Body Fluids and Circulation

Body Fluids and Circulation Notes

Overview

  • All living cells require nutrients, oxygen (O₂), and removal of waste products for proper functioning.

  • Different organisms have developed specialized transport mechanisms for these substances.

  • Simple organisms (e.g., sponges and coelenterates) circulate water for substance exchange, while more complex organisms use specialized fluids like blood and lymph.

Blood

  • Blood is categorized as a special connective tissue composed of:

  • Plasma (fluid matrix)

  • Formed Elements (cells)

15.1.1 Plasma

  • Composition: 55% of blood volume; 90-92% is water, 6-8% proteins.

  • Major Proteins:

  • Fibrinogen: essential for blood clotting.

  • Globulins: involved in immune response and defense mechanisms.

  • Albumins: maintain osmotic balance.

  • Other Components:

  • Minerals (Na⁺, Ca²⁺, Mg²⁺, HCO₃⁻, Cl⁻)

  • Glucose, lipids, amino acids (nutrients in transit)

  • Clotting factors (inactive form; serum is plasma minus clotting factors)

15.1.2 Formed Elements

  • Constitute ~45% of blood volume.

  • Erythrocytes (Red Blood Cells, RBCs):

  • Most abundant; avg. 5-5.5 million/mm³ in adults.

  • Formed in red bone marrow; biconcave, enucleated.

  • Contain hemoglobin (~12-16g per 100ml blood); main role in oxygen transport.

  • Lifespan: ~120 days; destroyed in the spleen.

  • Leucocytes (White Blood Cells, WBCs):

  • Colorless, nucleated; avg. 6000-8000/mm³.

  • Categories:

    • Granulocytes: Neutrophils, eosinophils, basophils.

    • Neutrophils (60-65% WBCs): phagocytic (destroy pathogens).

    • Eosinophils (2-3%): combat infections, allergies.

    • Basophils (0.5-1%): participate in inflammatory responses.

    • Agranulocytes: Lymphocytes (20-25%) and monocytes (6-8%).

    • Lymphocytes: responsible for immune responses (B and T cells).

  • Platelets (Thrombocytes):

  • Cell fragments from megakaryocytes; 150,000-350,000/mm³.

  • Key in blood clotting; low levels result in clotting disorders.

15.1.3 Blood Groups

  • ABO System: Based on presence of A and B antigens on RBC surface.

  • Blood Groups:

    • Group A: A antigen, anti-B antibodies

    • Group B: B antigen, anti-A antibodies

    • Group AB: A and B antigens, no antibodies (universal recipient)

    • Group O: No antigens, anti-A and anti-B antibodies (universal donor)

  • Rh Factor:

  • Rh+ (presence of Rh antigen) vs. Rh- (absence of Rh antigen).

  • Rh incompatibility risk in pregnancy leading to erythroblastosis foetalis if Rh- mother carries an Rh+ fetus.

15.1.4 Coagulation of Blood

  • Blood clotting prevents excessive bleeding during injuries.

  • The process:

  • Fibrinogen is converted to fibrin (clot framework) by thrombin.

  • Prothrombin is activated to thrombin with calcium ions and thrombokinase.

  • Triggered by platelets and tissue factors at injury sites.

Lymph (Tissue Fluid)

  • Formed when blood plasma exits capillaries, becoming interstitial fluid.

  • Returns via the lymphatic system:

  • Contains lymphocytes for immune responses.

  • Transports nutrients and hormones; fats absorbed through lacteals (intestinal villi).

Circulatory Pathways

  • Open vs. Closed Circulation:

  • Open: Blood flows through sinuses (arthropods, mollusks).

  • Closed: Blood contained in vessels (vertebrates).

  • Heart Structure:

  • Fishes: 2-chambered heart (single circulation).

  • Amphibians/Reptiles: 3-chambered heart (incomplete double circulation).

  • Birds/Mammals: 4-chambered heart (double circulation).

Human Circulatory System

  • Comprises: muscular heart, closed vessel network, blood.

  • Heart Structure:

  • 4 chambers: 2 atria, 2 ventricles.

  • Valves ensure unidirectional blood flow (tricuspid, bicuspid, semilunar)

  • Cardiac muscle with nodal tissues regulating rhythm (SAN as pacemaker).

Cardiac Cycle

  • Phases: Diastole (relaxation) and systole (contraction).

  • Heart Rate: Average 70-75 beats/min; cardiac cycle approx. 0.8 seconds.

  • Each ventricle pumps ~70 mL of blood (stroke volume) per beat.

  • Cardiac output = Stroke Volume × Heart Rate (~5 L/min).

  • Heart sounds:

  • "Lub" (closure of AV valves)

  • "Dub" (closure of semilunar valves).

Electrocardiography (ECG)

  • Graphical representation of heart’s electrical activity.

  • Each segment represents specific cardiac events:

  • P-wave: Atrial depolarization.

  • QRS complex: Ventricular depolarization.

  • T-wave: Ventricular repolarization.

Double Circulation

  • Refers to systemic and pulmonary circuits:

  • Pulmonary: Deoxygenated blood from right ventricle to lungs, then oxygenated blood back to left atrium.

  • Systemic: Oxygenated blood from left ventricle to body, returning deoxygenated blood to right atrium via vena cava.

Regulation of Cardiac Activity

  • Heart rate is auto-regulated:

  • Sympathetic NS: Increases heart rate/output.

  • Parasympathetic NS: Decreases heart rate/output.

  • Influence of hormonal signals (e.g., adrenal hormones increase output).

Disorders of Circulatory System

  • Hypertension: Blood pressure >140/90 mm Hg; risks for heart/kidney damage.

  • Coronary Artery Disease (CAD): Narrowing of heart blood supply vessels.

  • Angina: Chest pain due to inadequate oxygen to heart muscle.

  • Heart Failure: Ineffective pumping of heart; may cause congestion.