4.5.3.1 - Human Endocrine System

Hormonal coordination

A gland is an organ or group of cells that secretes a substance. An endocrine gland secretes chemicals called hormones directly into the bloodstream. The endocrine system is the group of these glands working together to coordinate and control body processes.

This is the basic sequence for hormonal coordination:

1. An endocrine gland secretes a hormone.
2. The hormone enters the bloodstream directly.
3. The blood carries the hormone around the body.
4. The hormone reaches a target organ.
5. The target organ responds and produces an effect.

The word directly matters. Endocrine glands do not release their hormones through ducts for this GCSE point; they release them into the blood.

Target organs

A target organ is the organ that a hormone acts on. The hormone may be carried all around the body in the blood, but the exam idea is that it produces its effect at the target organ.

Target-organ wording helps you avoid vague answers. Instead of writing "hormones travel around the body and do things", write that a hormone is carried in the blood to a target organ, where it produces a specific effect.

For this lesson, you do not need to learn named hormone effects such as insulin lowering blood glucose, ADH affecting the kidney, or reproductive hormones controlling the menstrual cycle. Those are later specification points. Here, the assessable principle is the route and the idea of a target organ.

When a question asks for a definition, keep it shorter than the full route. Name the organ and say that the hormone produces its effect there.

Compared with nervous coordination

Hormonal coordination is different from nervous coordination. AQA expects one simple comparison here: hormonal effects are usually slower but act for longer.

Nervous coordination uses electrical impulses along neurones. That can produce a very fast response, such as moving your hand away from something hot. Hormonal coordination uses chemicals carried in the blood. Because the hormones travel in the bloodstream and act through target organs, the effect usually takes longer to start.

Once a hormone has produced its effect, that effect can last longer than many nervous responses. A hormonal response is often useful when the body needs coordination over minutes, hours or longer rather than an immediate movement.

The pituitary as a master gland

The pituitary gland is in the brain. AQA describes it as a master gland because it secretes several hormones into the blood in response to body conditions.

Some pituitary hormones act on other glands. These other glands then release their own hormones, bringing about effects in the body. That means the pituitary can coordinate a chain of hormonal control: