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.