The human cardiovascular system

The heart and the circulatory system make up the human cardiovascular system. It is the transport system of the body that helps in circulating substances in blood. Blood delivers oxygen and nutrients to every cell and removes carbon dioxide and waste products made by those cells. This tubular system comprising of blood vessels is propelled by a pumping heart.

The human cardiovascular system comprises of two circuits – pulmonary and the systemic and they consist of arterial, capillary and venous components. Put your science knowledge to the test with this challenging 6th Grade Science Worksheet! Read each question carefully and choose the response that you feel is correct.

Pulmonary and systemic circuits

During breathing, the air we inhale reaches our lungs, which is then carried by blood vessels to the heart. The heart pumps it further to all the cells in various parts of the body. The carbon dioxide from the cells is then carried by another set of blood vessels to the heart that pumps it back to the lungs for exhalation. This can be divided into two circuits for easier study –Doubts? A 6th-grade science tutor can help.

B) The systemic circuit (between heart and the rest of the body)

It is that part of the circulatory system that carries oxygenated blood away from the heart, delivers to organs, tissues and cells and returns deoxygenated blood from the cells back to the heart.

Function of the chambers

• The right atrium receives blood from the veins and pumps it to the right ventricle.
• The right ventricle receives blood from the right atrium and pumps it to the lungs for oxygenation.
• The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
• The left ventricle which is the strongest chamber pumps this oxygen-rich blood to the rest of the body. Its vigorous contractions create our blood pressure.

Blood vessels

There are three main types of blood vessels –

Arteries, Capillaries and Veins.

Arteries –

Arteries are the blood vessels that carry blood away from the heart to all parts of the body (tissues, lungs, brain etc.). Most of the arteries carry oxygenated blood. The Aorta is the largest artery in the body that originates in the heart and distributes oxygenated blood to all the parts of the body. Arteries carry blood at higher pressure due to pumping of the heart. The thicker walls in arteries help them to withstand the pressure.

Exception: The Pulmonary Arteries carry deoxygenated blood from the heart to the lungs for removal from the body during exhalation.

Veins –

Veins are the blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the cells back to the heart. The blood flows at lower pressure in the veins and its walls are thinner. Veins have valves present in them to stop the blood from flowing back as they mostly travel against gravity. Veins are present closer to the surface of the skin as compared to arteries that are deeper.

Exception: The Pulmonary Veins carry oxygenated blood from the lungs to the heart for further circulation in the body.

Blood and its components

Blood is the transport liquid, which is both a tissue and a fluid. There are four main components of blood – plasma, red blood cells, white blood cells and platelets.

Plasma is the liquid portion of the blood. It is yellowish in color and is mostly made up of water. It also contains proteins, glucose, hormones and minerals.  It transports water and nutrients to body tissues. It also transports carbon dioxide from the cells for their removal.

Plasma has three types of cells suspended in it –

1) Red Blood Cells –

They form 45% of the blood volume. They contain an iron-containing protein called hemoglobin that helps in carrying oxygen. When hemoglobin is attached to oxygen it brightens in color and when oxygen is removed, it darkens in appearance.  Arteries that carry oxygen thus, appear red.  After oxygen is delivered in tissues, the blood enters the veins and thus veins appear darker.

2) White Blood Cells –

They account for just 1% of the blood but they are crucial for our existence. They ensure good health and protect us from diseases and ailments by attacking foreign bodies like viruses and bacteria.

3) Platelets –

The smallest of the blood cells, they control bleeding. When there is a wound, they form a cluster around the wound and plug it until it heals.

Check point

1. Name the artery that carries carbon dioxide rich blood from the heart to the lungs.
2. Name the protein in red blood cells that binds with oxygen and carries it.
3. The three types of cells in blood are _____________.
4. Name the valve between the right atrium and the right ventricle.
5. Which blood cells help us fight against a viral disease like Covid-19?
6. How does the excretory system work with the cardiovascular system?

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