Blood
Understanding Blood
- Blood is a connective tissue consisting of plasma, red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes).
Components of Blood
- Plasma: This is a pale, yellow liquid where the cells and platelets are suspended. Plasma is responsible for transporting nutrients, hormones, waste products, and heat.
- Red Blood Cells (erythrocytes): These are biconcave, disk-shaped cells that carry oxygen from the lungs to all body tissues. Erythrocytes contain a red pigment called haemoglobin which binds with oxygen to form oxyhaemoglobin.
- White Blood Cells (leukocytes): These cells are part of the immune system and help fight infections. There are several types of leukocytes, including lymphocytes and phagocytes.
- Platelets (thrombocytes): These are tiny fragments of cells that aid in blood clotting to prevent excessive bleeding after injury.
Functions of Blood
- Supply of Oxygen and Nutrients: Blood transports oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. It also carries nutrients from the digestive system to the cells.
- Removal of Waste: Blood transports waste products, including carbon dioxide and urea, to the appropriate organs (lungs, kidneys) for elimination.
- Distribution of Heat: Blood helps distribute heat throughout the body, contributing to maintaining body temperature.
- Defence against disease: Leukocytes in the blood attack and destroy foreign substances or organisms entering the body.
- Clotting: Platelets in the blood clot at the site of a wound to prevent excessive bleeding.
Blood Groups
- Human blood is categorised into four groups; A, B, AB, and O, based on the presence or absence of antigens on the surface of red blood cells.
- Each group can be Rh-positive or Rh-negative, depending on the presence or absence of the Rh factor. This leads to eight main blood types in humans: A+, A-, B+, B-, AB+, AB-, O+, and O-.
- Understanding blood groups is crucial for safe blood transfusions. Receiving blood from a group incompatible with one’s own can result in life-threatening reactions.
Blood Vessels
- Blood is transported through the body via blood vessels. There are three main types of blood vessels: arteries, veins, and capillaries.
- Arteries: These carry blood away from the heart to the tissues. They typically carry oxygenated blood, except for the pulmonary artery.
- Veins: These carry blood towards the heart. They are responsible for returning deoxygenated blood from the tissues to the heart, except for the pulmonary veins.
- Capillaries: These are extremely small vessels where substances are exchanged between the blood and body tissues.