11.1 Circulatory System

Subject: Biology (5090) | Level: O Level | Topic: Transport in Humans

2026 📋 Syllabus Objectives

By the end of these notes, you should be able to:

  1. Describe the circulatory system as a system of blood vessels with a pump and valves to ensure one-way flow of blood.
  2. Describe a double circulation as a system in which blood passes through the heart twice for each complete circuit.
  3. Understand that a double circulation provides a low pressure circulation to the lungs and a high pressure circulation to the body tissues.

📖 Main Content

https://cambridgeassistant.com

1. What Is the Circulatory System?

The circulatory system is the body's transport system. Its job is to move blood around the body so that substances — like oxygen, nutrients, and waste products — can be delivered to or collected from every cell.

Think of it like a delivery network. Just as roads connect towns and lorries carry goods, blood vessels connect all parts of the body and blood carries materials.

The circulatory system has three main parts working together:

  • Blood vessels — the tubes that carry blood around the body
  • A pump (the heart) — the muscular organ that pushes blood through the vessels
  • Valves — small flaps inside the heart and some vessels that make sure blood only travels in one direction

2. Blood Vessels — The Tubes of the System

Blood vessels are the tubes through which blood flows. There are different types, but for this subtopic, what matters is understanding that they form a large network connected to the heart.

Blood is pushed out of the heart, travels through blood vessels to reach all parts of the body, and then returns to the heart. This forms a continuous loop — the blood never stops moving (as long as you are alive).

3. The Heart — The Pump

The heart is a muscular pump located in the chest. It contracts (squeezes) and relaxes rhythmically — this is your heartbeat.

Every time the heart contracts, it pushes blood forward through the blood vessels. This pressure keeps the blood moving around the entire body.

💡 Simple analogy: The heart works like a water pump in a central heating system — it pushes fluid through pipes so it can flow to every part of the house.

Sign in to view full notes