Body Temperature; Regulation &

Associated Factors

Dr. Wasif Haq

Introduction• Temperature: Sensible intensity of heat

of a substance• Measure of average kinetic energy of

molecules in a substance.

Types of Body Temperature

Core temperatureTemperature of deep tissues of the body

Skin temperatureChanges & varies in accordance to surrounding temperature

Variation & Fluctuation

• Normal temperature range: 36 0 C – 37. 5 0 C

• Circadian variation in Core temperature; lowest in morning and highest in evening. Falls down in sleep. Relation with stress?

• Oral temperature 0.5 0 C higher than skin temperature.

• Rectal temperature representative of core body temperature, 0.5 0 C higher than oral temperature.

The “Set Point”- Thermostat

• A temperature set point/fixed point in Hypothalmus.

• Body responds whenever any factor tries to alter the set point.

• It is the disturbance of “set point” that leads to fever.

Where Does Body Heat Come From?

• Heat by-product of metabolism.• Metabolic rate of body: Determine the

rate of heat production and includes:• (i) Basal rate of metabolism of all body

cells.• (ii) Increased metabolism by shivering of

muscles.• (iii) Chemical thermogenesis.

Body Response To Temperature Change

• If temperature or heat production is more; Promotion of heat loss and decrease in heat generation.

• If temperature falls down or heat production is less; Inhibition of heat losing mechanisms and stimulation of heat production mechanisms.

Insulation in Humans

• Insulating layer comprises of skin, subcutaneous and fat cells.

• Role in maintaining constant core temperature.

How is Heat Lost?• Heat transfer from deeper tissues and

organs such as liver, brain, heart and muscles.

• Rate of heat loss determined by:• (i) How rapidly heat is conducted from

core to skin• (ii) How fast is exchange of heat from

skin to environment.

Some Basic Physics Terms

• Radiation: Heat loss in the form of infra-red rays.

• Conduction: Heat loss by direct contact with the surface of the body.

• Convection: Process of heat transfer through gas and liquids by bulk motion of hotter material into coller region.

How is Heat Lost?• Heat also exchanged through wind and

water. • Evaporation: Insensible water loss. 700

ml/day.• Sweating: 100 ml/day.

The Sweating Mechanism

• Structure of sweat gland: (a) Coiled portion producing “Primary secretion” or Pre-cursor secretion and (b) Duct portion causing modification of primary secretion.

• Weak stimulation causes more Na+, Cl-

and H20 reabsorption, resulting in higher excretion of Urea, Lactic acid & K+ ions.

• Strong stimulation causes lesser reabsorption of Na+, Cl- and H20, consequently more excretion.

Regulation of Sweating

• Preoptic area in anterior hypothalmus.• Impulses transmitted to spinal cord

through autonomic nerve fibers and from spinal cord to the sweat glands through Sympathetic Cholinergic fibers.

Regulation of Body Temperature

Temperature Sensing

• Temperature detection through skin and receptors from deep body structures (Spinal cord, Abdominal viscera and great veins)

• Skin and deep body temperature receptors can alter the set point of hypothalmus temperature control center.

• Cold receptors 10 times more abundant than hot receptors- Prevention of hypothermia.

• If skin is cooled: • (i) Increased shivering.• (ii) Increased vasoconstriction.• (iii) Decreased sweating.

Temperature Regulation-

Hypothalmus• Hypothalmus is the controlling center.• Preoptic area and Anterior hypothalmic nuclei.• Preoptic area: When heated; sweating,

vasodilation & inhibition of heat production.• Anterior hypothalmic nuclei: Contain cold & heat

sensitive neurons. Increased firing of respective neuron according to temperature increase or decrease.

• Posterior hypothalmus: Impulses from anterior hypothalmus & preoptic area conveyed to posterior hypothalmus. Primary motor center for shivering located here.

Body Response• If body encounters increased temperature:• (i) Vasodilation (through inhibition of

Sympathetic vasoconstrictor center in posterior hypothalmus). 8 times more heat loss.

• (ii) Increased sweating: 1 0 C rise in body temperature causes removal of 10 times the basal rate of body heat.

• (iii) Inhibition of heat production: Shivering, Chemical thermogenesis.

• If body encounters decreased temperature:• (i) Vasoconstriction (Vasoconstrictor area

stimulation)• (ii) Chemical thermogenesis.• (iii)Piloerrection (Sympathetic stimulation)

You have to stand guard over the development and maintenance of Islamic democracy, Islamic social justice and the equality of manhood in your own native soil.

Sir.Mohammad Ali Jinnah

Behavioral Control• The conscious sense and feeling of

temperature difference.• Protection in spinal cord injuries patients.

Temperature Acclimatization• Physiological adjustment made by the

body to repeated or prolonged exposure to heat.

• Achieved by short daily exposure to heat.

• Develops in initial 4-7 days, completed by 14 days of successive heat exposure.

• Benefits: More sweating rate, increased plasma volume and lesser salt loss due to increased aldosterone secretion.

Fever• Set point of hypothalmus increase by

pyrogens which include bacteria, viruses, parasites & protein breakdown products.

• Body attempts to match the new set point.• Leucocytes, macrophages & natural killer

cells produce Interleukin 1 which causes Prostaglandin formation.

• Role of Aspirin.• Protective effect of fever: Prevents growth

of certain micro-organism, antibody production rises & slowing of growth of some tumors.

Heat Stroke• The wet, humidified air increases body

temperature beyond the level where heat can be lost through sweating.

• Depression of heat regulating ability of hypothalmus.

• Occurs when temperature rises above 106 0 F -108 0 F.

• Symptoms: Dizziness, abdominal distress, loss of consciousness. Circulatory shock may ensue.

• Consequences: Liver, kidney failure, hemorrhages, brain damage and death.

http://coolbluez.t15.org