Important Notes For NEET Biology – Body Fluids and Circulation

Blood

Composition of Blood:

• Blood is a fluid connective tissue consisting of cells (RBCs, WBCs, and platelets).
• Plasma constitutes 55% of blood volume. It is a viscous fluid containing 90-92% water, 6-8% proteins (fibrinogens, albumins, globulins), amino acids, glucose, and electrolytes (Na+, Ca++, Cl–).
• Formed Elements include erythrocytes, leukocytes, and platelets.

Erythrocytes (RBCs):

• Most abundant cells in blood.
• Formed in bone marrow, biconcave, anucleate.
• Lifespan of 120 days, destroyed in the spleen.

Leukocytes (WBCs):

• Colorless due to the absence of hemoglobin.
• Life span of 3-4 days.
• Granulocytes: Neutrophils, Eosinophils, Basophils.
• Agranulocytes: Lymphocytes, Monocytes.

Blood Platelets (Thrombocytes):

• Formed from megakaryocytes in bone marrow.
• Involved in blood clotting.

Blood Groups

ABO Blood Group System:

• Four types: A, B, AB, O.
• Based on surface antigens on RBCs (A and B antigens).
• Blood Group A: Antigen A, Anti-B antibodies.
• Blood Group B: Antigen B, Anti-A antibodies.
• Blood Group AB: Antigens A and B, no antibodies (universal acceptor).
• Blood Group O: No antigens, Anti-A and Anti-B antibodies (universal donor).

Rh Grouping:

• Rh antigen present in 80% of people (Rh+).
• Erythroblastosis fetalis: Mother is Rh–, father is Rh+, fetus is Rh+. The condition can be managed by administering anti-Rh antibodies to the mother after the first childbirth.

Coagulation of Blood

• Blood clotting prevents excessive blood loss from injuries.
• Clot consists of fibrin, which traps blood cells.
• Clotting process:
  • Inactive fibrinogen → Fibrin (by Thrombin).
  • Prothrombin → Thrombin (by Thrombokinase).
• Ca++ is crucial in the coagulation process.

Lymph

• Lymph is a fluid connective tissue that drains interstitial fluid back to major veins.
• Contains lymphocytes, part of the immune system.
• Absorbs fats in the intestine through lacteals and transports them to blood.

Circulatory Pathways

Types:

• Open Circulatory System: Blood is in open cavities (sinuses), found in arthropods and molluscs.
• Closed Circulatory System: Blood circulates in vessels, found in annelids and chordates.

Human Circulatory System:

• Heart: Four-chambered, mesodermal origin, located between lungs in the thoracic cavity, protected by pericardium.
• Heart Structure:
  • Valves: Bicuspid (mitral) between left atrium and ventricle; Tricuspid between right atrium and ventricle; Semilunar at openings of pulmonary artery and aorta.
  • Nodal Tissue: SAN (pacemaker), AVN, Bundle of His, Purkinje fibers.
  • Blood Vessels: Arteries, veins, and capillaries; made of tunica intima, media, and externa.

Cardiac Cycle

• Joint Diastole: All four chambers relaxed.
• Atrial Systole: SAN initiates contraction.
• Ventricular Systole: AVN transfers action potential, ventricles contract.
• Ventricular Diastole: Semilunar valves close.
• Stroke Volume: Blood pumped by each ventricle per cycle (~70 ml).
• Cardiac Output: Total blood output per minute (~5 L).

Heart Sounds:

• Lub: Closure of bicuspid and tricuspid valves during ventricular systole.
• Dub: Closure of semilunar valves during ventricular diastole.

Electrocardiogram (ECG)

• P Wave: Atrial depolarization.
• QRS Complex: Ventricular depolarization.
• T Wave: Ventricular repolarization.
• Measures heart rate and detects abnormalities.

Double Circulation

• Pulmonary Circulation: Deoxygenated blood to lungs via pulmonary artery; oxygenated blood to left atrium via pulmonary vein.
• Systemic Circulation: Oxygenated blood from left ventricle to body; deoxygenated blood returns to right atrium.

Hepatic Portal System: Connects liver and digestive tract, transporting nutrients.

Regulation of Cardiac Activity

• Myogenic Heart: Activity regulated by nodal tissue.
• ANS Regulation: Sympathetic (increases rate) and parasympathetic (decreases rate) neural signals from medulla oblongata.

Disorders of the Circulatory System

• Hypertension: High blood pressure (>140/90 mm Hg).
• Coronary Artery Disease (CAD): Narrowing of arteries due to plaque.
• Angina: Chest pain due to insufficient oxygen to heart muscles.
• Heart Failure: Inability to pump sufficient blood.
• Coronary Thrombosis: Clot in coronary artery leading to heart attack.

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