
7.5-8.0
Serous secretion
Parotid Gland
Mixed secretions
Submandibular, Sublingual Gland
Effect of Parasympathetic NS and Sympathetic NS
Increases Salivation
Final saliva is High in
HCO3 & K
Final saliva is Low in
Na & Cl
At high flow rates, saliva has
High Na, Cl, & HCO3; Low K
At low flow rates, saliva is
Low Na, Cl, & HCO3; High K
Cells that create Initial saliva
Acinar Cells
Cells that modifies initial saliva
Ductal Cells
Hormone involved in ductal cells
Aldosterone
Contains Mucus Neck Cells, Parietal Cells and Chief Cells
Oxyntic Glands (Body)
Contains G Cells, Mucus Cells
Pyloric Glands (Antrum)
Secretes Mucus and HCO3
Mucus cells, Mucus Neck Cells
Secretes HCl and IF
Parietal/Oxyntic Cells
Secretes Gastrin
G cells
Secretes Serotonin
Enterochromaffin Cells
Secretes Histamine
ECL Cells (Enterochromaffin-like)
Secretes Pepsinogen
Chief/Peptic Cells
What are the 3 substances that stimulate HCl secretion?
Histamine acting on H2 receptorsAcH acting on M3 receptorsGastrin acting on CCK-B receptors
What are the inhibitors of HCl secretion?
Low pH (<3.0) of the stomachSomatostatinProstaglandins
Give examples of anti-muscarinic drug, H2-blocker, PPI?
Atropine, Cimetidine, Omeprazole
What substances protects the mucosa from HCl and Pepsin?
HCO3 and mucus
What are the protective factors against PUD?
ProstaglandinsMucosal Blood FlowGrowth Factors
What are the damaging factors?
H. Pylori, NSAIDs, stress, smoking, alcohol
Active component of Bile
Bile Acids
Emulsify fats, forms micelles for fat absorption, removes cholesterol from the body; Stored and concentrated in the Gallbladder; Release in “pulsatile spurts”
Bile
Chemical breakdown of ingested foods into absorbable molecules
Digestion
The movement of nutrients, water and electrolytes from the lumen of the intestine into the blood
Absorption
Digestion of Carbohydrates: Mouth
Ptyalin
Digestion of Carbohydrates: Stomach
None
Digestion of Carbohydrates: S.I.
Pancreatic amylaseBrush border enzymesDisaccharidases
How do you absorb Glucose and Galactose from lumen to intestinal cell?
SGLT-1
How do you absorb Fructose from lumen to intestinal cell?
GLUT-5
How do you absorb Glucose, Galactose, and Fructose from lumen to intestinal cell to the blood?
GLUT-2
Digestion of Proteins: Mouth
None
Digestion of Proteins: Stomach
Pepsin, Denaturation by HCl
Digestion of Proteins: S.I.
Enterokinases, Trypsin, Chymotrypsin, Carboxypeptidases, Peptidases
What is the optimum pH for pepsin activity?
pH 1.0-3.0Inactivated at pH>5.0
What is the optimum pH for pancreatic lipase activity?
pH 6.0
Is Pepsin essential for protein digestion?
No
Is Trypsin essential for protein digestion?
Yes
Digestion of Triglycerides: Mouth
Lingual Lipase
Digestion of Triglycerides: Stomach
Lingual lipase activated, Gastric lipase activated, mechanical pulverization of fat, CCK decreasing gastric emptying
Digestion of Triglycerides: S.I.
Emulsification by bile salts, Pancreatic lipase activated
Bile salts inactivates pancreatic lipase. What pancreatic coenzyme is secreted to prevent this from happening?
Procolipase to Colipase
What is the only product of triglyceride metabolism that is not hydrophobic?
Glycerol
What type of fatty acids go directly to the portal vein instead of the lacteals?
Short chain and medium chain fatty acids
What are the causes of steatorrhea?
Pancreatitis/Cystic FibrosisGastrinomaIleal resectionBacterial overgrowthTropical sprue/ Gluten- EnteropathyAbetalipoproteinemia
Main site for water absorption
Jejunum
Potassium is absorbed and secreted at the ff. sites respectively
Small intestines, Large intestines
Primary ion secreted in the intestinal lumen
Chloride (Na and H2O follows)
Needed to absorb Vit B12
Intrinsic Factor (IF)
Needed to absorb Calcium
1,25 (OH)2 Cholecalciferol
Needed to absorb Iron
Vitamin C
Part of the metabolism of these vitamins involved colonic flora
Vit K, Vit B1, Vit B2, Vit B12
Functional unit of the liver; Hexagonal in shape
Classic Liver Lobule
Liver Acinus Model: High O2 & Nutrients
Zone 1 (Periportal)
Liver Acinus Model: Low O2 & Nutrients
Zone 3 (Centrilobular)
Liver Acinus Model: Middle area
Zone 2 (Midzonal)