Class 11 Biology Notes Chapter 18 (Chapter 18) – Examplar Problems (English) Book

Detailed Notes with MCQs of Chapter 18: Body Fluids and Circulation from your Biology Exemplar. This chapter is crucial not just for your Class 11 understanding but also forms a significant part of the syllabus for various government exams where Biology is tested. Pay close attention to the details.

Chapter 18: Body Fluids and Circulation - Detailed Notes

Introduction:
All living cells require nutrients, O₂, and other essential substances. Also, waste or harmful substances produced need continuous removal for healthy tissue function. Different groups of animals have evolved various methods for this transport. Simple organisms (sponges, coelenterates) circulate water from their surroundings through their body cavities. More complex organisms use special body fluids. Blood is the most common, and lymph also aids in transporting certain substances.

1. Blood

• Connective Tissue: Blood is a fluid connective tissue.
• Composition: Consists of:
  • Plasma: Straw-coloured, viscous fluid constituting nearly 55% of the blood.
    • Water: 90-92% of plasma.
    • Proteins: 6-8%. Major proteins are:
      • Fibrinogen: Needed for clotting or coagulation.
      • Globulins: Primarily involved in defense mechanisms (antibodies).
      • Albumins: Help in osmotic balance.
    • Minerals: Na⁺, Ca⁺⁺, Mg⁺⁺, HCO₃⁻, Cl⁻, etc.
    • Nutrients: Glucose, amino acids, lipids, etc.
    • Other substances: Clotting factors (inactive form), hormones, dissolved gases, waste products.
    • Serum: Plasma without the clotting factors (especially fibrinogen).
  • Formed Elements: Constitute about 45% of the blood. Include Erythrocytes, Leucocytes, and Platelets.
    • Erythrocytes (Red Blood Cells - RBCs):
      • Abundance: Most abundant of all cells in blood (5 to 5.5 million per mm³).
      • Formation: Erythropoiesis (occurs in red bone marrow in adults).
      • Structure: Biconcave shape, devoid of nucleus in most mammals (enucleated), lack mitochondria and other organelles. This increases surface area for gas exchange and allows more space for haemoglobin.
      • Haemoglobin (Hb): Red coloured, iron-containing complex protein. Each Hb molecule can carry 4 molecules of O₂. A healthy individual has 12-16 gms of Hb per 100 ml of blood.
      • Function: Transport of respiratory gases (mainly O₂, some CO₂).
      • Lifespan: Average 120 days. Destroyed in the spleen (graveyard of RBCs).
    • Leucocytes (White Blood Cells - WBCs):
      • Characteristics: Colourless (lack Hb), nucleated.
      • Abundance: Relatively lesser in number (6000-8000 per mm³). Generally short-lived.
      • Function: Part of the immune system, defense against pathogens.
      • Types:
        • Granulocytes: Contain granules in cytoplasm.
          • Neutrophils (60-65%): Most abundant WBCs. Phagocytic (destroy foreign organisms). Multi-lobed nucleus.
          • Eosinophils (2-3%): Resist infections, associated with allergic reactions. Bilobed nucleus. Stain with acidic dyes (eosin).
          • Basophils (0.5-1%): Least abundant. Secrete histamine, serotonin, heparin (involved in inflammatory reactions). S-shaped or lobed nucleus. Stain with basic dyes.
        • Agranulocytes: Lack granules in cytoplasm.
          • Lymphocytes (20-25%): Second most abundant. Large, round nucleus. Two major types:
            • B-lymphocytes: Produce antibodies (humoral immunity).
            • T-lymphocytes: Mediate cell-mediated immunity.
          • Monocytes (6-8%): Largest WBCs. Kidney or horse-shoe shaped nucleus. Phagocytic; differentiate into macrophages in tissues.
    • Platelets (Thrombocytes):
      • Origin: Cell fragments produced from megakaryocytes (special cells in bone marrow).
      • Abundance: 1,500,00 - 3,500,00 per mm³.
      • Function: Involved in coagulation or clotting of blood. Release platelet factors that initiate the clotting cascade. A reduction in number can lead to clotting disorders (excessive blood loss).

2. Blood Groups

• Based on the presence or absence of specific antigens (chemicals that induce immune response) on the surface of RBCs and corresponding antibodies in the plasma.
• ABO Grouping:
  • Based on presence/absence of A and B antigens on RBCs.
  • Plasma contains corresponding antibodies (anti-A, anti-B).
  • Group A: Antigen A, Antibody anti-B.
  • Group B: Antigen B, Antibody anti-A.
  • Group AB: Antigens A and B, No antibodies. (Universal Recipient)
  • Group O: No antigens, Antibodies anti-A and anti-B. (Universal Donor)
  • Blood Transfusion: Compatibility is crucial to avoid agglutination (clumping) of RBCs. Donor's antigens must not react with recipient's antibodies.
• Rh Grouping:
  • Based on the presence (Rh positive, Rh+) or absence (Rh negative, Rh-) of Rh antigen (similar to one found in Rhesus monkeys) on RBC surface.
  • About 80% of humans are Rh+.
  • Rh Incompatibility: Can occur if Rh- person is exposed to Rh+ blood (e.g., transfusion, pregnancy). Antibodies against Rh antigen develop.
  • Erythroblastosis Fetalis: A severe haemolytic disease of the newborn. Occurs when an Rh- mother carries an Rh+ fetus (father is Rh+). During the first delivery, some fetal Rh+ RBCs may enter the mother's circulation, causing her to produce anti-Rh antibodies. In subsequent Rh+ pregnancies, these antibodies can cross the placenta and destroy fetal RBCs. Can be prevented by administering anti-Rh antibodies (RhoGAM) to the mother immediately after the delivery of the first child.

3. Coagulation of Blood

• Mechanism to prevent excessive blood loss upon injury. Involves a cascade of enzymatic reactions.
• Process:
  1. Injury Site: Platelets aggregate and release platelet factors (e.g., thromboplastin). Injured tissues also release thromboplastin.
  2. Prothrombin Activator Complex: Formed by a series of linked enzymatic reactions (cascade process) involving plasma clotting factors (Factors I-XIII, mostly inactive proteins) and Ca⁺⁺ ions.
  3. Conversion of Prothrombin: The enzyme complex converts inactive plasma protein Prothrombin into active Thrombin.
  4. Conversion of Fibrinogen: Thrombin acts as an enzyme to convert inactive soluble plasma protein Fibrinogen into active insoluble Fibrin.
  5. Clot Formation: Fibrin molecules polymerize to form a network of threads that trap dead and damaged formed elements, forming a clot or coagulum.
• Key Requirements: Platelets, Plasma Clotting Factors, Vitamin K (essential for synthesis of some clotting factors in the liver), Ca⁺⁺ ions.

4. Lymph (Tissue Fluid)

• As blood passes through capillaries, water and small water-soluble substances move out into the spaces between cells of tissues, forming the interstitial fluid or tissue fluid.
• Composition: Similar to plasma but has fewer proteins, no RBCs, fewer platelets, but more lymphocytes. Same mineral distribution as plasma.
• Lymphatic System: An elaborate network of vessels (lymphatic capillaries and vessels), nodes, and organs (spleen, thymus, tonsils). Collects interstitial fluid and returns it to the major veins.
• Formation of Lymph: Interstitial fluid that enters the lymphatic vessels is called lymph.
• Functions:
  • Returns interstitial fluid and proteins to the blood.
  • Carries nutrients, hormones, etc.
  • Fat Absorption: Fats are absorbed through lymph (lacteals) in the intestinal villi.
  • Immune Response: Lymph nodes filter lymph and trap microorganisms. Lymphocytes and macrophages in lymph nodes destroy pathogens.

5. Circulatory Pathways

• Open Circulatory System: Found in arthropods and molluscs. Blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. Tissues are directly bathed in blood (haemolymph). Less efficient, slow flow.
• Closed Circulatory System: Found in annelids and vertebrates. Blood is confined to a network of vessels (arteries, veins, capillaries). Blood flow is more rapid and regulated. More efficient transport.
• Heart Chambers: Fish (2 chambers: 1 atrium, 1 ventricle), Amphibians & most Reptiles (3 chambers: 2 atria, 1 ventricle - mixing of oxygenated/deoxygenated blood in ventricle), Crocodiles, Birds & Mammals (4 chambers: 2 atria, 2 ventricles - complete separation of oxygenated/deoxygenated blood).
• Circulation Types:
  • Single Circulation: Blood passes through the heart only once in a complete circuit (e.g., Fish). Heart pumps deoxygenated blood to gills -> oxygenation -> supplied to body parts -> deoxygenated blood returns to heart.
  • Double Circulation: Blood passes through the heart twice in a complete circuit (e.g., Birds, Mammals).
    • Pulmonary Circulation: Right ventricle pumps deoxygenated blood to lungs -> oxygenation -> oxygenated blood returns to left atrium.
    • Systemic Circulation: Left ventricle pumps oxygenated blood to body tissues -> deoxygenation -> deoxygenated blood returns to right atrium.
  • Incomplete Double Circulation: Found in amphibians and reptiles (except crocodiles). The single ventricle receives both oxygenated (from lungs/skin) and deoxygenated (from body) blood, leading to some mixing.

6. Human Circulatory System

• Heart: Muscular pumping organ. Located in the thoracic cavity, between the lungs, slightly tilted to the left.
  • Size: Clenched fist.
  • Protection: Enclosed in a double-walled membranous bag, pericardium, containing pericardial fluid (reduces friction).
  • Walls: Epicardium (outer), Myocardium (middle, cardiac muscle), Endocardium (inner).
  • Chambers: Four chambers - two relatively small upper chambers called atria (right and left) and two larger lower chambers called ventricles (right and left).
  • Septa: Inter-atrial septum (separates atria), Inter-ventricular septum (separates ventricles), Atrio-ventricular septum (separates atrium and ventricle on each side).
  • Valves: Prevent backflow of blood.
    • Tricuspid Valve: Between right atrium and right ventricle (3 muscular flaps/cusps).
    • Bicuspid (Mitral) Valve: Between left atrium and left ventricle (2 cusps).
    • Semilunar Valves: At the base of pulmonary artery (leaving right ventricle) and aorta (leaving left ventricle). Prevent backflow into ventricles.
• Nodal Tissue (Conducting System): Specialized cardiac musculature responsible for initiation and conduction of heart beat. Auto-excitable.
  • Sino-atrial Node (SA Node): Patch of nodal tissue in the upper right corner of the right atrium. Pacemaker - initiates cardiac impulse (max rate: 70-75/min).
  • Atrio-ventricular Node (AV Node): Mass of nodal tissue in the lower-left corner of the right atrium, close to the AV septum. Receives impulse from SA node.
  • AV Bundle (Bundle of His): Bundle of nodal fibres continuing from AV node, passes through AV septum to the top of inter-ventricular septum.
  • Purkinje Fibres: Branches of AV bundle that spread throughout the ventricular musculature.
  • Conduction Pathway: SA node -> Atrial contraction -> AV node (slight delay) -> Bundle of His -> Purkinje fibres -> Ventricular contraction.

7. Cardiac Cycle

• Sequential events in the heart which are cyclically repeated. Consists of systole (contraction) and diastole (relaxation) of atria and ventricles.
• Duration: Approx 0.8 seconds (assuming 72 beats/min).
• Phases:
  1. Joint Diastole (approx 0.4 sec): All four chambers are relaxed. Blood flows passively from pulmonary veins and vena cava into left and right atria respectively, and then into ventricles (AV valves open). Semilunar valves are closed.
  2. Atrial Systole (approx 0.1 sec): SA node generates action potential, atria contract. Remaining blood (about 30% increase) is forced into ventricles.
  3. Ventricular Systole (approx 0.3 sec): Impulse reaches ventricles via AV bundle/Purkinje fibres, ventricles contract.
     • Ventricular pressure increases, causing closure of AV valves ("Lub" sound - first heart sound, longer duration).
     • Ventricular pressure exceeds pressure in pulmonary artery and aorta, forcing semilunar valves open. Blood is ejected into these arteries.
  4. Ventricular Diastole: Ventricles relax. Ventricular pressure falls.
     • Closure of semilunar valves ("Dub" sound - second heart sound, shorter duration) prevents backflow from arteries.
     • As ventricular pressure falls below atrial pressure, AV valves open, initiating the next cycle (return to Joint Diastole).
• Stroke Volume (SV): Volume of blood pumped by each ventricle per beat (approx 70 mL).
• Cardiac Output (CO): Volume of blood pumped by each ventricle per minute. CO = SV × Heart Rate (HR). (Approx 70 mL/beat × 72 beats/min ≈ 5040 mL/min or 5 Litres/min). Can be altered by physiological demands.

8. Electrocardiograph (ECG)

• Graphical representation of the electrical activity of the heart during a cardiac cycle. Machine used is electrocardiograph; the graph is electrocardiogram.
• Procedure: Standard ECG uses 3 electrical leads attached to wrists and left ankle (or multiple leads attached to chest region).
• Waves:
  • P Wave: Represents electrical excitation (or depolarisation) of the atria, leading to atrial contraction.
  • QRS Complex: Represents depolarisation of the ventricles, initiating ventricular contraction. (Q marks beginning, S marks end). Atrial repolarisation occurs during this phase but is masked.
  • T Wave: Represents the return of the ventricles from excited to normal state (repolarisation). Marks the end of systole.
• Clinical Significance: Deviations from the normal ECG shape indicate possible abnormality or disease. Counting QRS complexes determines heart rate.

9. Double Circulation

• As seen in humans, blood flows through two distinct circuits:
  • Pulmonary Circulation: Right Ventricle → Pulmonary Artery (deoxygenated blood) → Lungs (oxygenation) → Pulmonary Veins (oxygenated blood) → Left Atrium.
  • Systemic Circulation: Left Ventricle → Aorta (oxygenated blood) → Arteries → Arterioles → Capillaries (in tissues, exchange occurs) → Venules → Veins → Vena Cava (deoxygenated blood) → Right Atrium.
• Hepatic Portal System: Unique vascular connection between the digestive tract and liver. Hepatic portal vein carries blood from intestine to the liver before it is delivered to the systemic circulation. Allows liver to process absorbed nutrients and detoxify substances.
• Significance: Complete segregation of oxygenated and deoxygenated blood allows for efficient oxygen supply to body tissues, necessary for warm-blooded animals (birds, mammals) with high metabolic rates.

10. Regulation of Cardiac Activity

• Normal heart activities are auto-regulated (by SA node). However, they can be moderated by neural and hormonal mechanisms.
• Neural Control: Medulla oblongata has a cardiac centre.
  • Sympathetic Nerves (part of Autonomic Nervous System - ANS): Increase heart rate, strength of ventricular contraction, and cardiac output.
  • Parasympathetic Nerves (Vagus nerve, part of ANS): Decrease heart rate, speed of conduction of action potential, and cardiac output.
• Hormonal Control: Adrenal medullary hormones (epinephrine/adrenaline and norepinephrine/noradrenaline) increase cardiac output during stress/emergency.

11. Disorders of Circulatory System

• Hypertension (High Blood Pressure): BP higher than normal (120/80 mmHg; 120=systolic, 80=diastolic). Persistent BP of 140/90 or higher is hypertension. Can damage heart, brain, kidneys. Lifestyle factors contribute.
• Coronary Artery Disease (CAD): Also called Atherosclerosis. Affects vessels supplying blood to the heart muscle. Caused by deposition of calcium, fat, cholesterol, and fibrous tissues in coronary arteries, making the lumen narrower. Reduces blood flow to heart muscle.
• Angina (Angina Pectoris): Symptom of acute chest pain appearing when not enough oxygen is reaching the heart muscle (often due to CAD). Occurs more often during exertion. Common in middle-aged and elderly.
• Heart Failure: State where the heart is not pumping blood effectively enough to meet the needs of the body. Sometimes called congestive heart failure because congestion of the lungs is a main symptom. Different from cardiac arrest (heart stops beating) or heart attack (heart muscle suddenly damaged).
• Myocardial Infarction (Heart Attack): Sudden damage or death of heart muscle tissue (myocardium) due to inadequate blood supply (usually caused by blockage of a coronary artery).
• Cardiac Arrest: Complete cessation of heartbeat.

Multiple Choice Questions (MCQs)

1. Which of the following plasma proteins is primarily involved in the osmotic balance of blood?
   a) Fibrinogen
   b) Globulin
   c) Albumin
   d) Prothrombin

2. Erythroblastosis fetalis can occur if:
   a) Mother is Rh+ and fetus is Rh-
   b) Mother is Rh- and fetus is Rh+
   c) Both mother and fetus are Rh-
   d) Both mother and fetus are Rh+

3. The second heart sound ("Dub") is associated with the closure of which valves?
   a) Tricuspid valve
   b) Bicuspid (Mitral) valve
   c) Semilunar valves
   d) Both Tricuspid and Bicuspid valves

4. Which component of the ECG represents ventricular repolarisation?
   a) P wave
   b) QRS complex
   c) T wave
   d) U wave

5. Which type of leucocyte is most abundant in human blood and acts as a primary phagocytic cell?
   a) Lymphocyte
   b) Eosinophil
   c) Basophil
   d) Neutrophil

6. The pacemaker of the human heart is:
   a) AV node
   b) SA node
   c) Purkinje fibres
   d) Bundle of His

7. Incomplete double circulation, where oxygenated and deoxygenated blood mix in the ventricle, is characteristic of:
   a) Fish
   b) Birds
   c) Amphibians
   d) Mammals

8. The process of blood coagulation requires the presence of which ion?
   a) Na⁺
   b) K⁺
   c) Ca⁺⁺
   d) Mg⁺⁺

9. Serum differs from blood plasma in lacking:
   a) Albumins
   b) Globulins
   c) Clotting factors (like Fibrinogen)
   d) Antibodies

10. What is the approximate duration of the cardiac cycle in a healthy human at rest?
    a) 0.5 seconds
    b) 0.8 seconds
    c) 1.0 second
    d) 1.2 seconds

Answer Key for MCQs:

1. c) Albumin
2. b) Mother is Rh- and fetus is Rh+
3. c) Semilunar valves
4. c) T wave
5. d) Neutrophil
6. b) SA node
7. c) Amphibians
8. c) Ca⁺⁺
9. c) Clotting factors (like Fibrinogen)
10. b) 0.8 seconds

Study these notes thoroughly. Remember to correlate this information with diagrams from your textbook, especially the structure of the heart, ECG waves, and the circulatory pathways. Understanding the mechanisms, like coagulation and the cardiac cycle, is key for competitive exams. Let me know if any specific part needs further clarification. Good luck with your preparation!