Endocrine System

The messengers of the hormone system are the body’s own signal substances called hormones. They control and regulate the metabolism, growth and function of many organs and are essential for reproduction, for example. Hormones are mainly produced by glands and nerve cells, but many organs have individual cells that are also capable of producing hormones. Once produced, hormones can be released and distributed through the bloodstream or along nerve fibers in the body and act on their respective target structures. The hormone-producing organs include

  • Parts of the brain and the pituitary gland
  • The thyroid gland
  • The parathyroid glands
  • The adrenal gland
  • The stomach
  • The Pancreas
  • The ovaries or testicles.

Classification and control

In the simplest case, the formation and release of a hormone is directly controlled by the influencing metabolic parameter and is independent of the brain. The increase or decrease of this parameter results in increased or decreased hormone production. For example, an increase in blood sugar levels after ingestion of food leads to an increased release of insulin.

Insulin is a hormone that is produced in the pancreas and is responsible for lowering blood sugar levels. In addition to this, insulin has the hormone glucagon as its antagonist, which ensures that the blood sugar level does not drop too much. Through such a control loop, it is possible for the body to keep the blood sugar level relatively constant, although the body has to absorb and process a lot of sugar in a short period of time through a meal or drink and must not be hypoglycaemic even in phases of food abstinence.

A much more complicated control loop consists of three hierarchically arranged stages: The top control level in the hormone system is formed by the hormones of the hypothalamus, a part of the brain. They travel via blood vessels to their target organ, the pituitary gland, where they promote or prevent the release of further hormones. This pituitary gland is the center of the hormone system, through which a further series of hormones are released, which finally trigger the production of effector hormones in the downstream hormone glands.

These are called effector hormones because they have an effect on the target organ as a last resort. On the other hand, hormones are released here which can have an effect on their target organ without an intermediate stage. These include hormones that are responsible for controlling the thyroid, the reproductive organs and the adrenal cortex.

These effector hormones reach your successful organs via the bloodstream, but they can also reach the brain and the pituitary gland via feedback here to stop the production of further hormones. This effect is called negative feedback. It is very important to avoid overproduction of hormones and to keep the hormone concentration constant.

On the other hand, this negative feedback can also be absent and thus lead to an increased production of the hormone. In the human body, many control loops interlock and overlap, so that a disturbance has numerous effects. In addition, hormones can be classified according to their chemical properties.

A distinction is made here between water-soluble and fat-soluble hormones, which can affect their target structure in different ways. In addition, these hormones differ in their time of action. The fat-soluble hormones have a much longer effect because their structure protects them from rapid degradation.

In addition to being broken down, hormones can also be inactivated by the body. This happens mainly in the liver. After this inactivation, they can be further utilized or excreted through the urine or bile.