MYP Integrated Sciences Topic Hormones Revision Notes

What Are Hormones?

Definition

Hormone

A chemical messenger released by glands that travels in the bloodstream to target organs, where it produces a specific response.

Hormones are chemical messengers released by endocrine glands.
They travel through the bloodstream to reach specific target cells in different organs.
Only cells with the correct receptors respond, which ensures each hormone triggers the right effect.
Hormones coordinate slow, long-lasting changes, such as growth, metabolism, and internal balance.

Definition

Receptor

A molecule on a target cell that detects and responds to a specific hormone.

Hint

Unlike nerves, which act quickly and locally, hormones regulate processes that need sustained control such as growth, metabolism, and blood composition.

Why Does the Body Need Hormones?

Hormones ensure different organ systems work together smoothly.
They adjust processes such as blood glucose levels, water balance, growth, and reproduction.
Because hormones travel in the blood, one signal can coordinate responses across the whole body.

Example

Insulin lowers blood glucose.
Adrenaline prepares the body for sudden action.
ADH controls water reabsorption in the kidneys.

What Is the Endocrine System?

Definition

Endocrine gland

A gland that makes and releases hormones directly into the bloodstream.

The endocrine system is the network of glands that produce and release hormones.
Major endocrine glands:
1. Pituitary gland: regulates many other glands.; often called the “master gland.”
2. Pancreas: controls blood glucose using insulin and glucagon.
3. Adrenal glands: release adrenaline during stress.
4. Thyroid gland: controls metabolic rate.
5. Ovaries/testes: produce sex hormones for reproduction and development.

How Does the Body Use Hormones to Maintain Homeostasis?

Hormones often work through negative feedback, a system that reverses changes to keep conditions stable.
When a factor moves outside a safe range, hormones are released to bring it back to normal.
When the factor returns to the correct level, hormone release decreases.

Example

Just as we covered in homeostasis, blood glucose levels are a good example of negative feedback:
- High glucose → insulin released → glucose stored → levels return to normal
- Low glucose → glucagon released → glucose released from liver → levels rise

What Does Adrenaline Do?

Adrenaline prepares the body for quick action during stress ("fight or flight").
It increases heart rate, widens air passages, and releases stored glucose for immediate energy.
These effects act quickly but last only a short time.

Common Mistake

Adrenaline does not control long-term stress.
It is a short-term emergency hormone.

How Do Hormones Control Growth and Development?

Growth hormone stimulates cell division and protein synthesis.
Sex hormones (oestrogen and testosterone) trigger puberty and the development of secondary sexual characteristics.
These changes occur gradually because hormones act over long periods.

What Are the Key Differences Between Nerves and Hormones?

Feature	Nervous System	Endocrine (Hormonal) System
Type of signal	Electrical impulses	Chemical signals (hormones) in the bloodstream
Speed	Very fast	Slower
Duration	Short-lasting	Long-lasting
Response nature	Precise and localized	Widespread but only affects target cells
Typical function	Immediate actions and rapid responses	Regulation of long-term processes and homeostasis

Active recall

What makes a hormone affect only certain cells?
How do insulin and glucagon act as a negative feedback pair?
Why is ADH essential for water balance?
Why are hormonal responses slower than nervous responses?
How does adrenaline prepare the body for rapid action?

What Are Hormones?

Definition

Hormone

A chemical messenger released by glands that travels in the bloodstream to target organs, where it produces a specific response.

Hormones are chemical messengers released by endocrine glands.
They travel through the bloodstream to reach specific target cells in different organs.
Only cells with the correct receptors respond, which ensures each hormone triggers the right effect.
Hormones coordinate slow, long-lasting changes, such as growth, metabolism, and internal balance.

Definition

Receptor

A molecule on a target cell that detects and responds to a specific hormone.

Hint

Unlike nerves, which act quickly and locally, hormones regulate processes that need sustained control such as growth, metabolism, and blood composition.

Why Does the Body Need Hormones?

Hormones ensure different organ systems work together smoothly.
They adjust processes such as blood glucose levels, water balance, growth, and reproduction.
Because hormones travel in the blood, one signal can coordinate responses across the whole body.

Example

Insulin lowers blood glucose.
Adrenaline prepares the body for sudden action.
ADH controls water reabsorption in the kidneys.

What Is the Endocrine System?

Definition

Endocrine gland

A gland that makes and releases hormones directly into the bloodstream.

The endocrine system is the network of glands that produce and release hormones.
Major endocrine glands:
1. Pituitary gland: regulates many other glands.; often called the “master gland.”
2. Pancreas: controls blood glucose using insulin and glucagon.
3. Adrenal glands: release adrenaline during stress.
4. Thyroid gland: controls metabolic rate.
5. Ovaries/testes: produce sex hormones for reproduction and development.

How Does the Body Use Hormones to Maintain Homeostasis?

Hormones often work through negative feedback, a system that reverses changes to keep conditions stable.
When a factor moves outside a safe range, hormones are released to bring it back to normal.
When the factor returns to the correct level, hormone release decreases.

Example

Just as we covered in homeostasis, blood glucose levels are a good example of negative feedback:
- High glucose → insulin released → glucose stored → levels return to normal
- Low glucose → glucagon released → glucose released from liver → levels rise

What Does Adrenaline Do?

Adrenaline prepares the body for quick action during stress ("fight or flight").
It increases heart rate, widens air passages, and releases stored glucose for immediate energy.
These effects act quickly but last only a short time.

Common Mistake

Adrenaline does not control long-term stress.
It is a short-term emergency hormone.

How Do Hormones Control Growth and Development?

Growth hormone stimulates cell division and protein synthesis.
Sex hormones (oestrogen and testosterone) trigger puberty and the development of secondary sexual characteristics.
These changes occur gradually because hormones act over long periods.

What Are the Key Differences Between Nerves and Hormones?

Feature	Nervous System	Endocrine (Hormonal) System
Type of signal	Electrical impulses	Chemical signals (hormones) in the bloodstream
Speed	Very fast	Slower
Duration	Short-lasting	Long-lasting
Response nature	Precise and localized	Widespread but only affects target cells
Typical function	Immediate actions and rapid responses	Regulation of long-term processes and homeostasis

Active recall

What makes a hormone affect only certain cells?
How do insulin and glucagon act as a negative feedback pair?
Why is ADH essential for water balance?
Why are hormonal responses slower than nervous responses?
How does adrenaline prepare the body for rapid action?

MYP Integrated Sciences Hormones Notes

MYP Integrated Sciences Hormones Notes

What Are Hormones?

Why Does the Body Need Hormones?

What Is the Endocrine System?

How Does the Body Use Hormones to Maintain Homeostasis?

What Does Adrenaline Do?

How Do Hormones Control Growth and Development?

What Are the Key Differences Between Nerves and Hormones?

What Are Hormones?

Why Does the Body Need Hormones?

What Is the Endocrine System?

How Does the Body Use Hormones to Maintain Homeostasis?

What Does Adrenaline Do?

How Do Hormones Control Growth and Development?

What Are the Key Differences Between Nerves and Hormones?

Science skills

Scale and structure

Classification and organisation

Materials and bonding

Chemical reactions

Energy

Forces and motion

Thermal physics

Electricity and magnetism

Waves

Atoms and space

Genetics and evolution

Body systems

Ecosystems and environment

Human impact and sustainability

Biotechnology and the future

MYP Integrated Sciences Hormones Notes

Science skills

Scale and structure

Classification and organisation

Materials and bonding

Chemical reactions

Energy

Forces and motion

Thermal physics

Electricity and magnetism

Waves

Atoms and space

Genetics and evolution

Body systems

Ecosystems and environment

Human impact and sustainability

Biotechnology and the future

MYP Integrated Sciences Hormones Notes

What Are Hormones?

Why Does the Body Need Hormones?

What Is the Endocrine System?

How Does the Body Use Hormones to Maintain Homeostasis?

What Does Adrenaline Do?

How Do Hormones Control Growth and Development?

What Are the Key Differences Between Nerves and Hormones?

What Are Hormones?

Why Does the Body Need Hormones?

What Is the Endocrine System?

How Does the Body Use Hormones to Maintain Homeostasis?

What Does Adrenaline Do?

How Do Hormones Control Growth and Development?

What Are the Key Differences Between Nerves and Hormones?