Digestion: Digestion Digestion is like a factory in reverse. The body takes a product and breaks it into small subunits. Diseases of the digestive system are: A. E. Coli, and cholera. These produce similar toxins that change the way the cells lining the intestine work. The poison causes water to leave these cells rapidly and enter the intestine, where it passes out of the body in diarrhea. In less than 4 hours, people can lose 25% of their body fluid. The infected person quickly becomes dehydrated and dies.


Mechanical Digestion in the Mouth: Mechanical Digestion in the Mouth Most food is broken apart in the mouth. Herbivores, such as horse and cattle, have front teeth called incisors.


Mechanical Digestion in the Mouth: Mechanical Digestion in the Mouth A rodent’s incisors grow continually, and small molars grid their food. Carnivores such as dogs and cats have well-developed canines (also called cuspids) which are used to tear and shred food. Human teeth do not grow continually. By the age of 6, the 20 primary teeth are gradually replaced by 32 permanent teeth that require continuous care to last a lifetime.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach Saliva is a liquid which contains enzymes that initiate carbohydrate digestion. Amylase and other enzymes join in, breaking long chains of starch, a carbohydrate, into smaller sugars such as maltose. Enzymes are proteins that speed up a reaction and aren't used up in the process.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach Saliva enters your mouth from glands under your tongue. The chewed food is swallowed. It passes through the pharynx into the esophagus.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach The pharynx is part of the digestive treact between the mouth and the esophagus and is shared by the respiratory system. \A flap of cartilage called the epiglottis closes the trachea so that food won’t enter the lungs. Peristalsis pushes the chewed food through the esophagus to the stomach.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach The stomach is a specialized section of the food-processing tube that runs through your body. The stomach holds about 1.2 liters of food.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach Primarily, it digests protein. Small glands just below the inner surface of this muscular organ produce hydrochloric acid (HCL), and enzyme called pepsin, and alkaline mucus. The HCL unfolds the twisted proteins so that pepsin can cut them into amino acids. Pepsin works only in this acidic environment. Eventually, the amino acids are absorbed in the intestines and transported to the various cells of the body. These, cells reassemble them into the specific proteins that they need. The mucus coats the ling of the stomach so that the HCL and pepsin don’t digest the stomach itself.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach The acid in the stomach inactivates the enzymes that began digesting carbohydrates in the mouth. It also destroys most bacteria that are eaten with the food and those in the mucus draining from the nasal area. One bacterium, called helicobacter, an survive in the acid environment, infecting the lining and causing an ulcer.


Chemical Digestion in the Mouth and Stomach: Chemical Digestion in the Mouth and Stomach The liquid content of the stomach is called chyme. The stomach releases chyme into the first part of the small intestine, a digestive organ that lies just below the stomach.


Enzymes in the Small Intestine: Enzymes in the Small Intestine Food travels from the stomach to the small intestine. This portion of the digestive tract is about 3 m long and about 2-3 cm in diameter. As the acidic chyme enters, the pancreas, a digestive gland, pumps, sodium bicarbonate into the lumen to neutralize the acid.


Enzymes in the Small Intestine: Enzymes in the Small Intestine The pancreas produces enzymes that break carbohydrates into sugars and others that finish digesting protein. Some intestinal wall cells make enzymes, such as lactase. Lactase breaks down lactose (milk sugar) into simple sugars that the intestinal wall can absorb. Some people are lactose intolerant: this condition means that their bodies no longer make this particular enzyme and can’t digest lactose.


Enzymes in the Small Intestine: Enzymes in the Small Intestine Gastritis is linked to alcoholism, over production of HCL, infections, and sometimes stress.


Absorption in the Intestines: Absorption in the Intestines The small intestine is lined with fingerlike projections called villi, which increase the absorption area.


Absorption in the Intestines: Absorption in the Intestines If the villi in one person could be stretched flat, they would cover about half of a tennis court.


Absorption in the Intestines: Absorption in the Intestines Some nutrients, such as amino acids, diffuse through the villi cells much as the iodine passed through the plastic bag in activity 13.1. Others, including iron and vitamin B12, are actively transported into the villi cells. They pass through the cells and enter the extensive capillary network underneath the villi. Once they enter the bloodstream, their first stop is the liver on their way to the heart.


Absorption in the Intestines: Absorption in the Intestines Food that is not absorbed passes into the large intestine (also called the colon), a digestive organ that is responsible for the removal of water from undigested material. The cells that line the colon reabsorbs water and salts that are needed for electrolyte balance. When water isn’t properly reabsorbed, diarrhea occurs. Bacteria that live in the colon help to break down food residue and may crate gas; Other bacteria make vitamin K, and some make B vitamins.


Absorption in the Intestines: Absorption in the Intestines These nutrients are absorbed through the colon wall. Bacteria, excess bile, and undigested food exit the body through the anus. The trip through the entire digestive tract takes about 12 hours.


Other Digestive Organs: Other Digestive Organs The pancreas is a long, flattened gland that makes digestive juices. The pancreas makes many of the enzymes that break apart carbohydrates and fats, and it produces the sodium bicarbonate that neutralizes stomach acid. The gland also makes insulin the glucagons, which will be discussed in chapter 14. These digestive juices enter the small intestine through a duct.


Other Digestive Organs: Other Digestive Organs The liver is tucked under the lower right ribs, just below the diaphragm. It is the 2nd largest organ in the human body and has many lobes or sections.


Other Digestive Organs: Other Digestive Organs The liver processes all the nutrient-rich blood leaving the intestine. When the villi absorb nutrients, active transport and diffusion carry them into a capillary network that surrounds the small intestine. Thse blood vessels go into veins that lead to the liver. The liver is likes a car’s oil filter. As the blood flows trough tiny openings, the cells lining the openings filter out old blood cells, process proteins, and convert sugars into animal starch called glycogen, a highly branched polymer of glucose. When the body needs more sugar, the liver converts the glycogen to glucose, which inters the bloodstream.


Other Digestive Organs: Other Digestive Organs An important liver function is to detoxify incoming substances, such as pesticides, solvents, drugs and alcohol. The drug rehabilitation specialist counsels alcoholics and their families about the damage that alcohol does to the stomach ling and the liver. With continued abuse, an alcoholic may destroy this vital filtering system and die. After the liver filters nutrients, they travel in the blood to the heart for distribution throughout the body.


Other Digestive Organs: Other Digestive Organs The liver is an amazing chemical factory. It filters out old red blood cells, recycles the iron in bone marrow to make new red blood cells, and synthesizes bile. This greenish fluid is stored in the gallbladder, which is in a hollow area in a lobe of the liver. When you eat fatty foods, smooth muscles contract around the gallbladder, squeezing bile into a duct leading to the small intestine.


Other Digestive Organs: Other Digestive Organs Bile breaks up the fat in chyme into very small droplets, which are suspended in solution. Then the lipases can split them into glycerol and fatty acids. These molecules can pass through the intestinal wall, for transport to the circulatory system.


13.3 Nutrition: 13.3 Nutrition You are what you eat. Diet is linked to heart disease, cancer, and longevity. The food pyramid is a diagram that is used as a guide for the development of a nutritional diet. A calorie with a small “c” is the heat energy needed to raise 1 g of water 1 degree C. Energy in food is measured in calories (big C); 1 calorie = 1000 calories. Foods contain six major types of nutrients: carbohydrates, fats, proteins, vitamins, minerals, and water.


13.3 Nutrition: 13.3 Nutrition Not all mammals need the same combination of nutrients. A. Pork producers may supplement the diets of pigs with B vitamins.


13.3 Nutrition: 13.3 Nutrition B. Most other livestock get their B vitamins from the microorganisms in their intestines.


13.3 Nutrition: 13.3 Nutrition C. Animal breeders who raise guinea pigs include food with vitamin C; D. Dog foods don’t need vitamin C because dogs produce this nutrient. Dogs have enzymes that effectively break down proteins from meat but not vegetable proteins. Many dog foods include protein from plant sources, which is useless because a dog doesn’t have the enzymes to digest it.


Carbohydrates: Carbohydrates Carbohydrates are mainly plant sugars and starches. Glucose, fructose, and galactose are simple sugars, or monosaccharides.


Carbohydrates: Carbohydrates Each contains the same number of carbon, hydrogen, and oxygen atoms, but the atoms are arranged differently. Two monosaccharides can join to make a disaccharide, such as maltose, sucrose, and lactose. Lactose comes from an animal, not from plants. Fruits, desserts, soft drinks, and candy all contain sugar.


Carbohydrates: Carbohydrates Sugars can be joined in long chains called starches or complex carbohydrates. Plants make starches to store energy. The enzyme amylase in saliva begins the digestion of starch, breaking it into sugar units. You can chew a cracker for several minutes and detect that it tastes sweeter; This taste is the work of the enzyme. Once the sugars circulate, cell respiration metabolizes them for energy.


Carbo-loading: Carbo-loading Athletic trainer plan carbohydrate-loading diets for long-distance runners and other endurance athletes. Carbo-loading maximizes the storage of human starch, glycogen, in the muscles, which need energy to run the race.


Carbo-loading: Carbo-loading A carbo-loading diet may include potatoes, peas, pasta, breads, and cereals. Carbohydrates are the body\s main source of energy, and the food pyramid recommends 6-11 servings daily. How many servings an individual should have depends on how much she or he is growing , how many calories are used in daily activities, and any special condition, such as pregnancy, that require additional calories.


Fats: Fats Fat is a very concentrated source of energy. One gram of carbohydrate supplies 4 calories, while 1 g of fat supplies 9 calories.


Fats: Fats Some fats contain fat-soluble vitamins, such as the vitamin A in milk fat. Fats add flavor to food and stay in your stomach a long time, making you feel full.


Fats: Fats The excess calories are stored as body fat. When you look at the food pyramid (figure 13.16) the small circles indicate that not only salad dressings, butter, sour cream, and oils contain fat, but also milk, meat, poultry, eggs, and nuts. Dietitians recommend that people eat these fatty foods, sparingly, so many food producers have developed reduced-fat products and leaner animals.


Vitamins: Vitamins Vitamins are organic substances that an organism can’t make. They are often key components of enzymes. Vitamins A, C, and D are often lacking in the American diet.


Vitamins: Vitamins Milk is a good source of vitamin A. Beta carotene, a plant pigment that humans convert into vitamin A, is found in dark green leafy vegetables and many yellow and red fruits and vegetables.


Vitamins: Vitamins Vitamin A is essential for good vision.


Vitamins: Vitamins People who don’t get enough vitamin A for a long time may develop night blindness: their eyes don’t adjust well to dim light. Vitamin A also contributes to healthy skin. Dermatologists prescribe a form of vitamin A to reduce acne and improve the health of skin.


Vitamins: Vitamins Vitamin C is a key component of collagen, a connective tissue that wraps muscle cells, surrounds organs, and is found in skin and bones. Sailors during the age of discovery and the 49ers of the god rush didn’t get enough vitamin C. Gradually, their teeth would loosen and fall out, sores on their skin wouldn’t heal, and eventually the people would die. This extreme deficiency is called scurvy.


Vitamins: Vitamins Potatoes, broccoli, strawberries, and citrus fruits are all good sources of vitamin C. Vitamin C is in the watery pulp of fruits and vegetables. It is easily oxidized, so the more the food is exposed to air and heat, the more vitamin C deteriorates.


Vitamins: Vitamins Vitamin D is crucial for absorption of calcium and phosphorus through the intestinal wall. It is added to milk so that vitamin D and the minerals are together in the digestive tract. Older women and others who have osteoporosis may take vitamin D and calcium supplements to maintain bone strength. Skin that is exposed to sunlight produces vitamin D.


Vitamins: Vitamins The B vitamins mainly regulate the energy that is released from carbohydrates, protein, and fat. Meat, eggs, and grain products, such as breads and noodles, contain B vitamins.


Minerals: Minerals Mineral are inorganic substances; They don’t contain carbon. Plants provide most of the minerals that humans need. Iron and calcium are lacking in many diets. Iron, supplied by red meat, dried beans, and many leafy green vegetables, is part of the hemoglobin molecule that carries oxygen in red blood cells.


Minerals: Minerals People who do not have enough iron are anemic and feel tired much of the time. Mild and some vegetables, such as broccoli, supply calcium.


Minerals: Minerals Calcium is important in bone formation, muscle contraction, and blood clotting. Sodium, potassium, and chloride are all electrolytes that help to maintain the water balance of the body. After a hard workout, sports drinks may help to replace quickly, electrolytes that are lost in sweating.


Proteins: Proteins Proteins are found in every living tissue; They form part of cell membranes, genetic material, hormones, and enzymes, among other things.


Proteins: Proteins Proteins are long chains of amino acids. Out of the 20 amino acids, eight are not made in the human body. These must be supplied by food. Foods that contain the eight essential amino acids in the proportion in which they are used are complete proteins and most often come from animal sources.


Proteins: Proteins Many cultures in the world are vegetarian. Some do not eat any animal products and receive all the complete proteins they need from plant sources. A lack of protein can produce severe side effects endangering life. In developing countries, some children don’t get enough protein. They lose weight, are listless, and catch more infections because of a condition called kwashiorkor. The child consumes a chronically low-calorie diet, using the little protein that is eaten as an energy source, not for growth and development.


Proteins: Proteins A similar condition is marasmus. The symptoms of marasmus are inadequate growth, weakness, edema (swelling), and loss of appetite. Both kwashiorkor and marasmus can be fatal. The food pyramid recommends 2-3 servings of meat, dried beans, or eggs and 2-3 servings of dairy products daily. Both of these categories supply complete protein.


Water: Water Water is an essential nutrient. About 2 thirds of the body’s weight is water. Water is in every cell.


Water: Water The circulation system depends on watery plasma to carry nutrients, gases and other molecules throughout the body. Water is not only in what you drink, but also in many foods. Watermelon, tomatoes, and soups contain lots of water.