HYPOTHALAMUS: FUNCTIONS, ANATOMY AND DISEASES - ANATOMY AND PHYSIOLOGY - 2025

The hypothalamus is a small brain structure that is located under the thalamus and is part of the floor of the third ventricle of the brain. It comes from the Greek “ὑπό”, which means “under” and “θάλαμος” which would be “thalamus” (a term that refers to “bed”).

This structure is cone-shaped and projects downward from the brain, ending in the pituitary gland. With this gland it maintains a complex interaction.

Hypothalamus marked yellow

The hypothalamus performs very important functions, integrating a wide variety of information. It is considered an essential part of the nervous system and the endocrine system, since it is responsible for releasing hormones and other substances that regulate different cells and organs.

The hormones of the hypothalamus maintain homeostasis in the body, that is, they ensure its correct functioning by correcting certain imbalances. In this way you can control physiological functions such as thirst, hunger, sleep, temperature, mood, sexual desire…

Additionally, the hypothalamus is also involved in metabolism, growth, and even certain involuntary behaviors. It is linked to another endocrine gland, called the pituitary or pituitary. Specifically, it sends signals to the gland to release certain hormones from the body.

Where is the hypothalamus located?

The hypothalamus is a subcortical structure that is located inside our brain. Its location is practically central, allowing it to establish relationships with a multitude of brain areas. It is present in all vertebrates, and in humans its size is similar to that of an almond.

It is part of the diencephalon, a set of structures in the brain. Above the hypothalamus are the hypothalamic sulcus, the thalamus, and the choroid plexus of the third ventricle. Below this are the supraoptic recess and ridge, the brain stem, and the pituitary gland (pituitary).

In the anterior part of the hypothalamus, the anterior commissure and the terminal lamina are located. While later, there are the mammillary bodies, the perforated substance, the cerebral peduncle, and the aqueduct of Silvio.

Parts

The hypothalamus can be divided into three structurally different parts; the anterior, middle and posterior regions. They are also commonly known as the supraoptic, tuberal, and nipple regions.

All of these areas work together to produce different hormones and chemicals important to modulate the activity of different organs in the body.

In addition, each area has specific functions that are explained in the following sections.

Anterior or supraoptic region

As its name suggests, it is located just above the optic chiasm. The most prominent nuclei in this area are the paraventricular and the supraoptic. Other nuclei that can be found are the preoptic, the anterior hypothalamus and the suprachiasmatic.

The latter work together to secrete hormones such as oxytocin, vasopressin, somatostatin, and corticotropin-releasing hormone.

Thanks to the supraoptic region, circadian rhythms, thermoregulation of the body, sweating and the development of the body's sexual characteristics are controlled. Later, the functions in which the hypothalamus is involved will be discussed in more detail.

Middle or tuberal region

The middle region of the hypothalamus is located in the tuber cinereum. It is divided into two parts, the medial and the lateral.

Medially, the dorsomedial and ventromedial nuclei influence the control of the feeding impulse. The dorsomedial nucleus is related to appetite. The ventromedial nucleus, the largest and one of the most important, is responsible for regulating the feeling of fullness or satiety.

The arcuate nucleus is also located in this region, which blocks milk production in women by inhibiting the release of a hormone called prolactin.

Other functions associated with the middle or tuberal region are blood pressure, heart rate, and gastrointestinal activity.

Posterior or mamillary region

This area is also divided into two parts: medial and lateral. The medial zone includes two classes of hypothalamic nuclei, called the mammillary nucleus and the posterior nucleus.

These nuclei are involved in functions such as blood pressure, tremors, energy balance, hunger, sleep, and activation. As well as memory and learning.

Features

The main function of the hypothalamus is to maintain homeostasis or balance of the whole body. This structure performs a multitude of essential functions for the normal functioning of the body.

For example, it is the reason why we know when we are thirsty or hungry, or why we always maintain a constant temperature.

The hypothalamus receives information from nearly the entire nervous system, and is involved in a multitude of autonomic nervous system functions. Each of the functions of this structure are explained below.

Endocrine functions

The hypothalamus acts as an intermediary between the nervous system and the endocrine system. Its fundamental endocrine function is the control of the pituitary gland so that it releases hormones when necessary. This gland is essential, as it modulates all the other endocrine glands in the body.

This system is known as the hypothalamic-pituitary axis. When the hypothalamus receives certain signals from the nervous system, it releases substances called neurohormones. These stimulate or inhibit the secretion of hormones from the pituitary gland, which in turn will control the release of hormones from other glands in the body.

The hypothalamus has neurons that release and capture norepinephrine, serotonin, and dopamine, allowing the regulation of hormone levels.

The most prominent hormones of the hypothalamus are:

- Corticotropin-releasing hormone. As the name suggests, it promotes the release of corticotropin. In this way, it sends signals to the pituitary gland to stimulate the adrenal glands. The latter release corticosteroids (cortisol), a substance important for metabolism and the immune system.

When cortisol levels are low, fatigue, weakness, hypoglycemia, lack of sexual desire, and decreased body hair occur.

- Antidiuretic hormone, also called arginine vasopressin. It controls the amount of fluids, glucose and salts in the blood. In addition to producing a higher concentration in the urine, as well as a decrease in its quantity.

- Gonadotropin-releasing hormone. It is essential for sexual reproduction. This hormone stimulates the pituitary (pituitary) to release two essential hormones for the proper functioning of the ovaries or testicles. These are follicle stimulating hormone (FSH) and luteinizing hormone (LH).

- Growth hormone releasing hormone (somatocrinin). It secretes growth hormone, which is used to maintain an adequate size and body composition in children. In adults, it is useful for maintaining healthy bones and good muscle mass. It also seems to influence the distribution of fat.

The hypothalamus also releases a hormone that has the opposite effect, the growth hormone inhibiting hormone (somatostatin).

- Oxytocin: it is a hormone that has a wide variety of functions. It is mainly related to sexual reproduction, orgasm, childbirth, and the production of milk from the mammary glands.

- Prolactin-releasing hormone. Essentially this hormone is useful for the production of breast milk.

- Hormone stimulants of thyroid hormones. They regulate energy levels, development, and metabolism.

The hypothalamus receives signals from the body that tell it to “give orders” to increase or inhibit the production of certain hormones when necessary.

Basic vital functions

On the other hand, it also helps to stimulate or inhibit fundamental processes such as: heart rate, blood pressure, or body temperature. It also regulates fluid and electrolyte levels, thirst, appetite, and weight.

Functioning of the gastrointestinal system

The hypothalamus also regulates the glandular secretions of the stomach and intestines.

Biological rhythms

Control of the circadian rhythm, also known as the biological rhythms. It is a system that regulates our periods of sleep, activity or hunger. For example, thanks to biological rhythms we tend to get sleepy at the same time every day.

Reproductive, attachment and nurturing behaviors

Some areas of the hypothalamus seem to influence sexual appetite, recognition, protection and feeding of the young.

Learning and memory

The hypothalamus is involved in brain circuits that allow the retrieval of information stored in our memory, mainly its mammillary area. It also appears to be involved in learning simple associations.

Emotions

This structure has also been related to emotional expression. In the hypothalamus, several chemicals that produce emotions in humans are grouped, such as sadness, amazement, anger, affection or sexual satisfaction.

Diseases

A physical head injury that affects the hypothalamus is one of the most common causes of hypothalamic disease. Although malnutrition, inflammation (meningitis or encephalitis), neoplasms, strokes, or infections also impair its functioning.

Hypothalamic tumors appear to be very rare. In the case in which they appear, they can cause hyperactivation or hypoactivation of the pituitary.

On the other hand, the hypothalamus may be damaged by radiation therapy or surgical interventions performed prior to symptoms.

Sleep and appetite disorders are the most frequent manifestations, since the hypothalamus regulates these functions.

Sometimes it can be difficult to know if certain symptoms are due to a lesion in the hypothalamus, since it can be confused with lesions in the pituitary gland (for example). Since both are connected and work together to modulate different functions.

When the hypothalamic-pituitary circuit is damaged, these cases are known as hypothalamic-pituitary disorders.

An example of this is hypopituitarism or panhypopituitarism. In this condition, the hypothalamus does not function properly, inhibiting hormonal secretions from the pituitary gland. Thus, they affect the basic vital functions of the body and growth.

Other examples would be gigantism, dwarfism, absence of menstruation or irregular cycles in women, sexual dysfunctions, etc.

Damage to the hypothalamus has been shown to cause some of the following symptoms:

- Lesions in the hypothalamus influence the sleep-wake cycle. This is due to the existing connections between the ocular retina and the suprachiasmatic nucleus, which regulate circadian rhythms. By influencing alertness, it may be that damage to the hypothalamus causes continued drowsiness and tiredness.

- Sight loss.

- Precocious puberty, or delay in development.

- Macrocephaly, that is, exaggerated increase in the size of the head.

- Because the hypothalamus secretes vasopressin (antidiuretic hormone), when there is damage to it, it is expected that the production of vasopressin is blocked. This leads to the inability of the kidneys to conserve fluid, a condition called diabetes insipidus.

- Memory and emotional expression problems, especially if the mammillary bodies of the hypothalamus are damaged. This is because the hypothalamus is part of the Papez circuit, connecting with regions of the limbic system. This system is essential for the memory and experimentation of emotions.

- Hyperthermia, produced by a lesion in the anterior nucleus of the hypothalamus. Since it is involved in thermoregulation by stimulating the parasympathetic nervous system.

- Malnutrition or conditions of extreme starvation such as anorexia nervosa, can lead to the destruction of the lateral part of the tuberal region of the hypothalamus. This area is responsible for regulating appetite and eating.

As the hypothalamus regulates appetite and metabolism, it is possible that if there is a failure in this there is an increase or decrease in weight.

- Related to the above, the hypothalamic obesity disorder may also occur. What happens with these patients is that after taking the pertinent analyzes to verify what their obesity is due to, they only find differences in thyroid hormones.

However, when they take the necessary hormone replacement medication they feel worse and do not lose weight as expected.

But with a deeper analysis, they can realize that the origin of the problem is in the hypothalamus. Treatment in this case would be behavioral therapy combined with drug therapy for the hypothalamic pathways involved in satiety and metabolism.

References

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