VIII Put the sentences in the right order:

1. Blood flows through the left atrium into the left ventricle.
2. Blood flows through the right atrium into the right ventricle.
3. The right ventricle pumps the blood to the lungs, where the blood releases waste gases & picks
up oxygen.
4. Oxygen-poor blood flows from the body into the right atrium.
5. The newly oxygen-rich blood returns to the heart & enters the left atrium.
6. The left ventricle pumps the oxygen-rich blood to all parts of the body.

The cardiovascular system is the system of blood circulation. It means the heart, the arteries, the
veins & capillaries of the human body.
An adult's heart weighs about 300g, and is roughly the size of a fist. Your heart is a muscular
organ, divided into left and right sides. The heart has three layers. The smooth, inside lining of
the heart is called the endocardium. The middle layer of heart muscle is called the myocardium.
It is surrounded by a fluid filled sac call the pericardium.
The right side of your heart receives deoxygenated blood though the veins. It pumps this blood to
your lungs where it picks up more oxygen. This oxygenated blood then returns to the left side of
your heart, which pumps it out to the rest of your body through the arteries. The left side is
slightly larger because it has more work to do, pumping blood around your body.
Each side of your heart is divided into an upper chamber called an atrium and a larger, lower
chamber, called a ventricle. Blood flows from the atria to the ventricles through
one-way valves. Your heart works as a pump, with its muscular walls contracting to force the
movement of blood.