Digestive System Anatomy Digestive tract – (mouth to anus) Alimentary tract or canal GI tract (stomach and intestines) Accessory organs Primarily glands Regions Mouth or oral cavity Pharynx Esophagus Stomach Small intestine Large intestine Anus

Oral Cavity 2 Mouth or oral cavity Vestibule: Space between lips or cheeks and alveolar processes Oral cavity proper Tongue: Involved in speech, taste, mastication, swallowing Frenula – hold lip to alveolar process Lips (labia) Palate: Oral cavity roof hard and soft Fauces - throat opening into the pharynx Palatine tonsils 3 6 4 7 5 1 2

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

Teeth

Salivary Glands Produce saliva Prevents bacterial infection Lubrication Contains salivary amylase Breaks down starch Mucous Secreted by the submandibular and sublingual glands lubricate Three pairs Parotid: Largest, located ant. to ear. Submandibular: below mandible Sublingual: Smallest, below the tongue.

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

Pharynx and Esophagus Pharynx Nasopharynx Oropharynx: Transmits food Laryngopharynx: Transmits food Extends from oropharynx to esophagus and post. to the larynx. Esophagus Transports food from pharynx to stomach Passes through esophageal hiatus (opening) of diaphragm and ends at stomach Sphincters Upper Lower Regulate movement of material into and out of the esophagus

Stomach

Peritoneum and Mesenteries Visceral: Covers organs Parietal: Covers interior surface of body wall Retroperitoneal: Behind peritoneum as kidneys, pancreas, duodenum (no mesenteries) Mesenteries Hold organs in place Routes which vessels and nerves pass from body wall to organs. 1 2 Greater omentum – extends from greater curvature and transverse colon Lesser omentum – connects the lesser curvature of the stomach and the proximal end of the duodenum of the liver and diaphragm

Digestive Tract Histology (Assist in local nervous control) Digestive tube consists of four major layers or tunics from the esophagus to the anus. Three glands are associated with the tract. Unicellular mucous (mucosa) Multicellular (mucosa and submuxossa) Multicellular accessory glands (Outside the digestive tract) 4 1 2 3

Stomach Anatomy Openings Regions Gastroesophageal or cardiac: to fundus Pyloric: to duodenum Regions Cardiac Fundus Body Pyloric 3 1 4 2 8 7 6 5 10 9 Located in the left superior abdomen

Stomach Histology Layers Serosa or visceral peritoneum: Outermost Muscularis: Three layers Outer longitudinal Middle circular Inner oblique Submucosa Mucosa 3 sub layers 1 3 1 2 3 2

Stomach Histology Rugae: Folds in stomach when empty Gastric pits: Openings for gastric glands Mucosa cells Endocrine – regulatory hormones Chief - pepsinogen Parietal - hydorchloric acid & intrinsic factor Mucous neck - mucus

Mucosa cells Chief pepsinogen contacts hydrocloric acid and is converted to pepsin which assists in the break down of some proteins. Parietal hydorchloric acid – main function is to kill bacteria intrinsic factor – glycoprotein that binds with vit. B-12 to make it more easily absorbed in the illium Mucous neck mucus - lubricates and protects the epithelial cells from the damaging effects of acids, chyme and pepsin Enteroendocrine cells – see chart on next slide

Movements in Stomach Ingested food and stomach secretion mixed together

Small Intestine Site of greatest amount of digestion and absorption Divisions Duodenum Jejunum Ileum: Peyer’s patches or lymph nodules in mucosa and submucosa where some absorption of nutrients take place Illeocecal sphincter – junction between the ileum and the large intestine

Duodenum Anatomy and Histology 3 2 1 Modifications The mucosa and submucosa form a series of folds (Circular folds or plicae) At the top of each fold are located villi which are covered in microvilli Lacteal – capillary network

Epithelial cells are produced in the mucosa within the intestinal gland or crypts of lieberkuhn. Duodenal glands or Brunner’s glands open to the base of the intestinal glands and secrete mucus Intestinal glands, duodenal glands, and goblet cells all secrete mucus which protects against the irritating effects of acids, chyme, and enzymes entering the duodenum from the pancreas

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 (brunners’ glands) Stimulated by vagus nerve, secretin, chemical or tactile irritation of duodenal mucosa

Pancreas Anatomy Secretions Endocrine Pancreatic islets produce insulin and glucagon Control blood levels of nutrients such as glucose, amino acids Exocrine Acini produce digestive enzymes Regions: Head, body, tail Secretions Pancreatic juice (exocrine) produced in the pancreas and delivered through the pancreatic duct to the small intestine. Trypsin Chymotrypsin Carboxypeptidase Pancreatic amylase Pancreatic lipases Enzymes that reduce DNA and ribonucleic acid

Functions of the Liver Bile production Storage Salts emulsify fats, contain pigments as bilirubin (results from break down of hemoglobin) No digestive enzymes but plays an important role in digestion by neutralizing stomach acid making it suitable for pancreatic enzymes Storage Glycogen, fat, vitamins (A, B12, D, E, 7 K), 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

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

Functions Ingestion: Introduction of food into stomach Mastication: Chewing Propulsion Deglutition: Swallowing Peristalsis: Moves material through digestive tract 1. Wave of circular smooth muscle relaxation moves ahead of the bolus allowing the digestive tract to expand 2. A wave of contraction of the circular smooth muscle behind the bolus propels it through the tract

Reflexes in Colon and Rectum

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

Blood and Bile Flow

Carbohydrates Consist of starches, glycogen, sucrose, lactose, glucose, fructose Polysaccharides broken down to monosaccharides Monosaccharides taken up by active transport or facilitated diffusion and carried to liver Glucose is transported to cells requiring energy Insulin influences rate of transport

Lipids Include triglycerides, phospholipids, steroids, fat-soluble vitamins Emulsification breaks down large lipid droplets to small

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

Proteins Pepsin breaks proteins into smaller polypeptide chains Proteolytic enzymes produce small peptide chains Dipeptides, tripeptides, amino acids

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