circulatory system

• The main constituents of the circulatory system in the human body are the heart and blood vessels
• The circulatory system supplies food and oxygen to the cells of the body and carries away carbon dioxide and other metabolic wastes
• The circulatory system contains two main kinds of fluids: blood and lymph
• Blood is a liquid connective tissue that is red in colour, salty in taste, and has a pH of 7.4
• The total quantity of blood in a full-grown human body is 4 to 6 litres
• The blood of all vertebrates is red due to red blood cells containing an iron-containing pigment called haemoglobin
• Functions of the Blood:

  • Transports digested food from the alimentary canal to tissues
  • Transports oxygen from the lungs to the tissues
  • Transports carbon dioxide from the tissues to the lungs
  • Transports excretory materials from the tissues to the liver, kidneys, and skin
  • Distributes hormones secreted by the endocrine glands to the target organs
  • Regulates body temperature by distributing heat uniformly
  • Protects against diseases by engulfing bacteria
• The blood consists of plasma, red blood cells (RBCs), white blood cells (WBCs), and platelets
• Red blood cells (erythrocytes) have a colourless spongy body containing haemoglobin, which carries oxygen to tissue cells and picks up carbon dioxide
• Red blood cells have a biconvex disc-like shape and are produced in the bone marrow by stem cells
• The life cycle of red blood cells is about 100-120 days before they are destroyed in the liver and spleen
• White blood cells (leucocytes) have a nucleus and are produced in the bone marrow or lymphoid tissues
• Platelets (thrombocytes) are non-nucleated structures that help in blood clotting at the time of injuries
• The blood is divided into four types in the ABO system: A, B, AB, and O
• Blood transfusion is necessary when a person loses a lot of blood, and it is crucial for the blood group of the donor to match with the receiver
• The O type blood can be donated to any blood group, making it the universal donor, while AB type blood can receive blood of any group and is called the universal recipient
• The circulatory system consists of the heart, arteries, veins, and capillaries
• The human heart has four chambers: two auricles and two ventricles
• Superior vena cava brings deoxygenated blood from the upper body, while inferior vena cava brings deoxygenated blood from the lower body to the heart
• The pulmonary artery carries deoxygenated blood to the lungs, and the aorta carries oxygenated blood to all parts of the body
• The sequence of events in a single heart beat is known as the cardiac cycle, involving contraction and relaxation of atria and ventricles
• The conduction system of the human heart initiates and controls a heartbeat, with cells in the sinoatrial node acting as a pacemaker
• Lymph is a fluid that flows more slowly than blood and acts as a middleman for the exchange of materials between blood and body tissues
• Blood pressure is the force exerted by the blood against the walls of the arteries, and pulse is the alternate expansion and elastic recoil of the arterial wall during ventricular systole