1. Food and Your Digestive System The basics

2. We need food for 2 things: Nutrients  Serve as building blocks  Used to maintain and build tissues Energy  Release energy when metabolized in cells  Break down large organic molecules to make ATP

3. The chemical composition of your body is roughly equal to the proportions of the same elements and molecules in the food you eat. (You are what you eat!)

4. Nutrient  Any component of the food that we eat that our body needs to function properly.  Macro: essential elements we need in large amounts  Micro: essential elements we need in very small amounts

5. Getting to the Matter and Energy  Most foods have essential and nonessential nutrients the we use  If our diet isn’t balanced:  Get too much or too little of a particular nutrient  Get too much or too little energy

6. Key Info Carbs  Used for energy, DNA/RNA, digestion  Excess converted to glycogen and fats Lipids  Give food flavor and tenderness  Carry vitamins A, D, E & K  Used for alternate fuel, insulation, cell membranes, emulsifiers, hormones, bile salts

7. Key Info Proteins  2 kinds: animal & plant  Enzymes, fiber (collagen), active transport, salt/water balance, energy alternative, hormones, antibodies, hemoglobin Vitamins & Minerals  Vitamins: cell formation, antioxidant, calcium absorption, blood clotting, vision, growth, bone remodeling, immune system  Minerals: bones and teeth, nerve transport, muscle contractions, heart rhythm, ATP, nerve impulses

8. Some Thoughts  We take in energy continuously  We use energy periodically  Optimal: energy input = energy output  Any calories above daily need are converted and stored as fat

9. Food and Energy  Energy available in food is measured by “burning” food.  Energy in food is converted to heat and measured as a calorie  Energy stored in food called dietary Calories (capital “C”).  One Calorie = 1000 calories

10. Digestion – the Players  Mouth  Pharynx  Esophagus  Stomach  Small Intestine  Large Intestine  Function: Convert foods into simpler molecules for absorption and use by cells. Chapter 38

11. Mouth & Esophagus  Teeth – cutting, tearing, crushing food  Saliva – secreted by salivary glands;  Moisten food  Start chemical digestion of starches with enzyme called amylase.  Create chewed clump of food (“bolus”)  Bolus travels down esophagus to stomach by peristalsis Chapter 38

12. Stomach  Large, muscular sac  Chemical digestion: Needs glands!  Mucus – protects stomach lining  Hydrochloric acid – makes contents acidic  Pepsin – enzyme to digest proteins  Mechanical digestion: Needs muscle!  Muscles contract to churn and mix stomach fluids and food. Result: chyme Chapter 38

13. Small Intestine  Pyloric valve opens and chyme flows from stomach to small intestine.  Most chemical digestion and absorption happens in small intestine.  First of three parts of SI: duodenum  Where almost all digestive enzymes enter  Enzymes from pancreas, liver and lining of duodenum Chapter 38

14. Small Intestine & Accessory Structures  Other two parts of SI: jejunum and ileum  About 6 meters long!  Small intestine lined with villi (finger-like projections)  Increase surface area for absorption of nutrient molecules  Pancreas – regulate blood sugar levels  Liver – produces bile to break down fatty molecules Chapter 38

15. Accessory Structures Pancreas  Gland  Produces enzymes for carbs, proteins, lipids, and nucleic acids  Produces sodium bicarbonate – neutralizes stomach acids so enzymes can work Liver  Organ  Bile – acts like a detergent  Allows enzymes to reach smaller fat molecules Chapter 38

16. Absorption in Small Intestine  When chyme enters jejunum and ileum, it has become mix of small and medium nutrient molecules  These molecules rapidly absorbed into the cells lining the SI  Capillaries in the villi – carbs and protein  Lymph vessels – undigested fat and fatty acids  What’s left: water, cellulose, other undigestible substances Chapter 38

17. Large Intestine (Colon)  Removes water from undigested material  Bacteria in the large intestine produce vitamin K  Concentrated waste material exits through the rectum (poop) Chapter 38

18. Chewing amylase Mouth chemical mechanical Stomach Chemical Absorption Small Intestine Water Bacteria Large Intestine Chemical: acid and enzymes Mechanical: muscle contractions Chemical: enzymes Food leaves nutrient-free Pancreas & Liver play role here Amylase: breaks down starches Poop Vitamin K RECAP! Chapter 38 bolus chyme

19. Disorders  Peptic ulcers – hole in stomach wall  Vitamin K deficiency – loss of bacteria in LI  Diarrhea & Constipation – disruption in the removal of water by large intestine  Recall: enzymes are proteins  No sodium bicarbonate = enzymes can change shape and become ineffective (active site doesn’t match substrate) Chapter 38

20. Organs of Excretion  Skin – excretes excess water, salts, and small amount of urea  Lungs – excrete carbon dioxide  Liver – converts amino acids, producing nitrogen waste. Then converts nitrogen waste into urea.  Kidneys – principle organs of excretion  Remove waste products from blood  Maintain blood pH  Regulate water content of blood (blood volume) Chapter 38 - 3