GI OSU physio 3200 online

Digestion

The process of dissolving and breaking down food into small molecules

Secretion

The release of substances into the GI tract from the liver and exocrine glands

Absorption

The movement of digested products along with water and vitamins from the lumen across a layer of epithelial cells into the blood or lymph

Motility

Contractions of smooth muscle in the GI tract wall that mix and move the luminal contents from the mouth to the anus

Lumen

The inner open space or cavity of a tubular organ where food passes and digestion occurs

Mucosa

The innermost layer of the GI wall facing the lumen composed of the surface epithelium and lamina propria and muscularis mucosa

Lamina Propria

A layer of connective tissue through which small blood vessels and lymphatic vessels and nerve fibers pass

Muscularis Mucosa

A thin layer of smooth muscle within the mucosa that may be involved in the structural movement of intestinal villi

Submucos

The second connective tissue layer containing major blood and lymph vessels whose branches penetrate into surrounding layers

Submucosal Nerve Plexus

A network of neurons in the submucosa that projects to the myenteric plexus and to the luminal surface epithelia to influence secretory activity

Muscularis Externa

The main muscular layer consisting of inner circular muscle and outer longitudinal muscle that contracts to provide forces for mixing and moving GI contents

Myenteric Nerve Plexus

A neuron network situated between the circular and longitudinal muscle layers that influences smooth muscle motility and interfaces with the autonomic system

Serosa

The outermost thin layer of connective tissue connected by thin sheets to the abdominal cavity to support the GI tract

Circular Fold

Large macroscopic folds of the mucosa and submucosa layers within the small intestine that increase surface area

Villus

Fingerlike projections covering the circular folds of the small intestine underlying nutrient absorption

Microvillus

Tiny membrane projections on the surface of individual luminal epithelial cells collectively forming the brush border

Lacteal

A blind ended lymphatic vessel found in the center of each intestinal villus responsible for absorbing dietary fats

Goblet Cells

Specialized epithelial cells interspersed between other cells that secrete mucus to lubricate the small intestine

Chyme

A saclike organ byproduct consisting of a slushy mixture of protein or carbohydrate fragments along with fat droplets and water and salts produced by stomach breakdown

Salivary Amylase

An enzyme that digests complex carbohydrates into maltose and shorter glucose chains

Pancreatic Amylase

An enzyme secreted by the pancreas that continues carbohydrate breakdown in the small intestine

GLUT

A glucose transporter on epithelial cell membranes responsible for the facilitated diffusion of fructose

SGLT

A sodium glucose cotransporter responsible for the secondary active transport of glucose and galactose coupled to sodium ions

Fiber

Complex polysaccharides like cellulose found in vegetable matter that escape small intestine enzyme digestion and pass to the large intestine for bacterial metabolism

Ferritin

An intracellular protein iron complex that functions as the primary cellular storage pool for iron inside intestinal epithelial cells

Pancreatic Lipase

A water soluble enzyme that breaks down water insoluble triglycerides into monoglycerides and two free fatty acids

Emulsification Droplets

Large fat globules mechanically disrupted by motility into tiny droplets stabilized by bile salts and phospholipids

Micelles

Small temporary aggregates of bile salts and fatty acids and monoglycerides in equilibrium with free lipid molecules keeping them in solution prior to diffusion

Chylomicrons

Resynthesized triglyceride fat droplets coated with amphipathic proteins that pinch off from the epithelial ER or Golgi and enter villi lacteals via exocytosis

Intrinsic Factor

A specialized binding protein secreted by gastric parietal cells that complexes with Vitamin B12 to allow endocytosis in the ileum

Enteric Nervous System

The local independent autonomic nervous system embedded directly within the GI tract walls composed of the myenteric and submucosal plexuses

Short Reflexes

Neural pathways traveling strictly from local luminal receptors through the enteric nerve plexuses directly to effector smooth muscle or glands

Long Reflexes

Neural pathways traveling from GI tract receptors up to the central nervous system via afferent nerves and back to effectors via autonomic fibers

Gastrin

A hormone produced by endocrine cells in the stomach antrum stimulated by amino acids or peptides and parasympathetic tone to trigger gastric acid secretion and stomach motility

Cholecystokinin (CCK)

A hormone produced by small intestine endocrine cells in response to fatty and amino acids that coordinates gallbladder contraction and pancreatic enzyme secretion and sphincter of Oddi relaxation

Secretin

A hormone produced by small intestine endocrine cells triggered by luminal acidity that acts as the primary stimulant for pancreatic and hepatic bicarbonate secretion

Glucose-dependent Insulinotropic Peptide (GIP)

A small intestine hormone triggered by glucose and fat that stimulates the endocrine pancreas to release insulin

Somatostatin

A paracrine peptide secreted by gastric D cells that downregulates acid production by directly inhibiting parietal cells and gastrin cells and histamine release

Cephalic Phase

GI reflex responses initiated by receptors located in the head stimulated by the sight or smell or taste or chewing of food or emotional states

Gastric Phase

GI responses initiated by stimuli within the stomach including luminal distension and high acidity and the presence of amino acids or peptides

Intestinal Phase

GI responses initiated by stimuli within the intestinal tract including lumen distension and acidity and osmolarity and digestive fragments

Parietal Cells

Cells lining gastric glands that produce hydrochloric acid and intrinsic factor featuring invaginated luminal membranes called canaliculi

Chief Cells

Cells lining the deep sections of gastric glands that secrete the proteolytic zymogen pepsinogen

ECL Cells

Paracrine cells that release histamine to stimulate parietal cell acid output

Zymogen

An inactive protein precursor that requires cleavage to prevent intracellular self digestion

Receptive Relaxation

Parasympathetic mediated relaxation of smooth muscle in the stomach fundus and body occurring before food arrives to accommodate volume changes

Retropulsion

The powerful backward motion of chyme in the stomach antrum caused by pyloric sphincter closure which exerts high shear forces to enhance mixing

Segmentation

Stationary rhythmic contraction and relaxation of small intestine circular smooth muscle that mixes chyme and maximizes contact with the wall

Interstitial Cells of Cajal

Specialized pacemaker cells in the circular smooth muscle layer that automatically initiate baseline segmentation movements

Migrating Myoelectrical Complex (MMC)

Rhythmic traveling peristaltic waves initiated by the hormone motilin after a meal is absorbed to sweep undigested material into the large intestine

Mass Movement

Intense sweeping waves of contraction occurring 3 to 4 times a day over the transverse colon that rapidly drive fecal material toward the rectum

Enterokinase

An enzyme embedded in the luminal membranes of intestinal epithelial cells that cleaves inactive trypsinogen into active trypsin

Hepatic Lobule

The structural and functional micro unit of the liver

Portal Triad

A micro anatomical collection within hepatic lobules composed of branches of the bile duct and the hepatic portal vein and the hepatic artery

Sphincter of Oddi

The muscular valve regulating the entrance of combined pancreatic secretions and liver or gallbladder bile into the duodenum

Enterohepatic Circulation

The efficient recycling loop where 95 percent of bile salts are actively reabsorbed in the ileum and returned to the liver via the hepatic portal vein

GERD

Gastroesophageal reflux disease caused by an inefficient lower esophageal sphincter allowing acidic stomach contents to escape upward and cause heartburn

Ulcer

A structural breakdown of the mucosal layer affecting the stomach or duodenum exposing underlying tissues to acid and potential blood vessel bleeding

Helicobacter pylori

A specific strain of bacteria whose infection is clinically necessary but not sufficient to trigger ulcer formation

Cystic Fibrosis

A genetic pathology where a mutated CFTR chloride channel reduces pancreatic bicarbonate secretion leading to thickened secretions that clog ducts with fibrotic scar tissue

Steatorrhea

A malabsorption sign characterized by unabsorbed and un emulsified fat appearing in the feces

Jaundice

A yellowish tint of the skin and eyes indicating a dangerous tissue accumulation of bilirubin due to bile duct blockages or neonatal liver immaturity

Cholecystectomy

Surgical removal of the gallbladder

Retching

A rhythmic pre vomiting reflex characterized by deep breaths and glottis closure and abdominal contractions forcing gastric contents into the esophagus without expelling them

Vomiting

A coordinated brainstem reflex causing forceful expulsion of stomach and intestinal contents through the upper esophageal sphincter

Celiac Disease

An autoimmune mediated destruction and loss of intestinal villi surface area caused by a hyper sensitivity to dietary gluten proteins

Pernicious Anemia

Erythrocyte formation failure resulting from a Vitamin B12 deficiency typically caused by autoimmune destruction of intrinsic factor producing parietal cells

mucus cell

at the opening of glands, a type of exocrine cell

law of mass action

the rate of any chemical reaction is proportional to the product of the masses of the reacting substances, applies to HCl production and secreting in GI tract.

what chemical messangers impact HCl production and in which ways do they impact it

gastrin +

acetylcholine +

histamine +

somatostatin -

What does amylase digest

carbs

what does pepsin digest

protein

what does pancreatic lipase digest

fats