Hormonal communication

• Hormones

  = Chemical messengers that respond to changes in the environment.

  • Secreted directly into the blood when a gland is stimulated.
  • This can occur as a result of a stimulus, hormone, nerve impulse.
  • Once secreted, the hormone is transported in blood plasma.
  • Hormones diffuse out the blood and bind to specific receptors found on membranes of target cells.
  • Once bound to their receptors the hormone stimulate the target cell to produce a response.
• Steriod hormone

  = Lipid soluble.

  • They pass through the lipid component of the cell membrane and bind to steriod hormone receptors to form a hormone-receptor complex.
  • The receptors may be present in the cytoplasm or the nucleus.
  • The hormone- receptor complex acts as a transcriptional factor which facilitates or inhibits the transcription of a specific gene. Eg: oestrogen
• Non-steriod hormone

  = Are hydrophilic so cant pass directly through the cell membrane.

  • Instead they bind to specific receptors on the cell surface membrane of the target cell.
  • This triggers a cascade reaction mediated by chemicals called second messengers. Eg: adrenaline
• Adrenal glands

  Capsule- cortex- medulla

  • Cortex= cortisol hormone (controls metabolic rate) Androgens hormone (sex characteristics)
  • Medulla= adrenaline hormone (increased heart rate, glycogen-glucose) Noradrenaline (pupils dilate, increased heart rate)
• Endocrine gland= group of cells which are specialised to secrete hormones into the bloodstream.
• Pituitary gland= produces growth hormone and anti-diuretic hormone which controls the reabsorption of water from kidneys)
• Thyroid gland= produces thyroxine which controls rate of metabolism
• Pineal gland= produces melatonin
• Thymus gland= produces thymosin which promotes production and maturation of white blood cells.
• Adrenal gland= produces adrenaline