Hormonal Coordination in Humans

• Endocrine system


  The body's coordination system which involves hormones
• Hormone


  A chemical messenger secreted by a gland, that travels in the blood to a target organ and causes a response
• Gland


  An organ that secretes hormones
• Pituitary gland

  The 'master gland' that secretes a wide range of hormones, some of which may stimulate other endocrine glands
• Roles of the pituitary gland

  • Secretes human growth hormone - controls human growth
  • Stimulates the thyroid gland
  • Stimulates ovulation and the production of oestrogen in the ovaries
  • Stimulates the production of sperm and testosterone in the testes
• Thyroid gland

  Secretes the hormone thyroxine - controls metabolism, heart rate and body temperature
• Pancreas

  Secretes the hormone insulin - controls blood glucose levels
• Adrenal gland

  Secretes adrenaline - controls the body's 'fight or flight' response
• Ovaries


  Secrete oestrogen, which coordinates the menstrual cycle and the development of female secondary sexual characteristics
• Testes


  Secrete testosterone, which coordinates the production of sperm and the development of male secondary sexual characteristics
• Pancreas


  Monitors and controls blood glucose concentration
• Pancreas response to high blood glucose

  Secretes the hormone insulin, which binds to receptors on the liver and muscles, causing excess glucose to be converted into glycogen and stored
• Pancreas response to low blood glucose

  Secretes the hormone glucagon, which binds to liver cells, causing glycogen to be converted into glucose and released into the blood
• Blood glucose concentration control via negative feedback loop


  When the blood glucose concentration rises or falls below the optimum, a hormone is secreted by the pancreas. The action of either hormone (insulin or glucagon) helps bring back the concentration to the correct level.
• Type 1 diabetes

  An autoimmune disorder in which the pancreas does not produce sufficient insulin to control the blood glucose concentration, leading to high blood glucose levels, excessive urination, tiredness and weight loss
• Treatment of Type 1 diabetes

  1. Insulin injections before meals - allows glucose to be converted into glycogen

  2. Limiting carbohydrate intake

  3. Attempts using pancreas and pancreatic cell transplants; investigations into genetic engineering of pancreatic cells
• Type 2 diabetes


  A disorder in which the body's cells stop responding to insulin, leading to an uncontrolled blood glucose concentration. Its onset is linked with increasing age and obesity.
• Treatment of Type 2 diabetes


  1. Following a carefully-controlled diet

  2. Doing regular exercise

  3. Losing weight

  4. Use of drugs which increase insulin production and effectiveness
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Ways water is lost from the body

  • During exhalation via the lungs
  • Sweating
  • Urine (some reabsorbed in the kidney)
• Ways ions are lost from the body

  • Sweating
  • Urine (some reabsorbed in the kidney)
• Excretion of excess amino acids

  1. Excess amino acids are deaminated in the liver to form ammonia

  2. Ammonia is converted into urea

  3. Urea is excreted from the body via sweat and urine
• The kidneys maintain the balance of water and other substances in the body
• Ways ions are lost from the body

  • Sweating
  • Urine (some reabsorbed in the kidney)
• How excess amino acids are excreted from the body

  1. Excess amino acids are deaminated in the liver to form ammonia

  2. Ammonia is toxic, therefore it is converted into urea

  3. Urea is excreted from the body via sweat and urine
• How the kidneys maintain the balance of water and other substances in the body

  1. Filter blood in order to remove waste products eg. urea

  2. Selectively reabsorb useful molecules eg. glucose, water, ions
• ADH

  Anti-diuretic hormone
• Where ADH is secreted

  The pituitary gland of the brain
• How ADH affects the reabsorption of water in the kidneys

  1. When the blood is too concentrated, the pituitary gland secretes more ADH

  2. ADH travels in the bloodstream to the kidney and increases the permeability of kidney tubules to water

  3. More water is reabsorbed in the kidneys, resulting in a smaller volume of more concentrated urine
• Why kidney failure is dangerous
• Ways of treating kidney failure

  • Dialysis
  • Transplant
• Kidney dialysis

  The use of a specialist machine to carry out the function of kidneys. Dialysis fluid contains the same concentration of glucose and ions as healthy blood. As a result, only excess and waste molecules are lost from the blood, and glucose and ions remain
• Function of reproductive hormones during puberty

  • Males: cause the development of secondary sexual characteristics
  • Females: cause the development of secondary sexual characteristics and the maturation of eggs
• Main male reproductive hormone

  Testosterone, which is produced by the testes and controls sperm production
• Main female reproductive hormone

  Oestrogen, which is produced by the ovaries and is involved in the menstrual cycle
• Menstrual cycle


  The monthly cycle of physiological changes that occur in females, involving the shedding of the uterus lining (menstruation) and ovulation
• Events of the menstrual cycle

  1. Uterus lining thickens and eggs begin to mature in the ovaries

  2. An egg is released from one of the ovaries (ovulation) - uterus lining remains thick

  3. If the egg is fertilised, pregnancy may occur. If not, both the egg and the uterus lining are shed during menstruation
• Ovulation


  The release of a mature egg from the ovaries, which occurs approximately every 28 days
• Main hormones involved in the menstrual cycle

  • Oestrogen
  • Progesterone
  • Follicle stimulating hormone (FSH)
  • Luteinising hormone (LH)
• Role of FSH in the menstrual cycle

  FSH is secreted by the pituitary gland. It controls the maturation of eggs within the ovaries (inside a follicle) and triggers the production of oestrogen by the ovaries