homeostasis and response

• homeostasis


  the regulation of a consistent internal environment to ensure optimum conditions for metabolism and changes in response to both internal and external fluctuations
• conditions regulated by homeostasis in humans

  • blood glucose levels
  • body temperature
  • CO₂ levels
  • water levels
• automatic control systems


  can be nervous responses (coordinated by the nervous system) or chemical responses (coordinated by the endocrine system)
• information processing in response to a stimulus

  1. detected by a receptor
  2. processed by a central coordination system
  3. response initiated by an effector
• synapse


  the gap where the ends of two neurones meet
• transmission of information across a synapse


  message transmitted by chemical neurotransmitters
• nervous pathway

  1. stimulus received by receptor and sent as a electrical impulse along a sensory neutrone towards the central nervous system (CNS)
  2. impulse passed through relay neurones and a responce coordinated
  3. CNS sends information about the response along motor neurone as an electrical impulse
  4. effector carries out the response
• receptors

  • rod and cone cells within the eye which responds to light and allow us to see
  • cells in the skin which respond to pressure or temperature changes allowing us to feel
• effetors

  • muscle might contract to make a movement
  • gland releases a chemical into the body
• human nervous system


  allows a fast, short-lived response to a stimulus in the surroundings
• hormones are chemical messengers transported in the bloodstream to an effector where they can activate a response
• major glands of the endocrine system

  • pituitary gland
  • pancreas
  • ovaries
  • testes
• hormones are chemical messengers transported in the bloodstream to an effector where they can activate a response they are produced and released from glands around the body which all make up the endocrine system
• the hormones released travel in the blood plasma to their target cells and affect only those certain cells. hormones act on organs or cells where constant adjustments are made to maintain a stable state
• hormones


  pituitary gland produces FSH and LH to regulate the menstrual cycle
• the pituitary gland acts as a master gland because many of the hormones, it releases control and coordinate the release of other hormones from other glands in the body
• type 1 diabetes affects the pancreas by not producing enough insulin to control blood sugar levels
• type 1 diabetes is usually treated by injections of insulin
• type 2 diabetes is a disorder of effector cells which no longer respond to the hormones released from the pancreas
• type 2 diabetes can usually be managed through lifestyle choices such as maintaining a carbohydrate-controlled diet and regular exercise
• the risk of developing type 2 diabetes is higher in people who are obese
• oestrogen is the main reproductive hormone in females, produced in the ovaries. it stimulates ovulation
• testosterone is the main reproductive hormone in males, produced in the testes. it stimulates the production of sperm
• reflex arc


  begins with a stimulus detected by receptor cells, transmitted along sensory neurone, passes through relay neurones, response coordinated and sent along motor neurone to effector cells
• A reflex is a fast and automatic response to a particular stimulus which may be harmful to the organism. They are quick because there is no conscious thought or process to deliver the response (they are an involuntary action). The pathway which carries the information about a reflex action is called a reflex arc
• The pancreas monitors and regulates the blood glucose concentration. If the blood glucose concentration becomes too low, a negative feedback loop is triggered and the pancreas releases another hormone, glucagon, which acts on the liver and muscles to cause the stored glycogen to be converted back into glucose and released into the bloodstream
• The menstrual cycle occurs in females approximately every 28 days. It involves the building of the lining of the uterus and ovulation. If the egg becomes fertilised, pregnancy follows. If not, the lining of the uterus is shed away during menstruation