Biology-Homeostasis

• 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 information from receptors
  • Effectors - bring about responses to return conditions to optimum levels
• Response to a stimulus

  1. Receptor cells convert stimulus into electrical impulse

  2. Impulse travels along sensory neurons to central nervous system

  3. Information processed and appropriate response coordinated

  4. Impulse sent along motor neurons to effectors

  5. Effectors carry out response
• Reflex

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

  1. Stimulus detected by receptors

  2. Impulses sent along sensory neuron

  3. Impulse passes to relay neuron in central nervous system

  4. Impulses sent along motor neuron

  5. Impulse reaches effector resulting in response
• Synapse


  The gap between two neurons where a chemical is released to trigger the impulse in the next neuron
• Reaction time


  How long it takes 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 cannot always reach the brain
  • 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 near object: Ciliary muscles contract, suspensory ligaments loosen, lens becomes thicker and more curved

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

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


  Long sightedness - lens is too flat so it cannot refract light enough
• Treatments for eye defects

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


  • Monitors and controls body temperature
  • Has receptors that monitor blood temperature
  • Has receptors in skin that send impulses
• Mechanisms to regulate body temperature when too high

  1. Sweat is produced from sweat glands

  2. Vasodilation - more blood flows closer to skin surface
• Mechanisms to regulate body temperature when too low

  1. Sweating stops

  2. Skeletal muscles contract rapidly (shivering)

  3. Hairs stand on end to create insulating layer

  4. Vasoconstriction - blood does not flow as close to surface
• Endocrine system


  Communication system that sends hormones (chemical messengers) around the body
• Glands in 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
• Blood glucose concentration

  Needs to be kept within a certain limit as glucose is needed by cells for respiration
• Pituitary gland

  Controls metabolic rate, heart rate and temperature
• Adrenal gland

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

  • Secretes oestrogen
  • Is involved in the menstrual cycle and the development of female secondary sexual characteristics (different features that develop during puberty that distinguish a female from a male)
• Testes


  • Secretes testosterone
  • Is 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
• 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
• 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
• 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
  • Doctors are attempting to cure diabetes with pancreas and pancreatic cell transplants, and genetically engineering pancreatic cells from mice to make insulin
• 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
• Kidneys

  • Very important in maintaining the balance of water and other substances in the body
  • As blood moves through the body, it makes urine by filtering out the waste products and 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
  • An increased amount of ADH reaching the tubules increases their permeability to water, so more moves out of the tubule and back into the bloodstream
  • This results in a smaller volume of more concentrated (yellow) urine and the blood becoming less concentrated as more water moves into it