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Chapter 24 The Digestive System Functions of the Digestive System • • • • Ingest food Digest food Absorb nutrients Eliminate indigestible waste Digestive anatomy overview Organization of the Digestive organs Alimentary Canal Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus Accessory organs Teeth Tongue Salivary glands Gall bladder Liver Pancreas The Digestive Process Ingestion Propulsion Mechanical Digestion Chemical Digestion Absorption Defecation Daddy, what does “retroperitoneal” mean? This is your basic alimentary tract structure. Sagittal view of abdominal viscera Mesenteries Figure 24–2a, b Mesenteries Figure 24–2c, d Peristalsis Figure 24–4 Segmentation • Cycles of contraction: – Churn and fragment bolus – mix contents with intestinal secretions • Does not follow a set pattern: – does not push materials in any 1 direction The oral cavity and pharynx Say “ahhh” Salivary Glands Road map of the tongue Anatomy of Teeth Primary and Secondary Dentitions Figure 24–9 Histology of the Esophagus Gastroesophageal junction Esophagus Stomach Stratified squamous epithelium Simple columnar epithelium The Swallowing Process Figure 24–11 The Stomach Figure 24–12a The Stomach Figure 24–12b The Stomach Lining Figure 24–13 It’s the pits! (Gastric pits that is…) Micrograph of the Fundic region of the gastric mucosa Secretion of HCl Details of HCl secretion The Regulation of Digestive Activities Figure 24–5 Stimulus and control of gastric activity The phases of gastric secretion Control mechanisms of gastric contractions The duodenum, gall bladder and pancreas Hormonal Regulation of Pancreatic secretions The small intestine Histology of the small intestine Cells of the mucosa Duodenal wall Duodenal mucosa You only find us here, In the duodenum! Brunner’s (duodenal) glands Crypts of Lieberkuhn! Paneth cells Peyer’s patches in the ileum The Pancreas Figure 24–18 Exocrine tissues of the pancreas Pancreas: Acinar cells Activation of pancreatic proteases in the duodenum Regulatory mechanisms for release of pancreatic juice The Liver • Is the largest visceral organ (1.5 kg) • Lies in right hypochondriac and epigastric regions • Extends to left hypochondriac and umbilical regions • Performs essential metabolic and synthetic functions The Anatomy of the Liver Figure 24–19 Liver Histology Figure 24–20 3 Functions of the Liver 1. Metabolic regulation 2. Hematological regulation 3. Bile production Metabolic Regulation • The liver regulates: 1. 2. 3. 4. 5. composition of circulating blood nutrient metabolism waste product removal nutrient storage drug inactivation Metabolic Activities of the Liver • • • • • • • Carbohydrate metabolism Lipid metabolism Amino acid metabolism Waste product removal Vitamin storage Mineral storage Drug inactivation The Gallbladder and Bile Ducts Figure 24–21 The Gallbladder • Stores bile • Releases bile into duodenum: – only under stimulation of hormone cholecystokinin (CCK) Gallstones • Are crystals of insoluble minerals and salts • Form if bile is too concentrated • Small stones may be flushed through bile duct and excreted Activities of Major Digestive Tract Hormones Figure 24–22 Hormones of Duodenal Enteroendocrine Cells • Coordinate digestive functions: – secretin – cholecystokinin (CCK) – gastric inhibitory peptide (GIP) – vasoactive intestinal peptide (VIP) – gastrin – enterocrinin Absorption of Nutrients • Nearly all occurs in the small intestine. – 80% of the electrolytes and virtually all food • Most nutrients are absorbed by active transport. – Glucose, amino acids, & nucleic acids are absorbed by secondary active transport with sodium. – Iron and calcium require transport proteins (ferritin) or cofactors (vitamin D). – Anions follow Na+. • Vitamins – Fat soluble (A, D, E & K) vitamins are carried with micelles. Much of the K is absorbed in the colon. – Water soluble vitamins diffuse with the exception of B12, which requires intrinsic factor. Chemical Digestion & absorption of nutrients Movement of absorbed nutrients Chemical Digestion Carbohydrates & proteins Chemical Digestion Lipids & Nucleic acids Protein digestion in the small intestine Bile salts emulsify fats Absorption of lipid Dietary fats are absorbed into the “lacteals” of the lymphatic system before being transferred to the circulatory system. Digestive Secretion and Absorption Figure 24–27 Absorption of Ions and Vitamins Table 24–4 Lacteals Anatomy of the large intestine The rectum and anus 3 Parts of the Large Intestine 1. Cecum: – the pouchlike first portion 2. Colon: – the largest portion 3. Rectum: – the last 15 cm of digestive tract Histology of the colon The Colon Look at all those goblet cells! Large intestine wall Close-up of the colonic mucosa Characteristics of the Colon • Lack of villi • Abundance of goblet cells • Presence distinctive intestinal glands The Defecation reflex Absorption of Nutrients: redux • Nearly all occurs in the small intestine. – 80% of the electrolytes and virtually all food • Most nutrients are absorbed by active transport. – Glucose, amino acids, & nucleic acids are absorbed by secondary active transport with sodium. – Iron and calcium require transport proteins (ferritin) or cofactors (vitamin D). – Anions follow Na+. • Vitamins – Fat soluble (A, D, E & K) vitamins are carried with micelles. Much of the K is absorbed in the colon. – Water soluble vitamins diffuse with the exception of B12, which requires intrinsic factor. Summary: Chemical Events in Digestion Figure 24–26 Clinical terms • Ascites – Fluid accumulation in the peritoneal cavity. Possible causes: hypertension, cirrhosis, renal or heart disease • Bulimia & anorexia nervosa – eating disorders • Cholecystitis – gallbladder inflammation. Can be caused by gallstones. • Diverticuliosis/diverticulitis – herniations of the colon wall which may become inflammed. • Dysphagia – difficulty swallowing. • GERD – Gastroesophogeal reflux disease. Excess acid and/or dyfunction of the gastroesophogeal sphincter. • IBS – inflammatory bowel syndrome. Related to Crohn’s disease or ulcerative colitis. • Pancreatitis – inflammation of the pancreas. Pancreatic enzymes activated in the within the duct. Can be caused by excessive dietary fats hyperstimulating the pancreatic secretion. • Peptic ulcers – usually caused by Helicobacter pylori. Helicobacter pylori Worldwide Distribution of H. pylori The End Next, Energy Metabolism