The Endocrine System

Endocrine system

The system in the body responsible for sending information as chemical signals through glands and hormones.

Gland

A group of specialised cells that secrete useful substances like hormones.

Hormones

Chemical messengers that are secreted by glands in response to stimuli and travel through the blood to specific target cells.

Target cells

Cells with specific receptors for a particular hormone, where the hormone triggers a response.

What is the stimulus triggered by hormones?

Low blood glucose concentration

What are the receptors?

Receptors on pancreas cells detect the low blood glucose concentration

What is the hormone?

The pancreas releases the hormone glucagon into the blood

What are the effectors?

Target cells in the liver detect glucagon and convert glycogen into glucose

What is the response to the hormone being triggered?

Glucose is released into the blood, so glucose concentration increases

Hypothalamus

Produces hormones that control the pituitary gland and plays a role in coordinating the 'fight or flight' response.

Pituitary gland

Known as the 'master gland,' it releases hormones that control other glands in the endocrine system.

Pineal gland

Responsible for the production of melatonin, which plays a role in the control of sleep patterns

Thyroid gland

Produces hormones such as thyroxine. The is responsible for controlling the body’s metabolic rate, as well as regulating growth and maturation

Parathyroid gland

Produces a hormone called the parathyroid hormone. This helps control the levels of minerals such as calcium within the body

Thymus Gland

Regulates the immune system

Adrenal glands

Produce hormones like adrenaline and are responsible for the 'fight or flight' response in stressful situations.

Pancreas

Releases insulin and glucagon to regulate blood sugar levels.

Gonads (ovaries and testes)

Produce sex hormones, e.g. testosterone and oestrogen. These are important in reproduction and the development of sex organs and secondary sexual characteristics

Why is the endocrine system’s communication slower, long-lasting and widespread?

• Hormones aren’t released directly onto their target cells- they must travel in the blood to get there. This means that chemical communication (by hormones) is slower than electrical communication (by nerves

• They aren’t broken down as quickly as neurotransmitters, so the effects of hormones can last for much longer

• Hormones are transported all over the body, so the response may be widespread if the target cells are widespread

'Fight or flight' response

A physiological reaction triggered by the hypothalamus in response to stress, preparing the body for action.

What happens when the ‘fight or flight’ response is activated?

• Heart: Heart rate increases, pushing blood to the heart, muscles, and other vital organs 

• Lungs: The breathing rate increases, and the small airways in the lungs open to allow for more oxygen intake 

• Blood sugar: The liver releases glucose, and the body breaks down glycogen to increase blood glucose concentrations 

• Senses: Pupils dilate, and sight, hearing, and other senses become sharper 

• Skin: Skin may become pale or flushed, and blood flow increases to muscles 

• Adrenaline: Adrenaline surges into the bloodstream 

• Bladder: The bladder relaxes

Noradrenaline

Hormone released by the adrenal medulla in response to stress, affecting blood pressure, heart rate, and other bodily functions.