Nutrition, Digestion & Metabolism PDF

# Nutrition, Digestion & Metabolism ## Nutrition (Ingestion) All substances taken into the body and used to build up protoplasm and to produce energy needed for performing the various life are considered foods. Foods constituents may be classified according to their chemical composition (i.e. int...

# Nutrition, Digestion & Metabolism ## Nutrition (Ingestion) All substances taken into the body and used to build up protoplasm and to produce energy needed for performing the various life are considered foods. Foods constituents may be classified according to their chemical composition (i.e. into carbohydrate, lipids, and proteins, mineral salts, water and vitamins), or they may be classified according to their functions. Where they include: * **Body builders:** * Which help in the building up of the body i.e. form part of the composition of the body e.g. proteins, mineral salts and water. * **Energy producers:** * Which on oxidation yield the energy necessary for the various body activities e.g. carbohydrates and fats which are good examples of energy producers (1 gm of carbohydrates or proteins yield 4.1 calories while that of fat is 9.3 cal.). * **Regulators:** * Such as mineral salts and vitamin. They serve to regulate and coordinate the different functional activities of the body. **A balanced diet is a mixture of food containing all substances essential for the development, growth and maintenance of the individual.** * **Balanced diet:** * Balanced diet must have adequate amounts of protein, fat, carbohydrate, salts, vitamins and water. Special requirements must be taken into account in special cases, e.g. during pregnancy, lactation and illness. ## Digestion Digestion is the breakdown of complex food substance into simpler food substance which can be absorbed into the blood stream for body use. Digestion is important because your body needs nutrients from the food you eat and the liquids you drink in order to stay healthy and function properly. Nutrients include carbohydrates, proteins, fats, vitamins, minerals and water. Your digestive system breaks down and absorbs nutrients from the food and liquids you consume to use for important things like energy, growth and repairing cells. ## Metabolism Metabolism is a term that is used to describe all chemical reactions involved in maintaining the living state of the cells and the organism. Metabolism can be conveniently divided into two categories: * **Catabolism** - the breakdown of molecules to obtain energy * **Anabolism** - the synthesis of all compounds needed by the cells Metabolism is closely linked to nutrition and the availability of nutrients. Bioenergetics is a term that describes the biochemical or metabolic pathways by which the cell ultimately obtains energy. Energy formation is one of the vital components of metabolism. ### Important Points * Nutrients, which the body uses for energy, growth, and cell repair are taken to the body by a process known as **ingestion**. * **Digestion** works by moving food through the gastrointestinal (GI) tract * Digestion begins in the mouth with chewing and ends in the small intestine * As food passes through the GI tract, it mixes with digestive juices, causing large molecules of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the blood stream (**absorption**), which delivers them to the rest of the body * Waste products of digestion pass through the large intestine and out of the body as a solid matter called stool (**excretion**) * Digestive juices contain enzymes that break food down into different nutrients * The small intestine absorbs most digested food molecules, as well as water and minerals, and passes them on to other parts of the body for storage or further chemical change (**metabolism**). Hormone and nerve regulators control the digestive process, finally: * Proteins break into amino acids * Fats break into fatty acids and glycerol * Carbohydrates break into simple sugars ## I- Carbohydrates Carbohydrates are widely distributed both in animal and in plant tissues. They are the cheapest source of calories. They provide about 50% of the calories in most diets. ### Physiological Importance of carbohydrates 1. They form about 50-60% of human diet 2. They form about 0.6% of human body weight. 3. Stored in liver & muscles as glycogen. 4. Act as a source of energy (4.2 Kcal/g). 5. May be converted to fats or proteins. 6. They form a part of mucous membranes. 7. The pentose (ribose) sugar is a part of DNA & RNA. ### Carbohydrates are classified into the following: * **A- Monosaccharides:** - Simple sugars composed of a single sugar unit. * Are classified according to the number of carbon atom into: trioses (3C), tetroses (4C), pentoses (5C), hexoses (6C). * E.g. of pentoses is ribose. * E.g. of hexoses are glucose, galactose & fructose. * **B- Disaccharides:** -Compound sugars formed of 2 molecules of monosaccharides. * E.g. maltose, lactose & sucrose. * **C- Polysaccharides:** -Consist of long chain of monosaccharide units. * E.g. -starch, dextrins & cellulose (plant source), as well as glycogen (animal source). ### Digestion of carbohydrates * **In mouth:** Salivary amylase starts the digestion of starch: * $Starch \xrightarrow{amylase} dextrins \xrightarrow{amylase} maltose$ * **In stomach:** no digestion, but hydrolysis of carbohydrates by HCl. * **In small intestine:** * **a- By pancreatic juice** * $Starch \xrightarrow{amylase} dextrins \xrightarrow{amylase} maltose$ * **B- By intestinal juice:** * $Maltose \xrightarrow{maltase} glucose + glucose$ * $Lactose \xrightarrow{lactase} glucose + galactose$ * $Sucrose \xrightarrow{sucrase} glucose + fructose$ ### Absorption of sugars; * Through blood route to portal vein by both simple diffusion & active transport. ### Metabolism of carbohydrates (Fated absorbed carbohydrates) 1. **Glycogenesis:** formation of glycogen from glucose in liver & muscle. 2. **Glycogenolysis:** breakdown of glycogen to glucose in liver & to pyruvic acid in muscles. 3. **Glycolysis:** conversion of glucose (6C)→ 2 pyruvic add (3C). 4. **Krebs Cycle:** conversion of pyruvic acid → $CO_2 + H_2O + E$. * Krebs cycle starts by a reaction between oxaloacetic acid and acetyl CO-enzyme (acetyl COA) and formation of citric acid, which undergoes many oxidation-reduction reactions to finally provide $CO_2$, $H_2O$ & E. 5. **Gluconeogenesis:** formation of glucose from non-carbohydrate sources. *