Comprehensive Notes on Body Fluids and Circulation

Body Fluids and Circulation

Introduction

  • All living cells require nutrients, O2, and the removal of waste.
  • Efficient mechanisms are essential for substance movement to and from cells.
  • Simple organisms (sponges, coelenterates) circulate water through body cavities.
  • Complex organisms use special body fluids for transport; blood is most common.
  • Lymph is another body fluid that aids in transport.

15.1 Blood

  • Special connective tissue consists of fluid matrix, plasma, and formed elements.
15.1.1 Plasma
  • Straw-colored, viscous fluid; about 55% of blood.
  • Composition:
    • 90-92% water.
    • 6-8% proteins (fibrinogen, globulins, albumins).
    • Small amounts of minerals (Na+, Ca++, Mg++, HCO3–, Cl–, etc.).
    • Glucose, amino acids, lipids.
    • Clotting factors (inactive form).
  • Fibrinogens: involved in clotting/coagulation.
  • Globulins: involved in defense mechanisms.
  • Albumins: help in osmotic balance.
  • Serum: plasma without clotting factors.
15.1.2 Formed Elements
  • Erythrocytes, leucocytes, and platelets; about 45% of blood.
  • Erythrocytes (Red Blood Cells - RBCs):
    • Most abundant.
    • 5−5.55 - 5.5 million RBCs mm−3mm^{-3} of blood (healthy adult male).
    • Formed in red bone marrow (adults).
    • Devoid of nucleus (most mammals), biconcave shape.
    • Contain hemoglobin (iron-containing complex protein).
    • 12-16 gms of haemoglobin in every 100 ml of blood.
    • Transport respiratory gases.
    • Life span: 120 days; destroyed in the spleen (graveyard of RBCs).
  • Leucocytes (White Blood Cells - WBCs):
    • Colorless (lack hemoglobin).
    • Nucleated, lesser in number: 6000−80006000 - 8000 mm−3mm^{-3} of blood.
    • Generally short-lived.
    • Two main categories: granulocytes and agranulocytes.
      • Granulocytes: Neutrophils, eosinophils, and basophils.
      • Agranulocytes: Lymphocytes and monocytes.
    • Neutrophils: Most abundant (60-65% of total WBCs).
    • Basophils: Least abundant (0.5-1%). Secrete histamine, serotonin, heparin; involved in inflammatory reactions.
    • Eosinophils: (2-3%) resist infections, associated with allergic reactions.
    • Neutrophils and monocytes (6-8%) are phagocytic cells.
    • Lymphocytes (20-25%): B and T forms; responsible for immune responses.
  • Platelets (Thrombocytes):
    • Cell fragments from megakaryocytes (bone marrow).
    • 150,000−350,000150,000 - 350,000 platelets mm−3mm^{-3}.
    • Release substances for coagulation/clotting.
    • Reduction in number leads to clotting disorders.
15.1.3 Blood Groups
  • ABO and Rh groupings are widely used.
15.1.3.1 ABO Grouping
  • Based on presence/absence of A and B surface antigens on RBCs.
  • Plasma contains natural antibodies (anti-A, anti-B).
  • Four blood groups: A, B, AB, O.
  • Blood transfusion requires matching donor and recipient blood to avoid clumping.
  • Group O: universal donors (can donate to any group).
  • Group AB: universal recipients (can receive blood from any group).
15.1.3.2 Rh Grouping
  • Rh antigen (similar to Rhesus monkeys) present on RBCs of most humans (80%).
  • Rh positive (Rh+ve): have the antigen.
  • Rh negative (Rh-ve): lack the antigen.
  • Rh-ve person exposed to Rh+ve blood forms antibodies.
  • Rh group must be matched before transfusions.
  • Rh Incompatibility: Rh-ve mother with Rh+ve foetus.
    • First pregnancy: no exposure, but mother may develop antibodies during delivery.
    • Subsequent pregnancies: maternal Rh antibodies can attack foetal RBCs.
    • Erythroblastosis foetalis: can be fatal to the foetus, cause anaemia and jaundice.
    • Prevention: administer anti-Rh antibodies to the mother after the first delivery.
15.1.4 Coagulation of Blood
  • Clotting prevents excessive blood loss after injury.
  • Dark reddish-brown scum (clot/coagulum) forms at the injury site.
  • Fibrins: network of threads trapping dead/damaged formed elements.
  • Fibrin formation: inactive fibrinogens converted by thrombin.
  • Thrombin formation: from inactive prothrombin, requires thrombokinase.
  • Thrombokinase formation: cascade process involving plasma factors.
  • Injury stimulates platelets to release factors activating coagulation.
  • Tissue factors at injury site can initiate coagulation.
  • Calcium ions play a crucial role in clotting.

15.2 Lymph (Tissue Fluid)

  • Water and small water-soluble substances move out of blood capillaries into tissue spaces.
  • Interstitial fluid/tissue fluid: fluid released out.
  • Same mineral distribution as plasma.
  • Nutrient/gas exchange between blood and cells occurs through this fluid.
  • Lymphatic system: network of vessels collecting fluid and returning it to veins.
  • Lymph: colourless fluid containing lymphocytes (immune responses).
  • Important carrier for nutrients, hormones.
  • Fats absorbed through lymph in lacteals of intestinal villi.

15.3 Circulatory Pathways

  • Two types: open and closed.
  • Open circulatory system: arthropods and molluscs; blood passes through large vessels into open spaces/sinuses.
  • Closed circulatory system: annelids and chordates; blood circulates through closed network of vessels.
  • Closed system more advantageous: precise regulation of fluid flow.
  • Vertebrates: muscular chambered heart.
    • Fishes: 2-chambered heart (1 atrium, 1 ventricle); single circulation.
    • Amphibians and reptiles (except crocodiles): 3-chambered heart (2 atria, 1 ventricle); incomplete double circulation.
    • Crocodiles, birds, and mammals: 4-chambered heart (2 atria, 2 ventricles); double circulation.
  • Single circulation (fish): heart pumps deoxygenated blood to gills for oxygenation.
  • Incomplete double circulation (amphibians, reptiles): mixing of oxygenated and deoxygenated blood in the single ventricle.
  • Double circulation (birds, mammals): separate pathways for oxygenated and deoxygenated blood.
15.3.1 Human Circulatory System
  • Blood vascular system: muscular chambered heart, closed branching blood vessels, and circulating blood.
  • Heart: mesodermally derived, in thoracic cavity between lungs, tilted left; size of clenched fist.
  • Protected by pericardium (double-walled membranous bag) enclosing pericardial fluid.
  • Four chambers: 2 atria (upper, smaller), 2 ventricles (lower, larger).
  • Inter-atrial septum: separates atria.
  • Inter-ventricular septum: separates ventricles.
  • Atrio-ventricular septum: separates atria and ventricles; openings allow connection.
  • Tricuspid valve: between right atrium and right ventricle (3 flaps/cusps).
  • Bicuspid/mitral valve: between left atrium and left ventricle.
  • Semilunar valves: at openings of right ventricle into pulmonary artery, and left ventricle into aorta.
  • Valves allow one-way flow: atria to ventricles, ventricles to pulmonary artery/aorta; prevent backflow.
  • Heart made of cardiac muscles.
  • Ventricle walls thicker than atria.
  • Nodal tissue: specialized cardiac musculature.
    • Sino-atrial node (SAN): right upper corner of right atrium.
    • Atrio-ventricular node (AVN): lower left corner of right atrium, close to atrio-ventricular septum.
    • Atrio-ventricular bundle (AV bundle): from AVN, passes through atrio-ventricular septa, divides into right and left bundles.
    • Purkinje fibres: arise from bundle branches, spread throughout ventricular musculature.
  • Nodal musculature: autoexcitable (generates action potentials without external stimuli).
  • SAN generates maximum action potentials (70-75 min-1); pacemaker.
  • Heart beats normally 70-75 times per minute (average 72 beats min-1).
15.3.2 Cardiac Cycle
  • Joint diastole: all four chambers relaxed; tricuspid and bicuspid valves open; blood flows from pulmonary veins/vena cava into ventricles.
  • Semilunar valves closed.
  • SAN generates action potential causing atrial systole (atrial contraction).
  • Increases blood flow into ventricles by about 30%.
  • Action potential travels to AVN and AV bundle -> bundle of His -> ventricular musculature.
  • Ventricular systole (ventricular contraction): atria relax (diastole).
  • Ventricular pressure increases: tricuspid and bicuspid valves close (prevent backflow).
  • Semilunar valves open: blood flows into pulmonary artery and aorta.
  • Ventricular diastole (ventricles relax): ventricular pressure falls, semilunar valves close (prevent backflow).
  • Tricuspid and bicuspid valves open: blood moves from atria to ventricles.
  • Joint diastole: ventricles and atria relaxed.
  • SAN generates new action potential: cycle repeats.
  • Cardiac cycle: sequential events in heart, cyclically repeated (systole and diastole of atria and ventricles).
  • Heart beats 72 times per minute: 72 cardiac cycles per minute.
  • Duration of cardiac cycle: 0.8 seconds.
  • Stroke volume: each ventricle pumps out approximately 70 mL of blood per cycle.
  • Cardiac output: volume of blood pumped out by each ventricle per minute.
    • Cardiac output == stroke volume ∗* heart rate.
    • Averages 5000 mL or 5 litres in a healthy individual.
  • Body can alter stroke volume/heart rate to change cardiac output.
  • Athlete's cardiac output higher than ordinary man's.
  • Heart sounds:
    • First heart sound (lub): closure of tricuspid and bicuspid valves.
    • Second heart sound (dub): closure of semilunar valves.
    • Clinically significant for diagnosis.
15.3.3 Electrocardiogram (ECG)
  • Graphical representation of electrical activity of heart during a cardiac cycle.
  • Obtained using an electrocardiograph.
  • Standard ECG: three electrical leads (wrists and left ankle).
  • Multiple leads for detailed evaluation.
  • P-wave: atrial depolarisation (excitation), leads to atrial contraction.
  • QRS complex: ventricular depolarisation, initiates ventricular contraction (systole).
  • T-wave: ventricular repolarisation (return to normal state); end of systole.
  • Heartbeat rate determined by counting QRS complexes.
  • Deviations from normal ECG shape indicate possible abnormality/disease.

15.4 Double Circulation

  • Blood flows through arteries and veins.
  • Arteries and veins have three layers:
    • Tunica intima: inner lining of squamous endothelium.
    • Tunica media: middle layer of smooth muscle and elastic fibres; thinner in veins.
    • Tunica externa: external layer of fibrous connective tissue with collagen fibres.
  • Pulmonary circulation: right ventricle pumps deoxygenated blood to lungs; oxygenated blood returns to left atrium via pulmonary veins.
  • Systemic circulation: left ventricle pumps oxygenated blood to tissues via aorta; deoxygenated blood returns to right atrium via venules, veins, and vena cava.
  • Systemic circulation provides nutrients, O2, and removes CO2 and waste.
  • Hepatic portal system: unique vascular connection between digestive tract and liver (hepatic portal vein).
  • Coronary system: blood vessels for circulation to/from cardiac musculature.

15.5 Regulation of Cardiac Activity

  • Normal activities auto-regulated by nodal tissue: myogenic.
  • Medulla oblongata: neural center moderating cardiac function via autonomic nervous system (ANS).
  • Sympathetic nerves (ANS): increase heart rate, ventricular contraction strength, and cardiac output.
  • Parasympathetic nerves (ANS): decrease heart rate, conduction speed, and cardiac output.
  • Adrenal medullary hormones: increase cardiac output.

15.6 Disorders of Circulatory System

  • Hypertension (High Blood Pressure): blood pressure higher than normal (120/80 mm Hg).
    • Systolic pressure: 120 mm Hg (pumping pressure).
    • Diastolic pressure: 80 mm Hg (resting pressure).
    • Hypertension: repeated checks >=140/90>= 140/90 mm Hg.
    • Leads to heart diseases and affects vital organs (brain, kidney).
  • Coronary Artery Disease (CAD) / Atherosclerosis: affects vessels supplying blood to heart muscle.
    • Caused by calcium, fat, cholesterol, and fibrous tissue deposits narrowing artery lumen.
  • Angina (Angina Pectoris): acute chest pain due to insufficient oxygen reaching heart muscle.
    • More common in middle-aged and elderly, affects both men and women.
    • Occurs due to reduced blood flow.
  • Heart Failure: heart not pumping blood effectively enough to meet body's needs.
    • Congestive heart failure: congestion of lungs is a main symptom.
    • Not the same as cardiac arrest (heart stops) or heart attack (sudden damage due to inadequate blood supply).