Hormones and Negative Feedback Systems

• Hormones are chemicals produced in various glands called endocrine glands. They are released directly into the blood, which carries them ti different parts of the body
• The cells that hormones effect are called target cells, which have the right receptors to respond to the hormone. The organ which contains the target cell is called the target organ
• Once a hormone is used, it is destroyed by the liver
• The effects of hormones are much slower than the effect of the nervous system, however the effects last longer
• Types of glands in the body

  A) pitutiary

  B) adrenal

  C) thyroid

  D) pancreas

  E) testes

  F) ovaries

  G) thyroxine

  H) insulin

  I) adrenaline

  J) testosterone

  K) oestrogen

  
• The pituitary gland in the brain is known as the ' master gland '. It secretes several hormones into the blood in response to the bodys condition, such as water content in blood. These hormones can also act on other glands to stimulate release of other hormones
• The hypothalamus, a part of the brain, regulates hunger, mood, and body temperature by detecting changes and signaling the pituitary gland to release hormones to maintain bodily balance
• ADH is a hormone from the pituitiary gland in the base of the brain which detects if plasma in the blood is too concentrated e.g. due to loss of water from sweat.
• ADH increases permeability of kidneys to allow them to reabsorb water from the urine through osmosis
• Adrenaline works by activating processes that provide glucose and oxygen to cells, to prepare the body for fight or flight
• Adrenaline binds to receptors in the heart to make heart muscle contract more frequently so blood pressure increases
• Adrenaline also binds to receptors in the liver to break down glycogen into glucose, to allow glucose into the blood to be transported into cells
• Insulin is released from the pancreas glands in the liver, which converts glucose from the blood into glycogen to lower the glucose concentration
• The body can control levels of hormones in the blood using negative feedback. When the levels of hormones is above or below normal levels, it triggers a response to bring the body back to normal
• Thyroxine is a hormone that is produced by the thyroid gland in the neck. It regulates the rate of metabolism and regulates the rate of growth and processes such as protein synthesis
• The pituitary gland releases a thyroid stimulating hormone, which then triggers the release of thyroxine
• A negative feedback system keep amounts of thyroxine in the blood at the right level. If level is thyroxine in blood is higher than normal, thyroid stimulating hormone is released less, so decreases thyroxine from the thyroid gland, so blood levels go back to normal
• As thyroxine levels increase, they might temporarily overshoot the normal range. The hypothalamus and pituitary gland then reduce the production of TSH, causing thyroxine levels to decrease