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 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 Rugae- folds in the stomach lining that allow it to expand with more food How do we vomit?

Pyloric Sphincter 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 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): 1. Receives stomach contents, pancreatic juice and bile 2. Neutralizes stomach acid and pepsin 3. Pancreatic enzymes and bile take over chemical digestion Fig 25.22

Anatomy of the Small Intestine Jejunum (2.5m) Ileum (3.6 m) – Reabsorbs bile acids

Functions of the Small Intestine Motility: smooth muscle contract Digestion: chemical enzymes received from the pancreas, liver and gall bladder Nutrient reabsorption: microvilli increase surface area Microvilli

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 identify – Esophagus – Stomach – Small Intestine – Large Intestine Ascending colon Transverse colon Descending colon Also know accessory organs – Tongue – Teeth – Gall Bladder – Liver

Conclusion Review today’s material – Dynamic Human Overview Know cat anatomy Lab Practical II returned – well done! Next week – Endocrine!!!