Digestive System - Anatomy and Physiology I | BIO 2330, Study notes of Physiology

Download Digestive System - Anatomy and Physiology I | BIO 2330 and more Study notes Physiology in PDF only on Docsity! 1 Digestive System What Do You Get From Studying Digestion and Nutrition? A stomach ache? No… • Humans are adapted to eating a variety of foods • Foods must be significantly processed in order for absorption to occur; what can’t be processed is expelled unabsorbed • Distinctive layering of organs provides useful function • Body must protect itself from strong digestive chemicals; breakdown in protection leads to damage 2 What Do You Get From Studying Digestion and Nutrition? A yummy feeling? Well maybe, but also... Digestion is coordinated by nervous and hormonal mechanisms • No enzyme, no digestion • Within limits, metabolic pathways exist to convert one nutrient to another or to energy as needed • Human nutritional needs well understood, how to deliver nutrition impacted by marketing General Functions • Processing food – Mastication – Enzyme production – Mixing (segmentation) • Storage • Protection • Absorption • Propulsion – Deglutition – Lubrication – Peristalsis – elimination • Excretion (be careful here) 5 Why don’t you bite your tongue when chewing? Mastication reflex: medulla oblongata provides coordination through involuntary control. Controls basic movements involved in chewing descending pathways from cerebrum provide conscious control Back Tongue • Muscular with free anterior surface and attached posterior surface. Covered with moist stratified squamous epithelium. – Intrinsic muscles: change shape – Extrinsic muscles: protrude or retract tongue, move side to side • Anterior part: papillae, some of which have taste buds • Posterior part: no papillae and a few scattered taste buds. Lymphoid tissue embedded in posterior surface: lingual tonsil • Moves food in mouth, participates in speech and swallowing Back 6 Salivary Glands Saliva Compound alveolar salivary glands produce saliva • Parasympathetic input causes salivary production back 7 Three Phases of Swallowing •Voluntary •Pharyngeal involuntary •Upper esophageal sphincter •Esophageal involuntary •Lower esophageal sphincter •esophageal hiatus Moving Food Through – DS Histology • Four tunics • Critical to function 10 Stomach Anatomy Stomach Functions • Food storage • Release to small intestine • Begin chemical breakdown • Disinfection • Some absorption 11 Stomach Histology • Layers – Serosa or visceral peritoneum: outermost – Muscularis: three layers – Submucosa – Mucosa • Rugae: folds in stomach when empty. Mucosa and submucosa. Stomach Histology Gastric pits: openings for gastric glands. Lined with simple columnar epithelium Cells of gastric pits • Surface mucus: mucus that protects stomach lining from acid and digestive enzymes • Mucous neck: mucus • Parietal: hydrochloric acid and intrinsic factor • Chief: pepsinogen • Endocrine: regulatory hormones – Enterochromaffin-like cells: histamine that stimulates acid secretion – Gastrin-containing cells: secrete gastrin – Somatostatin-containing cells: secrete somatostatin that inhibits gastrin and insulin secretion 12 Stomach Contents and Mixing • Chyme: ingested food plus stomach secretions • Combination of mixing waves (80%) and peristaltic waves (20%) • Both esophageal and pyloric sphincters are closed. • Released to duodenum in spurts • 2-3 liters of gastric secretions per day; 700 ml per meal Cephalic Phase Peristalsis — Digestive tract Bolus Wave of relaxation Wave of contraction Segmentation Secretion or food Contraction waves » 3 E Contraction waves oa Back 15 16 Small Intestine • Site of greatest amount of digestion and absorption of nutrients and water • Divisions – Duodenum- first 25 cm beyond the pyloric sphincter. – Jejunum- 2.5 m – Ileum- 3.5 m Modifications to Increase Surface Area • Increase surface area 600 fold – Plicae circulares (circular folds) • Major and minor duodenal papillae: openings to ducts from liver and/or pancreas. More on surface area On to mucosa and submucosa 17 Modifications to Increase Surface Area • Increase surface area 600 fold – Villi that contain capillaries and lacteals. Folds of the mucosa More on Microvilli Microvilli • Extension of plasma membrane • Increase the cell surface area • Normally many on each cell • Do not move like cilia Back to ducts 20 Large Intestine • Extends from ileocecal junction to anus • Consists of cecum, colon, rectum, anal canal – vermiform appendix • Ascending, transverse, descending, sigmoid – teniae coli • Internal anal sphincter (smooth muscle) • External anal sphincter (skeletal muscle) • Haustra • epiploic appendages 21 Large Intestine • Absorption of water and salts, secretion of mucus, extensive action of microorganisms – chyme converted to feces • 1500 mL chyme enter the cecum, 90% of volume reabsorbed yielding 80-150 mL of feces Secretions of Large Intestine • Mucus provides protection • Secretions to counteract bacterial acids • Not much enzymatic activity here 22 Movement in Large Intestine Slow peristalsis and periodic… – Movements sluggish (18-24 hours) • …Mass movements – Common after meals – Segmentation unnecessary, not much longitudinal muscle available Feces formation • Bacterial actions produce gases (flatus) • Bacteria produce vitamin K which is then absorbed • Feces consists of water, undigested food (cellulose), microorganisms and their wastes, sloughed-off epithelial cells, inorganic salts Reflexes and the Colon and Rectum 25 Functions of the Liver • Bile production: 600-1000 mL/day. Bile salts (bilirubin), cholesterol, fats, fat-soluble hormones, lecithin • Storage • Nutrient interconversion • Detoxification • Phagocytosis • Synthesis Gallbladder • Sac lined with mucosa folded into rugae, inner muscularis, outer serosa • Bile arrives constantly from liver is stored and concentrated • Release stimulated by cholecystokinin (from the intestine) and vagal stimulation • Bile exits through cystic duct then into common bile duct 26 Control of Bile Secretion and Release Pancreas• Pancreas both endocrine and exocrine • Head, body and tail • Endocrine: pancreatic islets • Exocrine: acini form lobules • Pancreatic duct joins common bile duct and enters duodenum at the hepatopancreatic ampulla 27 Pancreatic Secretions: Pancreatic Juice • Aqueous. Produced by columnar epithelium lining smaller ducts. Na+, K+, HCO3-, water. Bicarbonate lowers pH inhibiting pepsin and providing proper pH for enzymes • Enzymatic portion: – Trypsinogen – Chymotrypsinogen – Procarboxypeptidase – Pancreatic amylase – Pancreatic lipases – Deoxyribonucleases and ribonucleases Control of Pancreatic Secretion