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)
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)
Diencephalon (diencephalon)

It is situated beneath the hypothalamic sulcus,

Hypothalamic sulcus (sulcus hypothalamicus)
Hypothalamic sulcus (sulcus hypothalamicus)

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

Third ventricle (ventriculus tertius)
Third ventricle (ventriculus tertius)
Third ventricle (ventriculus tertius)
Third ventricle (ventriculus tertius)

The optic chiasm is located anteriorly to the organ.

Optic chiasm (chiasma opticum)
Optic chiasm (chiasma opticum)
Optic chiasm (chiasma opticum)
Optic chiasm (chiasma opticum)

The hypothalamus consists of several parts:

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

connects the hypothalamus to the pituitary gland (hypophysis)

Pituitary gland (hypophysis)
Pituitary gland (hypophysis)
Pituitary gland (hypophysis)
Pituitary gland (hypophysis)

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 (nuclei preoptici)
Preoptic nuclei (nuclei preoptici)
  • Anterior (or supraoptic)
Supraoptic nuclei (nucleus supraopticus)
Supraoptic nuclei (nucleus supraopticus)
  • 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 (nuclei preoptici)
Preoptic nuclei (nuclei preoptici)

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 (nucleus supraopticus)
Supraoptic nucleus (nucleus supraopticus)

the paraventricular nucleus,

Paraventricular nucleus (nucleus paraventricularis)
Paraventricular nucleus (nucleus paraventricularis)

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 (tractus hypothalamohypophysialis)
Hypothalamo-hypophyseal tract (tractus hypothalamohypophysialis)

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 (nucleus ventromedialis)
Ventromedial nucleus (nucleus ventromedialis)

the dorsomedial nucleus,

Dorsomedial nucleus (nucleus dorsomedialis)
Dorsomedial nucleus (nucleus dorsomedialis)

and the arcuate nucleus.

Arcuate nucleus (nucleus arcuatus)
Arcuate nucleus (nucleus arcuatus)

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 (nuclei corporis mamillaris)
Mammillary nuclei (nuclei corporis mamillaris)

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)
Hippocampus (hippocampus)
Fornix (fornix)
Fornix (fornix)
Mammillothalamic tract (fasciculus mamillothalamicus)
Mammillothalamic tract (fasciculus mamillothalamicus)

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 (nuclei preoptici)
Preoptic nucleI (nuclei preoptici)

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 (tractus hypothalamohypophysialis)
Hypothalamo-hypophyseal tract (tractus hypothalamohypophysialis)

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 (a. cerebri anterior)
Anterior cerebral artery (a. cerebri anterior)

anterior communicating,

Anterior communicating artery (a. communicans anterior)
Anterior communicating artery (a. communicans anterior)

posterior communicating, and posterior cerebral arteries.

Posterior communicating artery (a. communicans posterior)
Posterior communicating artery (a. communicans posterior)

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

Anterior choroidal arteriy (a. choroidea anterior)
Anterior choroidal arteriy (a. choroidea anterior)

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

Superior hypophyseal artery (a. hypophysialis superior)
Superior hypophyseal artery (a. hypophysialis superior)
Glossary

Hypothalamus

hypothalamus
hypothalamus
mamillary bodies
corpora mamillaria
tuber cinereum
tuber cinereum
median eminence
eminentia mediana
infundibulum
infundibulum
periventricular nucleus
nucleus periventricularis
medial preoptic nucleus
nucleus preopticus medialis
lateral preoptic nucleus
nucleus preopticus lateralis
supraoptic nucleus
nucleus supraopticus
paraventricular nucleus
nucleus paraventricularis
suprachiasmatic nucleus
nucleus suprachiasmaticus
anterior hypothalamic nucleus
nucleus anterior
ventromedial nucleus
nucleus ventromedialis
dorsomedial nucleus
nucleus dorsomedialis
arcuate nucleus
nucleus arcuatus
mamillary nuclei
nucleus mamillaris
posterior hypothalamic nucleus
nucleus posterior
lateral hypothalamic nucleus
nucleus lateralis
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