The Body's Highways

The Body's Highways 🫀

Every cell in you needs oxygen and food, and none of them can fetch it themselves. Your **circulatory system** is the delivery network — a pump, a road system, and the cargo. Meet the heart, the three types of blood vessel, and what actually flows through them.

The double pump ❤️

The heart has **four chambers** — two atria on top, two ventricles below — and works as a **double pump**: • The **right** side pumps **deoxygenated** blood to the **lungs**. • The **left** side pumps **oxygenated** blood to the **rest of the body**.

The strongest chamber

Which chamber has the thickest, most muscular wall, and why?

• The left ventricle — it pumps blood at high pressure all around the body
• The right ventricle — it pumps to the whole body
• The right atrium — it receives blood from the body
• The left atrium — it fills the heart

Round twice 🔁

Humans have a **double circulatory system**: in one full circuit, blood passes through the heart **twice** — once on a loop to the **lungs**, once on a loop to the **body**. The advantage: blood returning from the lungs is re-pressurised by the heart before going to the body, so it can be pumped at **higher pressure** and delivered **faster**.

Why loop twice?

What is the main advantage of a double circulatory system?

• Blood can be pumped to the body at higher pressure, delivering oxygen faster
• The body needs less blood in total
• The blood does not need to visit the lungs
• It keeps the blood cooler

Three kinds of road 🩸

Three vessels, each **built for its job**: • **Arteries** carry blood **away** from the heart at **high pressure** — thick, muscular, elastic walls; a narrow lumen. • **Veins** carry blood **back** to the heart at low pressure — thinner walls, a wide lumen, and **valves** to stop backflow. • **Capillaries** are the exchange vessels — walls just **one cell thick** for a **short diffusion distance**.

Name the vessels

An interactive activity.

Built for pressure

An interactive activity.

Structure fits function

What flows through 💧

Blood itself is four things: • **Plasma** — the liquid that carries dissolved substances (CO₂, glucose, urea, hormones). • **Red blood cells** — carry **oxygen** using **haemoglobin**. • **White blood cells** — defend against **pathogens**. • **Platelets** — cell fragments that help the blood **clot**.

What each part does

Adapted to carry oxygen

A red blood cell is a biconcave disc with no nucleus. Why is having **no nucleus** an advantage?

• It leaves more room for haemoglobin, so the cell carries more oxygen
• It makes the cell lighter so it flows faster
• It lets the cell divide more often
• It stops the cell changing shape

In the exam 🎓

Highways mapped. Grade-9 habits for circulation: • The **left ventricle** is thickest (high pressure to the body); the **double** system loops through the heart **twice**. • Make the **structure-function** link explicit: thick artery wall **withstands high pressure**; a capillary's one-cell wall gives a **short diffusion distance**. • Know the four blood parts: **plasma** (transport), **red cells** (oxygen), **white cells** (defence), **platelets** (clotting).