Hypothalamus

HypothalamusAnatomy and function of the hypothalamus. Hypothalamic nuclei. Releasing factors, statins, antidiuretic hormone, oxytocin
~ 9 min

In this note, we are going to discuss the anatomy and function of the hypothalamus.

Hypothalamus
Hypothalamus

It is one of the primary control centers of our body. Anatomically and functionally, it is connected to the pituitary gland, forming what is known as the hypothalamic-pituitary system.

Pituitary gland in the hypothalamic-pituitary system
Pituitary gland in the hypothalamic-pituitary system

The hypothalamus carries out its functions through interactions with other endocrine organs, the autonomic nervous system, and the limbic system.

The functioning of the hypothalamus is focused on maintaining homeostasis, including thermoregulation, regulation of blood pressure and circulation, appetite, fluid-electrolyte balance, metabolism, and reproductive functions.

Anatomy of the hypothalamus

The hypothalamus, along with the thalamus and epithalamus, is a part of the diencephalon.

Diencephalon
Diencephalon

It is situated beneath the hypothalamic sulcus,

Hypothalamic sulcus
(sulcus hypothalamicus)
Hypothalamic sulcus<br />
(sulcus hypothalamicus)

next to the third ventricle from below, forming its floor and the lower portion of the lateral wall.

Third ventricle
Third ventricle
Third ventricle
Third ventricle

The optic chiasm is located anteriorly to the organ.

Optic chiasm
Optic chiasm
Optic chiasm
Optic chiasm

The hypothalamus consists of several parts:

  • The hypothalamic nuclei
Hypothalamic nuclei
Hypothalamic nuclei
  • The mammillary bodies
Mammillary bodies
Mammillary bodies
Mammillary bodies
Mammillary bodies
  • The tuber cinereum, which has a median eminence
Tuber cinereum
Tuber cinereum
  • The infundibulum, extending from the median eminence,
infundibulum
infundibulum

connects the hypothalamus to the pituitary gland (hypophysis)

Pituitary gland
Pituitary gland
Pituitary gland
Pituitary gland

Let’s discuss the hypothalamic nuclei in greater detail.

Hypothalamic nuclei

In the frontal section, the hypothalamic nuclei can be divided into three zones or groups:

  • Periventricular
  • Intermediate or medial
  • Lateral

Within the intermediate zone, in the sagittal section, four groups of nuclei can be distinguished:

  • Preoptic
Preoptic nuclei
Preoptic nuclei
  • Anterior (or supraoptic)
Supraoptic nuclei
Supraoptic nuclei
  • Tuberal
Tuberal nuclei
Tuberal nuclei
  • Posterior (or mammillary)
Posterior | mammillary zone
Posterior | mammillary zone

Let’s start with the periventricular zone. It contains the periventricular nucleus, which produces some of the hormones that regulate the function of the adenohypophysis.

The preoptic group of nuclei includes the medial preoptic nucleus and the lateral preoptic nucleus. The latter can also be considered as part of the lateral group.

Preoptic nuclei
Preoptic nuclei

The medial preoptic nucleus regulates fluid-electrolyte balance and the synthesis of the pituitary’s gonadotropin-releasing hormone (GnRH).

The supraoptic group includes the supraoptic nucleus,

Supraoptic nucleus
 Supraoptic nucleus

the paraventricular nucleus,

Paraventricular nucleus
Paraventricular nucleus

the suprachiasmatic and the anterior hypothalamic nucleus.

The supraoptic nucleus produces antidiuretic hormone (ADH or vasopressin), while the paraventricular nucleus synthesizes oxytocin. These hormones are transported to the neurohypophysis via the hypothalamo-hypophyseal tract, and only then are they released into the bloodstream.

Hypothalamo-hypophyseal tract
Hypothalamo-hypophyseal tract

The effects of these hormones can be seen in the diagram.

The suprachiasmatic nucleus is involved in the regulation of circadian rhythms because it has connections with the retina and the pineal gland.

The anterior hypothalamic nucleus primarily plays a role in maintaining body temperature, acting as the so-called “cooling center”. By interacting with the parasympathetic system, this nucleus helps to lower body temperature.

The tuberal group contains three nuclei: the ventromedial nucleus,

Ventromedial nucleus
Ventromedial nucleus

the dorsomedial nucleus,

Dorsomedial nucleus
Dorsomedial nucleus

and the arcuate nucleus.

Arcuate nucleus
Arcuate nucleus

The ventromedial nucleus functions as the so-called satiety center.

The dorsomedial nucleus also participates in feeding behavior and plays a role in behavioral patterns related to the expression of aggression.

The arcuate nucleus produces some of the hormones that regulate the function of the adenohypophysis and is involved in the regulation of appetite, reproductive functions, and circulation.

The mammillary group, also known as the mammillary complex, contains the mammillary nuclei (lateral and medial) as well as the posterior hypothalamic nucleus.

Mammillary nuclei
Mammillary nuclei

The mammillary nuclei are involved in emotions, short-term memory, and states of wakefulness.

They receive impulses from the hippocampus via the fornix and redirect them to the thalamus via the mammillothalamic tract.

Hippocampus
Hippocampus
Fornix
Fornix
Mammillothalamic tract
Mammillothalamic tract

The posterior nucleus, in addition to regulating emotions, also controls circulation and body temperature. Stimulation of this nucleus activates the sympathetic nervous system, thereby increasing body temperature.

The lateral zone of the hypothalamus contains the previously mentioned lateral preoptic nucleus and the lateral hypothalamic nucleus.

Preoptic nucleI
Preoptic nucleI

The former participates in sleep regulation, while the latter is one of the centers for appetite regulation. When stimulated, it induces a feeling of hunger in an individual.

Hypothalamic-pituitary connections

Within the infundibulum of the hypothalamus, there are two systems that provide the functional interaction between the pituitary gland and the hypothalamus.

One of these is the hypophyseal portal system, which consists of blood vessels connected to the adenohypophysis (or anterior pituitary).

Pituitary vessels, including portal system
Pituitary vessels, including portal system

And the hypothalamo-hypophyseal tract (tractus hypothalamohypophysialis), which consists of nerve fibers connected to the neurohypophysis (or posterior pituitary).

Hypothalamo-hypophyseal tract
Hypothalamo-hypophyseal tract

We discussed these fibers when talking about the supraoptic and paraventricular nuclei.

Some hypothalamic nuclei (such as the periventricular, medial preoptic, and arcuate) produce so-called releasing factors, which stimulate the anterior pituitary, as well as statins, which have the opposite effect. These substances are transported to the pituitary gland via the hypophyseal portal system.

The releasing factors include:

The last two hormones are collectively known as gonadotropin-releasing hormone (GnRH).

There are only three hormones classified as statins:

Blood supply

Blood supply to the hypothalamus is provided by perforating branches from the anterior cerebral,

Anterior cerebral artery
Anterior cerebral artery

перanterior communicating,

Anterior communicating artery
Anterior communicating artery

posterior communicating, and posterior cerebral arteries.

Posterior communicating artery
Posterior communicating artery

Additionally, it gets small branches from the middle cerebral and anterior choroidal arteries.

Anterior choroidal arteriy
Anterior choroidal arteriy

Moreover, several small hypothalamic branches arise from the superior hypophyseal artery.

Superior hypophyseal artery
Superior hypophyseal artery
Golosary

Hypothalamus

diencephalon
diencephalon
thalamus
thalamus
interthalamic adhesion
adhesio interthalamica
internal medullary lamina
lamina medullaris interna
pulvinar of thalamus
pulvinar thalami
lateral geniculate body
corpus geniculatum laterale
medial geniculate body
corpus geniculatum mediale
reticular nucleus
nucleus reticularis
external medullary lamina
lamina medullaris externa
subthalamus
subthalamus
subthalamic nucleus
nucleus subthalamicus
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