Structure and functions of the diencephalon (thalamus, epithalamus, metathalamus and hypothalamus)

The hypothalamus is a small area located in the human diencephalon, consisting of many groups of cells that regulate the homeostasis of the body and the neuroendocrine function of the brain and includes more than 30 nuclei. The hypothalamus is part of the hypothalamic-pituitary axis, which also includes the pituitary gland. The hypothalamus is located slightly below the thalamus and slightly above the brain stem.

The hypothalamus communicates through nerve pathways with almost all parts of the central nervous system. This connection includes the hippocampus, cerebral cortex, cerebellum, amygdala, spinal cord and brain stem. The hypothalamus forms the ventral part of the diencephalon.

The hypothalamus connects the nervous system with the endocrine system through the pituitary gland.

The hypothalamus is responsible for many activities of the autonomic nervous system, in particular metabolic processes. Also in the hypothalamus, certain neurohormones are synthesized and released, which act on the pituitary gland, stimulating or inhibiting its secretion. Under the influence of the hypothalamus, body temperature is controlled, as well as feelings of hunger, thirst, fatigue, and sleep regulation.

Structure and nuclei of the hypothalamus

What kind of organ is this

The diencephalon section influences the stability of the internal environment, ensures the interaction and optimal combination of individual systems with the holistic functioning of the body. An important structure produces a complex of hormones of three subclasses.

Neurosecretory and nerve conduction cells are the basis of an important element of the diencephalon. Organic pathologies in combination with damage to functions disrupt the periodicity of many processes in the body.

The hypothalamus has extensive connections with other brain structures and continuously interacts with the cerebral cortex and subcortex, which ensures an optimal psycho-emotional state. Decortication provokes the development of imaginary rage syndrome.

Infection, tumor process, congenital anomalies, injuries to an important part of the brain negatively affect neurohumoral regulation, interfere with the transmission of impulses from the heart, lungs, digestive organs, and other elements of the body. Destruction of various lobes of the hypothalamus disrupts sleep, metabolic processes, provokes the development of epilepsy, diabetes insipidus, obesity, decreased temperature, and emotional disorders.

Not everyone knows where the hypothalamus is located. The diencephalon element is located under the hypothalamic sulcus, below the thalamus. The cellular groups of the structure smoothly transform into a transparent septum. The structure of the small organ is complex; it is formed from 32 pairs of hypothalamic nuclei, consisting of nerve cells.

The hypothalamus consists of three regions, with no clear boundary between them. The branches of the arterial circle ensure a complete supply of blood to an important part of the brain. A specific feature of the vessels of this element is the ability of protein molecules, even large ones, to penetrate through the walls.

Anatomical location of the hypothalamus

The hypothalamus is located in the diencephalon above the pituitary gland and below the third ventricle.

Afferent pathways approach the hypothalamic nuclei, most of which are located in the anterior hypothalamus, and come from the brainstem, thalamus, basal ganglia, cerebral cortex and olfactory areas.

One of the main efferent pathways of the hypothalamus is the hypothalamic-neurohypophyseal, which connects the paraventricular and supraoptic nuclei of the hypothalamus with nerve endings in the median eminence. The paraventricular nucleus produces oxytocin, and the supraoptic nucleus releases mainly antidiuretic hormone (ADH) and some oxytocin directly into the bloodstream. The pituitary gland consists of the adenohypophysis, also known as the anterior pituitary gland, and the neurohypophysis, also known as the posterior pituitary gland.

What is he responsible for?

Functions of the hypothalamus in the body:

• controls the functioning of the respiratory , digestion, heart, blood vessels, thermoregulation,
• maintains the optimal state of the endocrine and excretory systems,
• affects the functioning of the gonads, ovaries, pituitary gland, adrenal glands, pancreas and thyroid gland,
• responsible for human emotional behavior
• participates in the process of regulating wakefulness and sleep, produces the hormone melatonin, the deficiency of which develops insomnia and deteriorates the quality of sleep,
• Provides optimal body temperature. With pathological changes in the posterior part of the hypothalamus, the destruction of this zone, the temperature decreases, weakness develops, and metabolic processes proceed more slowly. Often there is a sudden rise in subfertile temperature,
• affects the transmission of nerve impulses,
• produces a complex of hormones, without a sufficient amount of which the proper functioning of the body is impossible.

The table below lists many of these functions and the core groups that are most closely associated with their performance.

General information

The diencephalon is the lower, most massive part of the brain stem that carries a huge functional load.
On the sides it is limited by the hemispheres (and covered with them on the sides and top, like a cap), in front - by the optic chiasm, on the upper side of the trunk - by the corpus callosum. The most important load is borne by nuclear formations: the thalamus (visual thalamus), hypothalamus (perituberal space), epithalamus and metathalamus.

The hypothalamus and pituitary gland form the hypothalamic-pituitary system.

Causes of problems

Damage to the structural elements of the hypothalamus is a consequence of the influence of several factors:

• traumatic brain injuries,
• bacterial, viral infections: lymphogranulomatosis, syphilis, basal meningitis, leukemia, sarcoidosis,
• tumor process,
• dysfunction of the endocrine glands,
• intoxication of the body,
• inflammatory processes of various kinds,
• vascular pathologies affecting the volume and rate of supply of nutrients and oxygen to the cells of the hypothalamus,
• disruption of physiological processes,
• violation of the permeability of the vascular wall due to the penetration of infectious agents.

Diseases

Negative processes occur against the background of direct dysfunction of an important structure. The tumor process in most cases is benign, but under the influence of negative factors cell malignancy often occurs.

Note! Treatment of hypothalamic lesions requires an integrated approach; therapy is associated with many risks and difficulties.

If oncological pathologies are detected, the neurosurgeon removes the tumor, then the patient undergoes chemotherapy and radiation therapy sessions. To stabilize the functioning of the problem department, a complex of medications is prescribed.

The main types of hypothalamic tumors are:

• teratomas,
• meningiomas,
• craniopharyngiomas,
• gliomas,
• adenomas (grow from the pituitary gland),
• pinealomas.

Symptoms

Impaired functioning of the hypothalamus provokes a complex of negative symptoms:

• eating disorders, uncontrolled appetite, sudden weight loss or severe obesity,
• tachycardia, fluctuations in blood pressure, pain in the sternum, arrhythmia,
• decreased libido, absence of menstruation,
• early puberty due to a dangerous hamartoma tumor,
• headaches, severe aggression, uncontrollable crying or fits of laughter, seizures,
• pronounced causeless aggression, fits of rage,
• hypothalamic epilepsy with a high frequency of seizures throughout the day,
• belching, diarrhea, pain in the epigastric region and abdomen,
• muscle weakness, the patient has difficulty standing and walking,
• neuropsychiatric disorders: hallucinations, psychoses, anxiety, depression, hypochondria, mood swings,
• severe headaches due to increased intracranial pressure,
• sleep disturbance, waking up several times during the night, fatigue, weakness, headaches in the morning. The reason is a lack of the important hormone melatonin. To eliminate the disturbances, you need to adjust your waking and night sleep patterns, and take a course of medications to restore the volume of an important regulator. A good therapeutic effect is provided by the drug Melaxen, a new generation drug with a minimum of side effects, without addiction syndrome,
• blurred vision, poor memory of new information,
• a sharp rise in temperature or decrease in indicators. When temperatures rise, it is often difficult to understand what is causing the negative changes. Damage to the hypothalamus can be suspected by a set of signs indicating damage to the endocrine system: uncontrolled hunger, thirst, obesity, increased urine output.

Conditions that develop when the hypothalamus is damaged

 The hypothalamus is part of the diencephalon, which plays a leading role in the regulation of many functions of the body, and above all the constancy of the internal environment (homeostasis); is the highest vegetative center, carrying out the complex integration of the functions of various internal systems and their adaptation to the integral activity of the body.

The hypothalamus includes about 50 pairs of nuclei with a very powerful blood supply. The capillaries in this part of the brain are highly permeable to large-molecular protein compounds (nucleoproteins), which indicates the high sensitivity of this region to neuroviral infections, toxins, and humoral changes [1].

The hypothalamus contains many centers responsible for certain functions:

1. Thermoregulation;
2. Center of hunger and satiety;
3. Maintaining water and electrolyte balance;
4. Regulation of puberty;
5. Regulation of sexual behavior (pleasure center);
6. Sleep-wake cycle;
7. Center of fear and rage.

All this is carried out due to the influence of the hypothalamus on the endocrine, somatic and autonomic nervous systems.

Information from many structures flows into the hypothalamus, including from the higher centers of the motivational system - the cerebral cortex and the reticular formation. The activity of the hypothalamus is also affected by the concentration of glucose and insulin in the blood.

The hypothalamus and pituitary gland synthesize enkephalins and endorphins, which help reduce stress levels and have an analgesic effect.

The causes of hypothalamic dysfunction may be the following:

1. Tumors and injuries affecting the hypothalamic region;
2. Neuroinfections and intoxications;
3. Vascular disorders (including osteochondrosis of the cervical spine);
4. Hormonal changes due to pregnancy;
5. Psychogenic disorders;
6. Constitutional factor [3].

Pathological conditions resulting from damage to the hypothalamus are commonly called hypothalamic syndromes:

Hypothalamic obesity. Hyperphagia (increased food consumption) and obesity occur due to many diseases of the hypothalamus, such as tumors, injuries, radiation therapy, there may also be genetic disorders (Prader-Willi syndrome), as well as side effects of drugs affecting the nervous system (psychotropics) and mutations in various genes involved in hypothalamic satiety signaling pathways. In addition, primary obesity may be accompanied by changes in various genes involved in the regulation of energy metabolism and body weight by the hypothalamus. The main clinical signs of hypothalamic obesity are hyperphagia with pronounced eating disorders and hypothalamic dysfunction of various types (most often - hypogonadotropic hypogonadism, and with structural damage to the hypothalamus - drowsiness, growth hormone deficiency, secondary hypocortisolism, central hypothyroidism and diabetes insipidus) [2].

Cachexia or diencephalic wasting is more rare in hypothalamic lesions than obesity. It is found, in particular, with tumors formed in the area above the sella turcica; in the later stages of Parkinson's syndrome, as well as as a consequence of lethargic encephalitis. Hypothalamic wasting syndrome has also been described in children under two years of age. This syndrome is most often caused by tumors of the diencephalon or optic nerve.

Disorders of sexual development and behavior. Damage to the hypothalamus can lead to developmental delay or involution of the gonads. Sexual infantilism in children and impotence and amenorrhea in adults are usually accompanied by obesity. Loss of sexual desire without structural changes in the gonads can occur with tumors of the base of the brain and as a result of destructive changes in the brain of various etiologies.

Sleep-wake disorder syndrome most often has a paroxysmal character. For example, narcolepsy - attacks of uncontrollable drowsiness of the patient even when walking, eating, etc. Sleep is short-lived. As a rule, it is superficial, and patients wake up at the slightest external influence. They can fall asleep during monotonous work (especially while sitting), while eating, in warmth and silence, etc. Narcolepsy is often combined with cataplexy - a paroxysmal loss of muscle tone, leading the patient to immobility for several seconds (sometimes for 10–15 minutes). Cataplexy attacks appear in a patient in a state of passion (laughter, anger, etc.).

Diabetes insipidus. In this case, we are dealing with central (hypothalamic) diabetes insipidus, which is based on a deficiency of the antidiuretic hormone arginine vasopressin, which is produced in the supraoptic and paraventricular nuclei of the hypothalamus. The main symptoms of diabetes insipidus are severe polyuria (urine output more than 2 l/m2 per day or 40 ml/kg per day in older children and adults), polydipsia (water consumption of about 3–18 l/day) and associated sleep disturbances.

Literature:

1. Autonomic disorders arising from damage to the hypothalamus // Medportal. URL: https://med-books.info/patologicheskaya-fiziologiya_7.. (access date: 08/30/2019).
2. Hypothalamic syndrome: causes of the disease, main symptoms, treatment and prevention // MebOboz. URL: https://www.obozrevatel.com/health/bolezni/gipotalami..(access date: 08/30/2019).
3. Hochberg I., Hochberg Z. Expanding the definition of hypothalamic obesity // Obesity and metabolism. - 2011. - No. 1. - P. 72–73.

Diagnostics

Symptoms of damage to the hypothalamus are so varied that several diagnostic procedures need to be performed. Highly informative methods: ultrasound, ECG, MRI. Be sure to examine the adrenal glands, thyroid gland, abdominal organs, ovaries, brain, and vasculature.

It is important to take blood and urine tests, check the levels of glucose, ESR, urea, leukocytes, and hormone levels. The patient visits an endocrinologist, urologist, gynecologist, ophthalmologist, endocrinologist, neurologist. If a tumor is detected, you will need to consult a specialist from the neurosurgery department.