Homeostasis

• Define ‘Homeostasis’


  The regulation of conditions inside the body to maintain a stable, internal environment in response to internal or external conditions
• What does our body use to recognise a change from optimal conditions, sending a signal to reverse this?


  Automatic control system
• Automatic control systems contain:

  Receptors - Detect a change

  Coordination centres- Interpret that change

  Effectors- Carry out the change, e.g muscles or glands
• What are muscles and glands?

  Muscles - Contract when stimulated

  Glands- Release hormomes
• What do the nervous system and the endocrine system do?


  Send signals
• What is negative feedback?


  Decreases/Increases specific levels e.g blood glucose levels
• Where is the source of the hormone ADH and what is it's target organ?

  Source: Pituitary gland

  Target organ: Kidneys
• What is the role of the hormone ADH?

  Controls the water content of the blood
• What effects does the hormone ADH have on the body?

  • Increases reabsorption of water by the collecting ducts
• Where is the source of the hormone adrenaline and what is it's target organ?

  Source: Adrenal glands

  Target organs: Respiratory and circulatory systems
• What is the role of the hormone adrenaline?

  Prepares the body for 'fight or flight'
• What are the effects of the hormone adrenaline?

  • Increases breathing rate
  • Increases heart rate
  • Increases flow of blood to muscles
  • Increases conversion of glycogen to glucose
• Where is the source of the hormone insulin and what is it's target organ?

  Source: Pancreas

  Target organ: Liver
• What is the effect of insulin?

  Increases conversion of glucose to glycogen for storage
• Which parts of the brain have a role in detecting and controlling thyroxine levels?

  Hypothalamus and pituitary gland
• What happens if thyroxine levels in the bloodstream are too low?

  • Stimulates the hypothalamus to release TRH
  • This causes the pituitary gland to release TSH so the thyroid releases more thyroxine
  • Blood levels return to normal
• What happens if thyroxine levels in the bloodstream are normal (to maintain it?)

  • Inhibit TRH release from the hypothalamus
  • This inhibits the release of TSH from the pituitary gland
  • Normal blood levels are maintained
• Is adrenaline controlled by negative feedback?

  No
• What is another effect that adrenaline has on the body?

  Diverts blood away from areas, such as the digestive system and towards the muscles
• What 2 hormones help changes occur in puberty?

  • Testosterone (Male)
  • Oestrogen (Female)
• State 4 changes that happens to boys during puberty:

  • Voice breaks
  • Hair grows on face and body
  • Body becomes more muscular
  • Testes start to produce sperm cells
• State 3 changes that happen to both boys and girls during puberty:

  • Pubic hair grows
  • Underarm hair grows
  • Sexual organs grow and develop
• State 4 changes that happen to girls during puberty:

  • Voice deepens gradually
  • Hips get wider
  • Breasts develop
  • Ovaries start to release egg cells (Menstruation starts)