Regulation of functions supporting the vital activity of the human body is achieved in two fundamentally different ways. The first is the 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 responds much faster to changes in the state of the body. This is a nervous regulation, the essence of which is to correct functions involving visceral and peripheral reflexes, while the influence of the humoral factor is the interaction of mediator molecules with receptor complexes of cells on target organs. In this case, the signal is transmitted through biological molecules, for the synthesis of which endocrine glands are present in the body. They secrete substances that are able to spread with the blood stream at a certain distance from the gland and exert influence on the controlled organs.
Endocrine glands: the structure of the humoral regulation system
The responsibility for the proper functioning of all systems and organs of a person lies with the brain, which is the highest center for the analysis of incoming information and a place for the synthesis of signals sent to target cells through the two above systems. And if the nerve effect is through numerous connections in a specialized type of tissue, then the humoral effect is realized directly due to the transport of bioactive molecules capable of activating receptor complexes on the cells of target organs. In this case, the endocrine glands are arranged in a special way and this fundamentally differs from exocrine ones. Firstly, the exocrine gland secretes its molecules outward, that is, into the external environment. This requires special excretory ducts that the 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 regulation is located in the brain, namely in the hypothalamus. Its glandular tissue of neural origin synthesizes statins that inhibit the synthesis of pituitary hormones and liberins, which, on the contrary, modulate its functions. Through this bi-directional effect, control of the functions of the entire system of endocrine glands of the body is achieved. At the same time, the pituitary gland is another center of hormonal regulation of functions - a structure that is approximately 20 times smaller than the hypothalamus, but which performs much-needed functions. It is also noteworthy that such a small gland performs the synthesis of high molecular weight compounds in large quantities, which are called hormones, while the higher structure produces only statins together with liberins, which are very simple in chemical structure, since they are dipeptides.
The remaining endocrine glands are simply controlled by the pituitary gland and their secretion cycle depends on the activity of the synthesis of tropic hormones. At the same time, the ADH, which regulates the reabsorption of water molecules in the collecting tubes of the kidney nephrons, and oxytocin, which is responsible for the reduction of uterine muscles during childbirth and the secretion of milk by the mammary glands, are also synthesized by the neurohypophysis. The adenohypophysis, or the anterior lobe of the gland, controls the body's growth processes, the thyroid hormone secretion cycle, decarboxylation in the adrenal medulla, and the synthesis of steroid hormones in the adrenal cortex.
Very important organs for humans are the pancreas and gonads. By their structure and functions, these are glands with a mixed type of secretion, that is, they have parts of the organ, one of which has an endocrine type of secretion, and the second is exocrine. So sex glands secrete sex cells into the environment, however, hormones enter directly into the blood. In this case, the endocrine function of the pancreas is reduced to the synthesis of glucagon, insulin and somatostatin, exocrine is the synthesis of peptidases and amylases for digestion in the duodenum 12. Therefore, the pancreas, exactly like the gonads, is an exocrine and endocrine gland at the same time.