Digestive System Obtaining nutrients

Energy Body cells need energy to run cell processes. Animals obtain chemical energy from food. Energy is derived from breaking chemical bonds. Food energy is measured in units called calories.

Lipids Lipids are fats, oils, and waxes. Lipids are energy dense, containing 9 calories per gram. Lipids are used for storing energy, making cell membranes, and synthesizing steroid hormones. Many lipids are made up of fatty acids and glycerine.

Carbohydrates Sugars and starch are the carbohydrates that humans can digest. “Fiber” is indigestible carbohydrates, such as cellulose and inulin. Glucose is needed by all body cells as energy. Nerve cells must have glucose to operate. Starch is made up of glucose.

Proteins Amino acids from digested proteins are used by cells to build all the proteins that our body needs. Humans need a balance of the 20 amino acids, which can be obtained from animal proteins, or by blending plant protein sources. Proteins are made up of amino acids.

Macromolecule summary PolymersMonomersRoles Complex Carbohydrates (i.e. starch) Glucose and other simple sugars Broken apart to get energy to make ATP. ProteinsAmino acids Used to make our own enzymes and other body proteins. Lipids (Fats, waxes, oils, and steroids) Fatty acid chains, glycerine (except steroids) Used for cellular energy and energy storage; used to make cell membranes, steroid hormones.

Minerals Sodium, potassium, zinc, iron, calcium, copper, and selenium are among the minerals that humans need. Most minerals can be found in whole grains, fruits, vegetables, nuts, and meats. Highly processed foods may be deficient.

Major Minerals MineralMajor rolesNatural sources CalciumBone and tooth formation; muscle and nerve function. Dairy products, leafy greens, dry beans. IronUsed to make hemoglobin and myoglobin. Red meats, eggs, nuts, whole grains, leafy greens. ZincComponent of certain enzymes, required for growth. Meats, whole grains, nuts, legumes. PhosphorousBone and tooth formation; pH of body fluids, phospholipids. Dairy products, grains. PotassiumMaintains pH of body fluids; used in action potentials. Many fruits and vegetables, meats, milk. SodiumMaintains pH of body fluids; used in action potentials. Table salt, meats. SeleniumUsed by the immune system.Nuts, esp. Brazil nuts; many fruits and vegetables.

Vitamins Vitamins play many different roles in metabolism. We do not obtain energy from vitamins; however, some vitamins are necessary to run energy-related processes in cells.

Major Vitamins VitaminsMajor rolesNatural sources Vitamin A (fat soluble Used to make visual pigments; maintains epithelial tissues; needed for normal growth. Orange and yellow fruits and vegetables, egg yolk, dairy products. B complex vitamins (water soluble) Used in cellular respiration to metabolize sugars and other carbon compounds. Whole grains, legumes, many fruits and vegetables. B 12 comes from animal sources. Vitamin C (water soluble) Used in collagen synthesis, possible role in immune function. Fresh fruits and vegetables. Vitamin D (fat soluble) Bone growth, calcium absorption, possible role in immune function. Eggs, dairy products. Sunlight on skin oils creates Vitamin D. Vitamin E (fat soluble) Antioxidant, reduces cellular damage. Nuts, whole grains, leafy vegetables. Vitamin KPlays a role in blood clotting.Produced by intestinal bacteria.

Digestion

Two-way digestion Simple animals have a single digestive pouch with a single opening. Food enters through the opening, waste leaves through the same opening. These organisms must finish digesting before eating again.

One-way digestion More complex animals have one-way digestion. Food enters one opening and waste leaves from another. Animals with one-way systems can eat any time, which is an advantage.

Mechanical digestion In humans, mechanical digestion takes place in the mouth. Human incisors and canines are adapted for tearing food, while molars are adapted for grinding food. Saliva, which contains enzymes, mixes with food.

Esophagus After food is proccessed by the mouth it is passed to the pharynx. The pharynx is an open area at the back of the mouth.

Esophagus From the pharynx a flap of tissue called the epiglottis prevents food from going down the trachea (wind pipe). Food is forced into the Esophagus by swalling

Esophagus The Esophagus has an inner muscle layer and an outer muscle layer. The two layers alternate contractions causing the swallowing action or peristalsis.

Stomach The stomach digests food by mechanical and chemical processes. First the many muscles making up the stomach continually churn of food.

Stomach Gastric Pits (the openings of glands) Secrete acids, enzymes and mucus. Pepsin, an enzyme that breaks up proteins, requires an acidic environment to become active. Hydrochloric Acid is produced in the pits.

Stomach At the top of the stomach the Cardiac Sphincter keeps food from coming back up. At the bottom of the stomach the Pyloric Sphincter keeps food in until it’s fully turned into Chyme.

Duodenum digestion continues in the upper small intestine, the duodenum. Enzymes that will continue the digestion need a basic (non Acidic) environment. The pancreas and liver secrete chemicals that turn the acid into a bas.

Pancreas and Liver Pancreas releases pancreatic juice, containing bicarbonate, lipases, proteases, and amylase. The liver makes bile, which emulsifies fats. Bile is made from cholesterol, which is made in the liver.

Small intestine The walls of the small intestine are lined with millions of microvilli. This is the site of nutrient absorption. Small intestines also produce many digestive enzymes to break large polymers completely down into monomers.

Villi and microvilli

Digestion and pH LocationpHEnzymesMolecules digested MouthneutralAmylaseStarch StomachacidicPepsin (a peptidase)Initial protein digestion Small intestineBasic to neutralMixture of amylase, peptidases, lipases Digestion of starches, final breakdown of proteins, digestion of lipids.

Large intestine Water from digested food is absorbed in the large intestine. Bacteria present in the large intestine feed on unabsorbed nutrients, and produce several vitamins. Fecal material is formed from fiber and other undigested material.

Hormones and digestion Many hormones produced by the digestive system itself are responsible for appetite and digestion. Gastrin in the stomach, produced when food is present, signals release of acid. Secretin signals the release of sodium bicarbonate by the pancreas. Ghrelin and Leptin, recently discovered, control appetite. Changes in these hormones cause overeating, because people with too little of these hormones don’t realize they’re full.