HOMEOSTASIS – TEMPERATURE REGULATION WALT – To understand that internal conditions of the body need to be controlled. To know that if the water or ion content is wrong then cells may be damaged. To be able to explain how the body regulates its temperature.

WILFS All students know that homeostasis is a model of how the body regulates its internal conditions. Most students understand that the water and ion content are regulated to prevent cellular damage. Most students can describe the way the body controls its temperature. Some students can explain this using the negative feedback model of temperature regulation

The organs of homeostasis

Too hot…or too cold?

A constant body temperature keeps enzymes working. At high temperatures the enzymes are denatured. At low temperatures work too slow to maintain body functions.

A constant body temperature keeps enzymes working. Controlled by the thermoregulatory centre in the brain. hypothalamus If body temperature deviates from 37 °C, the hypothalamus and skin receptors send out electrical signals that trigger actions or behaviours that increase or decrease heat loss.

Vasoconstriction and warming up Why do people go pale when they are cold? Vasoconstriction is caused by contraction of the muscular wall of the blood vessels. When core body temperature falls, blood vessels in the skin get narrower. This is called vasoconstriction. This reduces the volume of blood flowing near the skin surface, and reduces the amount of heat lost from the body.

When it is cold Sweating stops. Hair is erect to trap more warm air next to the skin. Blood vessels in the skin contract so reducing heat loss (vasoconstriction). Muscles start rapid movements called shivering. Produces extra heat from respiration

Vasodilation and cooling down Why do people turn red when they are hot? Additional cooling occurs with the production of sweat from sweat glands. Vasodilation allows a larger volume of blood to flow near the skin surface, transferring heat to the environment. This cools the body down. When core body temperature rises, blood vessels in the skin get wider. This is called vasodilation. As the sweat evaporates it transfers heat away from the body.

When it is hot You sweat a lot and the sweat evaporates and cools. Hair lies flat so less air is trapped. The blood vessels in the skin expand. More blood flows to the surface, so more heat lost by radiation (vasodilation).

Responding to change