Lab 8: Digestive System Announcements Exams Lab notes will be on reserve in library and on the web Goals of the Digestive System 1. Extract nutrients from food 2. Transform nutrients into useful forms Ex- oreo= glucose 3. Absorb nutrients and distribute them where they are needed Functions of the Digestive System Ingestion: intake of nutrients Digestion: breakdown of large particles into smaller ones Absorption: uptake of nutrient molecules Defecation: elimination of undigested residues Actions of the Digestive System 1. Motility - Breaks up food - Moves food through the GI tract (Peristalsis) - Mixes with digestive enzymes 2. Secretion - Release of enzymes and hormones for chemical digestion and regulation 3. Membrane Transport - Absorption of nutrients from the tissues by the blood and lymph for transport Stages of Digestion Mechanical: physical breakdown of food Chemical: digestive enzymes hydrolyze food particles to break larger molecules into smaller ones Some nutrients are absorbed with out digestion – Vitamins, minerals, cholesterol, water Anatomy of the Digestive System Oral Cavity Pharynx Esophagus Stomach Pyloric Sphincter Small Intestine Large Intestine Accessory Organs Teeth Tongue Salivary Glands Liver Gall Bladder Pancreas Oral Cavity Functions: – A. Ingestion: cheeks lips and tongue mobilize food – B. Digestion: Mechanical – Mastication Chemical – 3 salivary glands – Digests some starches and fat Pharynx Motility: pharyngeal constrictors force food down during swallowing Esophagus www.mywebmd.ca.com Straight muscular tube about 1 foot long Motility: muscular contraction moves food towards stomach Heartburn and the Esophagus Heartburn, “ acid reflux”, is caused by acid and food going from the stomach into the esophagus The diaphragm normally prevents acid reflux, in conjunction with the lower esophageal sphincter. When this fails, the burning sensation felt is known as “heartburn” May be linked to a rare type of cancer, adenocarcinoma Stomach Muscular sac on the left side of the peritoneal cavity Functions: – Food storage – Mechanical digestion – Chemical digestion Rugae in the Stomach http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion Rugae- folds in the stomach lining that allow it to expand with more food How do we vomit? Pyloric Sphincter http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion Ring of smooth muscle Regulates the passage of material from the stomach into the duodenum Digestion in the Stomach Mechanical Digestion: – Muscular contraction Chemical Digestion: – Secretes digestive enzymes and HCl Small Intestine http://www.afns.ualberta.ca/bbo/1/ANATOMY/SI1.asp 2 meters long, 1 inch in diameter, 5-6 meters in cadaver Functions: – Chemical Digestion – Nutrient Absorption – Motility Anatomy of the Small Intestine Duodenum (25 cm): Fig 25.22 1. Receives stomach contents, pancreatic juice and bile 2. Neutralizes stomach acid and pepsin 3. Pancreatic enzymes and bile take over chemical digestion Anatomy of the Small Intestine Jejunum (2.5m) Ileum (3.6 m) – Reabsorbs bile acids Functions of the Small Intestine Microvilli Motility: smooth muscle contract Digestion: chemical enzymes received from the pancreas, liver and gall bladder Nutrient reabsorption: microvilli increase surface area Dynamic Human: Microvilli Large Intestine Functions – Motility – Reabsorbtion of Water and Electrolytes Symbiotic bacteria – Synthesis Vitamins B & K Anatomy of the Large Intestine Transverse Colon: right to left Ascending Colon: Descending Colon: up the right side down the left side Cecum: sac on Sigmoid Colon: lower right side S-shaped Anatomy of the Large Intestine Rectum: straight down Anal Canal: out the body Appendix: hangs off cecum – Important in Immunity Enzymes Involved in Chemical Digestion Saliva: – Amylase: breaks down starch – Lipase: breaks down fats when it enters the stomach Low pH of the stomach activates the enzyme Enzymes Involved in Chemical Digestion • Stomach: • Digestive chemicals- • HCL: activates enzymes, breaks up foods • Pepsin: digests proteins • Renin: digests milk Pepsin Formation • Interactions between Cells • Chief Cells make pepsinogen • Parietal Cells make HCl • Pepsinogen is cleaved by HCl into Pepsin Dynamic Human: Pepsin Formation Enzymes Involved in Chemical Digestion • Small Intestine • Two sources of enzymes • Liver and Gall bladder • Pancreas Enzymes Involved in Chemical Digestion in the Small Intestine • Liver secretes bile that is active in the small intestine • Bile: aids in fat digestion and absorption •Activates pancreatic enzymes •Synthesized from cholesterol •Bacteria in the small intestine use bilirubin to make your feces brown • Gall bladder stores and concentrates bile Gall Stones What is a gall stone? How do they treat gall stones? How is the gall bladder removed? Enzymes Involved in Chemical Digestion in the Small Intestine Pancreas: secretes pancreatic juice 1. Amylase: breaks down starch 2. Lipase: breaks down fats 3. Ribonuclease (RNAase): breaks down RNA 4. Deoxyribonuclease (DNAase): breaks down DNA 5. Zymogens: inactive enzymes that activate in the small intestine Mechanism of Absorption Membrane Transport: – Nutrients pass through membrane surface – The greater the membrane surface area, the greater the amount of nutrients that can be transported Surface Area – Rugae – Microvilli Final Destinations of Digestion Products Starches bloodstream Fats lymph vessels (lacteals) Proteins bloodstream Dynamic Human: Visualization Cat Dissection Be able to locate and Also know accessory identify organs – Esophagus – Tongue – Stomach – Teeth – Small Intestine – Gall Bladder – Large Intestine – Liver Ascending colon Transverse colon Descending colon Conclusion Review today’s material – Dynamic Human Overview Know cat anatomy Lab Practical II returned – well done! Next week – Endocrine!!!