5 Homeostasis and Response (5.3 and 5.4)

• Endocrine System = coordinates the body's response to changes in the environment using chemical messenger, hormones
• Hormones are released by the endocrine glands into the bloodstream where they travel to target organs
• Name the 7 Endocrine Glands

  1. Pituitary Gland
  2. Thyroid Gland
  3. Thymus
  4. Adrenal Gland
  5. Pancreas
  6. Ovaries
  7. Testes
• Pituitary Gland is found in the brain, linked to the hypothalamus
• Hypothalamus is the part of the brain that receives signals from receptors
• The pituitary gland is knowns as the "master gland", as it releases hormones in response to changes detected by the hypothalamus
• The thyroid gland releases thyroxines which controls the rate that glucose is used up
• Thyroid gland is found in our neck
• the thyroid gland regulates metabolism, heart rate and temperature
• Adrenal gland are two glands situated above the kidney
• the adrenal gland releases adrenaline which triggers a "fight or flight" response when an organism is presented with danger
• Pancreas produces insulin and glucagon, which control blood glucose levels
• The ovaries release oestrogen and progesterone, which regulate the menstrual cycle
• The testes produce testosterone which controls puberty and sperm production
• The thymus is located in the chest between the lungs
• The thymus releases thymosin which promotes the productions of white blood cells
• Thyroxine regulates metabolism by controlling how quickly food is broken down into energy
• What happens if we have too much glucose?

  Water will leave red blood cells via osmosis through the cell membrane, this causes red bloods cells to shrivel and become unable to carry oxygen
• What happens if we have too little glucose?

  1. Water will move from the plasma to the red blood cells via osmosis, causing them to swell and even burst
  2. An organism cannot produce enough energy through respiration
• What happens in our body when blood sugar falls?

  1. Pancreas detects fall
  2. Pancreas secretes glucagon into the bloodstream
  3. Glucagon travels to the liver
  4. Liver converts glycogen to glucose and releases it into the blood
  5. Blood glucose returns to normal
• What happens in our body when blood sugar rises?

  1. Pancreas detects the rise in blood glucose
  2. Pancreas secretes insulin into the bloodstream
  3. Insulin travels to the liver
  4. Liver absorbs the glucose and converts it into glycogen
  5. Blood glucose returns to normal
• Diabetes is a disorder where a person cannot control their blood glucose concentration on their own
• Type 1 diabetes is caused by the body's immune system accidentally attacking pancreas cells, this causes the pancreas to no longer make insulin, so their blood sugar rises
• Type 2 diabetes is caused by poor diet and obesity over a period of time, this causes the liver to be unable to recognise insulin in blood as a consequence blood sugar rises
• What is the treatment for type 1 diabetes?

  Inject insulin when blood glucose levels rise (can also manage diet and health to keep blood glucose levels steady)
• What is the treatment for type 2 diabetes?


  Must manage diet and exercise to keep blood sugar levels steady
• How can type 1 diabetes be cured?

  People who suffer from it can receive a pancreas transplant from an organ donor who has died
• What are the symptoms of type 1 diabetes?

  Excess urine, feeling thirsty, losing weight or feeling tired
• What is negative feedback?


  A control system responds when conditions aren't ideal and return conditions to an ideal level, it is a continuous cycle
• What does thyroxine do?

  Controls the rate at which energy is used by an organism at rest
• thyroxine levels are controlled by negative feedback
• What happens when thyroxine levels fall?

  1. Stimulates the hypothalamus to release TRH
  2. causes the pituitary to release TSH
  3.  thyroid releases more thyroxine
  4. Blood levels return to normal
• What happens when thyroxine levels rise?

  1. inhibit TRH release from the hypothalamus 
  2. inhibits the release of TSH
  3. Normal blood levels remain
• What does adrenaline do?

  Heart rate and breathing rate increase, glycogen is converted to glucose for respiration, pupils dilate to let in more light, blood is diverted form digestive system to your muscles in your arms and legs
• Why are adrenaline levels not controlled by negative feedback?


  Once the danger is over organs return to normal as adrenaline is not released anymore, therefore not needing a negative feedback loop as it is only needed in certain circumstances
• Hormonal-based contraceptions = uses hormones (from the menstrual cycle) to prevent pregnancy
• How does the contraceptive pill work?

  Uses female hormones such as progesterone and oestrogen to inhibit FSH, so no eggs mature, preventing pregnancy
• What is a contraceptive implant?

  A small device inserted under the skin that releases progesterone to prevent pregnancy.
• How does the contraceptive patch work?

  It contains a mixture of oestrogen and progesterone, it is stuck onto your skin and the hormones are absorbed directly into your blood
• Spermicide = A chemical substance which will kill the sperm and prevent it from reaching the egg