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This 12 page Class Notes was uploaded by Jess Graff on Monday May 2, 2016. The Class Notes belongs to BMS 508 at University of New Hampshire taught by Mary Katherine Lockwood, PhD in Spring 2016. Since its upload, it has received 36 views. For similar materials see Human Anatomy and Physiology II in Biological Sciences at University of New Hampshire.
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Date Created: 05/02/16
BMS 508.03 4/20/2016 Chapter 25 Digestion & Metabolism (cont) Nutrition • MyPlate Plan • An arrangement of food groups • According to number of recommended daily servings • Considers level of physical activity • Food Groups and the MyPlate Plan • Complete proteins • Provide all essential amino acids in sufficient quantities • Found in beef, fish, poultry, eggs, and milk • Incomplete proteins • Are deficient in 1 or more essential amino acids • Found in plants • Nitrogen Balance • N Compounds include: • Amino acids • Framework of all proteins, glycoproteins, and lipoproteins • Purines and pyrimidines • Nitrogenous bases of RNA and DNA • Creatine • Energy storage in muscle (creatine phosphate) • Porphyrins • Bind metal ions, essential to hemoglobin, myoglobin, and cytochromes • N Compounds • Are not stored in the body • Must be obtained by: • Recycling N compounds in body • Or from diet • Nitrogen Balance • Occurs when: • Nitrogen absorbed from diet balances nitrogen lost in urine and feces • Positive nitrogen balance • Individuals actively synthesizing N compounds • Need to absorb more nitrogen than they excrete • For example, growing children, athletes, and pregnant women • Negative nitrogen balance • When excretion exceeds ingestion • Minerals • Are inorganic ions released through dissociation of electrolytes • Are important for three reasons • Ions such as sodium, chloride, and potassium determine osmotic concentrations of body fluids • Ions play a major role in physiological processes • Ions are essential cofactors in many enzymatic reactions • Metals • Each component of ETS requires an iron atom • Final cytochrome of ETS requires a copper ion • Mineral Reserves • The body contains significant mineral reserves • That help reduce effects of variations in diet • Vitamins • A vitamin is an essential organic nutrient that functions as a coenzyme in vital enzymatic reactions • Vitamins are assigned to either of 2 groups based on their chemical structure and characteristics 1. Fat-soluble vitamins 2. Water-soluble vitamins • Fat-Soluble Vitamins • Vitamins A, D, E, and K 1. Are absorbed primarily from the digestive tract along with lipids of micelles 2. Normally diffuse into plasma membranes and lipids in liver and adipose tissue • Vitamin A • A structural component of visual pigment retinal • Vitamin D • Is converted to calcitriol, which increases rate of intestinal calcium and phosphorus absorption • Vitamin E • Stabilizes intracellular membranes • Vitamin K • Helps synthesize several proteins, including three clotting factors • Vitamin Reserves • The body contains significant reserves of fat-soluble vitamins 1. Avitaminosis (vitamin deficiency disease) 2. Rare in fat-soluble vitamins 3. Hypervitaminosis more likely • Normal metabolism can continue several months without dietary sources • Water-Soluble Vitamins • Are components of coenzymes • Are rapidly exchanged between fluid in digestive tract and circulating blood 1. Excesses are excreted in urine • Vitamins and Bacteria • Bacterial inhabitants of intestines produce small amounts of: 1. Fat-soluble vitamin K 2. Five water-soluble vitamins • Vitamin B 12 • Intestinal epithelium absorbs all water-soluble vitamins except B 12 1. B 12molecule is too large • Must bind to intrinsic factor before absorption • Diet and Disease • Average U.S. diet contains excessive amounts of sodium, calories, and lipids • Poor diet contributes to: 1. Obesity 2. Heart disease 3. Atherosclerosis 4. Hypertension 5. Diabetes Metabolic Rate • Energy Gains and Losses • Energy is released • When chemical bonds are broken • In cells: • Energy is used to synthesize ATP • Some energy is lost as heat • Calories • Energy required to raise 1 g of water 1 degree Celsius is a calorie (cal) • Energy required to raise 1 kilogram of water 1 degree Celsius is a Calorie (Cal) = kilocalorie (kcal) • The Energy Content of Food • Lipids release 9.46 Cal/g • Carbohydrates release 4.18 Cal/g • Proteins release 4.32 Cal/g • Calorimetry • Measures total energy released when bonds of organic molecules are broken • Food is burned with oxygen and water in a calorimeter • Energy Expenditure: Metabolic Rate • Clinicians examine metabolism to determine calories used and measured in: • Calories per hour • Calories per day • Calories per unit of body weight per day • Metabolic Rate • Is the sum of all anabolic and catabolic processes in the body • Changes according to activity • Basal Metabolic Rate (BMR) • Is the minimum resting energy expenditure • Of an awake and alert person • Measured under standardized testing conditions • Measuring BMR • Involves monitoring respiratory activity • Energy utilization is proportional to oxygen consumption • Metabolic Rate • If daily energy intake exceeds energy demands: • Body stores excess energy as triglycerides in adipose tissue • If daily caloric expenditure exceeds dietary supply: • Body uses energy reserves, loses weight • Hormonal Effects • Thyroxine controls overall metabolism • T 4ssay measures thyroxine in blood • Cholecystokinin (CCK) and adrenocorticotropic hormone (ACTH) suppress appetite • Leptin is released by adipose tissues during absorptive state and binds to CNS neurons that suppress appetite • Ghrelin is released by empty stomach and increases appetite • Thermoregulation • Heat production • BMR estimates rate of energy use • Energy not captured is released as heat • Serves important homeostatic purpose • Body Temperature • Enzymes operate in a limited temperature range • Homeostatic mechanisms keep body temperature within limited range (thermoregulation) • The body produces heat as by-product of metabolism • Increased physical or metabolic activity generates more heat • Heat produced is retained by water in body • For body temperature to remain constant: • Heat must be lost to environment • Body controls heat gains and losses to maintain homeostasis • Mechanisms of Heat Transfer • Heat exchange with environment involves four processes • Radiation • Convection • Evaporation • Conduction • Radiation • Warm objects lose heat energy as infrared radiation • Depending on body and skin temperature • About 50% of indoor heat is lost by radiation • Convection • Results from conductive heat loss to air at body surfaces • As body conducts heat to air, that air warms and rises and is replaced by cooler air • Accounts for about 15% of indoor heat loss • Evaporation • Absorbs energy (0.58 Cal per gram of water evaporated) • Cools surface where evaporation occurs • Evaporation rates at skin are highly variable • Conduction • Is direct transfer of energy through physical contact • Is generally not effective in heat gain or loss • Insensible Water Loss • Each hour, 20–25 mL of water crosses epithelia and evaporates from alveolar surfaces and skin surface • Accounts for about 20% of indoor heat loss • Sensible Perspiration • From sweat glands • Depends on wide range of activity • From inactivity to secretory rates of 2–4 liters (2.1–4.2 quarts) per hour • The Regulation of Heat Gain and Heat Loss • Is coordinated by heat-gain center and heat-loss center in preoptic area of anterior hypothalamus • These centers modify activities of other hypothalamic nuclei • Temperature Control • Is achieved by regulating: • Rate of heat production • Rate of heat loss to environment • Further supported by behavioral modifications • Mechanisms for Increasing Heat Loss • When temperature at preoptic nucleus exceeds set point • The heat-loss center is stimulated • Three Actions of Heat-Loss Center • Inhibition of vasomotor center • Causes peripheral vasodilation • Warm blood flows to surface of body and skin temperatures rise • Radiation and convective losses increase • Sweat glands are stimulated to increase secretory output • Perspiration flows across body surface • Evaporative heat losses increase • Respiratory centers are stimulated • Depth of respiration increases • Mechanisms for Promoting Heat Gain • The heat-gain center prevents low body temperature (hypothermia) • When temperature at preoptic nucleus drops: • Heat-loss center is inhibited • Heat-gain center is activated • Heat Conservation • Sympathetic vasomotor center decreases blood flow to dermis • Reducing losses by radiation, convection, and conduction • In cold conditions: • Blood flow to skin is restricted • Blood returning from limbs is shunted to deep, insulated veins (countercurrent exchange) • Countercurrent exchange • Is heat exchange between fluids moving in opposite directions • Traps heat close to body core • Restricts heat loss in cold conditions • Mechanism of Countercurrent Exchange • Blood is diverted to a network of deep, insulated veins • Venous network wraps around deep arteries • Heat is conducted from warm blood flowing outward • To cooler blood returning from periphery • Heat Dissipation • In warm conditions: • Blood flows to superficial venous network • Heat is conducted outward to cooler surfaces • Heat Generation • Shivering Thermogenesis • Increased muscle tone increases energy consumption of skeletal muscle, which produces heat • Involves agonists and antagonists, and degree of stimulation varies with demand • Shivering increases heat generation up to 400 percent • Nonshivering Thermogenesis • Releases hormones that increase metabolic activity • Heat-gain center stimulates adrenal medullae • Via sympathetic division of ANS • Releasing epinephrine • Epinephrine increases: • Glycogenolysis in liver and skeletal muscle • Metabolic rate of most tissues • Preoptic nucleus regulates thyrotropin-releasing hormone (TRH) production by hypothalamus • Hormones and Thermogenesis • In children, low body temperature stimulates additional TRH release • Stimulating thyroid-stimulating hormone (TSH) • Released by adenohypophysis (anterior lobe of pituitary gland) • TSH stimulates thyroid gland • Increasing thyroxine release into blood • Increasing rate of carbohydrate catabolism • Increasing rate of catabolism of all other nutrients • Sources of Individual Variation in Thermoregulation • Thermoregulatory responses differ among individuals due to: • Acclimatization (adjustment to environment over time) • Variations in body size • Body Size and Thermoregulation • Heat is produced by body mass (volume) • Surface-to-volume ratio decreases with size • Heat generated by “volume” is lost at body surface • Thermoregulatory Problems of Infants • Temperature-regulating mechanisms are not fully functional • Lose heat quickly (due to small size) • Body temperatures are less stable • Metabolic rates decline during sleep and rise after awakening • Infants cannot shiver • Infant Thermogenesis Mechanism • Infants have brown fat • Highly vascularized adipose tissue • Adipocytes contain numerous mitochondria found: • Between shoulder blades • Around neck • In upper body • Function of Brown Fat in Infants • Individual adipocytes innervated by sympathetic autonomic fibers stimulate lipolysis in adipocytes • Energy released by fatty acid catabolism radiates into surrounding tissues as heat • Heat warms blood passing through surrounding vessels and is distributed throughout the body • Infant quickly accelerates metabolic heat generation by 100 percent • Brown Fat in Adults • With increasing age and size: • Body temperature becomes more stable • Importance of brown fat declines • Adults have little brown fat • Shivering thermogenesis is more effective • Thermoregulatory Variations among Adults • Normal thermal responses vary according to: • Body weight • Weight distribution • Relative weights of tissue types • Natural cycles • Adipose Tissue • Is an insulator • Individuals with more subcutaneous fat: • Shiver less than thinner people • Temperature Cycles • Daily oscillations in body temperature • Temperatures fall 1C to 2C at night • Peak during day or early evening • Timing varies by individual • The Ovulatory Cycle • Causes temperature fluctuations • Pyrexia • Is elevated body temperature • Usually temporary • Fever • Is body temperature maintained at greater than 37.2C (99F) • Occurs for many reasons, not always pathological • In young children, transient fevers can result from exercise in warm weather
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