Hormones: adrenaline and thyroxine - Higher

In a nutshell

Adrenaline and thyroxine are hormones produced by the body. The production of thyroxine is an example of negative feedback. Adrenaline is produced in response to stress.

Thyroxine

Thyroxine is a hormone produced by the thyroid gland. It controls metabolic rate which is the rate at which cells respire and is measured as the rate of energy transfers in the body. Thyroxine production is controlled by negative feedback.

Negative feedback

Definition

When the amount of something gets too high, the negative feedback system will decrease it. If the amount of something gets too low, the negative feedback system will increase it.

Biology; Animal coordination, control and homeostasis; KS4 Year 10; Hormones: adrenaline and thyroxine - Higher

Negative feedback and thyroxine

When the concentration of thyroxine in the blood is too low, a corrective mechanism will be stimulated. The hypothalamus will secrete more thyrotropin-releasing hormone which causes the pituitary gland to produce thyroid stimulating hormone. This will cause the thyroid to produce more thyroxine.

When the concentration of thyroxine is too high, thyrotropin-releasing hormone production by the hypothalamus is inhibited which causes less thyroxine to be produced.

Adrenaline

Adrenaline is a hormone produced by the adrenal glands in response to stress. When your brain detects stress, it sends nerve impulses to the adrenal glands, which causes them to secrete adrenaline.

Adrenaline is what causes the 'fight or flight' response. Fight or flight refers to either standing your ground in a threatening situation or bravely running away. It causes this response by activating processes that increase the supply of oxygen and glucose to cells.

Effects of adrenaline

Target organ	Effect
Liver	It binds to liver receptors and causes the liver to convert glycogen to glucose which is released into the blood. This increases the blood glucose level so there is more glucose in the blood to be transported to cells.
Heart	It binds to specific receptors in the heart that cause the heart muscle to contract more often and more forcefully. This increases heart rate and blood pressure. This increases blood flow to muscles so muscle cells receive more oxygen and glucose for respiration.
Blood vessels	It constricts some blood vessels to make blood pressure higher and dilates other blood vessels to increase blood flow to muscles.