The circulatory system

The circulatory system, also known as the cardiovascular system is a network of organs and blood vessels that work together to circulate blood around the body.

The circulatory system is made up of three main components:

1. Heart
2. Blood vessels
3. Blood

Fascinating facts

• If we could join all the blood vessels in a human body together end-to-end, they would wrap around the world twice!

• The heart is a powerful muscle that pumps approximately 9,092 litres of blood per day.

• Every second, your body produces millions of red blood cells to replace those that wear out.

• People have different blood types. There are four main blood types: A, B, AB and O.

• It takes about 20-30 seconds for blood to circulate completely throughout the body.

• Capillaries are the smallest blood vessels in our circulatory system.

• Veins contain valves which prevent the backflow of blood.

• There is evidence that the ancient Egyptians were studying the human circulatory system as early as the 16th century BC.

The human heart is a very strong muscle that pumps blood around the body. It is made of four chambers, two upper chambers and two lower chambers.

Blood enters the upper chambers which are called atria. These squeeze and push the blood into the lower chambers called ventricles which then squeeze and push the blood out of the heart.

1. The right side of the heart first pumps blood to the lungs. Here, the blood picks up oxygen from the air that has been breathed in.
2. The blood (now carrying oxygen) then travels back to the left side of the heart.
3. The heart gives the blood a second push. This time, it's sent to all the other parts of your body, including the brain, arms, legs and stomach. The blood delivers oxygen to them all.
4. The blood travels back to the right side of the heart, and it all begins again.
5. The tubes that carry blood away from your heart are called arteries. The tubes that carry blood back to your heart are called veins.

Your heart is a very strong muscular organ which repeatedly contracts (becomes smaller) and relaxes to pump blood around your body.

It has four chambers:

• the right atrium
• the right ventricle
• the left atrium
• the left ventricle

A heart beat varies from person to person, for an average person it beats 60 to 100 times a minute. You can feel this when you take your pulse.

This is the journey that blood takes:

Did you know?

The term cardiovascular comes from two latin words; the prefix cardio- which means heart and the word vascular which relates to tubular blood vessels.

Many other common medical words begin with the prefix cardio-, such as a cardiometer which measures the health of a person's heart, cardiology which is the scientific study of the heart, and cardiogram which is a scan used by doctors to look at a heart.

Blood vessels are tubes that carry blood throughout the body. There are three main types of blood vessels.

1. Arteries
   Arteries carry oxygenated blood away from the heart and to the body's cells.
2. Veins
   Veins carry deoxygenated blood from the body's cells and into the heart.
3. Capillaries
   Capillaries are tiny blood vessels that connect arteries to veins. They allow oxygen, nutrients and waste products to pass between the blood and the body's cells.

Did you know?

If you need an easy way to remember what veins and arteries do, then try this!

The word artery starts with the letter ‘a’ and so does the word ‘away’ and arteries carry blood away from the heart.

The word vein has the word ‘in’inside of it and veins carry blood back into the heart.

Blood is a liquid tissue that circulates throughout the body. It is made up of:

• Red blood cells
  Red blood cells carry oxygen to the body's cells.
• White blood cells
  White blood cells help the body to fight infection.
• Platelets
  Platelets are cells which help blood to clot and stop bleeding.
• Plasma
  Plasma is a liquid that carries nutrients, water and sugar around the body.

Did you know?

Our blood is red because it contains a red coloured protein called haemoglobin that carries oxygen.

Molluscs don't have haemoglobin, so their blood so is blue coloured!

Your pulse is a measure of how fast your heart is beating.

It is the number of beats your heart makes in one minute.

Your heart beats faster or slower depending on what you are doing.

When you exercise, your heart beats faster. This is because your muscles are working harder and need more oxygen to keep going.

Your lungs also work harder, making you breathe more quickly to take in more oxygen.

When you sleep, your muscles need less oxygen so your heart rate slows down.

Important words about the circulatory system!

Arteries - They take the blood with oxygen away from the heart and spreads it around your body.

Atria - The upper chambers of the heart.

Blood - A liquid tissue that circulates throughout the body, it is made up of red blood cells, white blood cells, platelets and plasma.

Blood vessels - Tubes that carry blood around the body.

Cardiovascular system - Another name for the circulatory system, see below.

Circulatory system - A network of organs and blood vessels that work together to circulate blood around the body.

Deoxygenated blood - Blood without oxygen.

Heart - The organ that pumps blood around your body.

Organs - Parts of our body that have a function like the skin, lungs, heart, stomach et al.

Oxygenated blood - Blood with oxygen.

Platelets - Help the blood to clot and stop bleeding.

Plasma - A liquid that carries nutrients, water and sugar around the body.

Pulse - A measure of how fast your heart is beating.

Red blood cells - They carry oxygen to the body's cells.

Veins - A type of blood vessel that takes deoxygenated blood to your heart.

Ventricles - The lower chambers of the heart.

White blood cells - They defend the body and help to fight infection.

Haemoglobin - A red coloured protein that carries oxygen.