The hypothalamus of the brain, or subthalamic region, is a small area located below the thalamus region in the diencephalon. Despite its small size, the hypothalamus neurons form from 30 to 50 groups of nuclei responsible for all possible homeostatic indices of the body, as well as regulating the majority of neuroendocrine functions of the brain and the body as a whole. Hypothalamic neurons have extensive connections with virtually all centers and sections of the central nervous system, with particular attention to the neuroendocrine connections of the hypothalamus and pituitary gland. They cause the formation of the so-called functionally unified hypothalamic-pituitary system responsible for the production of pituitary and hypothalamic hormones and is the central link between the nervous and endocrine systems. Let's analyze in more detail how the hypothalamus is arranged, what it is and what specific functions of the organism are provided by this small area of the brain.
Although the functional activity of the hypothalamus has been studied quite well, to date, there are not clear enough anatomical boundaries defining the hypothalamus. The structure in terms of anatomy and histology is associated with the formation of extensive neuronal connections of the hypothalamic region with other parts of the brain. So, the hypothalamus is in the subthalamic region (below the thalamus, which is why its name takes place) and takes part in the formation of the walls and bottom of the third ventricle of the brain. The terminal plate anatomically forms the anterior border of the hypothalamus, and its posterior boundary is formed by a hypothetical line passing from the posterior spike of the brain to the caudal region of the mastoid bodies.
Despite its small size, the structurally hypothalamic region is divided into several smaller anatomical-functional regions. In the lower part of the hypothalamus, structures such as the gray hillock, funnel and middle elevation are distinguished, and the lower often funnel passes anatomically into the pituitary foot.
Let's look at what nuclei are in the hypothalamus, what it is, and what groups they are divided into. Thus, under the nuclei in the central nervous system is meant the accumulation of gray matter (neuron bodies) in the thickness of the white matter (axon and dendritic terminals - conducting paths). Functionally, the nuclei provide the switching of nerve fibers from one nerve cell to another, as well as analysis, processing and synthesis of information.
Anatomically, three groups of clusters of neuronal bodies are formed, forming the nuclei of the hypothalamus: anterior, middle and posterior groups. To date, the exact number of nuclei of the hypothalamus is difficult to establish, as various data on their number are given in various domestic and foreign literary sources. The anterior group of nuclei is located in the area of the optic chiasm, the middle group lies in the region of the gray hillock, and the posterior group lies in the region of the mastoid bodies, forming the hypothalamus sections of the same name.
The anterior group of hypothalamic nuclei includes supraoptic and paraventricular nuclei; the middle group of nuclei corresponding to the funnel and gray hillock region includes lateral nuclei, as well as dorsomedial, tubular and ventromedial nuclei, and the posterior group includes mastoid bodies and posterior nuclei. In turn, the autonomic function of the hypothalamus is provided by the function of nuclear structures, anatomical and functional relationships with the rest of the brain, control of basic behavioral reactions and the release of hormones.
Hormones of the hypothalamus
The hypothalamic region secretes highly specific and biologically active substances, which have been called "hormones of the hypothalamus". The word "hormone" comes from the Greek "I excite," that is, hormones are highly active biological compounds that, in nanomolar concentrations, can lead to significant physiological changes in the body. Let's look at what hormones the hypothalamus exposes, what it is and what is their regulatory role in the functional activity of the whole organism.
By its functional activity and the point of application, hypothalamic hormones are divided into the following groups:
- releasing hormones, or liberins;
- hormones of the posterior lobe of the pituitary gland (vasopressin or antidiuretic hormone and oxytocin).
Functionally, the releasing hormones affect the activity and release of hormones by the cells of the anterior lobe of the pituitary gland, increasing their production. Hormones-statins perform the directly opposite function, stopping the production of biologically active substances. Hormones of the posterior lobe of the pituitary gland are actually produced in the supraoptic and paraventricular nuclei of the hypothalamus, and then along the axon terminals are transported to the posterior region of the pituitary gland. Thus, the hormones of the hypothalamus are a kind of controlling elements that regulate the production of other hormones. Liberians and statins regulate the production of tropic hormones in the pituitary gland, which in turn affect the target organs. Let's look at the main functional moments of the hypothalamic region, or what the hypothalamus in the body is responsible for.
Hypothalamus in the regulation of cardiovascular function
To date, it has been shown experimentally that electrostimulation of various hypothalamic regions can lead to the occurrence of any of the known neurogenic effects on the cardiovascular system. In particular, by stimulating the centers of the hypothalamus, it is possible to achieve an increase or decrease in the level of blood pressure, increase or decrease in the heart rate. It is shown that in different areas of the hypothalamus these functions are organized according to the reciprocal type (that is, there are centers responsible for increasing blood pressure and the centers responsible for its decrease): stimulation of the lateral and posterior hypothalamic region leads to an increase in the level of arterial pressure and frequency heartbeat, while stimulation of the hypothalamus in the area of the visual crossover can cause directly opposite effects. The anatomical basis of regulatory influences of this type is the specific centers regulating the activity of the cardiovascular system located in the reticular regions of the bridge and medulla oblongata, and the extensive neuronal connections passing from them to the hypothalamus. The functions of regulation are precisely provided by the close exchange of information between these regions of the brain.
The involvement of the hypothalamic region in maintaining a constant body temperature
Nuclear formations of the hypothalamic region take a direct part in regulating and maintaining the constancy of body temperature. In the preoptic region there is a group of neurons that are responsible for the constant monitoring of the temperature of the blood.
When the temperature of the flowing blood rises, this group of neurons can increase the impulse by transferring information to other structures of the brain, thereby triggering heat transfer mechanisms. With a decrease in blood temperature, impulses from neurons decrease, which causes the start of heat production processes.
Participation of the hypothalamus in the regulation of the body's water balance
Water-salt balance of the body, vasopressin, hypothalamus - what is it? The answer to these questions is later in this section. Hypothalamic regulation of the body's water balance is carried out in two main ways. The first is the formation of a sense of thirst and a motivational component, which includes behavioral mechanisms that lead to the satisfaction of the need. The second way is to regulate the loss of fluid in the body with urine.
Localized the center of thirst, which causes the formation of the same name, in the lateral hypothalamic region. In this case, sensitive neurons in this area constantly monitor not only the level of electrolytes in the blood plasma, but also the osmotic pressure, and with an increase in concentration cause the formation of a thirst, which leads to the formation of behavioral reactions aimed at finding water. After the water is found and thirst is satisfied, the osmotic pressure of the blood and the electrolyte composition are normalized, which returns the impulse of the neurons to normal. Thus, the role of the hypothalamus is reduced to the formation of the vegetative basis of behavioral mechanisms aimed at satisfying the emerging nutritional needs.
The regulation of the loss or release of water by the body through the kidneys lies on the so-called supraoptic and paraventricular nuclei of the hypothalamus, which are responsible for the production of a hormone called vasopressin, or antidiuretic hormone. As the name suggests, this hormone regulates the amount of water reabsorbed in the collecting tubes of nephrons. In this case, the synthesis of vasopressin is carried out in the aforementioned nuclei of the hypothalamus, and then along the axonal terminals it is transported to the posterior part of the pituitary, where it remains until the necessary moment. If necessary, the posterior lobe of the pituitary gland secrete this hormone into the blood, which increases the reabsorption of water in the renal tubules and leads to an increase in the concentration of excreted urine and a decrease in the level of electrolytes in the blood.
The involvement of the hypothalamus in the regulation of uterine contractile activity
Neurons of paraventricular nuclei produce a hormone such as oxytocin. This hormone is responsible for the contractility of the muscular fibers of the uterus during childbirth, and in the postpartum period - for the contractility of the breast ducts of the mammary glands. By the end of pregnancy, closer to birth, on the surface of the myometrium, there is an increase in specific receptors for oxytocin, which increases the sensitivity of the latter to the hormone. At the time of delivery, the high concentration of oxytocin and the sensitivity of the muscular fibers of the uterus to it facilitate the normal course of labor. After childbirth, when the baby takes the nipple, this leads to stimulation of oxytocin production, which causes the reduction of breast ducts of the mammary glands and the release of milk.
In addition, in the absence of pregnancy and breastfeeding, as well as in males, this hormone is responsible for the formation of a feeling of love and sympathy, for which he received his second name - "the hormone of love" or "the hormone of happiness."
Participation of the hypothalamus in the formation of hunger and satiety
In the lateral hypothalamic region there are specific centers organized according to the reciprocal type, responsible for the formation of a feeling of thirst and satiety. It has been shown experimentally that the stimulation of the centers responsible for the formation of a feeling of hunger leads to a behavioral reaction to the search and consumption of food, even in a full-bodied animal, and irritation of the saturation center to a refusal to eat an animal that has been starving for several days.
When the lateral hypothalamic region and the centers responsible for the formation of hunger are affected, so-called starvation may result, which leads to death, and in pathology and bilateral lesions of the ventromedial region, there is an irrepressible appetite and a lack of satiety, which leads to the formation of obesity.
The hypothalamus in the area of the mastoid bodies also takes part in the formation of behavioral reactions associated with food. Irritation of this area leads to the appearance of such reactions as licking and swallowing.
Regulation of behavioral activity
Despite its small size, which is only a few cubic centimeters, the hypothalamus takes part in the regulation of behavioral activity and emotional behavior, entering the limbic system. Moreover, the hypothalamus has extensive functional connections with the brain stem and the reticular formation of the midbrain, with the anterior thalamic region and limbic parts of the cerebral cortex, the funnel of the hypothalamus and the pituitary gland for the implementation and coordination of the secretory and endocrine functions of the latter.
Diseases of the hypothalamus
Pathogenetically, all diseases of the hypothalamus are divided into three large groups, depending on the characteristics of hormone production. Thus, the diseases associated with increased hormonal production of the hypothalamus, with a decreased hormonal production, as well as with a normal level of hormone production, are singled out. In addition, the diseases of the hypothalamus and pituitary gland are very closely related, which is due to the generality of blood supply, anatomical structure and functional activity. Often, the pathology of the hypothalamus and the pituitary gland is combined into a common group of diseases of the hypothalamic-pituitary system.
The most common cause leading to the emergence of clinical symptoms is the emergence of adenoma - a benign tumor from the glandular tissue of the pituitary gland. In this case, as a rule, its occurrence is accompanied by an increase in hormonal production with the corresponding typical manifestation of clinical symptoms. The most common are tumors that produce an excessive amount of corticotropin (corticotropin), somatotropin (somatotropinoma), thyrotropin (thyrotropinoma), and others.
Among the typical lesions of the hypothalamus, prolactin, a hormone-active tumor that produces prolactin, should be noted. This pathological condition is accompanied by a clinical diagnosis of hyperprolactinemia and is most characteristic of the female sex. Increased production of this hormone leads to violations of the menstrual cycle, the appearance of disorders of the genital area, cardiovascular system, etc.
Another terrible disease associated with a violation of the functional activity of the hypothalamic-pituitary system is the hypothalamic syndrome. This condition is characterized not only by hormonal imbalance, but also by the appearance of disorders from the vegetative sphere, the disturbance of metabolic and trophic processes. Diagnosis of this condition is sometimes extremely difficult, since individual symptoms are masked for the symptomatology of other diseases.
Thus, the hypothalamus, whose function in life support is difficult to overestimate, is the highest integrative center responsible for controlling the autonomic functions of the organism, as well as behavioral and motivational mechanisms. Being in a complex relationship with the rest of the brain, the hypothalamus takes part in the control of almost all vital constants of the body, and its defeat often leads to the appearance of severe diseases and death.