Bio paper 2

• Homeostasis


  The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
• What does Homeostasis controll

  • Maintains optimal conditions for enzyme action and all cell functions
  • Includes control of blood glucose concentration, body temperature, water levels
  • May involve nervous responses or chemical responses
• Homeostatic control systems

  1. Receptors detect stimuli (changes in the environment)

  2. Coordination centres (such as the brain, spinal cord and pancreas) receive and process information from receptors

  3. Effectors, muscles or glands, bring about responses which restore optimum levels
• what does the Nervous system allow

  Enables humans to react to their surroundings and to coordinate their behaviour
• how does the nervous system work

  1. Information from receptors

  2. Passes along cells (neurones) as electrical impulses

  3. To the central nervous system (CNS)

  4. CNS coordinates the response of effectors
• Central nervous system (CNS)


  The brain and spinal cord
• Effector- example

  Muscles contracting or glands secreting hormones
• Reflex arc


  • Sensory neurone
  • Synapse
  • Relay neurone
  • Motor neurone
• Reflex actions


  Automatic and rapid, do not involve the conscious part of the brain
• The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions. Neuroscientists have been able to map the regions of the brain to particular functions by studying patients with brain damage, electrically stimulating different parts of the brain and using MRI scanning techniques. The complexity and delicacy of the brain makes investigating and treating brain disorders very hard
• To focus on a near object: • the ciliary muscles contract • the suspensory ligaments loosen • the lens is then thicker and refracts light rays strongly. To focus on a distant object: • the ciliary muscles relax • the suspensory ligaments are pulled tight • the lens is then pulled thin and only slightly refracts light rays.
• Two common defects of the eyes are myopia (short sightedness) and hyperopia (long sightedness) in which rays of light do not focus on the retina. ;Generally these defects are treated with spectacle lenses which refract the light rays so that they do focus on the retina. ; New technologies now include hard and soft contact lenses, laser surgery to change the shape of the cornea and a replacement lens in the eye.
• Thermoregulatory centre


  Part of the brain that monitors and controls body temperature
• Thermoregulatory centre


  • Contains receptors sensitive to the temperature of the blood
  • Receives nervous impulses from temperature receptors in the skin
• Body temperature too high

  1. Blood vessels dilate (vasodilation)

  2. Sweat is produced from the sweat glands
• Blood vessels dilating and sweating


  Causes a transfer of energy from the skin to the environment
• Body temperature too low

  1. Blood vessels constrict (vasoconstriction)

  2. Sweating stops

  3. Skeletal muscles contract (shiver)
• The endocrine system is composed of glands which secrete chemicals called hormones directly into the bloodstream. The blood carries the hormone to a target organ where it produces an effect. Compared to the nervous system the effects are slower but act for longer.The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the blood in response to body conditions. These hormones in turn act on other glands to stimulate other hormones to be released to bring about effects.
• Blood glucose concentration


  Monitored and controlled by the pancreas
• When blood glucose is too high

  1. Pancreas produces insulin

  2. Insulin causes glucose to move from blood into cells

  3. Excess glucose converted to glycogen for storage in liver and muscle cells
• Type 1 diabetes


  • Disorder where pancreas fails to produce sufficient insulin
  • Characterised by uncontrolled high blood glucose levels
  • Normally treated with insulin injections
• Type 2 diabetes


  • Body cells no longer respond to insulin produced by pancreas
  • Commonly treated with carbohydrate controlled diet and exercise regime
• Obesity


  Risk factor for Type 2 diabetes
• When blood glucose is too low

  1. Pancreas produces glucagon

  2. Glucagon causes glycogen to be converted into glucose

  3. Glucose released into the blood
• Water loss from the body

  1. Exhalation from the lungs

  2. Sweat from the skin
• There is no control over water, ion or urea loss by the lungs or skin
• Removal of excess water, ions and urea


  Kidneys in the urine
• Body cells lose or gain too much water by osmosis


  They do not function efficiently
• Digestion of proteins from the diet

  1. Excess amino acids

  2. Deamination in the liver to form ammonia

  3. Conversion of ammonia to urea for safe excretion
• Kidneys produce urine


  1. Filtration of the blood

  2. Selective reabsorption of useful substances such as glucose, some ions and water
• ADH


  Hormone released by the pituitary gland when the blood is too concentrated, causing more water to be reabsorbed back into the blood from the kidney tubules
• ADH is controlled by negative feedback
• Kidney failure treatment


  • Organ transplant
  • Kidney dialysis
• Puberty


  when Reproductive hormones cause secondary sex characteristics to develop
• Oestrogen


  The main female reproductive hormone produced in the ovary
• Ovulation


  when One egg is released approximately every 28 days
• Testosterone


  • The main male reproductive hormone produced by the testes
  • It stimulates sperm production
• Hormones involved in the menstrual cycle

  • Follicle stimulating hormone (FSH)
  • Luteinising hormone (LH)
  • Oestrogen
  • Progesterone
• Follicle stimulating hormone (FSH)


  • Causes maturation of an egg in the ovary
• Luteinising hormone (LH)


  • Stimulates the release of the egg