Regulation of functions supportingvital activity of the human body, is achieved in two fundamentally different ways. The first is a humoral control mechanism, which is earlier, if we evaluate the functional and structural elements of the human body from the point of view of phylogenetic development. The second mechanism is more flexible and reacts much more quickly to changes in the state of the body. This is a nervous regulation, the essence of which is to correct functions with visceral and peripheral reflexes, whereas the effect of the humoral factor is the interaction of mediator molecules with receptor complexes of cells on target organs. In this case, signal transmission is carried out by means of biological molecules, for the synthesis of which there are endocrine glands in the body. They secrete substances that are able to travel with a blood flow a certain distance from the gland and have an effect on the organs under control.
Endocrine glands: the structure of the humoral regulation system
Responsibility for the proper operation of all systems andof the human organs is carried by the brain, which is the highest center of analysis of incoming information and the site of synthesis of signals sent to target cells through the two above systems. And if the nervous influence is through numerous connections in a specialized kind of tissue, then the humoral is realized apomorphically due to the transport of bioactive molecules capable of activating the receptor complexes on the cells of the target organs. In this case, the endocrine glands are arranged in a special way and this is fundamentally different from the exocrine glands. First, the exocrine gland secretes its molecules outward, that is, into the external environment. This requires the presence of special excretory ducts that endocrine glands do not have, the secretory cells of which release hormones directly into the bloodstream.
It is important that the highest center of humoral regulationis located in the brain, namely in the hypothalamus. Its glandular tissue of a neural origin synthesizes statins, which inhibit the synthesis of pituitary hormones, and liberins, which on the contrary modulate its functions. Through this bi-directional influence, the functions of the entire system of the endocrine glands of the organism are controlled. In this case, the other center for hormonal regulation of functions is the pituitary - a structure about 20 times smaller than the hypothalamus, but performing much needed functions. It is also noteworthy that such a small gland performs the synthesis of high molecular compounds in large quantities called hormones, whereas the higher structure produces only statins together with liberins, which are very simple in chemical structure, since they are dipeptides.
Other endocrine glands simplyunder the control of the pituitary gland and their cycle of secretion depends on the activity of the synthesis of tropic hormones. In addition, the neurohypophysis synthesizes also ADH, which regulates the reabsorption of water molecules in the collecting tubes of kidney nephrons, and oxytocin, responsible for the reduction of uterine musculature during labor and the secretion of milk by the mammary glands. Adenohypophysis, or anterior lobe of the gland, controls the growth processes of the body, the cycle of secretion of thyroid hormones, decarboxylation in the adrenal medulla, the synthesis of steroid hormones in the cortex of the adrenals.
Very important organs for humans arepancreas and gonads. In its structure and functions are glands with a mixed type of secretion, that is, they have areas of the body, some of which have an endocrine type of secretion, and the second - exocrine. So sex glands secrete germ cells into the environment, but hormones enter directly into the blood. In this case, the endocrine function of the pancreas reduces to the synthesis of glucagon, insulin and somatostatin, exocrine is the synthesis of peptidases and amylases for digestion in the 12 duodenum. Therefore the pancreas, exactly like the gonads, is the exocrine and endocrine gland simultaneously.
