Thermoregulation | Mechanism, Temperature Classification |

Thermoregulation.

The maintenance of internal temperature within a tolerable range is called thermoregulation.

Adaptation in Plants at Low and High Temperature

High temperature

High temperature denatures the enzymes and damage the metabolism. Thus, it harms or kills the plant. The plants cool their body by evaporation. So, evaporation controls their temperature. Hot and dry weather causes water deficiency. It results in closing of stomata. Thus plants face problems in such conditions. Most plants are adapted to heat stress. The plants of the temperate regions face the stress of 40°C and above temperature. The cells of these plants synthesize a special protein called heat-shock proteins. These proteins cover the enzymes and proteins. Thus it prevents the enzymes from denaturation.

Low temperature

At low temperature:

The lipid molecules of the membrane forms crystalline structure at low temperature. This crystalline structure changes the fluidity of the cell membrane. It affects the transport of solute. The crystalline structure also affects the structures membrane proteins. Plants increase the proportion of unsaturated fatty acid in response to cold stress. Unsaturated fatty acids prevent the crystal formation in the membrane. Thus the structure of membrane is maintained at low temperature. This adaptation requires time. Therefore, rapid chilling of plant is more stressful than the gradual drop in temperature.

At freezing temperature:

Freezing temperature causes ice crystal formation. The ice around the cell wall does not affect it badly and plant can survive in it. However, the formation of ice crystal within protoplasm perforates membranes and organelles. Hence it kills the cells. The native plants of the cold region like oak,

maples, roses and other plants shows adaptations. They bring change in the solute composition of cells. So their cytosol is super cooled without ice formation. But ice crystals can be formed in the cell wall. This crystal does not affect the cell.

Mechanism of Thermoregulation in Animals

Body Heat, Heat Gain and Loss

The temperature of an animals depends on:

➤ The rate of change of body heat.

➤ The rate of heat production through metabolic processes

➤ The rate of external heat gain

➤ The rate of external heat loss

The transfer of heat between animal and its environment takes place different methods. These are:

(a). Infrared thermal radiation, direct sunlight and reflected sunlight transfer heat into the animal.

(b). The radiation and evaporation transfer heat out from animals to outer environment.

Temperature Classification of Animals

Different animals deal with change in environmental temperature in different ways. There are two types of animals:

Poikilotherms:

The animals in which body temperature changes according environmental temperature are called poikilotherms. These are invertebrates, amphibians and reptiles.

Homeotherms:

The animals which maintain their body temperature constant in the changing environmental temperature are called homeotherms. The include birds and mammals. The biologist faces several difficulties in the uses of these terms. The difficulties are:

➤ It is observed that deep sea fishes have constant natural surrounding.  Thus their body temperature remains constant.

➤ Lizard regulates their body temperature.

➤ Similarly, the temperature of numerous birds and mammals change the body temperature.

Themoregulation in mammals (Human)

Regulatory Strategies

Mammals including human are endothermic. So they maintain their body temperature within a narrow range of 36 - 38° C. The birds and mammals have high metabolic rate due to endothermy. So energy is available to them round the clock. Thus they have greater ability to adapt in diversified region of the earth.

They regulate the rate of heat production. They balance it with the rate at which they gain or loss heat from the environment. They increase the rate of heat production by following methods:

1. Shivering thermogenesis:

The production of heat by the contraction and shivering of muscles is called shivering thermogenesis.

2. Non-shivering thermogenesis:

The production of heat by the stimulation of hormones like thyroid hormone is called non-shivering thermogenesis.

3. Brown fats:

Some animals possess brown fats. These fats are specialized for the rapid heat production.

4. Skin:

In case of overproduction of heat, blood supply is increased to the exposed surface area of skin. So heat is dissipated and temperature is lowered by evaporative cooling. Thus the skin of the mammals acts as organs of thermoregulation.

In cold temperature:

Mammals have various mechanisms that regulate the heat exchange with the environment in cold temperature: These are:

1. Vasodilatation and vasoconstriction affect the heat exchange. So there is difference of temperature

between the different parts of the body. The trunk has most vital organs of the body. Thus the temperature of the arms and leg is much lower than the trunk during a cool day.

2. Most land mammals raise their fur during cold days. So their fur traps the thick layer of still air. This air acts as good insulator between the animals skin and surrounding.

3. The humans have a layer of fats just under their skin, It acts as insulating material against the heat loss.

4. The marine mammals like whales and seals have thick layer of insulating fats called blubber. The blubber is present under the skin. So these animals can live in much colder water than their body temperature.

In warm temperature:

1. The marine animals have large number of blood vessels in the outer layer of the skin. These vessels are used to dissipate the excessive heat from the skin surface.

2. The terrestrial mammals have adapted the mechanism of evaporative cooling. Their temperature reduction strategy is based on sweat gland activity and evaporative cooling.

3. The evaporative cooling in the respiratory tract is called Panting. This mechanism of heat losing is present in the dogs.

4. Some animals like bat use saliva and urine for evaporative cooling.

Thermostat Function and Feedback Control in Human

The humans have complex homeostatic system to control the body temperature. It is helped by feedback mechanism. The homeostatic thermostat of man is present in the hypothalamus of brain. The 37° is a set point temperature for the human. The thermostat shows response in case of change of temperature from this set point.

➤ At hot temperature:

There are certain warm temperature sensitive thermoreceptors in the skin, hypothalamus and other part of the nervous system. In case of increase of temperature above the set point, these thermoreceptors send signals to the system. These system increases the blood flow to the skin. They also activate- the sweat glands. Thus sweat is evaporated for cooling.

➤ At cold temperature:

The cold receptors send signals to the hypothalamus in cold temperature. The thalamus inhibits the heat loss mechanism and activates the heat conservation mechanism. This includes constriction of superficial blood vessels (small arteries and capillaries). It also stimulates the shivering and non-shivering mechanism.