hypothalamus and pituitary

• The Endocrine System

  
• Hypothalamus & Pituitary
• A/Prof Elizabeth Beckett
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• hypothalamus


  Part of the brain

  
• pituitary gland


  Endocrine gland
• optic chiasm


  Part of the brain

  
• Location of the hypothalamus

  
• Hypothalamus


  • Links control systems
  • Hormone production and release from pituitary - which in turn influences thyroid gland (metabolism), adrenal gland (stress), gonads (reproduction)
  • Contraction of the uterus during labour
  • Milk production and release
  • Kidneys (water retention; sodium & potassium balance)
  • Growth and development

  
• Hypothalamic control centres


  Clusters of neurons, each identified as a nucleus e.g. paraventricular nucleus, supraoptic nucleus

  
• The MANY roles of the hypothalamus


  • Neural connections to other areas of brain
  • Major control centre for autonomic-mediated functions
  • Biological rhythms
  • Body temperature
  • Circulation
  • Food-water intake

  
• Extensive neural connections exist between the hypothalamus and the rest of brain. Hypothalamus is surrounded by the limbic lobe (associated with emotions).

  
• Pituitary gland


  Mainly controlled by the hypothalamus, physically connected via pituitary stalk/infundibulum. Many hormones released from the pituitary influence secretion from the other endocrine glands.

  
• Pituitary gland development


  • Up growth from oral cavity - has vascular connection with hypothalamus
  • Down growth from brain - has neural connection with hypothalamus

  
• The pituitary is mainly controlled by the hypothalamus. Physically connected via pituitary stalk/infundibulum.

  
• Posterior pituitary (neurohypophysis)


  • Nervous tissue - axons of neurosecretory cells
  • Pituicytes are a kind of glial cell - support
  • Capillaries are fenestrated - no BBB in post. pituitary

  
• Posterior pituitary hormones


  • Neurohormones (ADH & oxytocin) are synthesised in the cell bodies of neurons located in hypothalamic paraventricular and supraoptic nuclei
  • Vesicles (containing hormone) are transported along the long axons
  • Vesicles are stored in the hypothalamic neuron terminals (located in the posterior pituitary)
  • Hormones released into circulation

  
• Posterior pituitary


  • An 'extension' of the hypothalamus
  • Does not synthesise hormones
  • Stores hormones formed in the hypothalamic neurons
  • Secretes hormones directly into the blood
  • Releases two neurohormones: antidiuretic hormone - ADH (aka arginine vasopressin - AVP) and oxytocin

  
• Vasopressin


  Peptide hormone
• Oxytocin


  Peptide hormone
• Antidiuretic hormone (ADH)


  • Acts on blood vessels (including renal blood vessels) to cause vasoconstriction and increase blood pressure
  • Acts on the anterior pituitary gland to increase secretion of adrenocorticotropic hormone (ACTH), leading to increased aldosterone secretion and conservation of Na+ and H2O
  • Acts on kidneys to increase H2O reabsorption
• Oxytocin


  • Promotes ejection (smooth muscle contraction) of milk from the mammary glands
  • Involved in other behaviours (e.g. bonding, attachment)
• Contraction of the wall of the uterus is promoted by a hormone called oxytocin. Oxytocin is released from the posterior pituitary due to the activation of hypothalamic neurons. This is a positive feedback system.

  
• Sniffing oxytocin (in males) reduced the activity of the amygdala (the neural centre of 'fear').
• Anterior pituitary histology


  • Chromophils (actively secreting hormones) - acidophils (somatotrophs, lactotrophs) and basophils (corticotrophs, thyrotrophs, gonadotrophs)
  • Chromophobes (resting/degranulated chromophils)

  
• Anterior pituitary hormones


  • Thyroid-stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Growth hormone (GH)
  • Follicle-stimulating hormone (FSH)
  • Luteinizing hormone (LH)
  • Prolactin (PRL)
• Anterior pituitary hormones


  Stimulate/regulate the function of target endocrine glands

  
• Anterior pituitary hormones are controlled by hypophysiotropic hormones released from the hypothalamus.
• Hypophysiotropic hormones

  • Thyrotropin-releasing hormone (TRH)
  • Corticotropin-releasing hormone (CRH)
  • Gonadotropin-releasing hormone (GnRH)
  • Growth hormone-releasing hormone (GHRH)
  • Growth hormone-inhibiting hormone (GHIH, aka Somatostatin)
  • Prolactin-releasing hormone (PRH)
  • Prolactin-inhibiting hormone (PIH, aka Dopamine)
• Minute quantities of TRH stimulate the release of TSH from the pituitary gland, which, in turn stimulates release of thyroid hormones (T3 & T4) from the thyroid gland. Thyroid hormones also act back on the hypothalamus and pituitary to suppress release of TRH and TSH.