5.3 Thermoregulation

Thermoregulation

is the regulation of body temperature

Body Temp

Is constant at about 36.8 degrees.

Why is thermoregulation important?

Because chemical reactions in cells are so heat sensitive this is an important part of homeostasis. 37° is optimum for cellular reactions and so cells maintained at this temperature function in a stable manner.

How to achieve thermoregulation?

Heat gained from the body must be exactly equal to the heat lost from the body. Maintaining this balance is called thermoregulation.

What produces the bodies higher temperature?

The heat produced from metabolic activity maintains the higher temperature.

What does increase body temperature cause?

Nerve Malfunctions. Change in protein structure. Death

How is heat gained by the body?

Metabolism, respiration of the liver, respiration of muscle cells, heat gained from surroundings via conduction and radiation.

How is heat lost from the body?

It can be lost to surroundings via radiation conduction and convection, it can be lost through the evaporation of water from the skin and lungs. It can be lost through breathing out warm air, as well as the passing of warm urine and faeces.

Where does the energy we need from our body come from?

The carbohydrates, proteins, and lipids we eat contain energy in chemical bonds that hold the various parts of the molecule together. Energy is released when the food is oxidised during cellular respiration.

What is the energy is used for?

Muscle contractions, active transport of substances across the cell membrane, building new complex molecules, but most of it is released as heat.

Metabolic rate

The rate of which energy is released by the breakdown of food.

Factors that affect metabolic rate…

Exercise, stress and body temp.

What is the factor that most affects metabolic rate?

Exercise. During exercise, muscular activity can increase metabolic rate by up to 40 times, so very large quantities of heat are released.

Metabolic rate also increases in times of stress because of activities of the autonomic nervous system.

Stimulation of the sympathetic nerve’s releases noradrenaline from the nerve endings; noradrenaline increases the metabolic activity of cells. Strong sympathetic stimulation may cause dramatic increase in metabolic rate, but usually for only a few minutes.

Metabolic rate increases with body temperature

For every 1 degree increase the rate of biochemical reactions increases by about 10%.

Peripheral Thermoreceptor

Are located in the skin and mucous membranes, detect changes in the external environment and send this information to the hypothalamus.

Central Thermoreceptor

Located in the hypothalamus, detects the temperature of the internal environment.

Additional Thermoreceptors

Are located at various internal locations such as the spinal cord and the abdominal organs that provides the hypothalamus with information about the temperature of the internal environment.

Cold Receptor

Are stimulated by temperatures lower than normal. When stimulated, the hypothalamus receives the information, and initiates heat conservation and heat production mechanisms.

Heat Receptor

detect temperatures higher than normal. When stimulated mechanisms operate to reduce heat production and increase heat loss.

Skin and Temp regulation with the skin: 1

Large Surface Area and Location of the skin between the internal and external environment means that it is a very important organ in regulating body temperature.

Skin and Temp regulation with the skin: 2

Heat can be lost from the skin by conduction convection radiation and evaporation

Conduction

Transfer of heat by direct contact between particles

Convection

is the transfer of heat by the movement of a liquid or gas

Radiation

is the transfer of heat by infrared radiation being emitted by the objects.

Evaporation

is the process of a liquid forming a gas which absorbs heat energy.

Blood vessels and Heat Loss 1

Carries heat to the skin from the core of the body, diameter of these arterioles is controlled by the autonomic nerves.

How do the blood vessels control heat loss?

diameter is increased by vasodilation, more blood is transported to the capillaries in the skin, and the rate of heat loss increases. diameter is reduced by vasoconstriction, less blood is transported to the capillaries in the skin, and the rate of heat loss decreases.

Sweating and Heat Loss

When large amounts of body heat must be lost and skin blood vessels are already at max dilation, sweating must occur.

Sweating

Is the active secretion of fluid by the sweat glands and the periodic contraction of cells surrounding the ducts to pump the sweat to the skin surface.

What stimulates the production and transport of sweat to the skin surfaces?

Sympathetic Nerves

What is sweat made of?

Sweat is water containing dissolved substances, primarily NaCl and small amounts of urea, lactic acid, potassium ions.

How does sweat cool down the skin?

Evaporation of sweat from the skin has a cooling effect, heat is removed from the skin when sweat turns into vapour.

Even in the absence of sweating…

there is a continual loss of water by evaporation, this evaporation along with water that is evaporated from the lungs and respiratory passages, accounts for a considerable proportion of the daily heat loss from the body.

Shivering is due to…

an increase in skeletal muscle tone, producing rhythmic muscle tremors, that occur at a rate of around 10 to 20 per second. As no work is being done, the heat produced by the muscle is released as heat.

How does the hypothalamus prevent body temp from falling?

When the environment temperature drops, the cold receptors in the skin send messages to the hypothalamus. The hypothalamus then sends out impulses aimed at reducing heat loss and increasing heat production, so that body temperature is maintained.

Preventing body temp from lowering 1

Impulses from hypothalamus stimulates sympathetic nerves that cause arterioles in the skin constrict. Vasoconstriction decreases the flow of warm blood to the skin from the internal organs, thus decreasing the transfer of heat from the internal body organs to the skin. Skin becomes cooler because there is less warm blood flowing through it. Less heat will turn be lost from the body surface. In this way Vasoconstriction of skin arterioles helps maintain body temp in cold conditions.

Preventing body temp from lowering 2

A second response initiated by the hypothalamus is the stimulation of the adrenal medulla by autonomic nerves. This stimulation results in the medulla secreting adrenaline and noradrenaline into the blood. These hormones increase cellular metabolism, which leads to an increase in heat production. This helps maintain internal body temperature in conditions of rapid heat loss.

Preventing body temp from lowering 3

A fall in body temp causes the hypothalamus to send stimuli to the parts of the brain that causes shivering, which can increase body heat production several fold within minutes shivering is under the primary control of the hypothalamus but conscious input from cerebral cortex can suppress the urge to shiver.

Preventing body temp from lowering 4

response to a fall in body temperature is an increase in the production of thyroxine. The hypothalamus is able to cause pituitary to secrete thyroid-stimulating-hormone, which cause the thyroid gland to release thyroxine into the blood. Increase in thyroxine causes an increase in metabolic rate, resulting in an increase in body temperature. This response is slower to have an effect, but it is longer lasting than other responses.

Preventing body temp from lowering 5

A behavioural response may occur if we become consciously aware of cold conditions. If we feel cold, we can behave in a way that reduces heat loss.

Preventing body temp from rising 1

Vasodilation of skin arterioles increases blood flow through the skin. Skin becomes reddish colour; surface temperature rises and there is greater heat loss through radiation and convection.

Preventing body temp from rising 2

When temp is above 28 degrees, sweating is needed to increase heat loss from the body. The cooling effect of sweating is effective only in environments that are fairly dry. If the air is humid sweat cannot evaporate and therefore does not absorb heat from the body.

Preventing body temp from rising 3

In the long term, the metabolic rate can decrease, which means less heat is produced in the body. This decrease is brought about by a reduction in the secretion of thyroxine, a response that occurs in summer when there is much less heat loss than in winter.

Preventing body temp from rising 4

Behavioural responses can also help to prevent the body temperature rising. Actions such as turning on the fan or air conditioner, removing external clothing and reducing physical activity can all help to keep temperature constant.

What controls thermoregulation?

The hypothalamus exercises control over the various mechanisms involved in maintaining body temperature. The hypothalamus monitors the temperature of the blood and receives impulses from peripheral thermoreceptors.

Which core body temperature is dangerous? hot

42 degrees is dangerous, and 45 degrees is a death sentence.

Heat Stroke

When temperature and relative humidity is high it is difficult for the body to lose heat by radiation and evaporation, in this case, body temperature rises and the regulatory mechanisms cease. It can be very serious or even fatal, if brain cells are affected.

Treatment for Heat Stroke

Consists of cooling the body as quickly as possible by immersing the patient in cold water.

Heat Exhaustion

Occurs more frequently than heat stroke. Occurs as a result of extreme sweating and vasodilation to lose heat. The loss of water in sweating reduces the volume of blood plasma and the vasodilation reduces resistance to blood flow. Therefore, blood pressure is reduced and output from the heart decreases. Person may collapse, but body temperature is almost normal.

Which core body temperature is dangerous? cold

Below 33 degrees hypothermia, below 32 degrees is usually death, but people can survive even lower temperatures.

Hypothermia

Core body temperature is below 33 degrees the metabolic rate is so low that heat production is unable to replace the heat lost and the body temperature continues to fall.