Human hormonal coordination

• The body’s coordination system involving hormones is the endocrine system
• A hormone is a chemical messenger secreted by a gland. It travels in the blood to a target organ, where it causes a response
• Glands are the type of organ that secretes hormones
• The pituitary gland controls many other glands in the body and is considered a ‘master gland’
• The pituitary gland secretes human growth hormone, stimulates the thyroid gland, ovulation and oestrogen production in ovaries, and sperm and testosterone production in testes
• The thyroid gland secretes thyroxine, which controls metabolism, heart rate, and body temperature
• The pancreas secretes insulin, which controls blood glucose levels
• The adrenal gland secretes adrenaline, which controls the body’s ‘fight or flight’ response
• The ovaries secrete oestrogen, coordinating the menstrual cycle and female secondary sexual characteristics
• The testes secrete testosterone, coordinating sperm production and male secondary sexual characteristics
• The pancreas monitors and controls blood glucose concentration
• When blood glucose levels are too high, the pancreas secretes insulin to convert excess glucose into glycogen and store it
• When blood glucose levels are too low, the pancreas secretes glucagon to convert glycogen into glucose and release it into the blood
• Blood glucose concentration is controlled using a negative feedback loop where hormones (insulin or glucagon) help bring the concentration back to the correct level
• Type 1 diabetes is an autoimmune disorder where the pancreas does not produce sufficient insulin, leading to high blood glucose levels
• Type 1 diabetes can be treated with insulin injections, limiting carbohydrate intake, and pancreas or pancreatic cell transplants
• Type 2 diabetes is a disorder where the body’s cells stop responding to insulin, leading to uncontrolled blood glucose levels
• Type 2 diabetes can be treated by following a carefully-controlled diet, regular exercise, weight loss, and using drugs that increase insulin production and effectiveness
• Osmosis is the movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Water is lost from the body during exhalation via the lungs, sweating, and in urine (some reabsorbed in the kidney)
• Ions are lost from the body through sweating and in urine (some reabsorbed in the kidney)
• Excess amino acids are deaminated in the liver to form ammonia, which is converted into urea and excreted via sweat and urine
• The kidneys maintain the balance of water and other substances by filtering blood to remove waste products and selectively reabsorbing useful molecules
• The full name of the hormone ADH is Anti-diuretic hormone, secreted by the pituitary gland of the brain
• ADH affects the reabsorption of water in the kidneys by increasing the permeability of kidney tubules to water when blood is too concentrated
• Kidney failure is dangerous because it may lead to a build-up of toxic molecules in the body and an uncontrolled ion and water balance, damaging cells
• Kidney failure can be treated through dialysis or transplant
• Kidney dialysis is the use of a specialist machine to carry out the function of kidneys, maintaining the balance of glucose and ions in the blood
• Reproductive hormones during puberty cause the development of secondary sexual characteristics in males and females, and the maturation of eggs in females
• The main male reproductive hormone is testosterone
• The main male reproductive hormone is testosterone, produced by the testes and controls sperm production
• The main female reproductive hormone is oestrogen, produced by the ovaries and involved in the menstrual cycle
• The menstrual cycle is the monthly cycle of physiological changes in females, involving shedding of the uterus lining (menstruation) and ovulation
• Events of the menstrual cycle:

  • Uterus lining thickens and eggs begin to mature in the ovaries
  • An egg is released from one of the ovaries (ovulation) - uterus lining remains thick
  • If the egg is fertilised, pregnancy may occur. If not, both the egg and the uterus lining are shed during menstruation
• Ovulation is the release of a mature egg from the ovaries, occurring approximately every 28 days
• Four main hormones involved in the menstrual cycle:

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

  • Secreted by the pituitary gland
  • Controls maturation of eggs within the ovaries and triggers production of oestrogen by the ovaries
• Role of oestrogen in the menstrual cycle:

  • Produced by the ovaries and released due to the action of FSH
  • Causes regrowth of the uterus lining
  • Triggers production of LH and restricts release of more FSH
• Role of LH in the menstrual cycle:

  • Produced in the pituitary gland as a result of oestrogen
  • Its release triggers ovulation
• Role of progesterone in the menstrual cycle:

  • Secreted from the follicle of the ovary
  • Sustains the uterus lining and inhibits FSH and LH