Digestion

1. Digestion Anatomy and Physiology

2. Functions of the Digestive System • Ingestion – taking in the food • Digestion – breaking apart macromolecules found in food • Absorption – passing the monomers into the blood stream • Waste Elimination – removing the indigestible and unabsorbable foods

3. Path of Food Through the Body • Oral Cavity of Mouth – mechanical digestion and chemical digestion – saliva contains amylase which begins the breakdown of starch/it also has anti-bacterial agents • Pharynx – common passage of food and air – splits to form the esophagus and trachea – has 2 layers of smooth muscle to cause peristalsis • Esophagus – Peristalsis continues to the stomach

4. Path of Food Through the Body • Stomach (4-6 hrs.) • Mechanical digestion – smooth muscle contracts which grinds the stomach/rugae (folds of mucosa) helps grind and expand the stomach • Chemical Digestion • Chief cells – make pepsin which begins the breakdown of proteins • Parietal cells – make hydrochloric acid to activate the pepsin • Goblet cells – secrete mucous to protect the stomach lining which replaces itself every day • Little to no absorption of food in the stomach • Holds 1 gallon of food – turns it into chyme • Cardiac Sphincter – separates the esophagus from the stomach and keeps stomach acid from splashing back into the esophagus (heart burn or acid reflux) • Pyloric Sphincter – holds the food into the stomach until it’s ready to pass into the small intestine

5. Path of Food Through the Body • Small Intestine (4-8 hrs.) Major organ of digestion and absorption of nutrients (arranged into villi for ↑absorption and cells have microvilli • Duodenum (10”) – food empties in thru the pyloric sphincter • Pancreas empties sodium bicarbonate (base to neutralize the stomach acid) into it • Pancreas empties almost all the digestive enyzmes into it (digest proteins, carbs, lipids) • Liver empties bile to physically break apart fat so that enzymes have better access • Gallbladder empties concentrated bile • Jejunum to the Ileum (12’) – villi decrease as less is being absorbed

6. Path of Food Through the Body • Large Intestine (12-24 hours) Mostly to remove excess water from undigested food and move it to the rectum • Cecum – undigested food enters thru the ileocecal valve • It moves thru the ascending, transverse, descending and sigmoid colon • No villi, a lot of mucous producing cells and bacteria to digest the undigested food (produce gas) and make some vitamins • Rectum – storage until defecation • Anus – removal (anal sphincter – skeletal muscle

7. Accessory Organs of Digestion • Pancreas – dumps sodium bicarbonate into sm. intestine to neutralize stomach acid/dumps many digestive enzymes into the duodenum to break down proteins, sugars, and fats • Non-digestive function – insulin – controls blood sugar levels • Gallbladder – stores excess bile, concentrates it and dumps it into the duodenum • Salivary glands - make mucous and saliva (breaks down starch and kills bacteria) • Liver – makes bile (physically breaks down fat and helps with vitamin absorptionl) & dumps it into the duodenum

8. Accessory Organs of Digestion • Liver functions continued (not all digestive) • Removes aa, glucose, f.a. from blood to make blood proteins, cholesterol, and glycogen • Stores glycogen when too much glucose is in the blood, breaks it back down into glucose and releases it into the blood when blood glucose is low • Make LDL – carry cholesterol to cells and some deposits on the arteries • Make HDL – cleans arteries and brings fats to the liver to be disposed of • Makes albumin (blood homeostasis), and clotting proteins • Detoxifies drugs and alcohol • Kills bacteria that enter blood stream from the digestive tract

9. Summary of Digestion • Carbohydrates – begin digestion in the mouth/finish in the small intestine • Proteins – begin digestion in the stomach/finish in the small intestine • Fats – total digestion in the small intestine • Nucleic Acids (DNA & RNA) – total digestion in the small intestine

10. Vitamins - coenzymes • Water Soluble • B – coenyzmes for cellular respiration • C – collagen synthesis, anti-oxidants • Water Insoluble • A – visual pigments, anti-ox • E – prevent membrane damage, anti-ox • K – blood clotting • D – Calcium absorption

11. Minerals - Cofactors • Ca, Na, Cl, K – muscle contraction • Ca – harden bones • I – make thyroid hormone • Fe – need in hemoglobin to attach oxygen • P – to make ATP and activate enzymes • Mg, Zn, Cu, Mn, Se, Mb - cofactgors