Body fluids

• All living cells need nutrients, O2, and other essential substances for healthy functioning
• Waste or harmful substances produced by cells need to be continuously removed
• Efficient mechanisms for the movement of substances to and from cells are essential
• Different groups of animals have evolved different methods for transport
• Simple organisms like sponges and coelenterates circulate water through their body cavities for substance exchange
• More complex organisms use special fluids like blood and lymph for material transport
• Blood is a special connective tissue consisting of plasma and formed elements
• Plasma constitutes nearly 55% of blood and contains water, proteins (fibrinogen, globulins, albumins), minerals, glucose, amino acids, and lipids
• Formed elements in blood include erythrocytes (RBCs), leucocytes (WBCs), and platelets
• Erythrocytes are the most abundant cells in blood, lack a nucleus, contain haemoglobin, and have a lifespan of 120 days
• Leucocytes are colourless, nucleated, and involved in defense mechanisms
• Platelets are cell fragments involved in blood clotting
• Blood groups are classified into ABO and Rh groups
• ABO grouping is based on the presence of surface antigens (A and B) on RBCs and natural antibodies in plasma
• Rh grouping is based on the presence of Rh antigen on RBCs
• Blood coagulation is a mechanism to prevent excessive blood loss from the body
• Coagulation involves the conversion of fibrinogens to fibrins by thrombin, requiring calcium ions and other factors
• Interstitial fluid or tissue fluid is released from blood into tissues through capillaries and collected by the lymphatic system as lymph
• Lymph contains lymphocytes responsible for immune responses and is a carrier for nutrients, hormones, and fats
• Circulatory patterns can be open (arthropods, molluscs) or closed (annelids, chordates)
• Vertebrates have a muscular chambered heart with different numbers of chambers based on the species
• Human circulatory system consists of a muscular heart with four chambers (atria and ventricles) separated by septa and valves
• Cardiac muscles, nodal tissues (SAN, AVN, AV bundle), and valves ensure unidirectional blood flow in the heart
• The atrio-ventricular bundle (AV bundle) continues from the AVN and passes through the atrio-ventricular septa to emerge on the top of the inter-ventricular septum
• The AV bundle immediately divides into a right and left bundle, which give rise to minute fibres throughout the ventricular musculature of the respective sides called purkinje fibres
• The purkinje fibres along with the right and left bundles are known as the bundle of His
• The SAN can generate the maximum number of action potentials, 70-75 per minute, and is responsible for initiating and maintaining the rhythmic contractile activity of the heart, earning it the name "pacemaker"
• The heart normally beats 70-75 times per minute, with each ventricle pumping out approximately 70 mL of blood during a cardiac cycle
• The cardiac cycle consists of systole and diastole of both the atria and ventricles
• The P-wave in an ECG represents the electrical excitation (or depolarisation) of the atria, leading to their contraction
• The QRS complex in an ECG represents the depolarisation of the ventricles, initiating ventricular contraction
• The T-wave in an ECG represents the return of the ventricles from excited to normal state (repolarisation), marking the end of systole
• The heart is myogenic and can be regulated intrinsically by specialised muscles (nodal tissue) and extrinsically by the autonomic nervous system (ANS)
• High Blood Pressure (Hypertension) is when blood pressure is higher than normal (120/80), leading to heart diseases and affecting vital organs like the brain and kidneys
• Coronary Artery Disease (CAD) is caused by deposits in arteries, affecting blood supply to the heart muscle
• Angina pectoris is acute chest pain due to insufficient oxygen reaching the heart muscle
• Heart Failure is when the heart is not pumping blood effectively enough to meet the body's needs, leading to symptoms like congestion of the lungs