Definitions Glossary

Term	Definition	NEET Relevance
Plasma	Straw-coloured liquid portion of blood (55% of volume); contains water (90-92%), proteins, glucose, electrolytes, gases	Composition frequently tested; distinguish from serum
Serum	Plasma minus fibrinogen and clotting factors; fluid remaining after blood clots	Serum vs. plasma distinction is a direct definition question
Haematocrit (PCV)	Percentage of total blood volume occupied by RBCs after centrifugation (males ~42%, females ~40%)	Reflects oxygen-carrying capacity; anaemia vs. polycythaemia
Erythropoiesis	Process of RBC formation in red bone marrow; stimulated by erythropoietin (EPO) from kidneys	Site (red bone marrow) and stimulus (EPO, hypoxia) tested
Haemolysis	Rupture/destruction of RBCs with release of haemoglobin into plasma	Occurs in Rh incompatibility; hypotonic solutions
Thrombocytopenia	Abnormally low platelet count (<1.5 lakh/ $mm^{3}$ ); causes bleeding tendency	Associated with dengue fever — clinically relevant
Erythroblastosis fetalis	Haemolytic disease of newborn due to maternal anti-Rh IgG crossing placenta and destroying foetal RBCs	Mechanism and prevention (RhoGAM) are high-yield
Pacemaker (SAN)	Sinoatrial node; generates electrical impulses at 70-75 bpm, setting cardiac rhythm	Consistently tested — SAN is always the correct answer
Systole	Phase of cardiac muscle contraction (atrial: 0.1 s; ventricular: 0.3 s)	Phase durations are directly testable
Diastole	Phase of cardiac muscle relaxation; joint diastole = 0.4 s (all chambers relaxed)	Longest cardiac cycle phase
Depolarization	Electrical event where membrane potential changes from negative to positive; triggers contraction	QRS = ventricular depolarization; NOT contraction
Repolarization	Return of membrane potential to resting negative state; corresponds to relaxation	T wave = ventricular repolarization
Stroke Volume	Volume of blood ejected per beat per ventricle (~70 mL at rest)	Used in CO = SV × HR formula
Cardiac Output	Volume of blood pumped per minute = SV × HR (≈5 L/min at rest)	Formula and normal value directly tested
Atherosclerosis	Plaque formation (lipid, calcium, fibrous tissue) inside arterial walls, narrowing lumen	Cause of CAD and angina; risk factors tested
Angina Pectoris	Temporary chest pain due to insufficient $O_{2}$ supply to myocardium; reversible, no cell death	Distinguish from MI (irreversible cell death)
Myocardial Infarction	Prolonged coronary occlusion → irreversible cardiac muscle cell death (heart attack)	Caused by CAD; ST elevation on ECG
Mediastinum	Central thoracic cavity compartment where the heart is located (slightly left-tilted)	Heart location question