Chapter 3 Lecture Notes: The Physiology of NutritionPROBLEM: We have big macronutrients that cannot be digested without being broken down into smaller parts so we can digest it. Need a sieve to filter out all the bacteria: 1) Moutha) Chewing- smaller chunks and mixing with juices. Without it, it delays and complicated digestion. b) Digestive juice: saliva… moistens and lubricates the food. c) Saliva contains enzymes (protein catalyst) like amylase- (works on amylose or starch) to break down. i) Ex: chewing bread for a long time. Gets sweeter because the smaller it gets, the more it becomes sugar-like. 2) Esophagusa) Connects mouth to stomach. b) Peristalsis: keeps food moving forward with a wave of rhythmic contractions. Able to hear with stethoscope (gut noises). i) Proven it works because you can fight against gravity and swallow upside down. Muscle contractingii) Think of pushing a popsicle up through its wrapper. 3) Stomacha) Reservoir/Tank for the slow release of food into small intestine. b) Small intestine can’t handle food all at once. Stomach allows us to eat big meal and then slowly release it. i) People without stomach: have to graze all day… can’t handle food all at once. c) Very muscular. Allows for churning- muscular squeeze. Makes up for not chewing the food. (Doesn’t work as well because stomach has no teeth)d) Mixes with juicesi) Hydrochloric acid. (1) Denatures Protein- changes form. Opens it up and stretches it out, making it easy to break down. (2) Kills a lot of the bacteria. ii) Protease- breaks down proteins. Starts after denaturation. e) Mucus barrier on inside of stomach that protects stomach from acid and protease so you don’t digest yourself. Failure= ulcer. i) Infections in the stomach break down the mucus barrier. Stress secretes more acid, which can increase ulcers. f) Pyloric sphincter allows for gradual flow of chyme into small intestine. 4) Small Intestine- Mucosal cellsa) Most secretion.b) 3 sections: duodenum, jejunum, ilium. Folds to it, that increase the surface areai) Folds covered in villi which make it bigger and help pass. (1) Helps absorption (95%+ of macronutrients absorbed, thanks to big S.A.)(2) Villi is brush border. Fingerlike. Villi covered in microvilli- tons of absorbtion from all the S.A. ii) Peristalsis- wave of contraction. Moves things alongiii) Segmentation- Mixing of digestive juices. iv) Chemical Breakdown(1) Enzymes breaking down macronutrients. Tons of enzymes, made in the pancreas. (a) Lipase- works of lipid. (b) Amylase- breaks down amylose (starch) (diff than in saliva). (c) Protease- breaks down protein. (d) Sodium bicarbonate- baking soda- neutralizes the stomach acid so the small intestine is safe  Much milder and less harsh. (e) Bile- Produced in the liver and stored in the gall bladder. Serves as an emulsifier… (i) Breaks down fats into smaller drops. Allows for it to mix with the water and juices. Doesn’t allow for separation. 1. Needed to increase the surface area, which allows for lipaseto break the lipid (fat) down. (ii) Gallstones out= tough time digesting fat. Bile keeps drizzling down and there’s not enough to emulsify it. (f) disacaridases- produced here in small intestine. Breaks down lactose. (g) 17 feet long small intestine. 5) Large Intestine/ Colona) Major function: water reabsorption. b) Tons of water (7 liters) secreted with all the juices above. Keeps the food moist so it can move. c) Drink water on an empty stomach- Free water- not absorbed into the food- done in small intestine. Absorption. (NOT REABSORBTION- THAT’S LARGE INTESTINE) d) Large Bacteria population in colon. e) Some nutrient absorption. 6) Rectum- a) reservoir for elimination. 7) Major sites of absorptiona) Bloodstreami) Amino acids, vitamin c, monosacharides (EVENTUALLY TO LIVER) b) Into lymphatic system (fat goes there)8) Fiber in diet allows for good digestion. Without fiber, you’ll be constipated. a) Fiber allows for big soft stools to passb) Lack of fiber makes for small, hard, dry stools that stick to the color and don’t