MAVO Year 4 · Coordination and control · Section 10.6

The endocrine system

What is the endocrine system?

The endocrine system includes glands releasing hormones into the blood. Hormones coordinate processes such as growth, development, metabolism and reproduction. Only target cells with suitable receptors respond to a particular hormone, even though it circulates widely.

The pituitary and thyroid glands

The pituitary gland, beneath the brain, produces several hormones and helps control other endocrine glands. Growth hormone contributes to growth, including bone growth, and works with other hormones during the adolescent growth spurt. Excess growth hormone during childhood can cause unusually rapid growth; deficiency can cause reduced growth. Short stature has many possible causes.

The thyroid gland, in the neck, produces thyroid hormones which influence metabolic rate, growth and development. Too much can increase metabolic activity; too little can cause symptoms such as tiredness and feeling cold, and can affect development in children.

Blood glucose and the pancreatic islets

The islets of Langerhans in the pancreas contain cells producing insulin and glucagon. Together they help regulate blood glucose.

After a meal, insulin promotes glucose uptake in certain tissues and its storage as glycogen, especially in liver and muscle. This helps lower blood glucose. When blood glucose falls, glucagon stimulates the liver to release glucose, including by breaking down its glycogen. Muscle glycogen mainly supplies the muscle itself rather than being released directly as blood glucose.

In diabetes, insulin is absent, insufficient or less effective, allowing blood glucose to remain too high. Type 1 usually involves autoimmune destruction of insulin-producing cells and requires insulin treatment. Type 2 involves insulin resistance and often reduced insulin production; inherited susceptibility, age and other factors, including lifestyle, influence risk. It should not be reduced to a person's lifestyle alone.

Adrenaline and rapid action

The adrenal glands, above the kidneys, release adrenaline during stress, fear or excitement. It increases the availability of fuel, can raise blood glucose and increases heart activity and breathing. These changes prepare the body for rapid action.