Energy metabolism and body Energy metabolism and body temperaturetemperature

Outline of the lectureOutline of the lectureSection 1 Energy Metabolism1. Energy storage, liberation, transfer and

utilization

2. Energy balance

3. Metabolic rate

Section 2 Body Temperature1. Body temperature

2. Balance between heat production and heat loss

3. Regulation of the body temperature

materialsynthesis

materialbreakdown

releaseenergy

requireenergy

materialmetabolism

energy metabolism

Metabolism

Anabolism Catabolism

Energy storage, liberation, transfer and utilization

Energy balance

Energy input = energy output

heatFood heat heat ATP cellular functions heat

metabolismFood heat

metabolic ratemetabolic 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 rateMetabolic rate

Measurement of the metabolic rateDirect calorimetryIndirect calorimetry Caloric value / thermal equivalent of food Oxygen consumption / thermal equivalent of

oxygen （ 1 L ） Respiratory quotient （ CO2 / O2 ）

Factors that affect the metabolic rateFactors that affect the metabolic rate1. Exercise Exercise produces an increase in metabolic rate2. Ingestion of food Increase metabolic rate The specific dynamic action of protein3. Emotional state4. Environmental temperature 20-30 °C have stable metabolic rate < 20 or >30°C , metabolic rate is increased5. Other factors (sleep, sex, etc.)

Basal Metabolic Rate (BMR)Basal Metabolic Rate (BMR)

Metabolic rate during basal conditionsMinimum level of energy required for lifeUseful for diagnosing the diseases:

– Hyperthyroidism, hypothyroidism

Basal conditionsBasal 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 temperatureSection 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: 36.9-37.9 ℃ – Oral T: 36.7-37.7 ℃ – Axillary T: 36.0-37.4 ℃

Range of body temperatureRange of body temperature

Factors affecting normal temperatureFactors 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 Balancing between heat production and heat lossand 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) SweatingA. 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 temperatureRegulation 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 Feedback mechanisms of regulation of the body temperatureof 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

SummarySummary

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