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1.2.1 Composition of Human Blood

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Human blood consist of
  1. cellular components
  2. plasma


Cellular Components

There are three types of blood cells:
  1. erythrocytes (red blood cell)
  2. leucocytes (white blood cell)
  3. platelets

Erythrocyte (Red blood cells)

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  1. Biconcave disc-shaped. Can move quickly in blood capillaries and increases the TSA/V ratio to facilitate the exchange of gases.
  2. Carry large amount of haemoglobin.
  3. Haemoglobin is responsible for the transport of oxygen in the form of oxyhaemoglobin and carbon dioxide in the form of carbaminohaemoglobin.
  4. No nucleus when matured. This enables it to contain more haemoglobin to carry more oxygen.
  5. Produced in the bone marrow.
  6. Life span about 120 days. After that they are destroyed in the spleen and liver.

Leucocyte

  1. Has no fixed shape.
  2. Less than the erythrocytes, but bigger in size.
  3. Has a nucleus
  4. The function is to protect the body from diseases.
  5. There are two types of leucocytes:
    1. granulocyte
    2. agranulocyte

Granulocytes
  1. With granules in the cytoplasm.
  2. With lobed nucleus.
  3. Formed in red bone marrow.
  4. There are three types of granulocytes
    1. neutrophil (carry out phagocytosis to engulf invading bacteria)
    2. eosinophil (involve in regulating the allergic responses)
    3. basophil (produce heparin to prevent the blood clotting）

Agranulocytes
  1. Have no granules in the cytoplasm.
  2. There are two types of agranulocytes:
    1. lymphocytes (responsible for producing antibodies to protect the body against diseases.)
    2. monocytes (carry out phagocytosis to engulf invading bacteria)

Platelet (Thrombocytes)

  1. Platelets, or thrombocytes , are cell fragments (i.e. cells that do not have a nucleus) of larger cells in the bone marrow called megacaryocytes.
  2. The average lifespan of a platelet is normally just 5 to 9 days.
  3. Platelets circulate in the blood of mammals and are involved in hemostasis, leading to the formation of blood clots.

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Plasma

  1. Plasma is the liquid part of the blood.
  2. Plasma is a pale yellowish liquid consisting of water, plasma protein and other dissolved substances.
  3. Plasma without plasma protein is called blood serum.

Plasma Protein

  1. The plasma protein consist of 
    1. albumins, 
    2. immunoglobulins and 
    3. fibrinogen.
  2. The albumin controls osmitic pressure of blood and acts as buffer against pH changes.
  3. Immunoglobulins are antibodies involve in body's defense mechanism.
  4. Fibrinogen is a substance important in blood clotting.

Water and Dissolved Substances

  1. Other than plasma protein, the dissolved substances in plasma include
    1. products of digestion
    2. excretory products
    3. hormones
    4. minerals
    5. vitamins.
    6. dissolved gases such as carbon dioxide, oxygen and nitrogen.