Metabolism

Appetite Hunger and satiety are regulated by a complex interaction of multiple brain centers, hormones, and sensory and motor pathways.

Hunger center a region in the lateral hypothalamus that triggers the desire for food stimulateddestroyed

stimulateddestroyed Satiety center a region in the ventromedial hypothalamus that suppresses the desire for food

The satiety center has neurons called glucostats that rapidly absorb blood glucose after a meal. hypothesis: glucose uptake causes the satiety center to send inhibitory signals to the hunger center and thus suppresses the appetite. Satiety Center Hunger Center Blood glucose appetite + _ +

Gastric peristalsis stimulates hunger. Mild hunger contractions begin soon after the stomach is emptied and increase in intensity over a period of hours.

- Adipocytes (fat cells) secrete hormones (leptin) that regulate appetite and body weight. Role of Hormones in Appetite Regulation - Hormones from GI: cholecystokinin: suppressant ghrelin: stimulant PYY: suppressant (Science 299: )

Leptin's effects. Because of a gene defect, the boy doesn't make leptin, but treatment with the hormone, begun when he was 3.5 years old (top), brought his weight down to normal levels, as shown at age 8. (Science 299: )

Nutrients Major Classes of Nutrients : carbohydrates, lipids, proteins, minerals, vitamins, and water. Nutrients are used for: 1) providing energy 2) growth, repair, or maintenance of body cells

Metabolic Rate is the amount of energy released in the body per unit of time, expressed as kcal/hr or kcal/day

37  C38  C 1 Kg A kilocalorie (kcal) is the amount of heat that will raise the temperature of 1 kg of water by 1 o C.

An average adult needs 2,000-5,000 kcal/day, depending on physical activity, mental state, and other factors such as room temperature. 1,000 Kg water x  C

Caloric restriction (by 30%) prolongs life span by 30%-50% and reduces morbidity of aging-related diseases. These effects have been observed in many animal species, including worms, insects, rodents, and maybe primates. Proteins Low fat/cholesterol Vitamins Minerals Carbohydrates unchanged reduced by 30%

- ATP is the universal cellular energy, and can be produced from glucose, fat, and proteins. - A total of 38 ATP is generated per molecule of glucose in the presence of oxygen. Role of blood glucose in providing energy

Blood glucose is more important than fat and proteins in providing energy - Glucose can be used by all tissue cells. - Neurons and erythrocytes normally obtain energy only from glucose. hypoglycemia  weakness, coma Blood glucose level has to be maintained.

discussed in two states. 1) Absorptive State lasts about 4 hours after a meal. 2) Postabsorptive State Maintenance of blood glucose

Absorptive State - Blood glucose is readily available for ATP synthesis. - Glucose serves as a primary fuel and spares the body from having to draw on stored fuels.

Excessive glucose is stored as glycogen in the liver and muscles or as body fat. Absorptive State glycogen fat

Fats are taken by the tissues, especially adipose and muscular tissue. Absorptive State Amino acids become available for protein synthesis. Amino acids

Regulation of the Absorptive State - regulated largely by insulin, which stimulates nearly all cells to absorb glucose. glucose cell blood insulin receptors insulin glycogen muscle

Postabsorptive State (fasting) - prevails hours after meals and overnight. - The essence of this state is to regulate blood glucose levels, which is especially critical to the brain.

Glucose is drawn from the body's glycogen reserves in liver and muscles, or synthesized from fats (gluconeogenesis). glycogen fats

After 4 to 5 days of fasting, the brain begins to use ketone bodies as supplemental fuel. Postabsorptive State - from fat - acidosis

After glycogen and fat reserves are depleted - The body begins to burn proteins. - The first to go is skeletal muscle proteins. glycogen fats proteins

Regulation of the Postabsorptive State - by the sympathetic nervous system and several hormones. - The sympathoadrenal system can mobilize stored energy reserves in adipose tissue as needed. glycogen fats

Glucagon promotes: 1) glycogenolysis glycogen  glucose 2) gluconeogenesis AA/FFA  glucose 3) lipolysis triglyceride  FFA glycogen fats

Growth hormone also raises blood glucose concentrations.

Body Heat and Thermoregulation

Body Temperature - Body temperature fluctuates about 1 o C in a 24- hour cycle. lowest in the early morning highest in the late afternoon

Core temperature in the cranial, thoracic, and abdominal cavities close to rectal temperature 37.2   C (  F) Shell temperature - skin and oral 36.6   C (  F)

heat Heat Production Body heat is generated from: 1)nutrient oxidation (ATP production) energy in glucose ATP 2) ATP use energy in ATP mechanical energy

- At rest, mainly generated in brain, liver, heart, endocrine glands, and skeletal muscles (20-30%). - During vigorous exercise, skeletal muscles produce times as much heat as the rest of the body. Heat Production

The body loses heat through: Heat Loss ConductionEvaporationRadiation

Thermoregulation - Hypothalamic thermostat 1)monitors the blood temperature 2)receives signals from peripheral thermoreceptors in the skin.

Thermoregulation heat-losing center heat-promoting center in the hypothalamus thermostat 37.5  C

When blood temperature is too high heat-losing center stimulates 1)dilation of dermal arterioles 2)sweating

When blood temperature drops too low heat-promoting center stimulates 1)dermal vasoconstriction 2)shivering thermogenesis. 3) later increase in metabolic rate by 20-30% as adaptation.

Disturbances of Thermoregulation Exposure to excessive heat causes: 1) heat exhaustion hypotension, dizziness, vomiting, and sometimes fainting 2) heat stroke brain cell malfunction, convulsions, coma, and finally death

heat glucose ATP - refers to low body temperature - when below 33 o C (91 o F), the metabolic rate drops so low that heat production cannot keep pace with heat loss, and the temperature falls further. - Hypothermia enzyme

Hypothermia below 24 o C (75 o F) = fatal. Which way helps a person survive longer in ice-cold sea water? a.Swim vigorously b.Rest and keep awake