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• Hormones are blood borne messengers
  • Produced by one organ
  • Secreted into the blood
  • Carried to all parts of the body by the blood
  • Only those organs having the specific receptors respond to the hormone
  • Rapidly destroyed
  • Involved in homeostasis and adaptation
• Some hormones control the activity of other endocrine glands
• Examples include hormones produced by the anterior pituitary gland

Control of salt, water and osmotic pressure

• Homeostasis requires close regulation of body salt & water
• ADH (antidiuretic hormone) causes water resorption in the collecting ducts of the kidney
• Aldosterone increases Na reabsorption by the kidney
• If the blood osmotic pressure is increased ADH secretion is increased
• If the blood volume falls aldosterone production in the renal cortex will increase
• A number of hormones are involved in the control of Ca

Reproductive function

• Growth of the ovaries and testes and secretion of sex hormones is controlled by FSH and LH
• Oxytocin produced by the posterior pituitary causes contraction of uterine muscles
• Milk production involves many hormones, including prolactin
• Milk ejection when the baby suckles is controlled by oxytocin

Growth and metabolism

• Thyroxin increases the metabolic rate of many tissues
• Several hormones aid metabolism by raising blood glucose including
  • Glucagon
  • Adrenaline
  • Cortisol
  • Growth hormone
• Insulin lowers blood glucose
• Erythropoietin supports metabolism by regulating the number of red cells in the blood
• Important hormones regulating growth include
  • Growth hormone
  • Thyroxine

Author:  Dr Shakeeb Khan

Last updated: 05 January 2008

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