Homeostasis and Response

• Homeostasis


  The maintenance of a constant internal environment
• What homeostasis controls in the human body

  • Blood glucose concentration
  • Body temperature
  • Water levels
• Control systems


  • Receptors - cells that detect stimuli
  • Coordination centres - process the information received from the receptors
  • Effectors - bring about responses to bring the conditions in the body back to optimum levels
• Response to a stimulus

  1. Receptor cells convert a stimulus into an electrical impulse

  2. Electrical impulse travels along sensory neurons to the central nervous system

  3. Information is processed and the appropriate response is coordinated

  4. Electrical impulse is sent along motor neurons to effectors

  5. Effectors carry out the response
• Reflex


  Automatic responses which take place before you have time to think
• Reflex arc


  1. Stimulus is detected by receptors

  2. Impulses are sent along a sensory neuron

  3. In the CNS the impulse passes to a relay neuron

  4. Impulses are sent along a motor neuron

  5. The impulse reaches an effector resulting in the appropriate response
• Synapse


  The gaps between two neurons
• Reaction time


  How long it takes you to respond to a stimulus
• Components of the brain


  • Cerebral cortex
  • Cerebellum
  • Medulla
• Challenges in investigating brain function and treating brain damage/disease


  • It is complex and delicate
  • It is easily damaged
  • Drugs given to treat diseases cannot always reach the brain because of the membranes that surround it
  • It is not fully understood which part of the brain does what
• Methods used by neuroscientists to map brain function


  1. Studying patients with brain damage

  2. Electrically stimulating different parts of the brain

  3. Using MRI scanning techniques
• Structures within the eye


  • Retina
  • Optic nerve
  • Sclera
  • Cornea
  • Iris
  • Ciliary muscles and suspensory ligaments
• Accommodation


  1. To focus on a near object: Ciliary muscles contract, suspensory ligaments loosen, lens becomes thicker and more curved

  2. To focus on a distant object: Ciliary muscles relax, suspensory ligaments tighten, lens becomes thinner
• Myopia


  Short sightedness - the lens is too curved, so distant objects appear blurry
• Hyperopia


  Long sightedness - the lens is too flat, so it cannot refract light enough
• Treatment methods for eye defects


  • Spectacle lenses
  • Contact lenses
  • Laser eye surgery
  • Replacement lens
• Thermoregulatory centre


  • Monitors and controls body temperature
  • Has receptors that monitor the temperature of the blood
  • Has receptors in the skin that send impulses to the thermoregulatory centre
• Mechanisms to regulate body temperature when it is too high


  • Sweat is produced from sweat glands
  • Vasodilation - more blood flows closer to the surface of the skin
• Mechanisms to regulate body temperature when it is too low

  • Sweating stops
  • Skeletal muscles contract rapidly (shivering) to generate heat from respiration
  • Hairs stand on end to create an insulating layer, trapping warm air
  • Vasoconstriction - blood does not flow so close to the surface
• Endocrine system


  Communication system that sends hormones (chemical messengers) around the body
• Glands that make up the endocrine system


  • Pituitary gland
  • Pancreas
  • Thyroid
  • Adrenal gland
  • Ovary
  • Testes
• Compared to the nervous system, the hormonal system is much slower but it acts for longer
• Control of blood glucose concentration


  The concentration of glucose in your blood needs to be kept within a certain limit because glucose is needed by cells for respiration. It is controlled by the pancreas.
• Pituitary gland


  Secretes anti-diuretic hormone (ADH)
• Adrenal gland


  • Secretes adrenaline
  • Involved in the 'fight or flight' response (the body's response to stressful situations)
• Ovary


  • Secretes oestrogen
  • Involved in the menstrual cycle and the development of female secondary sexual characteristics
• Testes


  • Secretes testosterone
  • Involved in the production of sperm and the development of male secondary sexual characteristics
• The blood transports the hormone to a target organ or tissue where it has an effect
• Control of Blood Glucose Concentration


  1. Eating foods that contain carbohydrates increases the glucose levels in the blood

  2. If the glucose levels are too high, the pancreas produces the hormone insulin

  3. Insulin binds to cell in target organs (muscles and liver) causing glucose to move from the blood into muscle cells for respiration and excess glucose to be converted into glycogen which is stored in the liver

  4. The blood glucose concentration is reduced

  5. If glucose levels decrease, the pancreas produces the hormone glucagon

  6. Glucagon binds to to the liver cells causing glycogen to be broken down into glucose

  7. Glucose is released into the blood, increasing the blood glucose concentration
• Your blood glucose concentration is kept constant through using these two hormones (insulin and glucagon). They work in a negative feedback loop
• Negative feedback loop


  When blood glucose levels increase/decrease, a hormone is secreted to oppose the change. The action of this hormone cannot occur continually because when the blood arrives at a certain glucose concentration the other hormone is produced, resulting in the opposite effect
• Type 1 diabetes


  The pancreas cannot produce enough insulin. Blood glucose level can rise to a fatal amount. Glucose is excreted with urine and lots of urine is produced leaving the individual very thirsty. It is treated with insulin injections at meal times, which results in glucose being taken up from the bloodstream. It is also advised to limit the intake of simple carbohydrates which contain lots of glucose
• Type 2 diabetes


  The body cells no longer respond to insulin. Blood glucose levels can rise to a fatal amount. Obesity is a risk factor for this disease. Treatments include reducing the number of simple carbohydrates in diet, losing weight and increasing exercise. There are also drugs to make insulin more effective on body cells, help the pancreas make more insulin or reduce the amount of glucose absorbed from the gut
• Osmosis


  The process by which water molecules move from a place where they are in high concentration to a place where they are in low concentration
• If the water concentration of the blood increases


  Cells in the body take up water
• If the water concentration of the blood decreases


  Cells in the body lose water
• If body cells lose or gain too much water by osmosis, they do not function properly
• The Kidneys


  1. Filtering out the waste products

  2. Selectively reabsorbing useful substances such as glucose, ions and water
• Waste products processed at the kidney

  • Water
  • Ions
  • Urea
• Anti-diuretic hormone (ADH)


  A hormone involved in the control of the loss of water as urine. It is released into the pancreas by the pituitary gland when a receptor in the brain detects that the blood is too concentrated. It travels in the bloodstream to the kidney tubules and increases their permeability to water, so more moves out of the tubule and back into the bloodstream, resulting in a smaller volume of more concentrated urine and the blood becoming less concentrated