FOOD A nutrient is a substance required by

FOOD • A nutrient is a substance required by the body for energy, growth, repair, and maintenance. Nutrients in food and beverages include carbohydrates, lipids, proteins, vitamins, and minerals.

Energy and Building Materials • Carbohydrates, proteins, and lipids are involved in providing both energy and building materials to the cells.

Carbohydrates that exist as single sugar molecules are called monosaccharides or simple carbohydrates. Carbohydrates made of two or many sugar molecules linked together by chemical bonds are called complex carbohydrates. Complex carbohydrates must be broken down into simple sugars before cells can use their energy.

Proteins Amino acids from proteins are used by the body for making additional proteins. Extra amino acids in the diet are used for energy or converted to fat. The body needs 20 different amino acids to function. Ten amino acids (called essential amino acids) must be obtained directly from food.

Lipids The body uses lipids to make steroid hormones and cell membranes and to store energy. Fats are lipids that store energy in plants and animals. Fats are also stored around organs and act as padding and insulation.

• Vitamins are organic substances that occur in foods in small Vitamins, Minerals, and Water amounts. They are necessary in trace amounts for the normal metabolic functioning of the body. • Minerals are naturally occurring inorganic substances that re used to make certain body structures and substances. They are also needed for normal nerve and muscle function.

DIGESTION Organisms must break down their foodstuffs into their components for passing through the cell membrane. This process is called digestion.

TYPES OF DIGESTION There are two types of digestion. These are; • Mechanical digestion • Chemical digestion

MECHANICAL DIGESTION Pieces of food are firstly cut, crushed, or broken into smaller particles without being changed chemically. This process is called mechanical digestion. Mechanical breakdown increases the surface area of the food particles. . Protein

CHEMICAL DIGESTION • Chemical digestion is series of reactions in which foods are hydrolyzed, aided by water and enzymes. Food split into its monomers by means of chemical digestion. STARCH + WATER n GLUCOSE

TYPES OF DIGESTION ACCORDING TO THEIR MEDIUM • There are two types digestion according to their medium. These are • EXTRACELLULAR DIGESTION • INTRACELLULAR DIGESTION

INTRACELLULAR DIGESTION • In unicellular organisms foodstuffs are digested within food vacuoles in the cytoplasm. They are taken into cell by pinocytosis or phagocytosis.

EXTRACELLULAR DIGESTION In this process, digestion of food takes place within an area external to the organism by the secretion of digestive enzymes. Extracellular digestion is seen in protista, invertebrates and all vertebrates.

HUMAN DIGESTIVE SYSTEM The digestive system is made up of highly specialized digestive tube and several organs. Human Digestive System includes; • Mouth • Eusophagus • Stomach • Small Intestine • Large Intestine

MOUTH • Food enters the body through the mouth. • Mechanical and chemical digestion occur in mouth. Teeth help in mechanical digestion. • There are three pairs of salivary glands in the lining of the mouth. Salivary glands secrete saliva into the mouth. They help in chemical digestion

TEETH • Teeth are adapted for mechanical digestion of food. • Each tooth is composed of crown and root • The crown is covered with enamel. It is hardest material of our body.

TYPES OF TEETH • There are 4 types of teeth. These are 1 - Molars 12 2 - Pre molars 8 3 - Canines 4 4 - Incisors 8 TOTAL 32

ESOPHAGUS • After chewing of food, it is pushed by the tongue to the esophagus. The esophagus connects mouth with the stomach. • Peristalsis begins in the esophagus. Peristalsis is the series rhythmic muscles contraction and relaxations. Food moves through the digestion system by peristalsis.

STOMACH • Food is stored temporarily in the stomach. Mechanical and chemical digestion occur in mouth. Food is broken down mechanically into smaller particles by the contractions of the muscles. • Stomach secretes enzymes for chemical digestion

SMALL INTESTINE • Most digestion and absorption occur in small intestine. • All digestion is completed in the small intestine. • 6 meter long and the longest organ of the alimentary canal. • The small intestine has three parts. They are duodenum jejunum and ileum.

DUODENUM • The first 25 cm of small intestine is DUODENUM. It is a major crossroad. • It is here that CHYME from stomach mixes with digestive juice from -Pancreas - Liver -Gall bladder -Intestinal gland • Hormones of stomach and duodenum control digestive secretion in to duodenum.

A-Pancreatic Secretion • Secrete following chemicals; 1 -Alkaline solution: Rich in bicarbonate neutralizes the acidity of chyme. 2 - Trypsin, Chymotyripsin, Protease: Oxydize polypeptide and peptone to dipeptide and amino acids.

B-BILE PRODUCTION BY THE LIVER • Digestion of lipid in small intestine depend on production of BILE, that is produced by liver. • Bile contain BILE SALTS, which act as a detergents (emulsifiers) to lipids. • Bile is stored and concentrated in the gall bladder.

SECRETION OF THE SMALL INTESTINE • • • Most digestion is complated in duodenum. Intestinal juice contains the following enzymes: Erepsin—digests proteins into amino acids. Maltase—digests maltose into glucose, Lactase—digests lactose (milk sugar) into glucose and galactose. • Sucrase—digests sucrose (cane sugar) into glucose and fructose. • Lipase (Small quantities) —digest fats into fatty acids and glycerol.

HORMONAL CONTROL OF DIGESTION • GASTRIN HORMONE---from stomach---to blood---for secretion of gastric juice. • SECRETIN---from duodenum---to blood---stimulate the pancreas---to release sodium bicarbonate that neutralize chyme. • CHOLECYTOKININ(CCK): Secreted from duodenum-- Amino acid and Fatty acid in duodenum trigger secretion of CCK—stimulate release of enzyme from Pancreas and bile from gall bladder. At the same time AA and fatty acid in duodenum cause CCK production. This inhibit peristalsis and acid secretion from stomach.

ABSORBTION IN SMALL INTESTINE • To reach body tissues, most nutrients are absorbed from inner wall of the small intestine. • This organ has a huge surface area-300 m 2. • Large folds in the lining have finger like projections called VILLI. • Each epithelial cell of villus has on its apical surface many MICROVILLI. • Microvilli give the intestinal epithelium brush like appearance called BRUSH BORDER.

VILLI AND MICROVILLI

ABSORBTION • Depending on the nutrient, transport across the epithelial cells can be passive or active. • For example fructose transit across epithelium to blood capillaries by facilitated diffusion. • But amino acid, vitamins, small peptides, fatty acid are absorbed by epithelial cells with active transport.

PATHS OF ABSORBED NUTRIENTS • Most nutrients leave the intestine with the bloodstream. • But some products of fat (triglyceride) follow a different path. • After absorbtion by epithelial cells, fatty acid and glycerol are joined into triglyceride in those cells. These fats are coated with phospholipids, cholesterol and proteins forming water soluble globules called CHYLOMICRONS. These molecules are to large to pass blood capillaries. Instead, they are transported into a LACTEAL, a vessel at the core of the each villus.

PROTEIN AND SUGAR’S WAY • Lacteals are parts of the vertebrate lymphatic system. • Starting with lacteals lymph containing chylomicrons passes into the large vessel of the lymphy system finally come to heart. • At contrast with the lacteals, the capillaries and veins that carry nutrient rich blood opens to HEPATIC PORTAL VEIN, a blood vessel that leads directly to the liver. From the liver blood pass to the heart.

FUNCTION OF LIVER • Liver interconvert many organic molecules. For example may convert glucose to glycogen. • Second, liver remove toxic substances before blood circulation. Liver is the primary side for the detoxification of the many organic molecules, including drugs.

THE LARGE INTESTINE • The alimentary canal ends with the large intestine. • It includes cecum, colon and rectum. • Small int. joint with large int. from cecum. Fermentation occur in cecum thus it is long in ruminants and short in human. • The APPENDIX, a finger like extension of human cecum has dispensable role in immunity.

COLON • The major role of the colon is to recover water that has entered the large int. • About 7 lt water is secreted to alimentary canal each day. Together with small int. and colon absorb about 90% of water. • Absorbtion of water occur by osmosis.

• The FECES, the waste of the digestive system is moved along the colon by peristalsis. It takes nearly 12 -24 hours. • If lining of the colon irritated by bacterial infection less water may be reabsorbed, resulting in diarrhea. The opposite problem, constipation, occurs when feces move along the colon to slowly.

• A rich of harmless bacteria reside in the human colon(1/3 of the feces). One inhabitant is Escherichia Coli, a favorite resource organism of the molecular biologists. • Within the intestine E. coli and other bacteria live on unabsorbed organic material and produce a gases including methane and HSO 2 which has an offansive odor. • Some of the bacteria produce vitamins, such as biotin, vit K, several vit B, folic acid.

RECTUM • The terminal portion of the large int. is rectum. • Feces is stored in rectum until they can be eliminated. • Between rectum and anus there are 2 sphincters. First is involuntary and second is voluntary. • Contraction of the rectum enforce to defecate.

DIGESTION OF CARBOHYDRATES IN THE MOUTH • Chemical digestion of carbohydrate starts in mouth. Salivary glands secrete saliva into the mouth. Saliva is juice which contain digestive enzyme is called ptyalin or amylase. • Amylase breaks down starch into dextrin and maltose. Starch + Water Amylase Dextrin + Maltose

DIGESTION OF CARBOHYDRATES IN THE STOMACH • Stomach is an acidic area. Amylase can not work in acidic region. • Therefore chemical digestion of carbohydrates stop in stomach.

DIGESTION OF CARBOHYDRATES IN THE SMALL INTESTINE When food passes into the small intestine from stomach, it stimulates cells of small intestine. Than small intestine secretes two hormones into the blood. These hormones are secretin and cholecystokinin.

They stimulate pancreas and it secretes pancreatic enzymes to small intestine. Enzymes act on every types of carbohydrates. Pancreatic juice includes amylase, maltase, lactase and sucrase.

Dextrin + H 2 O Maltose + H 2 O Sucrose + H 2 O Lactose + H 2 O Amylase Maltase Sucrase Lactase Glucose +…… Glucose + Fructose Glucose + Galactose Digestion of carbohydrates is completed in small intestine.

DIGESTION OF PROTEINS • Digestion of protein starts in stomach and complete in small intestine. • When food enter the stomach, it stimulates some stomach cells. These cells secretes GASTRINE hormone. This hormone stimulates gastric gland it produces gastric juice. • Gastric Juice is composed of; Mucus, HCl and Pepsinogen

REACTIONS IN THE STOMACH Pepsinogen + HCl Protein + H 2 O Milk + H 2 O Casein+ H 2 O Pepsin Rennin Pepsin Peptones Casein Peptones + a. a….

DIGESTION OF PROTEINS IN THE INTESTINE • Tripsinogen and Chymotripsinogen take role in the digestion of proteins that are secreted by pancreas. • Enterocinase and Erepsin are secreted by intestinal glands to digest proteins.

DIGESTION OF PROTEINS IN THE SMALL INTESTINE Tripsinogen + Enterocinase Peptones+H 2 O Peptides+ H 2 O Tripsin Peptides + Amino acids Erepsin aa +…

DIGESTION OF LIPIDS • Digestion of lipid occurs only in small intestine. The cells of the liver produce bile. Than it is stored in gall bladder. When food enters to small intestine it secretes cholecystokinin hormone. This hormone causes removing of bile from gall bladder to small intestine.

• Bile does not contain enzyme but it aids mechanical digestion of lipid. This process is called emulsification.

Lipid Bile Small lipid particles Lipase is secreted from pancreas. Lipase breaks down lipid molecules into fatty acids and glycerol. Lipid + H 2 O Lipase 3 Fatty acid + Glycerol

• The digestive products of carbohydrates, aminoacids and vitamins pass from the microvilli to the venules (the small branches of the veins). • Fatty acids and glycerol pass from the microvilli to the lymph circulation.