Chapter 2: Blood and Constituents

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    Blood contains fluid part called plasma. Red blood cells [erythrocytes] have red pigment hemoglobin which binds oxygen and transports it to all cells. They are formed in the red bone marrow and have a lifetime of 120 days. They are destroyed in the spleen. White blood cells [leucocytes] fight against germs that enter the body. White blood cells is neutrophiles [destroy foreign bodies]; basophiles [inflammatory response], eosinophiles [allergic response], lymphocytes [immune response] and monocytes [destroy foreign bodies]. Platelets [thrombocytes] in blood are responsible for clotting

Types of Blood Group

    Blood cells can have two antigens A, B, AB [both] or O [none]. O blood group is universal donor and AB is universal recipient.

Blood's Flow

    Blood vessels are arteries that carry oxygen rich blood to different body parts. The walls are thick, elastic as blood flow is rapid and high pressure. Veins carry carbon dioxide rich blood to the heart. They have thin walls and valves that allow blood flow in one direction only.

    Our muscles release lactic acid during anaerobic respiration. This lactic acid causes cramps. When we are drowsy, we slow down breathing and body doesn’t get sufficient oxygen so we yawn to take excess air.

Blood Oxidation and Purification

    During respiration ribs move up and diaphragm moves down, this increases size of chest cavity and air comes in. During exhaling, ribs move down and in and diaphragm moves back to position and this reduces chest cavity so air is released. Respiration is an exothermic reaction i.e. heat is evolved. Reactions of decomposition of wastes into compost are also exothermic.Blood capillaries in the kidneys filter waste material as urine. This is passed into the urinary bladder through the ureters. The urethra is connected to the urinary opening through which urine is passed. In dialysis, blood is filtered by an artificial kidney, when the natural kidneys fail.
    Pulmonary artery carries CO2 rich blood from heart to lungs, Pulmonary vein carries oxygen rich blood to heart from lungs. Arteries divide to form capillaries to reachtissues, capillaries rejoin to form veins to take blood from tissues to heart.

    Carbon monoxide reduces oxygen carrying capacity of blood. It combines with hemoglobin to form carboxyhaemoglobin and this reduces the oxygen carrying capacity of blood.

Human Heart

Human heart
Fig. Human Heart

    Heart has four chambers, two atria and two ventricles. The right atria and ventricle have deoxygenated blood. The left atria and ventricle have oxygenated blood. Ventricles have thick walls as they have to pump blood to different organs.


     Organisms that need energy to regulate body temperature need separate oxygenated and de-oxygenated blood. Others who regulate temperature of body based on temperature of surroundings can tolerate mixing of blood.

     Hydra and sponges don’t have a circulatory system or blood. Water that flows through their body carries food and oxygen to different parts and waste material from parts is thrown out by it too.

   Birds, insects excrete uric acid [least toxic so doesn’t need water for excretion]. Fishes excrete ammonia [highly toxic so needs lots of water]. Mode of excretion depends on availability of water.

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