1.6.25

The Circulatory System

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The Heart

The heart pumps blood around the body. The heart's work ensures that cells have the oxygen needed for respiration.

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The heart

  • The heart is a muscle.
    • The heart pumps the newly oxygenated blood around the body.
    • The heart pumps deoxygenated blood back to the lungs.
  • Humans have one heart that is around the size of a person's fist.
    • The heart is located in the middle left of your chest.
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Unusual animal hearts

  • Cuttlefish and octopuses have three hearts.
    • These creatures have so many hearts to ensure that blood is pumped around their complex bodies.
  • Earthworms do not have hearts.
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Four chambers of the human heart

  • Left atrium
    • Where oxygenated blood comes from the lungs.
  • Left ventricle
    • Pumps oxygenated blood around the body.
  • Right atrium
    • Where the deoxygenated blood enters the heart from body.
  • Right ventricle
    • Pumps deoxygenated blood to the lungs.

The Blood

The blood delivers oxygen and removes carbon dioxide as it moves around the body. Blood is contains plasma, platelets, red blood cells, and white blood cells.

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Blood plasma

  • Blood plasma
    • Plasma is the straw-coloured liquid component of blood.
  • Plasma contains a variety of substances including:
    • Suspended nutrients
    • Antibodies
    • Proteins
    • Hormones
    • Urea
    • Blood cells
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Blood platelets

  • Blood platelets are found in the blood plasma.
    • Platelets are used in blood clotting.
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Red blood cells

  • Red blood cells are also called erythrocytes.
    • Red blood cells are made in the bone marrow.
    • Red blood cells contain a protein called haemoglobin which carries oxygen around the body.
  • Red blood cells have a biconcave disc shape and a nucleus.
    • This shape increases surface area to maxmise oxygen absorption.
    • Red blood cells are very thin to make diffusion more efficient.
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White blood cells

  • White blood cells are part of the body's immune system.
  • White blood cells engulf and destroy microorganisms that invade the body.

The Blood Vessels

Blood is carried around the body by three types of blood vessels: arteries, veins, and capillaries.

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Arteries

  • Arteries carry blood from the heart to the rest of the body.
    • The blood in the arteries is oxygenated and is under high pressure.
    • The walls of the arteries are thick and elastic-like.
    • The artery that takes blood away from the heart is called the aorta.
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Capillaries

  • Capillaries are small blood vessels that connect arteries to veins.
    • Capillaries are only one cell thick.
    • Oxygen diffuses from the oxygenated blood into the body cells.
    • Carbon dioxide diffuses from the body cells into the capillaries.
    • Urea is transported into the blood through the capillary walls.
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Veins

  • Veins take deoxygenated blood from the body back to the heart.
    • Blood in the veins is under much lower pressure.
    • Veins contain valves to prevent the backflow of blood.

Jump to other topics

1Biology

1.1Cells, Tissues & Organs

1.2Reproduction & Variation

1.3Ecological Relationships & Classification

1.4Digestion & Nutrition

1.5Plants & Photosynthesis

1.6Biological Systems & Processes

2Chemistry

2.1Particles

2.2Chemical Reactions

2.3Atoms, Elements, Compounds

2.4The Periodic Table

2.5Materials & the Earth

2.6Reactivity

2.7Energetics

2.8Properties of Materials

3Physics

3.1Energy

3.2Forces & Motion

3.3Waves

3.4Electricity & Magnetism

3.5Matter

3.6Space Physics

4Thinking Scientifically

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