NUTRITION AND METABOLISM

Nutrition – food, vitamins and minerals that are ingested and assimilated in the body. Nutrient - a substance that promotes normal growth, maintenance, and repair Major nutrients – carbohydrates, lipids, and proteins Other nutrients – vitamins and minerals (and technically speaking, water)

The food Pyramid

Metabolism – process of using food molecules as energy sources and as building blocks for our own molecules Catabolism – breaks food molecules down releasing stored energy; O2 used. Anabolism – builds food molecules into complex substances. Anabolic processes tend toward "building up" organs and tissues.

Liver cells play a role in all three types of food metabolism. Role of the Liver Processes blood immediately after it leaves the G.I. tract Helps maintain normal blood glucose level Site of protein and fat metabolism Removes toxins from the blood Hepatic portal vein receives blood from the GI tract directly Liver cells play a role in all three types of food metabolism.

The Liver Synthesis of blood proteins- prothrombin- clotting fibrinogen- clotting albumin –blood volume Storage of excess nutrients and vitamins including vitamin A and D

Carbohydrates The minimum amount of carbohydrates needed to maintain adequate blood glucose levels is 100 grams per day Starchy foods and milk have nutrients such as vitamins and minerals in addition to complex carbohydrates Refined carbohydrate foods (candy and soft drinks) provide energy sources only and are referred to as “empty calories”

Nutrient metabolism Carbohydrates – are primarily catabolized for energy but small amounts are anabolized for glycogenesis (changes glucose to glycogen for storage which occurs in liver cells) GLUCOSE CATABOLISM: 3 Stages 1. GLYCOLYSIS - The Splitting of Glucose. Changes glucose to pyruvic acid. Occurs in the cytosol of the cell. Glycolysis hyperlink Glycolysis

Aerobic Respiration - produces nearly 20 times as much ATP as is produced by glycolysis alone. 2. CITRIC ACID CYCLE (aka Kreb’s cycle)- takes place in the MITOCHONDRIA. Most of the energy released in the Kreb’s cycle is in the form of high-energy electrons. animation krebs cycle 3. ELECTRON TRANSFER CHAIN Located in the mitochondria. The electron’s energy is transferred to ADP and an inorganic phosphate is added to it, forming ATP. Electron Transport Chain: The Movie

ATP ATP transports chemical energy within cells for metabolism. Bonds between adjacent phosphates in an ATP molecule store the energy. When these bonds are broken, energy is released.

GLYCOGENESIS- Glucose storage Glucose that is not needed immediately for cellular functions is stored as GLYCOGEN (animal starch). This process occurs in the liver, and is activated during rest periods and also activated by insulin in response to high glucose levels. Insulin is the only hormone that lowers blood glucose levels. Hormones that increase blood glucose levels include growth hormone , hydrocortisone, epinephrine, and glucagon Blood glucose levels – normally between 70 -110 mg/100ml (deciliter).

Lipids The most abundant dietary lipids, triglycerides, are found in both animal and plant foods Essential fatty acids – linoleic and linolenic acid, found in most vegetables, must be ingested Dietary fats: Help the body to absorb vitamins Are a major energy fuel of hepatocytes and skeletal muscle Are a component of myelin sheaths and all cell membranes

Lipids Fatty deposits in adipose tissue provide: A protective cushion around body organs An insulating layer beneath the skin An easy-to-store concentrated source of energy Prostaglandins function in: Smooth muscle contraction Control of blood pressure Inflammation Cholesterol stabilizes membranes and is a precursor of bile salts and steroid hormones

FAT METABOLISM Catabolism - Fats must be broken into their component parts: a 3-carbon molecule called glycerol and 3 fatty acids. Glycerol is converted to glyceraldehyde-3-phosphate (GAP). GAP enters glycolysis and can be "burned" through the Kreb's (AKA the Citric acid) cycle or used by the liver to make glucose in a process called gluconeogenesis. ANABOLISM- Fat is stored as adipose tissue.

The American Heart Association suggests that: Fats should represent less than 30% of one’s total caloric intake Saturated fats should be limited to 10% or less of one’s total fat intake Daily cholesterol intake should not exceed 200 mg

Protein metabolism The body will only catabolize protein for energy when all other reserves are depleted. Proteins are broken down into _______ Protein anabolism – the building of amino acids into complex proteins that are used for____________________.

NONESSENTIAL AMINO ACIDS Must be ingested NONESSENTIAL AMINO ACIDS The body can make these. see table 16-1 for the list All amino acids must be present at the same time for protein synthesis to occur

Vitamins AND minerals Vitamins –organic molecules that are needed in small amounts for normal metabolism. Made by plants or animals (Table 16-2) Minerals – inorganic molecules required by the body for normal function. Come from the earth.

VITAMINS Many vitamins attach to enzymes or coenzymes to help them function properly. Without vitamins, many enzymes will not work. Vitamin A – retina function Vitamin D – aids calcium absorptionOnly vitamins D, K, and B are synthesized in the body; all others must be ingested Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract

Vitamins Vitamins C and E have antioxidant effects, an ability to bind free radicals that have been implicated in causing a variety of ailments ranging from heart diseases to cancers.

vitamins There are two types of vitamins: fat soluble and water soluble. Fat soluble are stored in fat tissue. Be careful of overdose. Ex: vitamins A, D, E and K. Water soluble vitamins are not stored, but circulate through the bloodstream. The vitamins that are not used are then voided. Dangers- B6 may cause nerve problems in large doses.

MINERALS Some minerals are required in moderate amounts (bulk minerals) or in small amounts (trace minerals). Seven minerals are required in moderate amounts Calcium, phosphorus, potassium, sulfur, sodium, chloride, and magnesium Dozens are required in trace amounts. See tables 16-2 and 16-3 for a complete list of essential vitamins and minerals.

Calcium, phosphorus, and magnesium salts harden bone Sodium and chloride help maintain normal osmolarity, water balance, and are essential in nerve and muscle function Uptake and excretion must be balanced to prevent toxic overload

Metabolism Metabolic processes to ensure cell survival Energy Values of Foods - expressed in calories – units of heat *food Calorie – equals the amount of heat required to raise the temperature of a kilogram of water 1 degree C. *When energy losses due to incomplete absorption & incomplete oxidation are taken into account, 1 gram of carbohydrate or 1 gram of protein yields about 4 calories, whereas 1 gram of fat yields about 9 calories

Metabolic Rates Basal metabolic rate – rate at which the body expends energy under basal conditions – when a person is awake & at rest, after an overnight fast, & is a comfortable in a controlled environment. *Factors that influence energy requirements include basal metabolic rate, muscular activity, body temperature, & nitrogen balance The number of calories of heat that must be produced per hour by catabolism to keep the body alive, awake and warm.

Energy balance caloric intake = caloric output *When caloric intake in the form of foods = output from the basal metabolic rate & muscular activities *If energy balance is positive, body weight increases; if energy balance is negative, body weight decreases

body temperature More than 60% of the energy released during catabolism is used in maintaining body temperature. Body temp (thermoregulation) is maintained by the hypothalamus using negative feedback loops.

The skin and negative feedback Radiation – flow of heat away from the body Conduction – transfer of heat energy to the skin and then to the external environment. Convection – transfer of heat energy to the air. Evaporation- absorption of heat energy by water vaporization.