15Class 11 Biology
Body Fluids and Circulation short notes
Short notes on blood, the heart, the cardiac cycle and ECG. Facts and figures are asked directly from this chapter.
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Blood
- Plasma is about 55% of blood, and formed elements 45%.
- RBCs: 5 to 5.5 million per mm³, no nucleus in mammals, and a life of 120 days.
- WBCs: 6000 to 8000 per mm³. Neutrophils are the most common, and basophils the least.
- Platelets: 1.5 to 3.5 lakh per mm³, and involved in clotting.
- Blood groups: A has antigen A and anti-B, B has antigen B and anti-A, AB has both antigens and neither antibody, and O has neither antigen and both antibodies.
- O is the universal donor, and AB the universal recipient.
- Clotting: thrombokinase turns prothrombin into thrombin, and thrombin turns fibrinogen into fibrin. Calcium is needed.
- Rh incompatibility can harm a second Rh-positive baby of an Rh-negative mother.
Heart
- A human heart has four chambers, and double circulation.
- The tricuspid valve is on the right, and the bicuspid (mitral) valve on the left.
- The SA node is the pacemaker, generating about 70 to 75 impulses a minute.
- The conduction path runs SA node, AV node, bundle of His, then Purkinje fibres.
Cardiac cycle and ECG
- One cycle takes about 0.8 seconds, at 72 beats a minute.
- Stroke volume is about 70 mL, so cardiac output is about 5 L a minute.
- Lub comes from the AV valves closing, and dub from the semilunar valves closing.
- ECG: P wave for atrial depolarisation, QRS for ventricular depolarisation, and T for ventricular repolarisation.
Where students slip up
- Calling O the universal recipient. It's the universal donor.
- Mixing up lub and dub.
- Reversing the valves: tricuspid is on the right side.
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