HYPOTHALAMUS

HYPOTHALAMUS:

Introduction:

·         Hypothalamus is the basal part of the diencephalon, forebrain and it regulates a wide spectrum of body functions.

·         Hypothalamus word comes from two Greek words that translate to hypo- under; thalamus- part of brain.

·         Hypothalamus contains several groups of neurosecretory cells called nuclei which produce hormones These hormones regulate the synthesis and secretion of pituitary hormones.

·         It is located underneath the thalamus and above the pituitary gland.

·         The hormones from the hypothalamus govern physiologic function such as temperature regulation, thirst, hunger, sleep, mood, sex derive, production of digestive juices, balancing of body fluids and the release of other hormone within the body.

·         As signals are sent to the brain from different areas of the body, they let the hypothalamus know if balance is not being achieved. The hypothalamus thus responds by releasing the right hormones into the blood stream to balance the body back out.

·         Hypothalamus is a small area in the centre of the brain that has many jobs. It plays an important role in hormone production and helps to stimulate many important processes in the body.

·         Hypothalamus acts as connector between the endocrine and nervous system.

·         The hypothalamus uses a set a point to regulate the body’s systems includes electrolytes and fluid balance, body temperature, blood pressure and body weight. It receives inputs from the body then makes the proper changes if anything differentiates from this set point. The set point can temporily change, but remains remarkably fixed from day to day.

Origin:

Hypothalamus is derived from the ectoderm of the embryo it lies below or inferior to the thalamus this connection is through the hypophysis of pituitary gland. The hypothalamus is connected to the anterior lobe of the pituitary gland by hypophysial portal vein; however it is connected to the posterior lobe of the pituitary gland mainly by axons of neuro-secretory cells. The hormones of the hypothalamus influence the functioning of the pituitary gland. The hypothalamus is often called the control centre or supreme commander of endocrine regulation.

Location:

Hypothalamus is located on the under surface of the brain. It lies just below the thalamus and above the pituitary gland and is connected with it via infundibulum to the posterior pituitary. It forms the ventral part of diencephalon and is almost about the size of almond. The hypothalamus sulcus is a groove in the lateral wall of third ventricle which separates superior portion of hypothalamus from thalamus.

Structure:

Hypothalamus is few cubic cm long and weighs about 4 gms. It is an extremely complex part of the brain containing many regions with highly specialized function. In humans, the hypothalamus is approximately the size of a pea and accounts less than 1% of the weight of the brain.

                   

Hormone of Hypothalamus:

Hypothalamus is responsible for creating or controlling many hormones of the body. The hypothalamus is closely related to the pituitary gland which makes and sends other important hormones of the body. This includes adrenal glands, kidneys and thyroid hormones secreted by the hypothalamus. The neurosecretory cells of hypothalamus secrete hormones called neuro- hormones (releasing factors). However the hormones produced by hypothalamus are of two types:

         i.            Releasing Hormones: These hormones stimulate the secretion of pituitary hormones.

Eg: A hypothalamic hormone called Gonadotrophin releasing hormone (GnRH) stimulates the pituitary synthesis and release of gonadotrophins.

       ii.            Inhibiting Hormones: They inhibit the secretion of pituitary hormones.

Eg: Somatostatin from the hypothalamus inhibits the release of growth hormone from the pituitary.

These hormones originating in the hypothalamic neurons pass from axons and are released from their nerve endings. These hormones reach the pituitary gland through a portal circulatory system and regulate the functions of the anterior pituitary. The posterior pituitary is under the direct neural regulation of the hypothalamus. 

                       

Cells in the hypothalamus are synthesizing at least nine different hormones. Such hormones are as follows:

        I.            Anti Diuretic Hormone (ADH):

These hormones increase water absorption into the blood by the kidneys. For example, Vasopressin.

      II.            Corticotrophic Releasing Hormone (CRH):

 This hormone sends a message to the anterior pituitary gland to stimulate the adrenal glands to release corticosteroids, which help in the regulation of metabolism and immune response.

    III.            Gonadotropin releasing hormone (GnRH):

It stimulates the anterior pituitary to release FSH and LH which work together to ensure normal functioning of the ovaries and testis.

    IV.            Growth hormone releasing hormone (GHRH) and Growth hormone inhibiting hormone (GHIH):

They are also known as somatostatin. GHRH prompts the anterior pituitary to release the Growth hormone; GHIH has opposite effect. In children, GH is essential for maintaining a healthy body composition. In adults, it aids in healthy bones and muscle mass and affects fat distribution. Growth hormone also directly affected by hypothalamus. It tells the pituitary gland to increase or decrease their number in the body. This is essential for both growing children and fully developed adults.

      V.            Oxytocin:

This hormone is involved in a variety of processes such as the ability to trust, body temperature, sleep cycles and the release of breast milk.

    VI.            Prolactin Releasing Hormone (PRH) or Prolactin Inhibiting Hormone (PIH):

 They are also known as Dopamine. PRH prompts the anterior pituitary to stimulate breast milk production through the production of prolactin. PIH inhibits prolactin and milk production.

  VII.            Thyrotropin Releasing Hormone (TRH):

TRH triggers the release of TSH (Thyroid Stimulating Hormone) which stimulates the release of thyroid hormone which regulates metabolism, energy, growth and development.

Function of Hypothalamus:

         i.            Hypothalamus helps in maintaining the body’s internal balance or homeostasis. This hormone keeps the human body in stable, constant condition including body temperature, hunger, feelings of being full up after eating, blood pressure and levels of hormones in the circulation. It also responds to stress and controls our daily bodily rhythms such as the night time secretion of melatonin from the pineal gland and the changes in cortisol (stress hormone) and body temperature over a 24 hour period. The hypothalamus collects and combines this information and puts changes in place to correct any imbalance.

                     

       ii.            Hypothalamus produces releasing and inhibiting hormone which start and stop the production of other hormones throughout the body.

      iii.            The hypothalamus is involved in many functions of the Autonomic Nervous System (ANS) as it receives information from nearly all parts of the nervous system. As a result, it is considered as the link between nervous system and the endocrine system.

     iv.            Body water relation: Hypothalamus perform two functions for keeping blood volume and blood pressure nearly constant this is achieved via two mechanism i.e. thirst mechanism and by controlling the excretion of water via kidneys

       v.            GIT regulation:

The lateral hypothalamic area when stimulated causes extreme hunger and desire to search for food. While the satiety centre that is located in the ventro- medial nuclei of hypothalamus does the opposite effect to those of lateral hypothalamic area i.e. its opposite desire for food and hunger

     vi.            Hypothalamic hormone control:

Hypothalamus is called the master switch board because it controls the secretion of pituitary gland which is known as the master gland of the body. It controls both anterior and posterior pituitary part of pituitary gland.

    vii.            Cardio- vascular regulation:

Hypothalamus helps in changing arterial pressure and heart rate. Stimulating posterior and lateral hypothalamus has always an increasing effect on both arterial pressure and heart rate which on the other hand stimulating preoptic areas results in the decrease in both arterial pressure and heart rate.

  viii.            Temperature regulation:

Hypothalamus plays an important role in regulating the body temperature. This function is carried out by the anterior part of pituitary gland. The preoptic areas of hypothalamus is sensitive to increase or decrease in temperature. The blood flowing through this area stimulates the nuclei of this area to perform homeostasis.

 

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