Digestion & Nutrition PDF

CHAPTER 14* Digestion and Nutrition *Optional HW for this chapter  You are what you eat! (So avoid nuts and pigs) Cells need raw material for constructing proteins, fats, sugars and nucleic acids, as well as energy sources, as well as vitamins and minerals and wat...

CHAPTER 14* Digestion and Nutrition *Optional HW for this chapter  You are what you eat! (So avoid nuts and pigs) Cells need raw material for constructing proteins, fats, sugars and nucleic acids, as well as energy sources, as well as vitamins and minerals and water. Large food molecules broken into small molecules by the digestive system and absorbed, then transported to the cells for present needs, or stored for future needs. Unabsorbed materials are eliminated when we defecate  Digestive system Gastrointestinal tract is a hollow tube: mouth  pharynx  esophagus  (S) stomach (S)  small intestine  large intestine  rectum  anus (S) (S) Sphincters (S) separate the acidic stomach from other regions, and control defecation Accessory organs: salivary glands (mouth), liver, gall bladder, pancreas Digestive System  The Mouth: Teeth Very hard, non-living, enamel coating (calcium and phosphate). Living dentin (bone like tissue) supplied by blood vessels in pulp and has nerves too. Incisors cut, canines tear, molars crush and grind. Wisdom teeth: a vestigial structure Brush your teeth! Bacteria live in the mouth on leftover food. Plaque: a sticky film of bacteria, proteins, food particles and mucus, may harden into tartar. Bacteria take up residence and produce acids leading to tooth decay. Gingivitis: infection / inflammation of the gums, due to bacterial toxins Periodontal disease: chronic inflammation  loss of bones and tissue holding teeth in place: tooth loss  The Mouth Mouth: begins enzymatic digestion of carbohydrates Tongue: skeletal muscle, positions food for teeth, five basic tastes with taste buds: sweet, sour, salty, bitter and umami (= broth). Saliva Source: salivary (exocrine) glands below tongue, beside jaw Composition: water, mucin (lubrication for swallowing, and holds food together), salivary amylase (begins breaking down carbohydrates), bicarbonate (counteracts acid produced by bacteria, keeps pH in range that salivary amylase works), lysozyme (kills bacteria)  fig 14.5  Swallowing: Delivers Food to Esophagus Voluntary phase: tongue pushes food into pharynx Involuntary phase/swallowing reflex: receptors in pharynx stimulated by presence of food 1) Vocal cords tighten across larynx 2) Soft palate rises (closes off nasal passageway) 3) Larynx rises slightly (helps close off trachea) 4) Epiglottis closes opening to trachea (fully closes trachea) 5) Back of tongue pushes food further into esophagus Swallowing: a reflex What should you do if someone’s choking? Heimlich Maneuver  Pharynx and Esophagus Pharynx Common passageway for air and food Participates in swallowing Esophagus: connects pharynx to stomach Mucus secreting cells: assist passage of food downward Food motility: gravity and peristalsis Lower esophageal sphincter: separates esophagus and stomach. Stomach is very acidic, and acid reflux is painful, may cause esophageal ulcers and cancer. Motility: Peristalsis (in esophagus) Muscle contractions from behind pushes food forward, muscles relax ahead of food ball (bolus).  Stomach Function Functions: Food storage (until digestion can proceed, stomach is quite elastic) Digestion (strong acids and protein digesting enzyme: pepsinogen  pepsin) Regulation of delivery (food delivered to small intestine in manageable amounts) Kills most bacteria in food Only a few things absorbed in stomach: alcohol, aspirin  Gastric juices Gastric juice: secreted by different cells in gastric pits Hydrochloric acid: produces a pH of about 2, denatures proteins (exposing bonds that hold amino acids together). Also kills most bacteria. Pepsinogen  pepsin: an enzyme, begins protein digestion into individual amino acids Mucus: protects stomach lining from acid. Stomach contents are in contact with mucus, not cells. Ulcers: when stomach inner lining is not protected. Helicobacter pylori bacterial infection causes most ulcers, cigarettes, alcohol and regular aspirin use also can cause ulcers. Gastric pits  Stomach Contraction (peristalsis) Stomach contractions: blend food (exposes all food to gastric juices) and squirts food into small intestine Three muscle layers for mixing Direction: from lower esophageal sphincter to pyloric sphincter and back. Small amounts of chyme (food) squeezed into small intestine each time. Chyme: result of mixing. Highly acidic chyme (needs more neutralization) and high fat (needs more digestion time) slows contractions / delivery to small intestine (hormones released by small intestine do this). Small Intestine (duodenum) Digestion in the duodenum: first 25cm of s. intestine 1) Neutralize acid from stomach (pancreas secretes a base, sodium bicarbonate. pH becomes 8) 2) Add bile (secreted by liver, stored by gall bladder) which breaks fat into smaller droplets for digestion / absorption = emulsification. Bile composed of water, cholesterol, bile salts, lecithin (phospholipid) and pigments (old heme groups) 3) Add digestive enzymes (pancreas and small intestine secrete enzymes for carbohydrate, protein, nucleic acid and fat (lipase) digestion) Digestion in duodenum  Absorption: After enzymatic breakdown of food into monosaccharides, amino acids, nucleotides, fatty acids and monoglycerides (basic components) 95% of food absorbed in 6 m of the remaining small intestine (jejunum and ileum).  Small Intestine, absorption Mucosa expands total surface area of small intestine: Huge surface area for absorption: folds in small intestine, each fold has villi and each villi has cells with small projections (microvilli) Motility: Segmentation in small intestine “Random” movements mixes contents, food is pressed against mucosa where nutrients are absorbed. Villi of small intestine Villi contain blood and lymph capillaries. Absorption of nutrients and water Amino acids and monosaccharides are actively transported into epithelial cells, diffuse to capillaries. Fatty acids and monoglycerides diffuse into cells. They reform into triglycerides. Fats then join with proteins in mucosa cells for transport, they are released by exocytosis and enter lymph capillaries (large spaces between cells). Lymph later joins with the blood circulation (lymph vessels join with veins near the heart). Vitamins and minerals: active transport for some vitamins and minerals, protein channels (diffusion) for others. Fat soluble vitamins transported similar to fats. Water: absorbed by osmosis in small intestine and large intestine Absorption of Proteins and Carbohydrates Absorption of Fats After absorption, transported to liver Hepatic portal system: blood from digestive tract (stomach, small intestine and large intestine) to liver before going to general circulation Some functions of the liver: 1) Stores: glucose as glycogen, fat soluble vitamins, some lipids 2) Manufactures: fibrinogen, albumin, other proteins, some lipids, bile (in part from cholesterol) 3) Detoxifies: poisons, including drugs and alcohol 4) Detoxifies: ammonia to urea 5) Breaks down old red blood cells (uses heme for bile, stores iron to create future red blood cells) 6) Removes excess cholesterol from blood, and adds it to bile. Fish oil helps this.  Large Intestine: Structure and Function Functions: absorbs remaining nutrients and remaining water, wastes stored then eliminated (rectum  anus) Structure: Cecum (receives chyme from small intestine), appendix. Appendix can get infected and inflamed in appendicitis, and is usually removed. It can rupture leading to death. Colon: ascending, transverse, descending, sigmoid Rectum, anus (with smooth muscle and skeletal muscle sphincters) Bacteria thrive in colon and are associated with feces: produce Biotin, Vitamin K and B6 but also gas A lot of research is showing that the types of bacteria in our large intestine influences our health, including: obesity, diabetes, depression, irritable bowel syndrome, colon cancer, Crohn’s disease, etc. Large Intestine  Nutrition: carbohydrates Carbohydrates: major energy source: we need glucose circulating in our blood. Can be converted to fats / glycogen for energy storage. Eat complex carbohydrates (bread, pasta, potatoes, rice, beans, etc.) not simple sugars: Simple sugars lead to surge in blood sugar and insulin (within minutes), sugars converted to fat, then low blood sugar (=hunger again) which causes you to eat more. Simple sugar also causes your liver to make more harmful (LDL) cholesterol. Complex carbohydrates are digested and absorbed gradually. Eat brown bread, brown pasta, brown rice instead of white: “Brown” carbohydrates do not have parts of the grain removed, and have move vitamins and minerals associated with them.  Nutrition: lipids Lipids: Also with a lot of energy. Fats and oils can be saturated or unsaturated. Healthy unsaturated fats include: corn oil, canola oil, olive oil, sunflower oil Saturated fats include: red meats, milk fats, butter, lard, but also palm oil and coconut oil Trans fats are often found in processed (manufactured) foods: cookies, crackers, doughnuts, cakes, deep-fried foods (french fries) and margarine. Saturated fats and trans fats tend to raise blood LDL (“bad”) cholesterol levels. Too much LDL cholesterol contributes to heart attacks, strokes, aneurysms, gallstones. Omega-3 fatty acids (found in certain fish) reduce your risk of heart disease.  Nutrition: proteins Proteins for our proteins and for energy: 20 amino acids, body manufactures 12. 8 essential amino acids that we must get through our diet. Animal proteins, including eggs, milk and milk products as well as soy bean products (like tofu) have all essential amino acids. Other plants (rice, beans, vegetables) will not have all the essential amino acids in one plant (so strict vegetarians must mix them: rice AND beans, for example). Proteins low in saturated fats and cholesterol include: fish and other seafood, vegetable proteins, low fat milk products and chicken without skin Nutrition: vitamins Vitamins are molecules needed in small quantities that humans (mostly) cannot manufacture themselves. What are good sources of vitamin A? Vitamin A Yellow, orange and green leafy veggies. Also fish, egg yolk, liver. Needed for pigment in rod cells of retina and maintaining skin. Deficiency: Night blindness and dry, scaly skin What are good sources of vitamin D? Vitamin D UV light on skin, fortified milk, oily fish, egg yolk. Absorption of calcium from digestive system. Deficiency: bone deformities in kids (rickets), bone weakening and osteoporosis for adults. What are good sources of vitamin K? Vitamin K Bacteria in large intestine, green leafy veggies. Needed for forming clotting proteins. Deficiency: severe bleeding and hemophilia What are good sources of vitamin C? Vitamin C Citrus fruits, berries and certain veggies like broccoli, brussel sprouts, peppers, cabbage. Needed for making collagen. Also an antioxidant. Deficiency: poor wound healing, teeth fall out (scurvy). Minerals (elements) What are good sources of calcium? Minerals: Calcium Milk products, dark green veggies. Bone and tooth formation, neurons and muscles. Deficiency: stunted growth, osteoporosis. Minerals (elements) What are good sources of iron? Minerals: iron Meat, liver, whole grains, green leafy veggies, nuts, eggs. Hemoglobin. Deficiency: anemia. Women need to worry about iron deficiency more than men: blood loss with monthly period. Minerals: iodine Iodine: seafood, iodized salt. Thyroid hormone formation. Deficiency: Enlarged thyroid (goiter). Minerals: Zinc Whole grains, nuts, meats, seafood. Role in normal growth, wound healing. Deficiency: impaired growth, scaly skin. Nutrition: antioxidants Examples of antioxidant foods: vitamin C, vitamin E, vitamin A / beta carotene, various berries, pinto beans, red beans, walnuts, coffee Nutrition: antioxidants What do antioxidants do? They donate electrons to free radicals, so that the free radicals do not take electrons from other molecules (like DNA) that may damage them. Damaged DNA may lead to mutations, which may lead to cancer. Green, leafy veggies: spinach, brussel sprouts and broccoli They have important vitamins and minerals, as well as antioxidants, soluble and insoluble fibers.  Energy: Utilized or Stored Until Needed Excess calories in any form (carbohydrates, lipids and proteins) are converted to glycogen or fat. Fat is stored in adipose tissue cells. Eating too many calories (more than you burn off), in any form, will result in weight gain. Too much weight gain can lead to obesity. Health risks of obesity High blood pressure  (heart attack, stroke, aneurysm) Type II diabetes Several types of cancer Sleep apnea (stop breathing while asleep, then wake up) Osteoarthritis (cartilage in joints under more strain) Gout (uric acid in blood deposited as crystals in joints painful arthritis, usually in the big toe) Gallstones (too much cholesterol in bile)  Weight Control: Energy Consumed Reducing the amount of fat you eat will help limit the calories you take in, as a gram of fat has more than twice the calories of a gram of protein or carbohydrate. If you eat proteins and complex carbohydrates, you will feel full (satisfied), but get less calories. Caloric content: Fat = 9 Calories / g Proteins and carbohydrates = 4 Calories / g Avoid simple sugars as well.  Weight Control: Energy Spent Exercising helps burn off excess calories, and dieting alone, without exercise often does not work for long-term weight loss. Basal Metabolic Rate (BMR) (70% of all energy use) influenced by: Gender (males more muscle  more energy used) Body composition (more muscles  more energy used) Age (muscles decline over time  less energy used) Stress (epinephrine / norepinephrine raise BMR) Food intake (fasting / dieting lowers BMR, the body thinks it’s starving!) Genetics (not known how) Food Guide A healthy diet includes high amounts of whole grains and vegetables, with lesser amounts of fruits and low- fat proteins, and even less low-fat dairy products.  General tips: 1) Eat a variety of foods. A single type of food may not have all the essential amino acids or essential minerals and vitamins you need. There are even some essential lipids (found in corn oil and olive oil, as examples). 2) Maintain a healthy weight and exercise (stop eating when full, eat more small meals, rather than few big meals, cut back on simple sugars and fats, exercise on a regular schedule, with a friend, exercise to feel better psychologically) 3) Eat fruits and veggies! (lots of vitamins, minerals). Fruits like apples and bananas also have soluble fibers (in other foods too, like oats and beans) that lower blood cholesterol. Soluble and insoluble fibers (cellulose fiber found in salads) can help prevent constipation, hemorrhoids and colon cancer.  General tips: 4) Avoid saturated fats, cholesterol and trans fats. 5) Avoid “junk foods” and fast food: they are usually high in salt, simple sugars, saturated fats and trans fats. They often are relatively low in vitamins and minerals. 6) Fish is good to eat (lowers blood cholesterol) and a good, low-fat source of proteins.