Thermoregulation Objective: * Identify the different structures on the diagram of a skin ** Describe how body temperature is kept constant *** Explain thermoregulation in terms ofvasodilation and vasoconstriction

Name the largest organ of the body. What are its functions? Protects body from damage Stops pathogen from entering Prevents too much water loss Detects changes in temperature Detects pressure (touch) and pain Loses heat by conduction, convection and radiation

the hypothalamus acts like the programmer in the central heating system. messages from the brain go to parts of the body that can have an effect - the effectors. temperature sensors in the skin are like the thermostats in the heating system. a ‘message’ from temperature sensors in the skin

Keeping constant temper ature To keep warm: Shivering – uses energy Releasing energy from food Vasoconstriction Exercising To keep cool: Sweating reduces temperature Removing energy from body Vasodilation Sit or lay down Controlled by the hypothalamus

body temperature normal body temperature falls hair stands up and a goose bump appears hair lies flat on the skin the muscle is relaxed the muscle contracts

Sweating Sweat is produced in sweat glands Sweat on your skin evaporates and it takes heat energy from your body to turn the liquid to a gas. This cools you down.

Hypothalamus (of a sheep)

Skin based effectors

Skin based effectors

Effector Response Skin based effectors – responding to heat gain Arterioles supplying skin capillaries The muscles relax – this is known as vasodilation. The effect of this is to increases the blood flow to the surface of the skin causing increased heat loss by radiation. Sweat glands The glands secrete sweat onto the surface of the skin. The sweat is composed mainly of water, which evaporates from the skin surface. As water has a high latent heat of evaporation the evaporating sweat removes heat from the surface of the skin. Hair erector muscles The muscles relax – this lowers the hairs on the skin surface. The hairs do not trap air when laid flat so they allow heat to be removed more easily by convection.

Effector Response Skin based effectors – responding to heat loss Arterioles supplying skin capillaries The muscle contract – this is known as vasoconstriction. Blood flows through the shunt vessel as this is the path of least resistance. Less blood flows to the surface of the skin so there is less heat loss by radiation. Sweat glands The sweat glands stop producing sweat therefore stopping the heat loss of evaporating sweat. Hair erector muscles The muscle contract – this raises the hairs on the surface of the skin. The effect of this is to reduce airflow therefore reducing convection of heat from the skin.

Skin based effectors

Other effectors and responses Another well-known response to a lowered core temperature is shivering. The effectors for this response are the body’s skeletal muscles which contract and relax involuntarily to generate heat. A lowered core temperature also stimulates the release of the hormones adreneline and thyroxine from the adrenal and thyroid glands. Both these hormones increase the body’s metabolic rate again generating heat.

Shivering

Responding to vigorous exercise ·        stimulus is the increase in blood temperature ·        this is caused by exercise/increased respiration/muscle contraction ·       the increase blood temperature is detected by receptors in the hypothalamus ·       the hypothalamus also acts as the co-ordinator ·        the effectors are muscles of arterioles ·        and sweat glands ·        response to arteriole muscles stimulation is vasodilation ·        which causes increased blood flow to the skin capillaries ·        which causes increased heat loss by radiation ·        response to sweat gland stimulation is increased sweating ·        which causes increased heat loss by the latent heat of evaporation

Exam questions 1. All living organisms exist in changing external environments and many are able to control their internal environments. (a) Explain how the body of a mammal may respond to a rise in the environmental temperature. (8marks)

Exam answers Thermoreceptors in skin; nervous impulse; to hypothalamus; blood temperature monitored; heat loss centre involved; vasodilation / dilation of arterioles; more blood to skin surface; more heat lost by radiation; piloerector muscles relax; hairs flatten on skin surface; less insulation; sweating initiated / increased; panting / licking; evaporation removes latent heat; thinner fur; migration; drop in metabolic rate / use less brown fat; accept long term changes such as less fat deposition; accept one behavioural process; max. 8