Hormones and the Endocrine System: Your Body’s Chemical Messengers

What Are Hormones?

• Hormones are chemical substances produced by glands that travel through your blood to target specific organs and tell them what to do.

Analogy: Think of hormones as letters sent to specific addresses (target organs). Only the right organ (the address) responds to the message.

 

The Endocrine System: Your Body’s “Postal Service”

• The endocrine system is a collection of glands that produce hormones.
• Unlike the nervous system, which uses electrical signals, the endocrine system works with chemical messages.

 

 

Gland	Hormone Produced	Target Organ(s)	Effect
Adrenal glands	Adrenaline	Heart, muscles, liver	Prepares the body for "fight or flight" (e.g., faster heart rate).
Pancreas	Insulin and glucagon	Liver, body cells	Regulates blood glucose levels.
Testes	Testosterone	Male reproductive organs	Controls development of male characteristics.
Ovaries	Oestrogen	Female reproductive organs	Controls development of female characteristics.

 

Endocrine and Transport around the body

 

• The endocrine glands transport blood directly to the bloodstream so they need a good blood supply. 
• The liver helps to control the amount of the hormone that is in the bloodstream. 
• It is important that the hormones only affect the intended receptor. As a result the cells have target receptors on the cell membrane  or inside the cell.
• The hormone can only bond to that particular target.

 

Important Hormones that the body creates

 

Hormone	Source	What it does	How it affects the body
Adrenaline	Adrenal gland	Allows the body to enter a 'fight or flight' state. Helps protect the body	Pupils dilates, increases the breating and heart rate
Testosterone	Testes	The main sex hormone in males	Develops the secondary sex characteritics in males
Oestrogen	Ovaries	The main sex hormone in females	Develops the secondary sex characteritics in females
Insulin	Pancreas		Tells the body to transport the extra glucose in the body to the liver where its turned into glycogen for storage

 

Adrenaline: The “Fight or Flight” Hormone

• When you face danger, your adrenal glands release adrenaline.
• This hormone prepares your body for action.

 

Effect	Why It Happens
Increased breathing rate	To supply more oxygen to muscles.
Increased heart rate	To pump blood (and oxygen) faster around the body.
Increased pupil diameter	To let in more light and improve vision.
Increased blood glucose concentration	To provide extra energy through respiration for muscles during the "fight or flight" response.

 

Nervous System vs. Hormonal Control

Feature	Nervous System	Hormonal System
Signal Type	Electrical signals (impulses).	Chemical signals (hormones).
Speed of Action	Very fast.	Slower.
Duration of Effect	Short-lived.	Long-lasting.
Transport Pathway	Nerves, spinal cord, brain	Glands

Analogy:
The nervous system is like sending a text message—instant but short-lived. The endocrine system is like sending a letter—slower but impactful over time.