Regulation of Body Temperature

What does homeostasis refer to?

Homeostasis refers to the ability of the body to maintain relatively stable internal conditions despite changes in external or internal conditions.

What is the other name of thermoregulation?

Heat regulation

What is thermoregulation?

Thermoregulation, also called Heat Regulation, is a process by which humans maintain a fairly steady body temperature even under a variety of external conditions

Why is the regulation of body temperature important?

because even slight shifts can disrupt the rates of metabolic reactions.

Normal temperature of the body?

Normally, the temperature of deeper body parts remains close to a set point of 37°C (98.6°F).

What mechanisms does the body use to maintain a stable temperature?

The maintenance of a stable temperature requires that the amount of heat the body loses be balanced by the amount it produces.

What is body temperature controlled by?

balancing heat production and heat loss.

What happens when heat production is greater? and the heat loss is greater?

• When the rate of heat production in the body is greater than the rate at which heat is being lost, heat builds up in the body and the body temperature rises.
• Conversely, when heat loss is greater, both body heat and body temperature decreases.

What is a principal by-product of metabolism?

Heat production

What is metabolism

the sum of the chemical reactions that take place within each cell of a living organism and that provide energy for vital processes and for synthesizing new organic material

Metabolism can be conveniently divided into-

two categories
Catabolism
Anabolism

Explain catabolism

the breakdown of complex molecules into smaller ones to obtain energy

Explain anabolism

the synthesis of relatively complex molecules formed in living cells from simpler units.

Most important factors that determine the rate of heat production-

1. basal rate of metabolism
2. by the effect of thyroxine (and, to a lesser extent, other hormones, such as growth hormone and testosterone) on the cells. Thyroid hormone increases the basal metabolic rate leading to increased heat production by cells in the body.
3. muscle activity, including muscle contractions caused by shivering;
4. epinephrine, norepinephrine, and sympathetic stimulation on the cells;
5. due to increased biochemical activity in the cells.
6. after ingestion of food. the body needs to burn calories for digestion, absorption, and storage of food (thermogenic effect of food).

Where is heat most produced from?

generated in the deep organs, especially the liver, brain, and heart, and in the skeletal muscles during exercise.
This heat is then transferred from the deeper organs and tissues to the skin, where it is lost to the air and other surroundings.

rate at which heat is lost is determined almost entirely by-

two factors
1. how rapidly heat can be conducted from where it is produced in the body core to the skin and
2. how rapidly heat can then be transferred from the skin to the surroundings

various methods by which heat is lost from the skin
to the surroundings include

radiation
conduction and convection
evaporation

Explain radiation

• The primary means of body heat loss is radiation. Radiation is the emission of heat in the form of infrared heat rays that escape from warmer surfaces to cooler surroundings without any direct contact.
• If the temperature of the body is greater than the temperature of the surroundings, a greater quantity of heat is radiated from the body than is radiated to the body.

Explain conduction

heat moves from the body directly into the molecules of cooler objects in direct contact with its surface.

Explain convection

• Heat is also lost by conduction to the air molecules that remain in contact with the body.
• As air becomes heated, it becomes less dense and moves away from the body, carrying heat with it, and is replaced by cooler air moving toward the body.
• This type of continuous circulation of air over a warm surface is convection.

Explain evaporation

▪ When the body temperature rises above normal, the nervous system stimulates sweat glands to release sweat onto the surface of the skin.
▪ As this fluid evaporates (changes from a liquid to a gas), it carries heat away from the surface, cooling the skin down

Which method releases less heat?

Conduction and convection

"Set Point" for Temperature Control

• At 37°C (98.6°F), drastic changes occur in the rates of both heat loss and heat production.
• At temperatures above this level, the rate of heat loss is greater than that of heat production, so the body temperature falls and approaches the 37°C level.
• At temperatures below this level, the rate of heat production is greater than that of heat loss, so the body temperature rises and again approaches the 37°C level.
• This crucial temperature level is called the "set point" or more precisely, the "hypothalamic set point" of the temperature control mechanism

important mechanisms to reduce body heat when the body temperature becomes too high

three mechanisms
1. Vasodilation of skin blood vessels
2. Sweating
3. Decrease in heat production.

explain Vasodilation of skin blood vessels

▪ In almost all areas of the body, the skin blood vessels become intensely dilated. This dilation is caused by inhibition of the sympathetic centers in the posterior hypothalamus which normally causes vasoconstriction.
▪ Full vasodilation can increase the rate of heat transfer to the skin as much as eightfold

Explain sweating

The effect of increased body temperature causes an increase in the rate of evaporative heat loss resulting from sweating when the body core temperature rises above the critical level of 37°C (98.6°F).

explain 'decrease in heat production'

The mechanisms that cause excess heat production, such as shivering and chemical thermogenesis, are strongly inhibited.

Temperature-Increasing Mechanisms When the Body Is Too Cold

1. Skin vasoconstriction throughout the body
2. Piloerection
3. Increase in thermogenesis (heat production)

Explain skin vasoconstriction throughout the body

caused by stimulation of the posterior hypothalamic centers

Explain piloerection

▪ Piloerection means hairs "standing on end."
▪ Sympathetic stimulation causes the errector pili muscles attached to the hair follicles to contract, which brings the hairs to an upright stance.
▪ This mechanism is not important in human beings, but in many animals, upright projection of the hairs allows them to entrap a thick layer of "insulator air" next to the skin, so transfer of the heat to the surroundings is reduced

Explain increase in thermogenesis (heat production)

Heat production is increased by promoting shivering, sympathetic excitation of heat production, and thyroxine secretion.

What is fever

• Fever, or pyrexia, is the elevation of core body temperature resulting from upward resetting of the hypothalamic thermostatic set-point
• increase in the body's 'set-point' temperature is often due to a physiological process brought about by infectious agents (pyrogens) or non-infectious causes such as inflammation, malignancy, or autoimmune processes. These processes involve the release of immunological mediators, which trigger the thermoregulatory center of the hypothalamus, leading to an increase in the body's core temperature

Some causes of fever include-

✓ bacterial or viral infections,
✓ Brain tumors, and
✓ environmental conditions

What can hypothermia result from?

prolonged exposure to cold or as part of an illness

When does hypothermia occur?

as our core body temperature falls below 95⁰F (35⁰C).

Hypothermia begins with-

• shivering and
• a feeling of extreme cold

if not treated, hypothermia progresses to

a. mental confusion;
b. lethargy;
c. loss of reflexes and
d. consciousness; and, eventually,
e. a shutting down of major organs

what happens when temperature drops a few degrees?

fatal respiratory failure or arrhythmia may result.

Who are at high risk of developing hypothermia?

people who has less adipose tissue in the subcutaneous layer beneath the skin (less insulation).
These include the very old, very thin individuals, and the homeless.
The very young with undeveloped nervous systems

What can prevent hypothermia?

Dressing appropriately and staying active in the cold can prevent hypothermia.