hormonal communication

• Steroid hormones are lipid-soluble so can pass directly through the cell membrane and bind to steroid hormone receptors.
• Non-steroid hormones are not lipid soluble (hydrophilic) so cannot 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 secondary messengers.
• The adrenal glands are made up of two distinct parts:

  • the adrenal cortex (outer region)
  • the adrenal medulla (inner region)
• The adrenal cortex produces hormones that are vital to life, such as cortisol and aldosterone.
• The adrenal medulla produces non-essential hormones such as adrenaline.
• Adrenaline = increases heart rate sending blood quickly to the muscles and brain. It also rapidly raises blood glucose concentration levels by converting glycogen into glucose in the liver.
• Noradrenaline = works with adrenaline in response to stress, producing effects such as increased heart rate, widened pupils, widening of air passages in the lungs and the narrowing of blood vessels in non-essential organs.
• There are three main types of hormones produced by the adrenal cortex:

  • glucocorticoids
  • mineralocorticoids
  • androgens