Hormonal control in humans

• Body's coordination system which involves hormones

  The endocrine system
• Hormone


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

  The pituitary gland
• Pituitary gland


  • It secretes a wide range of hormones, some of which may stimulate other endocrine glands
• Role of pituitary gland

  1. Secretes human growth hormone - controls human growth

  2. Stimulates the thyroid gland

  3. Stimulates ovulation and the production of oestrogen in the ovaries

  4. Stimulates the production of sperm and testosterone in the testes
• Role of thyroid gland

  Secretes the hormone thyroxine - controls metabolism, heart rate and body temperature
• Role of pancreas


  Secretes the hormone insulin - controls blood glucose levels
• Role of adrenal gland

  Secretes adrenaline - controls the body's 'fight or flight' response
• Role of ovaries


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


  Secrete testosterone, which coordinates the production of sperm and the development of male secondary sexual characteristics
• Organ that monitors and controls blood glucose concentration

  The pancreas
• How pancreas responds when blood glucose levels are too high

  The pancreas secretes the hormone insulin. Insulin binds to receptors on the liver and muscles, causing excess glucose to be converted into glycogen and stored.
• How pancreas responds when blood glucose levels are too low (higher only)

  The pancreas secretes the hormone glucagon. Glucagon binds to liver cells, causing glycogen to be converted into glucose and released into the blood.
• How blood glucose concentration is controlled using a negative feedback loop (higher only)


  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. As a result, blood glucose levels are often very high, leading to excessive urination, tiredness and weight loss.
• How Type 1 diabetes can be treated

  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.
• How Type 2 diabetes can be treated

  1. Following a carefully-controlled diet

  2. Doing regular exercise

  3. Losing weight

  4. Use of drugs which increase insulin production and effectiveness
• Osmosis (biology only)


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

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

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

  Excess amino acids are deaminated in the liver to form ammonia. Ammonia is toxic, therefore it is converted into urea. Urea is excreted from the body via sweat and urine.
• How the kidneys maintain the balance of water and other substances in the body (biology only)
• 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

  • When the kidneys are damaged, they may be unable to filter the blood properly. This may lead to: A build-up of toxic molecules (eg. urea) in the body, An uncontrolled ion and water balance and cells being damaged as a result of osmosis
• 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