Chapter 7: homeostasis

• Homeostasis


  Controlling and maintaining constant internal environment of the body
• Homeostasis


  • Everything inside the body must be up at constant level
  • Controlled by nerves
  • Controlled by hormones (endocrine system)
  • Chemical substances produced by glands
• Hormones


  • Chemical substances produced by glands and carried in the bloodstream to target organs
  • Regulate organ functions
  • Can act quickly but effects are slow
• How homeostasis is co-ordinated

  1. Receptor detects change (stimulus)

  2. Coordination centre receives and processes information

  3. Coordinator organises response

  4. Effector is activated and produces response to counteract the change and restore it to optimum levels
• Parts of the body involved in homeostasis

  • Skin
  • Kidneys
  • Lungs
• Homeostasis


  • Maintains constant body temperature
  • Maintains water and mineral levels
  • Maintains oxygen and carbon dioxide levels
• When a change is detected by receptor


  1. Coordination centre receives and processes information

  2. Coordinator organises response

  3. Effector is activated and produces response to counteract the change and restore it to optimum levels
• Removing waste products is part of homeostasis
• Waste products removed


  • Carbon dioxide produced during respiration
  • Urea
• Removal of waste products

  1. Waste products move out of cells into blood plasma

  2. Blood stream carries to lungs for gaseous exchange

  3. If not removed, dissolves in blood making it acidic which affects cell efficiency

  4. Urea produced in liver when excess amino acids are broken down

  5. Main waste product removed in urine, not reabsorbed by kidneys

  6. Also excreted through sweating
• Endocrine system


  Made up of all the body's different hormone-producing organs
• Endocrine system


  • Coordinator of organs which receive and process information from receptors in the body
  • Uses chemical messengers (hormones) that are long-lived and elicit a slow response
  • Contrasts with the nervous system which uses electrical impulses that are short-lived and elicit a rapid response
• Pituitary gland


  The master gland that controls the functions of all the other endocrine glands
• Negative feedback is a type of control system that acts to correct an imbalance in the body
• Homeostatic control


  If something rises, control systems reduce it, and if something fails, control systems raise it
• Osmoregulation


  The control of water and mineral balance in the body
• Kidney function


  1. Filtration of blood to remove toxic materials, waste products and excess water

  2. Reabsorption of useful substances like glucose and some salts

  3. Adjustment of water reabsorption to suit body needs
• Low water levels


  Hypothalamus detects this and signals the pituitary gland to release ADH
• ADH released


  Travels to the kidney and causes it to reabsorb more water, producing concentrated urine
• High water levels


  Hypothalamus detects this and signals the pituitary gland to reduce ADH release
• Reduced ADH


  Kidney reabsorbs less water, producing dilute urine
• Blood entering the kidney via the renal artery contains substances to be filtered
• Blood leaving the kidney via the renal vein has less urea as it has been filtered out
• Controlling body temperature


  • Factors that affect body temperature
  • Fever
• Thermoregulatory center


  Part of the brain that regulates body temperature
• Maintaining optimal body temperature

  1. Receptors in the skin send inputs to the thermoregulatory center

  2. Muscles/glands carry out changes to maintain optimal temperature

  3. Shivering generates heat from muscle contraction

  4. Sweating evaporates water to transfer heat to the environment

  5. Blood vessel dilation increases energy transferred
• Glycogen


  Stored form of glucose in the liver and muscles
• Insulin


  Hormone released by the pancreas when blood glucose is high, causes glucose to move into cells
• Glucagon


  Hormone released by the pancreas when blood glucose is low, converts glycogen into glucose to be released into the blood
• It is important to control blood sugar levels as too high or too low can have negative effects on cells