hypothalamus

Examples of hypothalamus in the following topics:

• Control of the Pituitary Gland by the Hypothalamus

  • The pituitary gland consists of two components: the anterior pituitary and the posterior pituitary, and is functionally linked to the hypothalamus by the pituitary stalk (also named the infundibular stem, or simply the infundibulum).
  • Whilst the pituitary gland is known as the master endocrine gland, both of the lobes are under the control of the hypothalamus: the anterior pituitary receives its signals from the parvocellular neurons, and the posterior pituitary receives its signals from magnocellular neurons.
  • The anterior lobe of the pituitary receives hypothalamic-releasing hormones from the hypothalamus that bind with receptors on endocrine cells in the anterior pituitary that regulate the release of adrenal hormones into the circulatory system.
  • Hormones from the hypothalamus are rapidly degraded in the anterior pituitary, which prevents them from entering the circulatory system.
  • The posterior lobe of the pituitary gland develops as an extension of the hypothalamus.

• Hypothalamus

  • The hypothalamus serves as a gateway between the nervous system and endocrine system.
  • The hypothalamus is located below the thalamus just above the brain stem.
  • All vertebrate brains contain a hypothalamus.
  • The hypothalamus functions as a type of thermostat for the body.
  • Also, the hypothalamus of homosexual men and heterosexual women both respond to testosterone.

• Overview of the Pituitary Gland

  • The pituitary gland is connected to the hypothalamus and secretes nine hormones that regulate body homeostasis.
  • It protrudes off the bottom of the hypothalamus at the base of the brain, and rests in a small, bony cavity.
  • The pituitary is functionally connected to the hypothalamus by a small tube called the infundibular stem, or, pituitary stalk.
  • The anterior pituitary receives signaling molecules from the hypothalamus, and in response, synthesizes and secretes seven important hormones including thyroid-stimulating hormone and growth hormone.
  • The posterior pituitary does not produce any hormones of its own, rather, it stores and secretes two hormones made in the hypothalamus—oxytocin and anti-diuretic hormone.

• The Posterior Pituitary

  • The posterior pituitary consists mainly of neuronal projections (axons) extending from the supraoptic and paraventricular nuclei of the hypothalamus.
  • The posterior pituitary is derived from the hypothalamus and is distinct from the more fleshy, vascularized anterior lobe.
  • The posterior pituitary stores two hormones secreted by the hypothalamus for later release:
  • Oxytocin, most of which is released from the paraventricular nucleus in the hypothalamus.
  • Antidiuretic hormone (ADH, also known as vasopressin), the majority of which is released from the supraoptic nucleus in the hypothalamus.

• Regulation of Water Intake

  • Thirst is a sensation created by the hypothalamus, the "Thirst Center" of the human body.
  • An osmoreceptor is a sensory receptor, primarily found in the hypothalamus of most homeothermic organisms, that detects changes in osmotic pressure.
  • When the osmoreceptors detect high plasma osmolarity (often reperesenting a low blood volume), they send signals to the hypothalamus, which creates the biological sensation of thirst, and also stimulates vasopressin (ADH) secretion, which starts the events that will reduce plasma osmolarity to normal levels.
  • The macula densa cells in the walls of the ascending loop of henle of the nephron is another type of osmoreceptor, however it stimulates the juxtaglomerular apparatus (JGA) instead of the hypothalamus.
  • Angiotensin II acts on the hypothalamus to cause the sensation of thirst.

• Control of Thyroid Hormone Release

  • TSH release, in turn, stimulates the hypothalamus to secrete thyrotropin-releasing hormone (TRH).
  • Thyroid hormones also provide negative feedback to the hypothalamus and anterior pituitary gland.
  • Thyroid hormones are produced from the thyroid under the influence of thyroid-stimulating hormone (TSH) from the anterior pituitary gland, which is itself under the control of thyroptropin-releasing hormone (TRH) secreted by the hypothalamus.

• Control of Hormone Secretion

  • Briefly, neurons in the hypothalamus secrete thyroid-releasing hormone that stimulate cells in the anterior pituitary to secrete thyroid-stimulating hormone.
  • When the blood concentration of thyroxine rises above the ideal value as detected by sensory neurons, the hypothalamus is signaled to stop thyroid-releasing hormone production, which eventually lowers the levels of thyroxine in the blood.
  • When these drop below the ideal value the hypothalamus is signaled to begin secreting thyroid-releasing hormone again.
  • During birth, as the baby moves through the birth canal, pressure receptors within the cervix signal the hypothalamus to stimulate the pituitary to secrete oxytocin.

• Homeostatic Control

  • Blood vessels have sensors called baroreceptors that detect if blood pressure is too high or too low and send a signal to the hypothalamus.
  • The hypothalamus then sends a message to the heart, blood vessels, and kidneys, which act as effectors in blood pressure regulation.
  • Nerve cells relay information about body temperature to the hypothalamus.
  • The hypothalamus then signals several effectors to return the body temperature to 37 degrees Celsius (the set point).
  • The hypothalamus secretes corticotropin-releasing hormone (CRH), which directs the anterior pituitary gland to secrete adrenocorticotropic hormone (ACTH).

• The Anterior Pituitary

  • The anterior pituitary itself is regulated by the hypothalamus and by negative feedback from these target organs.
  • Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the hypothalamus.
  • Neuroendocrine neurons in the hypothalamus project axons to the median eminence, at the base of the brain.
  • The anterior pituitary, in yellow, is linked to the hypothalamus by a portal system.
  • The hypothalamus releases signaling molecules that incite the anterior pituitary to produce hormones.

• Overview of Endocrine Glands

  • The hypothalamus makes up the lower region of the diencephalons and lies just above the brain stem.
  • The hypothalamus also controls the glandular secretion of the pituitary gland.
  • Communication between the hypothalamus and the posterior pituitary occurs through neurosecretory cells that span the short distance between them.
  • Communication between the hypothalamus and the anterior pituitary occurs through hormones (releasing hormones and inhibiting hormones) that are produced by the hypothalamus and delivered to the anterior pituitary via a portal network of capillaries.
  • The releasing and inhibiting hormones are produced by specialized neurons of the hypothalamus called neurosecretory cells.