In the human body, glands of internal, external, as well as glands of mixed secretion are isolated. The glands of external secretion include, for example, the salivary glands, which produce their own secret (in this case, saliva), which is excreted through special ducts. As for the endocrine glands (internal secretion), they produce specific substances - hormones - that are secreted directly into the blood.
Glands of mixed secretion are those formations that secrete hormones and other substances (enzymes, digestive juices, etc.) at the same time. These include the pancreas and sex glands, as well as the kidneys, glands of the stomach and duodenum.
The pancreas is a large gland of mixed secretion that is located behind the stomach. It consists of a head, tail and body.
As you know, this organ is part of the digestive system. The ducts of the gland open into the duodenum, where the so-called pancreatic juice is secreted. The enzymes contained in the juice are responsible for the breakdown of fats, carbohydrates and proteins.
For example, pancreatic amylase is responsible for the breakdown of dextrins and other carbohydrates. Fats break down into monomeric parts under the influence of lipase. In addition, the pancreas secretes chymotrypsinogen and trypsinogen - enzymes for the breakdown of protein compounds. These substances are activated already in the intestinal lumen.
The pancreatic secret also contains bicarbonate ions. Their main function is to neutralize the acidic environment of the chyme, which moves into the intestine from the stomach.
As for internal secretion, this function is carried out by specific parts of the gland - the islets of Langerhans. Several types of cells are distinguished:
- Beta - cells - are responsible for the synthesis of insulin ;
- Alpha - cells - synthesize the hormone glucagon;
- Delta - cells - are responsible for the production of somatostatin;
Insulin and glucagon are hormones that are responsible for the metabolism of carbohydrates and, in particular, glucose. Under the influence of insulin, the intensity of glycogen formation increases, which is subsequently deposited in the liver. Glucagon, in turn, acts as an antagonist - it stimulates the breakdown of glycogen and proteins. As for somatostatin, this substance is able to slow down the activity of both glucagon and insulin.
Female gonads are also glands of mixed secretion. These include the ovaries, in which the growth, maturation and release of eggs takes place. But the functions of the ovaries are not only in the production of offspring.
The main female hormones are estrogens (synthesized in follicles), as well as progesterone (produced by the corpus luteum). Estrogens are a group of substances under the influence of which the development of female sexual characteristics is carried out, as well as the growth and enlargement of the mammary glands, the growth of the uterus, vagina, fallopian tubes and ovaries. Thanks to them, hair growth is carried out according to the female type. In addition, it is estrogens that stimulate the formation of fats and their distribution throughout the body.
Progesterone is produced by the corpus luteum after the egg leaves the follicle. Its main function is to prepare the uterus for embryo implantation, as well as control over the normal course of pregnancy. During the bearing of a child under the influence of progesterone, the processes of ovulation are inhibited.
Male gonads are glands of mixed secretion that are responsible for the production of germ cells and hormones. In the testes, the formation, growth, development and maturation of spermatozoa occurs.
Male sex hormones are androgens, of which testosterone is the best known. Under the influence of this substance, the development of primary and secondary sexual characteristics is carried out - the growth of external and internal genital organs, a low voice, more developed muscles, body hair, etc.
As you can see, the glands of mixed secretion are of great importance in the work of the human body and maintaining homeostasis.