Hypothalamus Function

What is Hypothalamus? – Hypothalamus function

Hypothalamus is a gland in the brain regulating the hormone system. It produces hormones in a different part of the brain referred to as the pituitary gland that passes hormones to different structures.

The hypothalamus forms a part of the limbic system – a part of the brain which includes the amygdala, thalamus, cingulate gyrus and hippocampus. The limbic system in all the higher vertebrates is well-developed and is involved in activities like olfaction, emotional responses, long-term memory, acquiring new skills and is involved in different behavioral responses.

The hypothalamus is the site of thermoregulation regulating the temperature of the body and participates in regulating blood pressure, water balance and sensing hunger and thirst. There is a direct connection between the hypothalamus and the pituitary gland through a thin stalk referred to as the infundibulum. Several actions that are raised by the hypothalamus are communicated via secretions that are produced by the pituitary gland, found underneath.

Location of Hypothalamus – Hypothalamus Function

The hypothalamus is found at the base of the brain, forming the floor under the thalamus and the lower part of the lateral walls of the third ventricle. The hypothalamus is located at the forebrain part of the brain. It is deemed to be a part of the diencephalon, to be precise. Anteriorly, it stretches up to the optic chiasma, posteriorly it is in continuation with the tegmentum of the midbrain.

It is a vital structure though small and is about the size of an almond, weighing about 4g. It makes for about 1% of the total weight of the brain and is involved in a range of activities vital for sustenance of life.

Structure of Hypothalamus – Hypothalamus Function

The function of the hypothalamus is in modulating homeostasis required to survive and reproduce. The boundaries of the hypothalamus are established by the markers seen on the medial and ventral surfaces of the brain.

The optic chiasm forms the rostral periphery seen on the ventral surface of the brain, whereas the posterior periphery is defined by the mammillary bodies. On the ventricular surface of the brain, the other structures which contribute to the rostral boundary are evident, which are anterior commissure and lamina. Further, on the brain’s medial surface the hypothalamic sulcus is found that is the rostral continuation of the sulcus limitans which specifies the superior periphery of the hypothalamus. The lateral boundary is formed by the horizontal part of the brain, which has the internal capsule, only evident in this section.

The hypothalamus comprises three longitudinally arranged zones running the full rostrocaudal length of the hypothalamus.

The hypothalamus comprises a group of neurons organized into a nucleus that passes and receives fibres to other parts of the brain. Nuclei can be understood by dividing into two groups – medial zone and lateral zone.

Medial zone

The hypothalamus’ medial zone comprises these nuclei –

• Anterior nucleus
• Portions of the suprachiasmatic nucleus and lateral nucleus
• Dorsomedial nucleus
• Paraventricular nucleus
• Infundibular nucleus
• Ventromedial nucleus
• Posterior nucleus

Lateral zone

The hypothalamus’ lateral zone comprises these nuclei

• Parts of the suprachiasmatic nucleus and preoptic nucleus
• Tuberomammillary nucleus
• Lateral nucleus
• Lateral tubular nuclei

The suprachiasmatic, preoptic and mammillary nuclei can be seen in both the zones of the hypothalamus.

Hypothalamus Function in Endocrine system

This part of the brain is involved in maintaining the internal balance of the body (homeostasis). It forms an association between the nervous and endocrine systems. It secretes, releases and produces hormones that start and stop the production of some hormones all through the body.

The hypothalamus plays a vital role in the endocrine system. It is involved in maintaining the internal balance of the body, referred to as homeostasis. In order to perform this task, it triggers or inhibits different key processes such as –

• Body temperature, thermoregulation
• Bodyweight, appetite and insulin regulation
• Blood pressure and heart rate
• Sleep-wake cycle
• Electrolyte and fluid balance
• Emotion and short-term memory
• Secreting substances that influence the pituitary gland to secrete hormones
• Glandular secretions of the intestines and the stomach

Additionally, the hypothalamus is involved in performing the autonomic nervous system, as it obtains information from most parts of the nervous system. Hence, it serves as the association between the endocrine and the nervous system.

Secretion of Hormones – Hypothalamus hormones

The hypothalamus is greatly involved in the function of the pituitary gland. The hypothalamus is associated with the anterior lobe of the pituitary gland by the portal blood system. Through the neurons, the hypothalamus is connected to the posterior lobe of the pituitary gland directly. Consequently, it regulates the function of the pituitary gland. Upon receiving a signal from the nervous system, the hypothalamus produces neurohormones which initiate and terminate the secretion of the pituitary hormones.

The hypothalamus secretes the following primary hormones –

Autonomic functions of the Hypothalamus

The key function of the hypothalamus is in integrating the autonomic and the endocrine nervous system. It serves as a higher centre to control the autonomic functions of the spinal cord and the brain stem.

The sympathetic response is induced by stimulation of the posterior and the lateral nuclei of the hypothalamus. While the stimulation of the anterior nucleus and the preoptic area influences the parasympathetic responses in the body.

Endocrine control

The hypothalamus secretes inhibitory or releasing factors to control the hormones released by the pituitary gland. The factors are –

• Prolactin releasing and inhibiting hormone
• Growth hormone-releasing and inhibiting hormone
• Thyrotropin-releasing hormone
• Corticotropin-releasing hormone
• Luteinizing hormone-releasing hormone

These above-mentioned factors inhibit or promote the release of hormones from the anterior pituitary. This release of the factors is regulated by the negative and positive feedback mechanisms, based on the levels of the specific hormones in the blood.

This was a brief on the functions of the Hypothalamus, its role in the endocrine system and the different hormones of the hypothalamus.

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Also see:

• Short notes on Hind brain
• Function of Pons
• Sensory receptors
• Process of neural communication