Digestive System Anatomy Digestive tract Alimentary tract or canal GI tract Accessory organs Primarily glands Regions Mouth or oral cavity Pharynx Esophagus Stomach Small intestine Large intestine Anus

Functions Ingestion: Introduction of food into stomach Mastication: Chewing Propulsion Deglutition: Swallowing Peristalsis: Moves material through digestive tract

Functions Mixing: Segmental contraction that occurs in small intestine Secretion: Lubricate, liquefy, digest Digestion: Mechanical and chemical Absorption: Movement from tract into circulation or lymph Elimination: Waste products removed from body

Digestive Tract Histology

Digestive System Regulation Nervous regulation Involves enteric nervous system Types of neurons: sensory, motor, interneurons Coordinates peristalsis and regulates local reflexes Chemical regulation Production of hormones Gastrin, secretin Production of paracrine chemicals Histamine Help local reflexes in ENS control digestive environments as pH levels

Peritoneum and Mesenteries Visceral: Covers organs Parietal: Covers interior surface of body wall Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum Mesenteries Routes which vessels and nerves pass from body wall to organs Greater omentum Lesser omentum

Oral Cavity Mouth or oral cavity Lips (labia) and cheeks Vestibule: Space between lips or cheeks and alveolar processes Oral cavity proper Lips (labia) and cheeks Palate: Oral cavity roof Hard and soft Palatine tonsils Tongue: Involved in speech, taste, mastication, swallowing

Teeth Two sets Types Primary, deciduous, milk: Childhood Permanent or secondary: Adult (32) Types Incisors, canine, premolar and molars

Tooth structure:

Salivary Glands Produce saliva Three pairs Prevents bacterial infection Lubrication Contains salivary amylase Breaks down starch Three pairs Parotid: Largest Submandibular Sublingual: Smallest

Pharynx and Esophagus Esophagus Pharynx Transports food from pharynx to stomach Passes through esophageal hiatus (opening) of diaphragm and ends at stomach Hiatal hernia Sphincters Upper Lower Pharynx Nasopharynx Oropharynx: Transmits food normally Laryngopharynx: Transmits food normally

Deglutition (Swallowing) Three phases Voluntary Bolus of food moved by tongue from oral cavity to pharynx Pharyngeal Reflex: Upper esophageal sphincter relaxes, elevated pharynx opens the esophagus, food pushed into esophagus Esophageal Reflex: Epiglottis is tipped posteriorly, larynx elevated to prevent food from passing into larynx

Phases of Deglutition (Swallowing)

Stomach Anatomy: Openings Regions Gastroesophageal: To esophagus Pyloric: To duodenum Regions Cardiac Fundus Body Pyloric

Stomach Histology: Layers Serosa or visceral peritoneum: Outermost Muscularis: Three layers Outer longitudinal Middle circular Inner oblique Submucosa Mucosa

Stomach Histology Rugae: Folds in stomach when empty Gastric pits: Openings for gastric glands Contain cells Surface mucous: Mucus Mucous neck: Mucus Parietal: Hydrochloric acid and intrinsic factor Chief: Pepsinogen Endocrine: Regulatory hormones

Hydrochloric Acid Production

Movements in Stomach

Phases of Gastric Secretion

Small Intestine Site of greatest amount of digestion and absorption Divisions Duodenum Jejunum Ileum: Peyer’s patches or lymph nodules Modifications Circular folds or plicae circulares, villi, lacteal, microvilli Cells of mucosa Absorptive, goblet, granular, endocrine

Small Intestine Secretions Mucus Protects against digestive enzymes and stomach acids Digestive enzymes Disaccharidases: Break down disaccharides to monosaccharides Peptidases: Hydrolyze peptide bonds Nucleases: Break down nucleic acids Duodenal glands Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa

Duodenum and Pancreas

Duodenum Anatomy and Histology

Liver Lobes Ducts Major: Left and right Minor: Caudate and quadrate Common hepatic Cystic From gallbladder Common bile Joins pancreatic duct at hepatopancreatic ampulla

Functions of the Liver Bile production Storage Salts emulsify fats, contain pigments as bilirubin Storage Glycogen, fat, vitamins, copper and iron Nutrient interconversion Detoxification Hepatocytes remove ammonia and convert to urea Phagocytosis Kupffer cells phagocytize worn-out and dying red and white blood cells, some bacteria Synthesis Albumins, fibrinogen, globulins, heparin, clotting factors

Blood and Bile Flow

Duct System

Gallbladder Bile is stored and concentrated Stimulated by cholecystokinin and vegal stimulation Dumps into small intestine Production of gallstones possible Drastic dieting with rapid weight loss

Pancreas Anatomy Secretions Endocrine Pancreatic juice (exocrine) Pancreatic islets produce insulin and glucagon Exocrine Acini produce digestive enzymes Regions: Head, body, tail Secretions Pancreatic juice (exocrine) Trypsin Chymotrypsin Carboxypeptidase Pancreatic amylase Pancreatic lipases Enzymes that reduce DNA and ribonucleic acid

Bicarbonate Ion Production

Gastric hormones:

Large Intestine: Extends from ileocecal junction to anus Consists of cecum, colon, rectum, anal canal Movements sluggish (18-24 hours)

Large Intestine Cecum Colon Rectum Anal canal Blind sac, vermiform appendix attached Colon Ascending, transverse, descending, sigmoid Rectum Straight muscular tube Anal canal Internal anal sphincter (smooth muscle) External anal sphincter (skeletal muscle) Hemorrhoids: Vein enlargement or inflammation

Secretions of Large Intestine Mucus provides protection Parasympathetic stimulation increases rate of goblet cell secretion Pumps Exchange of bicarbonate ions for chloride ions Exchange of sodium ions for hydrogen ions Bacterial actions produce gases called flatus

Histology of Large Intestine

Movement in Large Intestine Mass movements Common after meals Local reflexes in enteric plexus Gastrocolic: Initiated by stomach Duodenocolic: Initiated by duodenum Defecation reflex Distension of the rectal wall by feces Defecation Usually accompanied by voluntary movements to expel feces through abdominal cavity pressure caused by inspiration

Reflexes in Colon and Rectum:

Digestion, Absorption, Transport Breakdown of food molecules for absorption into circulation Mechanical: Breaks large food particles to small Chemical: Breaking of covalent bonds by digestive enzymes Absorption and transport Molecules are moved out of digestive tract and into circulation for distribution throughout body

Lipoproteins Types Chylomicrons VLDL LDL HDL Enter lymph Transports cholesterol to cells HDL Transports cholesterol from cells to liver

Water and Ions: Water Ions Can move in either direction across wall of small intestine depending on osmotic gradients Ions Sodium, potassium, calcium, magnesium, phosphate are actively transported

Effects of Aging Decrease in mucus layer, connective tissue, muscles and secretions Increased susceptibility to infections and toxic agents Ulcerations and cancers