4.5.3.7 Negative Feedback (HT only)

Question 1

What are hormones?

Answer 1

• hormones are chemicals that are released directly into the bloodstream by glands
• hormones then cause an effect in specific target organs

Question 2

Examples of negative feedback cycles:

Answer 2

• control of blood glucose
• menstrual cycle
• thyroxine levels in blood

Question 3

Where are the adrenal glands located?

Answer 3

top of the kidney

Question 4

What is the function of the adrenal gland?

Answer 4

• during times of fear or stress the adrenal glands produce the hormone adrenaline
• the adrenaline is released into the blood

Question 5

What are the effects of the hormone adrenaline?

Answer 5

• increases the heart rate as the heart is beating faster more oxygen and glucose are delivered in the blood to the brain and muscles
• both oxygen and glucose needed for aerobic respiration
• prepares the body to fight or runaway - “fight or flight”

Question 6

Where is the thyroid gland located?

Answer 6

found in the base of the neck and this releases the hormone thyroxine

Question 7

What are the main affects of the hormone thyroxine?

Answer 7

• stimulates the body’s basal metabolic rate
  
  • metabolism is sum of all reactions in a cell or the body
  • so thyroxine makes the body’s chemical reactions take place at a faster rate
• plays an important role in growth and in development

Question 8

What is the level of thyroxine in the blood controlled by?

Answer 8

• levels of thyroxine is controlled by negative feedback
• the level of thyroxine in the blood is monitored by the brain
• when the thyroxine level falls the pituitary gland releases the hormone TSH into the bloodstream
• TSH triggers the thyroid gland to release more thyroxine into the blood
• the increased level of thyroxine is now detected by the brain - now prevents pituitary gland from releasing TSH
• as TSH level falls the thyroid gland releases less thyroxine
• if level of thyroxine falls events are triggered which cause the level of thyroxine to increase
• if the level of thyroxine becomes too high, events are triggered to bring it back down
• negative feedback cycle

Question 9

What does an increase in the activity of the thyroid gland cause?

Answer 9

• more thyroxine released into blood
• raises BMR
• increase in formation of glycogen/lipid/proteins
  OR
• increase in rate of respiration
  OR
• increase in breakdown of excess proteins