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Human Biology (BIOL 104) Talk Five: Digestion and Nutrition Chapter 11 So, what do we usually eat? • Carbohydrates: To give us ENERGY! We need energy for heat, movement, and chemical reactions in our bodies. • Proteins: Essential amino acid’s. Our body can’t make them; they must come from foods we eat. • Meat, milk, and eggs contain all the essential amino acids we need • Fats: Energy! We can use it or store it. Fat contains more energy than carbohydrates. 1 gram of Fat = 2x the energy in 1 gram of Carbs. • Used for Cell Membranes and Heat Insulation Carbohydrates Protein Lipids Copyright ©The McGraw-Hill Companies; used with permission So, how do we digest food? • In the human digestive system, the process of digestion has many stages, the first of which starts in the mouth (oral cavity). • Digestion involves the breakdown of food into smaller and smaller components which can be absorbed and assimilated into the body. • The secretion of saliva helps to produce a bolus which can be swallowed in the esophagus to pass down into the stomach. • This initially results in the production of chyme which when fully broken down in the small intestine is absorbed into the blood. • Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood, in the colon of the large intestine. • The waste products of digestion are defecated from the anus via the rectum. • 1: Mechanical processing and motility – Teeth, the tongue, and various muscle layers start the process and send food on its journey • 2: Secretion – Release of enzymes & chemicals for digestion and absorption • 3: Digestion – Chemical breakdown of food – small molecules absorbed • 4: Absorption – Nutrients move into the blood • 5: Elimination – Undigested and unabsorbed residues excreted Digestion occurs in 5 stages The first step- Chewing and swallowing • Types – Mechanical (physical) • Chew • Tear • Grind • Mash • Mix – Chemical • Enzymatic reactions to improve digestion of – Carbohydrates – Proteins – Lipids http://www.daviddarling.info/encyclopedia/T/teeth The first step- Chewing and swallowing • Teeth mechanically break down food into small pieces. • Tongue mixes food with saliva • Saliva contains amylase • Mucus • Buffers – helps break down starch. – protects soft lining of digestive system – lubricates food for easier swallowing • neutralizes acid to prevent tooth decay • Anti-bacterial chemicals • Epiglottis is a flap-like structure at the back of the throat that closes over the trachea preventing food from entering it. – kill bacteria that enter mouth with food From the wikimedia free licensed media file repository From the wikimedia free licensed media file repository Digestive Glands • Groups of specialized secretory cells. • Found in the lining of the alimentary canal or accessory organs. Taste Buds • As the food particles dissolve in the saliva they penetrate the cells of the taste buds located on the tongue and cheeks. • Humans can differentiate between • sweet • sour • salty • bitter From the wikimedia free licensed media file repository • Approximately 10” long • Functions include: – Secrete mucus – Moves food from the throat to the stomach using muscle movement called peristalsis The Esophagus • A good way to describe peristalsis is an ocean wave moving through the muscle. – Has no role in chemical digestion – all it does is bring food (BOLUS) to stomach. • Sphincters – ring of muscle that encircle tubes. – Contraction closes tubes – Keeps acid in stomach – usually! From the wikimedia free licensed media file repository The Stomach- Digestion and Storage • The stomach acts as a temporary storage site for food. • Food usually spends about 4 hours in the stomach. • It has ridges which allow it to expand to store about 1.5 litres of food. • The stomach is also the site of initial protein digestion. From the wikimedia free licensed media file repository The StomachDigestion and Storage • Millions of cells lining the stomach secrete various fluids known collectively as gastric fluids. • Gastric fluid consists of mucus, hydrochloric acid, pepsinogens and other substances. • Mucus coats and protects the lining of the stomach. • Hydrochloric acid kills any harmful substances that have been ingested and it also converts pepsinogen into pepsin. • Pepsin is a protein digesting enzyme that breaks large protein chains into smaller chains. From the wikimedia free licensed media file repository The Stomach- Digestion and Storage • Movement of food into and out of the stomach is controlled by circular muscles known as sphincters. • One at the top of the stomach allows food from the esophagus to enter and prevents food from going back up into the esophagus. • Another located at the bottom slowly releases partially digested food into the small intestine. • Alcohol and some water are absorbed here – food is not. • The partially digested food is called chyme. From the wikimedia free licensed media file repository The Intestines • The intestines are named for their diameter, not length. • The small intestine is up to 7 m in length but only 2.5 cm in diameter. • The large intestine (also known as the Colon) is only 1.5 m in length but 7.6 cm in diameter. The small intestine • Where much of the digestion and absorption of food takes place. • It receives bile juice and pancreatic juice through the hepato-pancreatic duct, controlled by a sphincter • The small intestine is where most chemical digestion takes place. • Most of the digestive enzymes that act in the small intestine are secreted by the pancreas and enter the small intestine via the pancreatic duct • Approx 20 feet in length – First 25 cm – Duodenum • A duct brings Bile (from Liver and Gallbladder) – emulsifies fat – disperses in water • A duct brings Pancreatic Juice from Pancreas. Contains – NaCHO3 – neutralizes chyme – enzymes to complete food digestion. • The small intestine contains Villi – absorb nutrients. • Sugars & amino acids enter blood capillaries • Glycerol and fatty acids enter lymph nodules • Almost 90% of our daily fluid intake is absorbed in the small intestine. The small intestine Small Intestine • Nutrients from the food pass into the bloodstream through the small intestine walls. • Absorbs: – 80% ingested water – Vitamins – Minerals – Carbohydrates – Proteins – Lipids • Secretes digestive enzymes Segmentation in the Small Intestine • Unlike peristalsis, which predominates in the esophagus, segmentation contractions occur in the large intestine and small intestine, while predominating in the latter • When the contractions of the intestinal wall move chyme in both directions to allow mixing with the secretions of the intestines. The small intestine - Villi • Increases surface area of small intestine • Each villus contains a capillary network along with a lacteal. • The lacteal is a vessel of the lymphatic system. • End products of protein and carbohydrate digestion enter the capillary network. • End products of fat digestion are absorbed into the lacteal. From the wikimedia free licensed media file repository The small intestine - Villi • The Hepatic Portal Vein takes all absorbed nutrients (except large fat molecules) from villi to the liver for further processing and storage. • 4-1/2 feet long – Absorbs water, salts and some vitamins The large Intestine • Stores indigestible material for defecation • Contains the: – Cecum (blind end of ascending colon). – Appendix located here. • Colon- Ascending, Transverse, Descending and Sigmoid. • The sigmoid Colon enters Rectum (last 20 cm of large intestine, where it opens at the Anus. • Feces: ¾ water and ¼ solid Copyright ©The McGraw-Hill Companies; used with permission • Functions The large Intestine • Bacterial digestion • Ferment carbohydrates • Protein breakdown • • Absorbs more water Concentrate wastes • Solid materials pass through the large intestine. • These are undigestible solids (fibers). • Water is absorbed. • Vitamins K and B are reabsorbed with the water. • Rectum- solid wastes exit the body. Copyright ©The McGraw-Hill Companies; used with permission The large Intestine – You’ve got company! • Living in the large intestine is a community of helpful bacteria – Escherichia coli (E. coli) • produce vitamins – vitamin K; B vitamins • generate gases – by-product of bacterial metabolism – methane, hydrogen sulfide The Accessory Organs • The Liver: • 100,000 lobules monitor and clean blood, produce bile for gallbladder. • Detoxify blood, store iron, vitamins A, D, E and K. • Helps regulate blood sugar (glycogen, glycerol, Amino acids), destroys old blood cells. • Helps regulate cholesterol (bile salts). • Makes urea which is worked on by kidneys Copyright ©The McGraw-Hill Companies; used with permission The Accessory Organs • The Gall Bladder: • Pouch structure located near the liver which concentrates and stores bile • Bile duct – a long tube that carries BILE. • The top half of the common bile duct is associated with the liver. • The bottom half of the common bile duct is associated with the pancreas, through which it passes on its way to the intestine. • Bile emulsifies lipids (physically breaks apart FATS) Copyright ©The McGraw-Hill Companies; used with permission The Accessory Organs • The pancreas: • An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine) • Pancreatic juice digests all major nutrient types. • Exocrine pancreas produces NaHCO3, amylase (starch), trypsin (protein) and lipase (fat). • Endocrine pancreas produces insulin and glucagon. Copyright ©The McGraw-Hill Companies; used with permission Human Nutrition • The provision to obtain the essential nutrients necessary to support life and health. • In general, people can survive for two to eight weeks without food, depending on stored body fat and muscle mass. • Poor nutrition is a chronic problem linked to poverty, poor nutrition understanding and practices, and deficient sanitation and food security. Copyright ©The McGraw-Hill Companies; used with permission Human Nutrition • Malnutrition globally provides many challenges to individuals and societies. • Lack of proper nutrition contributes to worse class performance, lower test scores, and eventually less successful students and a less productive and competitive economy. • Malnutrition and its consequences are immense contributors to deaths and disabilities worldwide. • Promoting good nutrition helps children grow, promotes human development and advances economic growth and eradication of poverty. Copyright ©The McGraw-Hill Companies; used with permission So, what do we usually eat? • Carbohydrates: To give us ENERGY! We need energy for heat, movement, and chemical reactions in our bodies. • Proteins: Essential amino acid’s. Our body can’t make them; they must come from foods we eat. • Meat, milk, and eggs contain all the essential amino acids we need • Fats: Energy! We can use it or store it. Fat contains more energy than carbohydrates. 1 gram of Fat = 2x the energy in 1 gram of Carbs. • Used for Cell Membranes and Heat Insulation Carbohydrates Protein Lipids Copyright ©The McGraw-Hill Companies; used with permission Eating a balanced diet • What happens if a human’s diet is missing an essential nutrient? – deficiency diseases • • • • scurvy — vitamin C (collagen production) rickets — vitamin D (calcium absorption) blindness — vitamin A (retinol production) anemia — vitamin B12 (energy production) Vegetarian diets • Need to make sure you get enough protein • 20 amino acids to make protein – 12 amino acids humans can produce – 8 we have to eat = “essential amino acids” • Grains (like corn) have 6 amino acids (orange box) – missing 2 • Beans (like soybean & red beans) have 6 amino acids (green box) – missing different 2 • mix beans & grains for complete group of amino acids – – – – rice & beans taco/tortilla & beans tofu & rice peanut butter & bread Copyright ©The McGraw-Hill Companies; used with permission Vitamins • Organic compounds needed by the body in small, but essential amounts • Cannot be synthesized by the body in sufficient amounts • Function in a variety of ways in metabolic reactions • Thirteen known vitamins • Water-Soluble Vitamins Versus Fat-soluble Vitamins Water-Soluble Vitamins C (ascorbic acid) B1 (thiamin) B2 (riboflavin) Niacin Pantothenic acid Biotin B12 (cyanocobalamin) Folic acid B6 (pyridoxine) Fat-soluble Vitamins Copyright ©The McGraw-Hill Companies; used with permission Vitamins • • • • • • • • • Vit A- Antioxidant: healthy eyes, hair, bones Vit D – Steroid: bones and teeth Vit E – Antioxidant: healthy unsaturated fats Vit K – Clotting blood Vit C – Antioxidant: Capillaries, bones teeth Vit B1 – coenzyme for cellular respiration Vit B6 – coenzyme for hormones and hemoglobin Vit B12 – coenzyme for synthesis of nucleic acid Biotin – coenzyme for metabolism of ammino acids and fatty acids Minerals • Essential inorganic elements • Involved in a variety of metabolic processes • Major minerals versus trace minerals From the wikimedia free licensed media file repository Essential dietary minerals • Chlorine: as chloride ions along with Sodium • Magnesium: required for processing ATP and related reactions – builds bone, causes strong peristalsis, increases flexibility, increases alkalinity. • Phosphorus: required component of bones; essential for energy processing Approximately 80% is found in inorganic portion of bones and teeth. Phosphorus is a component of every cell, as well as important metabolites, including DNA, RNA, ATP, and phospholipids. – Also important in pH regulation. Food sources include cheese, egg yolk, milk, meat, fish, poultry, whole-grain cereals, and many others. • Potassium: a very common electrolyte (heart and nerve health). With sodium, potassium is involved in maintaining normal water balance, osmotic equilibrium, and acid-base balance. – In addition to calcium, it is important in the regulation of neuromuscular activity. Food sources include bananas, avocados, vegetables, potatoes, legumes, and mushrooms. Trace minerals • Cobalt required for biosynthesis of vitamin B12 family of coenzymes • Copper required component of many redox enzymes, including cytochrome c oxidase • Chromium required for sugar metabolism • Iodine required for important organs as breast, stomach, salivary glands, thymus etc. • Iron required for many enzymes, and for hemoglobin and some other proteins • Manganese required for the processing of oxygen • Nickel present in urease • Zinc required for several enzymes such as carboxypeptidase, liver alcohol dehydrogenase, carbonic anhydrase