Anatomy U4 Digestive
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- Breakdown macromolecules into subunits
- Amino acids from proteins, simple sugars from carbohydrates, nucleotides from nucleic acids, fatty acids and glycerol from triglycerides, etc.);
- absorb nutrients into bloodstream
Inner layer of canal containing glands, goblet cells, etc; secretion and absorption functions
underlying mucosa with blood vessels, lymphatics, submucosal nerve plexus
circular and longitudinal muscle layers of smooth muscle (skeletal at oral end of esophagus) which cause peristalsis and segmentation contractions in alimentary canal
connective tissue around outside of digestive tube; below diaphragm becomes serosa with addition of epithelial tissue.
increases surface area for better contact between enzymes and macromolecules
Saliva: ptyalin (salivary amylase)
digests carbohydrates into disaccharides; lubricates food for swallowing; antimicrobial action.
activate digestive system through release of acetylcholine from vagus nerve fibers
- throat; common passageway for air to lungs and
- food/water to stomach
peristalsis results in movement of food from pharynx into stomach through cardiac sphincter.
Cardiac sphincter (lower esophageal sphincter)
closes in response to food entering stomach and prevents reflux of chyme from stomach into esophagus (gastroesophageal reflux).
regulates movement of chyme from stomach into duodenum
of stomach mucosa contain secretory cells
secrete gastrin which stimulates secretion of HCl and pepsinogen into stomach and stimulates motility of stomach
secrete bicarbonate rich mucin which protects lining of stomach from HCl.
secrete histamine when they are stimulated to do so by gastrin from G cells and acetylcholine from vagus nerve.
- Secrete HCl in response to stimulation by histamine which attaches to H2 receptors on these cells.
- HCl kills germs, curdles milk, dissolves connective tissue, activates pepsinogen;
- Recrete intrinsic factor used for the absorption of vitamin B12Receptors can be blocked by Tagamet, Zantac; proton pumps(hydrogen/potassium ATPase pumps) can be inhibited by Prevacid, Prilosec,Acifex);
secrete the zymogen pepsinogen which is converted into pepsin (a protease) by acid and autoactivation
impairs ability of stomach and intestine to defend itself from HCl; important factor in peptic ulcer formation.
duodenum, jejunum, ilium complete digestive process and absorb nutrients.
Receives bile from liver/gall bladder and digestive juice from ascinar cells of pancreas
release hormones secretin (stimulates release of bicarbonate from Brunner's glands and duct cells of pancreas to neutralize stomach acid), CCK (cholecystikinin; stimulates release of bile from gall bladder, relaxes sphincter of Oddi, stimulates release of digestive enzymes from pancreatic ascinar cells, stimulates satiety center of brain), and GIP (gastric inhibitory peptide or glucose-dependent insulinotropic peptide; inhibits motility of stomach and stomach emptying into duodenum and stimulates release of insulin from beta cells of islets of Langerhans of pancreas)
a brush border enzyme that activates trypsinogen into trypsin which in turn activates chymotrypsinogen, proelastase, procarboxypeptidase from pancreas.
secrete bicarbonate rich mucus to protect first part of duodenum.
Villi & microvilli
Increase surface area of intestine for better absorption, brush border enzymes
Jejunum & Ilium
Complete digestion of foods and absorb nutrients into bloodstream (capillaries in villi) or into lacteals (for larger fatty molecules)
Crypts of Lieberkuhn
(intestinal glands) secrete digestive enzymes into intestinal lumen
absorption of water, production of B vitamins and vit K by bacteria, preparation of mucus rich feces for elimination from body; tubular glands produce mucus
Produces bile with bile pigments (from breakdown of hemoglobin; bilirubin, biliverdin) and bile salts (cholic acid and chenodeoxycholic acid are both produced from cholesterol with carboxyl group; act as detergents to emulsify fats so that lipases in small intestine is able to digest those fats; recycled back into bloodstream by carrier molecules in the ileum)
stores bile, concentrates bile by absorption of water; contracts and secretes bile into the duodenum in response to CCK hormone released from enteroendocrine cells of the duodenum.
hepatic ducts, cystic duct and common bile duct
- Ascinar cells secrete digestive enzymes (lipases, amylases, nucleases, protease zymogens (trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase)) into duodenum through the pancreatic duct and ampulla of Vater in response to CCK hormone.
- Islet of Langerhans secrete hormones (alpha cells secrete glucagon during periods of hypoglycemia; beta cells secrete insulin during periods of hyperglycemia
- Duct cells release bicarbonate into duodenum in response to secretin hormone stimulation.
renal tubule (Bowman's capsule, PCT, loop of Henle, DCT, and collecting duct) and associated blood vessels (afferent arteriole, glomerulus, efferent arteriole, peritubular capillaries, vasa recta)
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