Biology Edexcel Topic 7 (Hormonal control)

7.1 to 7.3

What is the endocrine system

A network of glands that produce and secrete hormones into the bloodstream

What is a hormone

Chemical messengers released by glands into the blood and carried to a target organ or organs

Compare the endocrine and nervous systems

The endocrine system uses hormones, which travel in the bloodstream to reach the target organ, it has a slower response and lasts until all hormones have broken down (a long time), but the nervous system uses nerve impulses, which travel via neurones to reach the effectors, it has a faster response, and lasts until the nerve impulse stops (a short time)

What is the pituitary gland

An endocrine gland that produces hormones which control other glands

What are the adrenal glands

Endocrine glands that produce adrenaline

Where are the adrenal glands located

Above the kidneys

What is adrenaline

A hormone produced by the adrenal glands involved in the fight or flight response (where the body prepares to confront danger or flee from it)

State 4 effects of adrenaline on the body

Increases heart rate, blood pressure, blood flow to muscles and blood glucose levels

Describe how adrenaline increases heart rate and blood pressure

It travels in the blood to the heart, binding to specific receptors on the cells in the heart, causing the heart muscles to contract more forcefully and frequently, increasing heart rate and blood pressure

Describe how adrenaline increases blood sugar levels and respiration at muscle tissues

Adrenaline binds to specific receptors on cells in the liver, triggering the breakdown of glycogen and release of glucose, increasing blood glucose levels, the increased heart rate from adrenalin binding to cells in the heart causes greater blood flow to the muscles, so muscle cells receive more oxygen and glucose for respiration

What is negative feedback

A response to when conditions change from the ideal or set point which returns conditions to this set point

What is the thyroid gland

An endocrine gland that produces thyroxine

Where is the thyroid gland located

In the neck

What is thyroxine

A hormone secreted by the thyroid gland that controls metabolic rate, heart rate and temperature

What is metabolic rate

The rate at which biochemical reactions occur in cells

Describe how thyroxine is released

Hypothalamus releases TRH, which stimulates the pituitary gland to release TSH, which stimulates the release of thyroxine from the thyroid gland

What does TRH stand for

Thyrotropin releasing hormone

What does TSH stand for

Thyroid stimulating hormone

Describe how a negative feedback system controls blood thyroxine levels

If blood thyroxine levels increase above a set point, TRH secretion in inhibited, inhibiting TSH release, which causes less thyroxine to be produced by the thyroid gland, returning the thyroxine levels to normal, and if blood thyroxine levels decrease below a set point, TRH secretion is increased, increasing TSH release, which causes more thyroxine to be produced by the thyroid gland, returning thyroxine levels to normal

How do the ovaries act as an endocrine gland

They secrete oestrogen into the bloodstream

How do the testes act as an endocrine gland

They secrete testosterone into the bloodstream