Homeostasis

Homeostasis

The regulation of internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes

Examples of conditions controlled by homeostasis

Body temperature, blood glucose concentration and water content of the blood

Thermoregulation

The control of body temperature as part of homeostasis

Role of the skin in temperature regulation

The skin controls heat loss from the body by adjusting blood flow and sweat production

Vasodilation

Widening of blood vessels near the skin surface to increase heat loss

Vasoconstriction

Narrowing of blood vessels near the skin surface to reduce heat loss

Sweating

The release of sweat from sweat glands; evaporation of sweat removes heat from the body

Shivering

Rapid muscle contractions that release energy as heat to increase body temperature

ADH source

Antidiuretic hormone is produced by the pituitary gland

Effect of ADH

ADH increases water reabsorption in the kidneys, producing more concentrated urine

When ADH is released

When blood water concentration is low

Adrenaline source

Adrenaline is produced by the adrenal glands

Effects of adrenaline

Increase in heart rate, increase breathing rate, and increases glucose concentration in blood to prepare the body for action

Insulin source

produced by the pancreas

Effect of insulin

Insulin lowers glucose concentration in blood by increasing uptake of glucose by cells and conversion of glucose to glycogen

Testosterone source

testes

Effects of testosterone

Development of male secondary sexual characteristics and stimulation of sperm production

Oestrogen source

Oestrogen is produced in the ovaries

Effects of oestrogen

Development of female secondary sexual characteristics and regulation of the menstrual cycle

Progesterone source

Progesterone is produced by the ovaries

Effects of progesterone

Maintains the lining of the uterus during the menstrual cycle and pregnancy

Blood glucose control

Blood glucose concentration is controlled by insulin and glucagon as part of homeostasis

When blood glucose is high

Insulin is released to reduce blood glucose concentration

When blood glucose is low

Glucagon is released to increase blood glucose concentration

Role of glucagon

Glucagon increases blood glucose concentration by converting glycogen into glucose in the liver

Negative feedback in blood glucose control

Changes in blood glucose are reversed to return levels to normal