Body Fluids and Circulation
Vertebrates circulate blood, a fluid connective tissue, to transport essential substances to cells and carry away wastes. Another fluid, lymph (tissue fluid), also transports certain substances.
Blood
Blood is a special connective tissue made of a fluid matrix, plasma (about 55 per cent), and formed elements (about 45 per cent).- Plasma: straw-coloured, 90-92 per cent water, 6-8 per cent proteins. Proteins are fibrinogen (clotting), globulins (defense) and albumins (osmotic balance). Plasma without clotting factors is serum.
- Formed elements: RBCs (erythrocytes), WBCs (leucocytes) and platelets (thrombocytes).
Blood groups
- ABO: based on A and B antigens on RBCs. O = universal donor, AB = universal recipient.
- Rh: Rh antigen present in about 80 per cent of people (Rh+ve). Rh-ve mother with Rh+ve foetus can cause erythroblastosis foetalis in later pregnancies.
Coagulation
Clot is a network of fibrin. Fibrinogen to fibrin by thrombin; thrombin from prothrombin via thrombokinase; calcium ions essential.Heart and circulation
- Four-chambered heart; SAN = pacemaker (70-75 action potentials/min). Conduction: SAN to AVN to AV bundle (bundle of His) to purkinje fibres.
- Cardiac cycle = 0.8 s; stroke volume about 70 mL; cardiac output about 5 L/min. Lub (AV valves close), dub (semilunar valves close).
- ECG: P (atrial depolarisation), QRS (ventricular depolarisation), T (ventricular repolarisation).
- Double circulation: pulmonary (right ventricle to lungs to left atrium) and systemic (left ventricle to body to right atrium).
- Heart is myogenic; moderated by ANS (medulla) and adrenal hormones.