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Breathing and Circulation This chapter explains how the heart beats and pumps blood around the body. It also explains how the lungs function to supply the blood with oxygen.

Let’s generally see how the heart functions.


The heart is made up of a special type of muscle that acts like a pump


This muscle is called the cardiac muscle


The main function of the heart is to pump blood that carries oxygen TO all the body cells and collects waste materials FROM the body cells



In order for the heart to do such a job, it must have a specific structure which is as follow. [ you must label the chambers of the heart]

 The heart is made up of 4 chambers  The 2 top chambers are called ATRIA (Atrium - singular)  The 2 bottoms chambers are called VENTRICLES (Ventricle singular).

 The heart has 4 vessels that carry blood in and out of the heart.  Arteries are vessels that carry blood away from the heart  Veins are vessels that carries blood to the heart


Now let’s take a journey with the blood around the body by drawing arrows [YOU MUST USE A RED AND A BLUE PEN TO DRAW THE ARROWS].


Labels: 1- Left Atrium

A- Aorta (Artery)

2- Left Ventricle

B- Vena Cava (Vein)

3- Right Atrium

C- Pulmonary Artery

4- Right Ventricle

D- Pulmonary Vein

The journey of blood around the body 1- The left atrium beats and pumps oxygenated blood down to the left ventricle 2- The left ventricle beats and pumps the oxygenated blood out of the heart to all the body cells (blood travels to all the body cells through the AORTA). 3- As blood reaches the body cells, it will give up all the oxygen it is carrying and will collect CO2 from all the cells and returns back to the heart. [Note: Blood is now deoxygenated] 4- Deoxygenated blood travels back to the heart through a vein called the Vena Cava 5- Deoxygenated blood enters the heart through the right atrium. 6- The right atrium will beat to pump deoxygenated blood down to the right ventricle. 7- The right ventricle beats to pump deoxygenated blood to the lungs. (blood travels to the lungs through the Pulmonary Artery). 8- In the lungs, CO2 will leave the blood and Oxygen will take its place. Therefore, the blood becomes oxygenated. 9- Oxygenated blood travels back to the heart through the Pulmonary Vein and into the left Atrium. 10- The Left Atrium beat and the cycle is repeated over and over‌‌. 4

Blood Vessels: We learned that there are 2 TYPES of blood vessels 1- Arteries

2- Veins.




Thick muscular walls with lots of elastic tissue


Thin muscular walls with few elastic tissue


Narrow lumen


Wide lumen


Caries blood away from the heart at high pressure


Carries blood back to the heart at low pressure


Has no valves


Has valves


How do they look like?

Note: Veins have valves which prevent the back flow of blood since blood is traveling through them at low pressure. The figure shows a longitudinal section of a vein. The arrows represent the movement of blood through the valves.

Capillaries There is a third type of blood vessel that we haven’t mention and it is called the capillary. Capillaries are one cell thick which allows easy movement of gases (O2 and CO2) in and out of the circulatory system. How do capillaries look like?


Red Blood Cells -

Red blood cells are one type of cells that travel through the vessels of the circulatory system


Their main function is to carry oxygen to body cells and carry carbon dioxide away from the body cells


The figure below shows a red blood cell

Features of red blood cells: - They have NO NUCLEUS - They have a biconcave shape which gives them enough space to load oxygen.

Disorders of the circulatory system: -


The Lungs


Every human has a pair of lungs


The function of the lungs is to inhale oxygen from the atmosphere and diffuses it into the blood. At the same time, carbon dioxide will be diffused from the blood out to the atmosphere.


Why is it important to keep the airways clean? -

The trachea is lined with cells that produce mucus which is very sticky.


Anything that enters with air (such as dust) will stick to the mucus. this prevents anything harmful from reaching the lungs.


The trachea is also lined with cilia (microscopic hair) which constantly beat.


The beating of cilia will move the mucus upwards and keeps the airways clean.



People that smoke kill the cilia that line the trachea.


Since the cilia is dead, mucus will not be moves upward. Therefore, mucus will accumulate down in the lungs and cause lung infections


Proving that carbon dioxide is exhaled:


To test for the presence of carbon dioxide as we exhale, we could simple blow the exhaled air into a tube filled with limewater.


Limewater will turn milky proving the presence of carbon dioxide in exhaled air.

Yousef Yasin


Circulatory System  

Explanation of the hearts fuction along with the lungs

Circulatory System  

Explanation of the hearts fuction along with the lungs