Bio 2

• Homeostasis

  The regulation of the internal conditions of a cell or organism in response to internal and external changes
• Importance of homeostasis


  • Keeps conditions constant for optimal enzyme action and cell functions
  • Includes control of blood glucose concentration, body temperature, water and ion levels
• Automatic control systems


  1. Electrical responses using the nervous system

  2. Chemical responses using hormones
• Endocrine disorders can result from abnormalities in the production, secretion, or action of hormones.
• Hormones are chemical messengers produced by various organs or tissues, including the pituitary gland, thyroid gland, adrenal glands, pancreas, ovaries (in females), testes (in males), and placenta.
• The endocrine system is made up of glands that secrete hormones into the bloodstream.
• Specialised cells - receptors which detect stimuli
• Coordination centre -which receive and process information from receptors
• Effectors- carry out the responses that restore optimum levels
• Nervous system enables humans to respond to their environment and coordinate their behaviour.
• Information from receptors passes to the central nervous system
• Cns coordinates the response of effectors
• Reflex action are automatic and rapid so they can protect the body - do not involve the conscious part of the brain
• Pain stimulus detection


  1. Receptors detect the pain stimulus

  2. Impulses from the receptor pass along a sensory neurone to the CNS

  3. An impulse then passes through a relay neurone

  4. A motor neurone carries an impulse to the effector

  5. The effector (usually a muscle) responds, e.g. to rapidly withdraw a limb away from the source of pain without thought
• Neurones are not directly connected to each other
• Electrical impulse reaching a synapse

  1. A chemical is released

  2. The chemical diffuses across the gap

  3. This causes an electrical impulse to be generated in the second neurone
• Investigating reaction time


  1. The experimenter holds a metre ruler from the end

  2. The subject has their finger and thumb a small distance apart, either side of the ruler, on the 50cm line

  3. The experimenter lets go of the ruler and the subject has to trap it

  4. The distance the ruler travels from the 50cm line is measured
• Endocrine system is a system of glands that secrete hormones into the bloodstream
• Hormones are specific receptors that identify the cells in the organ - organ then produces an effect
• Compared to nervous system effects of hormones are slower and act for longer
• Pituitary gland in brain = master gland
• Thyroid gland controls growth rate and metabolism
• Adrenal gland releases adrenalin which prepares body for fight or flight response
• Ovaries release oestrogen and progesterone (female sex hormones)
• Testes produce testosterone (male sex hormone)
• Blood glucose concentration is monitored and controlled by the pancreas
• pancreas releases more of the hormone insulin
• Insulin causes glucose to move from the blood into the cells.
• in liver and muscle cells, excess glucose is converted to glycogen for storage
• Type 1 diabetes

  • cause = pancreas failing to produce sufficient insulin
  • result= uncontrolled high blood glucose levels
  • Treated = monitoring blood sugar levels and injecting insulin when they are too high
• Type 2 diabetes

  • caused = by body cells losing the ability to respond to insulin
  • obesity risk factor
  • treated = with carbohydrate controlled diet and regular exercise
  • have to take drugs to control blood sugar levels
• In people with type 1 diabetes the insulin lowers the blood glucose level by stimulating the liver to convert it into glycogen
• Hormones play roles in controlling human reproduction
• During puberty, sex hormones cause secondary sexual characteristics to develop
• Oestrogen- main female sex hormone at puberty eggs begin to mature and be released this is called ovulation
• Testosterone- main male sex hormone produced by the testes and stimulates sperm reproduction
• Progesterone - prepares uterus lining for implantation of fertilised egg if pregnancy occurs
• Fsh ( follicle stimulating hormone) secreted by pituitary gland causes eggs to mature in the ovaries in first part of the cycle
• Oestrogen- ovaries makes the lining of the uterus grow again after menstruation
• LH ( luteinising hormon) pituitary gland stimulates the release of the egg from the ovary