Glands that produce hormones are called glands of internal secretion, because the products of their activity they secrete into the blood or lymph. The glands of internal secretion include: anterior pituitary house, epiphysis, thyroid gland, two pairs of parathyroid glands, thymus gland, pancreas, adrenals and sex glands.
Most of the glands that produce hormones are extremely small. For example, the pituitary body weighs 0.6 kg, and all parathyroid glands together - only 0.15 kg.
They produce a relatively small amount of hormones. For example, the thyroid gland in the whole life of a person releases into the blood only 20 g of thyroxine hormone. However, even such a small amount is enough to call for necessary reactions in organs far away from the endocrine glands. At the slightest violations of the functional balance between the major hormonal systems, severe consequences can arise. Violation of hormonal balance is manifested by serious illnesses, a violation of physical and mental development. In addition, there are several hormones that are formed not in the endocrine glands, but in the tissues of the body. To this group, called tissue hormones, include hormones that regulate the digestive process, the production of gastrointestinal juices and the secretion of insulin. Another special subgroup of tissue hormones is neurohormones.
Hormones act as biocatalysts. In other words, hormones act only as carriers of information, they are called mediators (transmitters). They do not take part in the metabolic reactions caused by them, and therefore their composition does not change during these reactions. However, so that the concentration of hormones does not increase, they are regularly (for example, in the liver) cleaved or excreted through the kidneys. Therefore, in the body of a healthy person, the concentration of a hormone is almost always constant.
According to the chemical nature of hormones are divided into protein - prolactin, hormones of the pituitary, steroid - estrogens, progesterone and amino acid derivatives. Although hormones with blood and lymph spread throughout the body, but cause a reaction only in certain cells or organs. The interaction of the hormone with the receptors causes the entire cascade of biochemical reactions in the cell.
The activity of the hormonal system must be regulated reliably and unerringly. Because even the smallest failure will cause serious disturbances in the body.
The composition of hormonal contraceptives includes analogues of two female sex hormones, estrogen and progesterone. They can contribute to the manifestation of depression, migraine and varicose veins. Then the doctor selects another drug with less pronounced side effects.
The most important role of the hormonal system is played by the pituitary gland and part of the intermediate brain - the hypothalamus.
Growth hormone (growth hormone) regulates the growth of the human body. Prolactin provides milk production. Oxytracine causes contractions. Antidiuretic hormone inhibits the release of fluid through the kidneys.
Estrogen and progesterone control the menstrual cycle and support the course of pregnancy in a normal state.