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. The heart has **four chambers**, two atria on top and 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**. That is what makes ours a **double circulatory system**: in one full circuit the blood passes through the heart **twice**, once on a loop to the lungs and once on a loop to 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

Explain the double loop

Explain why a double circulatory system delivers oxygen to the body more effectively than a single one would. Take the reasoning through to the effect on the cells.

• Say what happens to the blood between the lung loop and the body loop
• Say what that does to the pressure it leaves the heart at
• Finish with what higher pressure means for how quickly cells get oxygen

Three kinds of road

Each vessel is **built for its job**. **Capillaries** are the exchange vessels, with walls just **one cell thick** for a **short diffusion distance**. The pair that costs marks is arteries against veins, because every feature follows from one thing: which way the blood is going.

Name the vessels

Here are the three vessels in cross-section. Label each one (hint: wall thickness and lumen size).

Built for pressure

Tap the vessel whose thick, muscular wall is adapted to **withstand high pressure**.

Structure fits function

What flows through

Blood itself is four things, and a question naming one will not accept another:

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).