The structure and activity of the intrasecretory glands is studied by a science such as endocrinology. Discipline also explores various types of hormones, their interaction, their formation pathways and effects on the body.
What is a hormone?
This compound enters the bloodstream and through it penetrates into various organs. Due to the activity of these substances, the activity of other cells called targets is reduced or increased. The hormones through them affect almost all of the vital functions of the human body.
The concentration of compounds produced depends on various factors. In particular, the time of day, age, emotional and physical condition are important. Hormones penetrate into the blood as needed, and are excreted from the body unchanged in small volumes through bile or urine. There are different types of compounds that have varying degrees of impact on the human condition. One of them are neurohormones. These compounds are produced in a special area of the brain. What are these substances? How are neurohormones formed? What effect do they have on systems in the body? About it further.
General information
Before you find out where and how neurohormones are formed, you should understand what these substances are in general. The definition itself has Greek roots. Literally translated as neuron (nerve) + hormaino (induce, set in motion). What are neurohormones? These are biologically active peptide compounds. They enter the pituitary gland and regulate its activity. Neurohormones are produced by the hypothalamus. Due to the activity of the compounds in question, the endocrine and nervous systems are connected to each other. This is due to the fact that neurosecretory cells are particularly susceptible to the activity of mediators - compounds that transmit an impulse to the working organ from the nerve ending. Thus, their participation extends to the regulation of the activity of intrasecretory glands during the development and growth of the body.
Classification
Two groups are distinguished in this category of compounds. The first includes liberins. These substances have a stimulating effect on the production of tropic pituitary secrets. This group, in particular, includes corticoliberin and tyroliberin, follyberin, luliberin, somatoliberin, melanoliberin, prolactoliberin. The second group of non-hormone hormones is statins. These compounds slow down the production of tropic pituitary secrets. This group, in particular, includes somatostatin, melanostatin and prolactostatin. According to the results of the studies, the activity of the hypothalamic neurohormones is not limited only to stimulation or inhibition of the production of biologically active tropic compounds. Substances have the ability to influence the processes of biosynthesis.
In what areas is the development carried out?
It was said above that the production of such compounds in humans is carried out in a special area of the brain. The formation of these substances occurs in both vertebrate and invertebrate animals. Where and how do neurohormones form in other organisms? In vertebrates, pinealocytes of the pineal gland, elements of the chromaffin tissue in the medulla of the adrenal ganglia, paraganglia and nerve trunks of the autonomic and peripheral nervous system participate in secretion. In secretory granules, neurohormones, as a rule, bind to carrier proteins.
Some features
In contrast to the classical type of nerve cells that produce chemical transmitters of nerve impulses - mediators, neurosecretory elements produce special compounds in the cytoplasm (in rare cases, in the nucleus). These substances are secreted mainly through nerve endings (terminal) into the blood, hemolymph, cerebrospinal fluid and tissue. Neurohormones have a regulatory effect on the activity of visceral organs (endocrine glands, in particular) and the central nervous system.
What are the functions of neurosecretory cells? The activity of these elements is controlled by classical neurons. Their axons form numerous synapses on the body and processes of neurosecretory cells, which have the ability to generate action potential and to propagate momentum along axons.
Location and concentration
Having found out where and how neurohormones are formed, their distribution in the nervous system should be considered. Compounds are distributed diffusely in invertebrate lower organisms. In phylogenesis, the concentration of bodies of neurosecretory cells in the corresponding centers is noted. So, in crustaceans, there is an accumulation in the X-organ, and in insects, for example, in prototserebrum. In this case, neurohemal organs and neurosecretory pathways appear. In vertebrates, the latter are concentrated in a certain area of the diencephalon (and in fish, also in the caudal region of the spinal cord, urofysis). As a result, two main neurosecretory systems are formed: the caudal (exclusively in fish) and the hypothalamic-pituitary.
Production stages
Where and how are neurohormones formed? The synthesis of compounds associated with carrier proteins is carried out on ribosomes. Accumulation occurs in the tubules of the endoplasmic reticulum. Elementary granules are finally formed in the Golgi complex. These components, whose diameter is from 50 to 500 nm, have a lipoprotein membrane. It is separated from the electron-dense center. It, in turn, consists of a carrier protein and a neurohormone. The movement of granules is carried out towards the axons. Some axons are in contact with capillaries in the neurohypophysis. Others - with glandular cells in the adenohypophysis (mainly its intermediate lobe). In fish, axons of the caudal neurosecretory system create axoventricular contacts. The direct isolation of the contents from the granules is carried out in the area of these contacts by means of exocytosis or into derivatives of neurohemal organs, into the precapillary space and into the intercellular clefts at the molecular level.
Possible pathologies
Neurohormones take part in maintaining hemostasis (water-salt and others), various aspects of metabolism, and regulation of smooth muscle tone. In addition, due to their activity, the stable activity of the elements of the endocrine glands is ensured. Also, the functioning of the considered peptide compounds contributes to the provision of protective and adaptive reactions of the body. Coming into hemolymph, into the cerebrospinal fluid or into tissue fluid, they have a long distant regulatory effect. In the case of serious violations of the hypothalamus and production, respectively, of the hypothalamic neurohormones, there are violations in the production of hormones in the pituitary gland and in other intracretory glands. A person begins to develop various pathologies of the endocrine system. In particular, they include hypothalamic-pituitary insufficiency, Itsenko-Cushing's disease, acromegaly, hypothyroidism and other ailments.