Hypothalamus & Pituitary

• Nervous System


  • Nerve impulses / Neurotransmitters
  • Faster responses, briefer effects, act on specific target
• Endocrine System


  • Hormone – mediator molecule released in 1 part of the body but regulates activity of cells in other parts
  • Slower responses, effects last longer, broader influence
• General Functions of Hormones

  • Growth & development
  • Reproduction
• Hormones have powerful effects when present in very low concentrations
• Hormones Regulate


  • Extracellular fluid
  • Metabolism
  • Biological clock
  • Concentration of cardiac & smooth muscle
  • Glandular secretion
  • Some immune functions
• Types of Glands


  • Exocrine
  • Endocrine
• Exocrine Glands


  Secrete products into ducts which empty into body cavities on body surface
• Endocrine Glands


  Secrete products (hormones) into interstitial fluid, diffuse into blood
• Endocrine Glands


  • Pituitary
  • Thyroid
  • Parathyroid
  • Adrenal
  • Pineal
• Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta are not exclusively endocrine glands
• Hormone Receptors


  Hormones only affect target cells with specific membrane proteins called receptors
• Down Regulation


  • Excess hormone leads to a decrease in number of receptors
  • Receptors undergo endocytosis and are degraded
  • Decreases sensitivity of target cell to hormone
• Up Regulation


  • Deficiency or hormone leads to an increase in the number of receptors
  • Target tissue becomes more sensitive to the hormone
• Types of Hormones


  • Circulating Hormones
  • Local Hormones
• Paracrine Hormones


  Act on neighbouring cells
• Autocrine Hormones


  Act on the same cell that secreted them
• Chemical Classes of Hormones

  • Lipid Soluble
  • Water Soluble
• Lipid Soluble Hormones


  Use Transport Proteins
• Lipid Soluble Hormone Types

  • Steroid
  • Thyroid
  • Nitric Oxide
• Water Soluble Hormones


  Circulate in 'Free' Form
• Water Soluble Hormone Types

  • Amine
  • Peptide / Protein
  • Eicosanoid
• Mechanism of Lipid Soluble Hormone Action

  • Hormone diffuses through phospholipid bilayer & into cell
  • Binds to receptor turning on/off specific genes
  • New mRNA is formed & directs synthesis of new proteins
  • New protein alters cells activity
• Mechanism of Water Soluble Hormone Action

  • Can not diffuse through plasma membrane
  • Hormone receptors are integral membrane proteins – act as 1st messengers
  • The hormone binds to the membrane receptor
  • The activated receptor activates a membrane G-protein which turns on adenylate cyclase
  • Adenylate cyclase converts ATP into cyclic AMP which activates protein kinases
  • Protein kinases phosphorylate enzymes which catalyse reactions that produce the physiological response
• Responsiveness of Target Cell

  • Depends on hormone concentration
  • Abundance of target cell receptors
  • Influence exerted by other hormones
• Influences on Target Cell Responsiveness

  • Permissive (Steroid priming of hypothalamus / pituitary)
  • Synergistic (Glucagon & Epinephrine)
  • Antagonistic Effects (Insulin & Glucagon)
• Control of Hormone Secretion


  Regulated by signals from nervous system, chemical changes in the blood or by other hormones
• Disorders of Hormone Secretion

  • Hyposecretion
  • Hypersecretion
• Negative Feedback


  Decreases / Increase in blood level is reversed
• Positive Feedback


  The change produced by the hormone causes more hormone to be released
• Nervous System


  • Nerve impulses / Neurotransmitters
  • Faster responses, briefer effects, act on specific target
• Hypothalamus


  • The major integrating link between the nervous and endocrine systems
  • Receives input from cortex, thalamus, limbic system & internal organs
  • Controls pituitary gland with 9 different releasing & inhibiting hormones
• Endocrine System


  • Hormone – mediator molecule released in 1 part of the body but regulates activity of cells in other parts
  • Slower responses, effects last longer, broader influence
• Pituitary Gland


  • Attached to hypothalamus by infundibulum
  • Anterior pituitary or adenohypophysis
  • Posterior pituitary or neurohypophysis
• General Functions of Hormones

  • Growth & development
  • Reproduction
  • Hormones have powerful effects when present in very low concentrations
• Hypothalamus to Anterior Pituitary

  Hormones transported via blood
• Hormones Regulate


  • Extracellular fluid
  • Metabolism
  • Biological clock
  • Concentration of cardiac & smooth muscle
  • Glandular secretion
  • Some immune functions
• Hypothalamus to Posterior Pituitary

  Hormones transported via axons of hypothalamic neurons and then stored in posterior pituitary
• Types of Glands


  • Exocrine - Secrete products into ducts which empty into body cavities on body surface
  • Endocrine - Secrete products (hormones) into interstitial fluid, diffuse into blood
• Human Growth Hormone (hGH)


  • The most plentiful anterior pituitary hormone
  • Produced by cells in the pituitary called somatotrophs
  • Released following the binding of HGH Releasing Factor to receptors on somatotrophs
  • Acts indirectly on tissues (liver, skeletal muscle, cartilage and bone) by promoting the synthesis and secretion of small protein hormones called insulin-like growth factors (IGFs)
  • IGFs stimulate general body growth and regulate various aspects of metabolism
• Endocrine Glands


  • Pituitary – thyroid, parathyroid, adrenal & pineal gland
  • Hypothalamus – thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta not exclusively endocrine glands