McCance Chapter 41 Structure and Function of the Digestive System

Submucosal plexus (Meissner plexus)

Located in the muscularis mucosae, regulate motility reflexes, blood flow, absorption, secretions, and immune response

Myenteric plexus (Auerbach plexus)

Located between the inner circular and outer longitudinal muscle layers in the muscularis, regulate motility reflexes, blood flow, absorption, secretions, and immune response

Salivary α-amylase (ptyalin)

Initiates carbohydrate digestion in the mouth and stomach

Peristalsis

A radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube, in an anterograde direction.

Upper esophageal sphincter (cricopharyngeal muscle)

Prevents entry of air into the esophagus during respiration

Lower esophageal sphincter (cardiac sphincter)

Prevents regurgitation from the stomach, located near the esophageal hiatus (opening in the diaphragm)

Pyloric sphincter

Located between the stomach and the duodenum, relaxes as food is propelled into the duodenum

Gastrin

Polypeptide hormones secreted by the gastrointestinal mucosa, stimulates secretion of HCl acid by parietal cells and aids in gastric motility, binds to cholecystokinin B receptors to stimulate the release of histamines in enterochromaffin-like cells, induces the insertion of K+/H+ ATPase pumps into the apical membrane of parietal cells. Its release is stimulated by peptides in the lumen of the stomach

Cholecystokinin

Polypeptide hormones secreted by the gastrointestinal mucosa, causes the release of digestive enzymes and bile from the pancreas and gallbladder in response to fatty acids and/or certain amino acids in the chyme entering the duodenum, inhibits gastric emtpying time and inhibits food intake, stimulates the contraction of the gall bladder and the relaxation of the sphincter of Oddi

Motilin

Polypeptide hormones secreted by the gastrointestinal mucosa, increases GI motility and stimulates the production of pepsin, improves peristalsis in the small intestine and clears out the gut to prepare for the next meal

Retropulsion

Peristaltic wave forces food back toward the body of stomach effectively mixing food with digestive juices, and breaks down large food particles

Osmoreceptors

Located in the duodenum, activated by hypertonic or hypotonic gastric contents, delays gastric emptying to facilitate formation of an isosmotic duodenal environment

Mucus

Viscous colloid containing inorganic salts, antiseptic enzymes (such as lysozymes), immunoglobulins, and glycoproteins such as lactoferrin[1] and mucins, forms a protective barrier against acid, secreted by goblet cells

Prostaglandins

Stimulate the secretion of mucus and bicarbonate and inhibit the secretion of acid

Nitric oxide

Stimulate the secretion of mucus and bicarbonate and inhibit the secretion of acid

Parietal cells (oxyntic cells)

Secrete HCl acid in the stomach

Hydrochloric acid

Converts pepsinogen to pepsin, responsible for the acidic pH in the Stomach (pH = 1.5-2)

Alkaline tide

At a high rate of gastric secretion, bicarbonate moves into the plasma (venous blood and urine)

Gastrin-releasing peptide

Stimulates the release of Gastrin from the G cells of the stomach

Histamine

Stimulated by ACH and gastrin, binds to histamine type 2 receptors in the stomach casuing HCl acid secretion

Pepsiongen

Zymogen (precursor) of pepsin (protease), acid stimulates a local cholinergic reflex and chief cells secrete pepsin, gastrin and secretin are weaker pepsinogen secretagogues, alkaline environment of the duodenum inactivates pepsin.

Gastroferrin

Facilitates small intestinal absorption of iron, produced by parietal cells

Enterochromaffin-like cells

Secrete histamine in response to acetylcholine and gastrin

Somatostatin

Secreted by D cells, inhibit acid secretion

Gastric lipase

"Produced by glands in the fundus of the stomach, break down fats, most effective in an acidic environment

Caffeine

Increases HCl acid secretion in parietal cells

Enterogastrones

Decrease acid secretion in parietal cells

Secretin

Decrease acid secretion in parietal cells

Gastroduodenal artery

A small branch of the celiac artery that supplies the duodenum

Superior mesenteric vein

Drains the duodenum into the hepatic portal circulation

Superior mesenteric artery

Supplies blood to the jejenum

Ileocecal valve (sphincter)

Controls the flow of digested material from the ileum into the large intestine and prevents reflux into the small intestine

Thoracic duct

Regional lymphatic vessels drain into the subclavian vein through this duct

Enteric nervous system

One of the main divisions of the nervous system that governs the function of the gastrointestinal tract

Lamina propria

Connective tissue layer of the mucosa, lies beneath the epithelial cells of the villi, contains lymphocytes (plasma cells- produce immunoglobulins) and macrophages

Lacteal

Lymphatic capillary, abosrbs and transports fat molecules

Intestinal stem cells

Precursors of columnar epithelial and goblet cells

Paneth epithelial cells

Located at the base of the crypts, produce defensins and other antibiotic peptides and proteins

Crypts of Lieberkühn

Intestinal glands located between the bases of the villi and extend to the submucosal layer.

Enterocytes

Absorptive columnar epithelial cells that adhere to each other by tight junctions

Pancreatic amylase

Break down starches to oligosaccharides by splitting α-1,4-glucosidic linkages of long-chain molecules in the stomach and duodenum

Sucrose

Disaccharide made up of fructose and glucose

Maltose

Disaccharide made up of two glucose molecules

Lactose

Disaccharide made up of galactose and glucose

Ribose

Monosaccharides

Glucose

Monosaccharides, tranposrted by sodium carrier (SGLT1)

Galactose

Monosaccharides, tranposrted by sodium carrier (SGLT1)

Fructose

Monosaccharides, transported by glucose transporter 5 (GLUT5) and GLUT7

Sucrase

Breaksdown sucrose into glucose and fructose

Maltase

Breaksdown maltose into two glucose molecules

Lactase

Breaksdown lactose into glucose and galactose

Cellulose

"Glucose polysaccharide found in plants, humans lack enzymes to digest it

Trypsin

Hydrolyzes the interior bonds of the large peptide molecules (endopeptidase), cleaves chymotrypsinogen to chymotrypsin, cleaves procarboxypeptidase to carboxypeptidase, cleaves proelastase to elastase

Chymotrypsin

Hydrolyzes the interior bonds of the large peptide molecules (endopeptidase)

Carboxypeptidase

Hydrolyzes the amino acids on the end of the large peptide molecules (ecopeptidase)

Emulsification

The breakdown of fat globules in the duodenum into tiny droplets, which provides a larger surface area on which the enzyme pancreatic lipase can act to digest the fats into fatty acids and glycerol, assisted by the action of bile salts

Lecithin

Emulsifier, mixtures of glycerophospholipids including phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidic acid

Bile salts

Emulsifiers made from cholesterol based acids like cholic acid, deoxycholic acid, chenodeoxycholic acid

Lipolysis

Metabolism of fats

Lipase

Cleaves triglyceride into free fatty acids and glycerol

Phospholipase

Cleaves fatty acids from phospholipids

Cholesterol esterase

Cleaves cholesterol esters into fatty acids and cholesterol

Micelle

Contain bile salts, products of fat hydrolysis, fat-soluble vitamins, and cholesterol, fats form the core and polar bile salts from the outer shell, maintain fat molecules in the dissolved or solubilized form allowing rapid movement toward the absorbing surface of the intestinal epithelium

Enterohepatic circulation

Bile salts remain in the lumen and are reabsorbed in the ileum and returned to the liver

Chylomicrons

Triglycerides are covered with phospholipids, lipoproteins, and cholesterol

Sodium-glucose ligand transporter

Active symporter that carries glucose and sodium across a cell membrane

Transferrin

Glycoprotein that binds iron in the lumen of intestine and transports it to various sites in the body

Ferritin

Intracellular protein that stores iron

Hepcidin

Protein that inhibits uptake of iron by enterocytes

Visceral peritoneum

Membrane that lies on the surface of the organs

Parietal peritoneum

Membrane that lines the wall of the body cavity

Peritonitis

Inflammation of the peritoneum

Segmentation

Localized rhythmic contractions of the circular smooth muscles, occurs more frequently than peristalsis, divides and mixes the chyme

Interstitial cells of Cajal

Pacemaker cells in the myenteric plexus of longitudinal smooth muscle

Ileogastric reflex

Inhibits gastric motility when the ileum is distended preventing continued movement of chyme into an already distended intestine

Intestinointestinal reflex

Inhibits intestinal motility when one part of the intestine is over distended

Gastroileal reflex

Empties the ileum and prepares it to receive more chyme, activated by an increase in gastric motility and secretion, stimulates an increase in ileal motility, causes relaxation of the ileocecal sphincter, regulated by gastrin, cholecystokinin or through the autonomic nerves.

Interdigestive myoelectric complex

"During prolonged fasting or between meals (overnight), slow waves sweep along the entire length of the intestinal tract from the stomach to the terminal ileum, propels residual gastric and intestinal contents, including bacteria, into the colon

Cecum

A pouch that receives chyme from the ileum

Appendix

A worm-like tube connected to the cecum that has no physiological function

Rectosigmoid sphincter

Controls the movement of feces from the sigmoid colon into the rectum

Internal anal sphincter

Thick portion of smooth muscle surrounds the anal canal, involuntary in a state of continuous maximal contraction to prevent leakage of fluid or gas, but is relaxed upon distention of the rectal ampulla, requiring voluntary contraction of the external anal sphincter

External anal sphincter

Striated skeletal muscle, always in a state of tonic contraction, it keeps the anal canal and orifice closed.

Teniae coli

Longitudinal bands of smooth muscle in the colon

Haustra

Circular muscles form outpouchings in the colon

Rugae

Series of ridges produced by folding of the wall of an organ

Pudendal nerve

Innervates the external anal sphincter

Gastrocolic reflex

Initiates propulsion in the entire colon usually during or immediately after eating (chyme entering the ileum) stimulating defecation

Aldosterone

"Increases colon membrane permeability to sodium increasing the diffusion of sodium into the cell and active transport of sodium across the basolateral membrane to the interstitial fluid

Rectosphincteric reflex

Defecation reflex, rectal wall stretches and constricted internal anal sphincter relaxes creating the urge to defecate

Valsalva maneuver

Inhaling and forcing the diaphragm and chest muscles against the closed glottis, increases intrathoracic and intra-abdominal pressure that is transmitted to the rectum

Falciform ligament

Separates the right and left lobes and attaches the liver to the anterior abdominal wall

Glisson capsule

Fibrous connective tissue surrounding the liver

Hepatic artery

Branches of the celiac artery that supplies blood to the liver

Hepatic portal vein

Receives deoxygenated blood from the splenic vein, and inferior and superior mesenteric veins, rich in nutrients that have been absorbed from the digestive tract

Hepatocytes

"Liver cells, capable of regeneration, secrete electrolytes, lipids, lecithin, bile acids, and cholesterol into the canaliculi, synthesize plasma proteins that are released into the bloodstream

Lipocytes

Star-shaped, liver cells that store lipids, including vitamin A

Sinusoids

Receive a mixture of venous and arterial blood from branches of the hepatic artery and hepatic portal vein

Kupffer cells

Macrophages in the liver that ingest bacteria and damaged red blood cells

Inferior vena cava

Transports deoxygentaed blood from the hepatic vein to the venae cavae and the right atrium