Homeostasis and response

• Examples of receptors


  • Rod and cone cells in the eye responding to light, skin cells responding to pressure or temperature changes
• Synapses


  Information transmission between neurons through chemical neurotransmitters at the gap where neurons meet
• Aspects of homeostasis in humans

  • Blood glucose levels, body temperature, CO₂ levels, water levels
• Hormones are produced and released from glands around the body which make up the endocrine system
• Human Nervous System


  • Allows fast, short-lived response to stimuli, information received by receptor, passed along neurons as electrical impulse, results in a response
• Nervous Pathway

  Stimulus detected by receptor, sent as electrical impulse along sensory neuron to CNS, relayed through CNS, response coordinated, information sent along motor neuron to effector
• Automatic control systems

  • Can be nervous responses (coordinated by the nervous system) or chemical responses (coordinated by the endocrine system)
• Homeostasis


  The regulation of a constant internal environment to ensure optimum conditions for metabolism and changes in response to internal and external fluctuations
• Examples of effectors

  • Muscles contracting for movement, glands releasing chemicals into the body
• Hormones are chemical messengers transported in the bloodstream to an effector where they activate a response
• Type 1 diabetes is usually treated by injections of insulin
• Hormones


  • Chemical messengers transported in the bloodstream to an effector where they can activate a response
  • Produced and released from glands around the body which make up the endocrine system
  • Travel in the blood plasma to their target cells and affect only those certain cells
  • Act on organs or cells where constant adjustments are made to maintain a stable state
• Oestrogen is the main reproductive hormone in females, produced in the ovaries, and stimulates ovulation
• Type 2 diabetes can usually be managed through lifestyle choices such as maintaining a carbohydrate-controlled diet and regular exercise
• 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
• Reflex arc

  Stimulus detected by receptor cells, electrical impulse transmitted along sensory neuron, passed through relay neurons, response coordinated automatically and sent along motor neuron to effector cells
• A reflex arc is the pathway which carries the information about a reflex action
• Control of blood glucose

  If blood glucose concentration becomes too low, a negative feedback loop is triggered and the pancreas releases glucagon to convert stored glycogen back into glucose and release it into the bloodstream
• If the egg is fertilised, pregnancy follows; if not, the uterine lining is shed away during menstruation
• Type 2 diabetes is a disorder of effector cells which no longer respond to the hormones released from the pancreas
• Type 1 diabetes affects the pancreas by not producing enough insulin to control blood sugar levels
• Hormones

  • FSH
  • LH
  • Insulin
  • Glucagon
  • Oestrogen
  • Testosterone
  • Progesterone
• Reflexes


  • Fast and automatic response to a particular stimulus which may be harmful to the organism
  • No conscious thought or process to deliver the response (involuntary action)
• Major glands of the endocrine system

  • Pituitary gland
  • Pancreas
  • Ovaries
  • Testes
• The risk of developing type 2 diabetes is higher in people who are obese (have a BMI >30)
• The pancreas monitors and regulates the blood glucose concentration
• Testosterone is the main reproductive hormone in males, produced in the testes, and stimulates the production of sperm
• Main reproductive hormones

  • FSH
  • Oestrogen
  • LH
  • Progesterone
• The menstrual cycle occurs in females approximately every 28 days, involving the building of the uterine lining and ovulation
• progesterone

  • Produced in the ovaries
  • Helps the uterus lining to maintain
  • Inhibits the production of LH
• oestrogen

  • Produced in the ovaries
  • Builds up and thickens the lining of the uterus
  • Stimulates the production of LH and inhibits the production of FSH
• Reproductive hormones

  • follicle stimulating hormone (FSH)
  • oestrogen
  • luteinising hormone (LH)
  • progesterone
• Thyroxine is a hormone produced
• LH

  • Produced in the pituitary gland
  • Causes ovulation at around day 14 of the cycle
  • Indirectly stimulates the production of progesterone
• Adrenaline is a hormone produced by the adrenal glands. It is released in response to stress or fear. The hormone acts on major organs including the heart and lungs. The effect is to increase the heart rate and breathing rate and cause vasodilation (widening of the blood vessels), in order to supply the brain and muscles with more oxygen and glucose. This prepares the body for a ‘flight or fight’ response to the fear or stress
• FSH

  • Produced in the pituitary gland
  • Causes an egg to develop in one of the ovaries
  • Stimulates the production of oestrogen
• Menstrual cycle

  Includes shedding of the lining of the uterus if the egg is not fertilised, leading to menstruation
• Adrenaline

  Hormone produced by the adrenal glands, released in response to stress or fear, acts on major organs including the heart and lungs to increase heart rate, breathing rate, and cause vasodilation to supply the brain and muscles with more oxygen and glucose, preparing the body for a 'flight or fight' response
• Underlying causes of infertility are not usually treated with fertility treatments
• Infertility treatments

  • FSH and LH can be given in a 'fertility drug' to help stimulate normal cyclic processes and enable pregnancy naturally
  • In Vitro Fertilisation (IVF) involves several stages