CORE Biology (Short Course) - 9221 OxfordAQA

Circulation In Humans

Muhtasari

Put a finger on the inside of your wrist and wait. That small, regular push is a muscular pump the size of your fist forcing blood out of your chest and down your arm, and it has done so without a single day off since before you were born. Every cell you own is fed and cleaned by that pump. Starve any part of the network for a few minutes and the tissue it serves begins to die.

This lesson takes the whole circulatory system apart and puts it back together: the four chambers of the heart and the order in which they squeeze, the two loops the blood travels round, the three kinds of vessel and why each one is built the way it is, and the four components of blood and the jobs they do. It finishes on the one idea that turns all of that into medicine, which is that the surface of every cell carries proteins telling your body whether the cell belongs to you, and on the judgement an examiner will ask you to make when an organ fails beyond repair and a patient has to choose between a donated organ and a machine.

Malengo

  1. Substances are transported from where they enter the body to the cells, or from the cells to where they are removed from the body, by the circulatory system (the heart, the blood vessels and the blood).
  2. The heart is an organ that pumps blood around the body in a double circulatory system. Much of the wall of the heart is made from muscle tissue.
  3. The heart has four main chambers (right and left atria and right and left ventricles).
  4. Blood enters the atria of the heart. The atria contract and force blood into the ventricles. The ventricles contract and force blood out of the heart. Valves in the heart ensure that blood flows in the correct direction. Knowledge of the names of the heart valves is not required.
  5. Blood flows from the heart to the organs through arteries and returns through veins. There are two separate circulation systems, one for the lungs and one for all other organs of the body. Knowledge of the blood vessels associated with the heart is limited to aorta, vena cava, pulmonary artery, pulmonary vein and coronary arteries.
  6. Arteries have thick walls containing muscle and elastic fibres. Veins have thinner walls and often have valves to prevent back-flow of blood.
  7. In the organs, blood flows through very narrow, thin-walled blood vessels called capillaries. Substances needed by the cells in body tissues pass out of the blood and substances produced by the cells pass into the blood, through the walls of the capillaries.
  8. Blood is a tissue consisting of a fluid called plasma, in which the white blood cells, platelets and red blood cells are suspended.
  9. Red blood cells have no nucleus. They are packed with a red pigment called haemoglobin that carries oxygen. Red blood cells transport oxygen from the lungs to the organs.
  10. White blood cells have a nucleus. They form part of the body’s defence system against microorganisms.
  11. Platelets are small fragments of cells. They have no nucleus. Platelets help blood to clot at the site of a wound.
  12. Antigens are proteins on the surface of cells.
  13. Students should be able to evaluate the advantages and disadvantages of treating organ failure by mechanical devices or transplant.

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Maelezo ya Somo

Diffusion is a superb way of moving a substance across a distance of one hundredth of a millimetre and a hopeless way of moving it across a metre. A human being is roughly a hundred thousand times too thick for diffusion alone to supply the cells in the middle. The answer evolution reached is not a better kind of diffusion; it is a plumbing system that carries substances at speed to within a hair's width of every cell, and then lets diffusion do the last, short step.

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  1. Which chamber of the heart pumps blood into the aorta? A. The right atrium B. The left atrium C. The right ventricle D. The left ventricle Answer: D
  2. Which blood vessel carries deoxygenated blood away from the heart? A. The aorta B. The pulmonary artery C. The pulmonary vein D. The vena cava Answer: B
  3. Which feature is found along the length of a vein but not usually along the length of an artery? A. A lumen B. Valves C. Muscle in the wall D. Elastic fibres in the wall Answer: B
  4. Which component of the blood has no nucleus and is packed with haemoglobin? A. The plasma B. A white blood cell C. A red blood cell D. A platelet Answer: C
  5. Which component of the blood has a nucleus? A. The plasma B. A platelet C. A red blood cell D. A white blood cell Answer: D

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Vitabu Vinavyopendekezwa

OxfordAQA International GCSE Biology (9201)
OxfordAQA International GCSE Biology (9201)
Manukuu: Student Book
Mchapishaji: Oxford University Press
Mwaka: 2016
ISBN: 978-0-19-837588-3
Maelezo: The endorsed student book for the 9201 specification, covering the full subject content with required practicals and exam guidance.
OxfordAQA International GCSE Combined Sciences Biology (9204)
OxfordAQA International GCSE Combined Sciences Biology (9204)
Manukuu: Student Book
Mchapishaji: Oxford University Press
Mwaka: 2016
ISBN: 978-0-19-840793-5
Maelezo: The biology half of the Combined Science series. A lighter parallel treatment of the same content, useful for a second explanation.

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