hormones and homeostasis

• Homeostasis


  Principles of hormonal coordination and control
• Endocrine system


  Made up of glands that secrete hormones directly into the bloodstream
• Hormones


  Chemical messengers carried in the blood to a target organ where they produce an effect
• Compared with effects of the nervous system


  The effects of hormones are slower and act for longer
• Pituitary gland


  A 'master gland' that secretes several hormones in response to body conditions
• Adrenaline


  Produced by the adrenal glands in times of fear or stress, increases heart rate and prepares the body for "flight or fight"
• Thyroxine


  Produced by the thyroid gland, increases metabolic rate and controls growth and development, controlled by negative feedback
• Control of blood glucose

  1. Blood glucose concentration is monitored and controlled by the pancreas

  2. If blood glucose is too high, pancreas releases insulin which causes glucose to move from blood into cells

  3. If blood glucose is too low, pancreas releases glucagon which stimulates glycogen to be converted into glucose and released into the blood
• Type 1 diabetes


  Caused by the pancreas failing to produce sufficient insulin, results in uncontrolled high blood glucose levels, normally treated with insulin injections
• Type 2 diabetes


  Caused by the body cells no longer responding to insulin, obesity is a risk factor, treated with carbohydrate-controlled diet and regular exercise
• Water balance


  1. Water leaves the body from breathing, sweating, and urinating

  2. If blood concentration changes, cells gain/lose water by osmosis

  3. Balance of water and ions regulated by kidneys

  4. Kidneys produce urine by filtering blood, selectively reabsorbing useful substances, leaving urea and excess water/ions to form urine
• ADH


  Hormone that controls water level in the body, when blood is too concentrated more ADH is released by pituitary gland which makes kidney tubules more permeable so more water is reabsorbed
• Urea is a waste product produced by the liver from the breakdown of proteins and contains nitrogen
• Urea production


  1. Digestion of proteins results in excess amino acids

  2. In the liver, these amino acids are converted to ammonia in a process called deamination

  3. Ammonia is toxic so it is converted to urea and sent to the kidneys for excretion
• People who suffer from kidney failure may be treated by organ transplant or kidney dialysis
• A dialysis machine takes over the role of the kidneys, used to remove waste products from the blood three times a week