Energy metabolism and body temperature

Outline of the lecture Section 1 Energy Metabolism 1. Energy storage, liberation, transfer and utilization 2. Energy balance 3. Metabolic rate Section 2 Body Temperature 1. Body temperature 2. Balance between heat production and heat loss 3. Regulation of the body temperature

material synthesis material breakdown release energy require energy material metabolism energy metabolism Metabolism AnabolismCatabolism

Energy storage, liberation, transfer and utilization

Energy balance Energy input = energy output heat Food heat heat ATP cellular functions heat metabolism Food heat

metabolic rate amount of energy liberated from a living organism per unit of time expressed in terms of the rate of heat liberation during the chemical reactions

Metabolic rate Measurement of the metabolic rate Direct calorimetry Indirect calorimetry Caloric value / thermal equivalent of food Oxygen consumption / thermal equivalent of oxygen （ 1 L ） Respiratory quotient （ CO 2 / O 2 ）

Factors that affect the metabolic rate 1. Exercise Exercise produces an increase in metabolic rate 2. Ingestion of food Increase metabolic rate The specific dynamic action of protein 3. Emotional state 4. Environmental temperature °C have stable metabolic rate 30°C, metabolic rate is increased 5. Other factors (sleep, sex, etc.)

Basal Metabolic Rate (BMR) Metabolic rate during basal conditions Minimum level of energy required for life Useful for diagnosing the diseases: – Hyperthyroidism, hypothyroidism

Basal conditions must not have eaten food for at least 12 hours after a night of restful sleep no strenuous activity is performed for at least 1 hour before the test all psychic factors that cause excitement must be eliminated the temperature of the air must be comfortable and between 25 – 30 °C no physical activity is permitted during the test

Section 2 Body temperature Skin temperature – temperature of the skin and tissues immediately underlying the skin. – rises and falls with the temperature of the surroundings Core temperature – the temperature of the deep tissues of the body – the “core” of the body. – remains almost exactly constant, varying not more than 1 ℃ – Rectal T: ℃ – Oral T: ℃ – Axillary T: ℃

Range of body temperature

Factors affecting normal temperature 1. Circadian rhythm In the early morning, the body T is the lowest. In late afternoon or early evening, it is the highest. 2. Age Newborn child > adult > old person 3. Sex Women > man 0.3 °C 4. Muscular activity Increase T 5. Other factors: emotion, eating, change in climate

Balancing between heat production and heat loss 1. Heat production – (1) BMR of all the cells – (2) Extra metabolism caused by muscle activity the the effect of hormone (thyroxine, growth hormone and testosterone) the effect of epinephrine, norepinephrine and sympathetic stimulation on the cells increased chemical activity in the cells themselves

2. Heat loss The major organ to loss heat is the skin Blood flow to the skin from the body core provides heat transfer

Methods of heat loss from the skin to the surroundings

Evaporation 1) Insensible perspiration 2) Sweating A. Innervation of the sweat gland Mainly sympathetic cholinergic nerve (acetylcholine) Caused by nervous reflex B. Mechanism of sweat secretion Primary secretion reabsorption Sweat (urea, lactic acid, K+ )

Regulation of the body temperature 1. Behavioral control of the body temperature For example: In freezing weather, we can move into a heated room 2. Autonomic control of the body temperature The temperature of the body is regulated almost entirely by nervous feedback mechanism through temperature regulating centers located in the hypothalamus.

Feedback mechanisms of regulation of the body temperature 1. Temperature receptor – 1) Peripheral temperature receptor A. Locations: skin, mucous, abdominal viscera B. Types: cold receptor and warmth receptor cold receptor > warmth receptor – 2) Central temperature receptor A. Locations: spinal cord, preoptic and anterior hypothalamic area of the hypothalamus (PO/AH) B. Types: heat-sensitive neurons and cold-sensitive neurons

2. Temperature-regulating center – 1) The thermoregulating center is mainly in the hypothalamus – 2) The PO/AH area is the basic thermostatic temperature controlling center

3. Efferent pathways: Control of the heat loss and heat production – 1) Control of the skin vascular tone and sweating by sympathetic nerve system – 2) Changes of the muscular tension by somatic motor nerve system – 3) Control of the metabolic rate by altering the function of endocrine system, mainly the hormone secretion of the thyroid glands or adrenal medulla

“Set-point” 37 °C PO/AH area T > 37 °C Production < loss T < 37 °C Production > loss

Fever

Summary Metabolism Metabolic rate heat body temperature BMR Heat production “set-point” PO/AH Heat loss