Homeostasis and response

• Explain how the body responds to the core temperature decreasing? (6 marks)

  • The receptors in the brain detect the temperature is too low
  • An electrical impulse is sent to the muscles that start to shiver, which allows the body to release energy through respiration, warming up the body.
  • Hair stands on end to trap heat in an insulating layer.
  • Blood vessels supplying the skin constrict so less energy is lost to the surroundings.
• Explain how the body responds if the core temperature is too high? (6 marks)

  • The receptors in the brain detect the temperature as too high.
  • Sends an electrical impulse to the sweat glands which release sweat, which evaporates and cools the skin.
  • Blood vessels widen so more heat can be lost into the surroundings through the skin.
• Explain how the brain monitors body temperature? (3 marks)

  • The thermoregulatory system has receptors that monitor blood temperature as it flows through the brain.
  • Additionally, temperature receptors in the skin send electrical impulses to the brain/ thermoregulatory system.
• How does the body control blood glucose levels? (6 marks)

  • The pancreas detects that the blood glucose is too high, so it releases insulin.
  • The insulin converts glucose into glycogen in the liver.
  • The pancreas detects that the blood glucose is too low, so it releases glucagon.
  • The glucagon converts glycogen back into glucose in the liver, increasing the levels of glucose in the blood.
• Describe how a healthy kidney produces urine (5 marks)

  • The kidney filters the blood.
  • Then it reabsorbs all the glucose.
  • It also reabsorbs some ions and some water.
  • The kidney releases urea in the urine.
• Describe how the water content of the blood is controlled (6 marks)

  • If water content is too low, the pituitary gland releases ADH into the blood.
  • This causes the kidneys to reabsorb more water into the blood so the urine becomes more concentrated/ has less water.
  • If the water content is too high, the pituitary gland releases less ADH into the blood.
  • This causes the kidney to reabsorb less water into the blood so the urine becomes more dilute with water.
• Amino acids cannot be stored in the body. Describe what happens to the acids that cannot be stored. (3 marks)

  • Amino acids are broken down into fats and carbohydrates by deamination.
  • Ammonia is a waste product of deamination.
  • Ammonia is converted into urea.
  • Urea is removed/filtered by the kidney and released in urine.
• Describe the advantages and disadvantages of having a kidney transplant over dialysis (4 marks)

  • Less risk of infection due to needles like dialysis.
  • Cheaper in the long term.
  • Less time spent in hospitals- dialysis is 3-4 hours 3 times a week.
  • There is a risk of the transplant being rejected by the body.
• What is meant by the term ‘reflex action?’ (2 marks)

  • A rapid, involuntary response to stimuli
  • That does not involve the conscious part of the brain.
• Describe how hormones control the menstrual cycle (5 marks)

  • Oestrogen is produced in the ovaries.
  • It inhibits FSH production and it stimulates LH production.
  • FSH is released from the pituitary gland.
  • It stimulates the maturation of an egg.
  • LH is released from the pituitary gland.
  • It stimulates ovulation.
  • Progesterone is released from the ovaries.
  • It inhibits FSH and LH production.
  • Oestrogen and Progesterone maintain the lining of the uterus.
• How does the eye respond as the light changes from dim to bright? (3 marks)

  • The circular muscles contract and the radial muscles relax.
  • This makes the pupil smaller
  • So less light is taken in so the eye does not get damaged.
• How does the eye respond to bright to dim light? (3 marks)

  • The circular muscles relax and the radial muscles contract.
  • This dilates the pupil so it becomes bigger
  • So it takes in more light so the person can see.
• How does the eye adjust when focusing on a near object? (3 marks)

  • The ciliary muscles contract and the suspensory ligaments slacken.
  • This makes the lens fatter/curved
  • So more light is refracted to focus the image at the retina.
• How does the eye adjust to seeing a distant object?

  • The ciliary muscles slacken and the suspensory ligaments contract.
  • This makes the lens thinner
  • So less light is refracted so that the image can be focused at the retina.