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).