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Lesson Note
Subject: Biology
Topic: Digestive System In Invertebrates.
Lesson Objectives: By the end of the lesson, the learners should be able to:

  1. State the Protective Function of Blood;Explain Circulatory System in Mammals;Explain the types of Blood Vessels;

  2. Explain Circulatory System in Mammals;Explain the types of Blood Vessels;

Explain Circulatory System in Mammals;Explain the types of Blood Vessels;

Explain the types of Blood Vessels;

  • State the differences between vein and artery.
    The blood performs two basic functions in mammals and
    These are:

    • Transportation of various substances
    • Protection of body against diseases

    The blood defends the body in major ways:
    Antibody production (Clumping): The lymphocytes produce antibodies which are any of a large variety of proteins normally present in the body or produced in response to an antigen which it neutralizes, thus producing an immune response. This can also be ensured by injecting small dose of the weaker or dead pathogens into the body. This process is known as vaccination or immunization.
    Neutralization: The whole blood will also produce antitoxins which neutralize the toxins produced by the pathogens.
    Phagocyte Action (Engulfing): Phagocytes engulf the pathogens and digest them.
    Clotting: The blood platelets clot the blood to prevent germs from entering the body and also prevent loss of blood

    When a blood vessel is damaged and exposed to air, platelets in the blood stream release an enzyme thrombokinase. The thrombokinase then converts prothrombin (inactive blood protein) to an enzyme called thrombin. The thrombin then converts the soluble fibrinogen in the plasma to insoluble fibrin in the presence of calcium ions. The threadlike fibrin then forms a network or mesh on the surface of the wound and blood cells are trapped within the network or mesh to form a clot. The clot dries to scab over the wound.

    The circulatory system in animals can be:

    • Closed or open
    • Single or double
    Closed Circulatory System: This involves the blood vessel called arteries which divides capillaries which later join up with other vessels called veins. Blood is therefore limited to the vessels and the heart it does not have direct contact with the body cells this system is observed in annelids and vertebrates.

    Opened Circulatory System: The blood vessels lead out of the heart but end in blood spaces called haemocoels within the body cavity. The blood has direct contact with the cells after which it is returned to the heart. Arthropods and some mollusks have open circulatory system

    Single Circulatory System: The blood passes through the heart once in a complete movement round the body e.g. fishes because of their two chambered heart have single circulatory system.

    Double Circulatory System: The blood passes twice in the heart every time it makes one complete movement round the body. Each time it passes through a separate path way e.g. mammals. Double circulation gives rise to pulmonary and systematic circulation.

                      BLOOD VESSELS
    Arteries: These are vessels that carry oxygenated blood away from the heart to the body’s organs except for pulmonary artery that carries deoxygenated blood.
    Arteriole: A branch of an artery that gives rise to capillaries.
    Veins: These are large vessels that carry deoxygenated blood toward the heart except for pulmonary vein which carries oxygenated blood.
    Venule: Small vessel that carries blood from the capillaries to the veins.
    Capillaries: They link the arteries with the veins around the tissues and organs. They are tiny and thin walled to facilitate easy exchange of gasses nutrients and waste products between the cells and the blood.

    Done studying? See all previous lessons in biology.
    Take a quick test for this lesson.

    1. What are the protective functions of the blood?
    2. Describe the mechanism of blood clotting.
    3. What is vaccination?

    4. Define (a) artery (b) venule (c) capillary
    5. What is double circulatory system?

    Questions answered correctly? Bravo!!

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