Digestive System Get out Tuesday’s notes, your journal, and a pencil.

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

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

Accessory Organs Teeth Tongue Salivary Glands Liver Gall Bladder Pancreas

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

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

Large Intestine Functions – Motility – Reabsorbtion of Water and Electrolytes Symbiotic bacteria – Synthesis Vitamins B & K

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

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

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

Final Destinations of Digestion Products Starches  bloodstream Fats  lymph vessels (lacteals) Proteins  bloodstream

Complete digestive system packet

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