class 11 notes

Class 11 Biology Notes Chapter 18 (Body fluids and circulation) – Biology Book

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Philoid

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Biology
Detailed Notes with MCQs of Chapter 18: Body Fluids and Circulation. This is a crucial chapter, not just for understanding human physiology but also frequently tested in various government examinations. Pay close attention to the details.

Chapter 18: Body Fluids and Circulation - Detailed Notes

1. Introduction

  • All living cells need nutrients, O2, and other essential substances. Also, waste or harmful substances produced need to be removed continuously for healthy functioning.
  • Different groups of animals have evolved different methods for this transport. Simple organisms (sponges, coelenterates) circulate water from their surroundings through their body cavities. More complex organisms use special body fluids.
  • Body Fluids: Blood is the most common. Lymph also helps in transport.

2. Blood

  • A special connective tissue consisting of a fluid matrix (Plasma) and Formed Elements.

    • A. Plasma:

      • Straw-coloured, viscous fluid constituting nearly 55% of the blood.
      • Composition: 90-92% water, 6-8% proteins.
      • Major Proteins:
        • Fibrinogen: Needed for clotting or coagulation of blood. Produced by the liver.
        • Globulins: Primarily involved in defense mechanisms (antibodies are gamma globulins). Also involved in transport.
        • Albumins: Help in maintaining osmotic balance. Most abundant plasma protein.
      • Also contains small amounts of minerals (Na+, Ca++, Mg++, HCO3–, Cl–, etc.), glucose, amino acids, lipids, hormones, urea, O2, CO2.
      • Serum: Plasma without the clotting factors (mainly fibrinogen).

    • B. Formed Elements:

      • Constitute about 45% of the blood.

      • Includes Erythrocytes (RBCs), Leucocytes (WBCs), and Thrombocytes (Platelets).

      • i. Erythrocytes (Red Blood Cells - RBCs):

        • Most abundant of all cells in blood.
        • Count: 5 million to 5.5 million RBCs mm–3 of blood (in healthy adult man).
        • Formation: Red bone marrow in adults (Erythropoiesis).
        • Structure: Biconcave shape. Devoid of nucleus in most mammals (enucleated). Lack mitochondria and other organelles. This maximizes space for haemoglobin and allows flexibility.
        • Haemoglobin (Hb): Red coloured, iron-containing complex protein. Essential for O2 transport. A healthy individual has 12-16 gms of Hb per 100 ml of blood.
        • Lifespan: Average 120 days.
        • Destruction: Destroyed in the spleen (hence, spleen is called the 'graveyard of RBCs').

      • ii. Leucocytes (White Blood Cells - WBCs):

        • Colourless due to lack of haemoglobin. Nucleated. Relatively lesser in number.
        • Count: Average 6000-8000 mm–3 of blood. Generally short-lived.
        • Function: Part of the immune system.
        • Two main categories:
          • Granulocytes: Contain granules in their cytoplasm. Include:
            • 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. Include:
            • Lymphocytes (20-25%): Second most abundant. Large round nucleus. Two major types: B-lymphocytes and T-lymphocytes. Responsible for specific immune responses.
            • Monocytes (6-8%): Largest WBCs. Kidney or horse-shoe shaped nucleus. Phagocytic cells; mature into macrophages in tissues.

      • iii. Thrombocytes (Platelets):

        • Cell fragments produced from megakaryocytes (special cells in bone marrow).
        • Count: 1,500,00 - 3,500,00 mm–3 of blood.
        • Function: Involved in coagulation or clotting of blood by releasing various substances (e.g., thromboplastin). Reduction in their number can lead to clotting disorders.

3. Blood Groups

  • Based on the presence or absence of specific chemicals (antigens) on the surface of RBCs and corresponding antibodies in the plasma.

  • A. ABO Grouping:

    • Based on the presence or absence of two surface antigens (A and B) on RBCs.
    • Plasma contains corresponding antibodies (anti-A and anti-B).
    • Four blood groups: A, B, AB, and O.
    Blood Group Antigen on RBC Antibody in Plasma Can Donate To Can Receive From
    A A anti-B A, AB A, O
    B B anti-A B, AB B, O
    AB A and B None AB A, B, AB, O
    O None anti-A and anti-B A, B, AB, O O
    • Universal Donor: Blood group O (no antigens on RBCs).
    • Universal Recipient: Blood group AB (no antibodies in plasma against A or B antigens).
    • Blood transfusion must be carefully matched to avoid agglutination (clumping) of RBCs.

  • B. Rh Grouping:

    • Based on the presence or absence of another antigen, the Rh antigen (similar to one present in Rhesus monkeys), on the surface of RBCs.
    • Rh positive (Rh+ve): Rh antigen present (approx. 80% of humans).
    • Rh negative (Rh-ve): Rh antigen absent.
    • Rh-ve person, if exposed to Rh+ve blood, will form anti-Rh antibodies.
    • Erythroblastosis Fetalis: A severe haemolytic disease of the newborn. Occurs when an Rh-ve mother carries an Rh+ve fetus (father is Rh+ve). During the first delivery, some fetal Rh+ve RBCs may enter the mother's circulation, causing her to develop anti-Rh antibodies. In subsequent Rh+ve pregnancies, these maternal 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.

4. Coagulation of Blood (Clotting)

  • Mechanism to prevent excessive blood loss upon injury.
  • Involves a cascade process (series of linked enzymatic reactions).
  • Steps:
    1. Injury site: Platelets and damaged tissues release thromboplastin (or thrombokinase).
    2. Thrombokinase activates Prothrombin (inactive plasma protein) into Thrombin (active enzyme). This step requires Ca++ ions.
    3. Thrombin acts as an enzyme to convert soluble Fibrinogen (plasma protein) into insoluble Fibrin threads.
    4. Fibrin threads form a network-like mesh at the site of injury, trapping dead and damaged formed elements (RBCs, WBCs, platelets) to form a clot or coagulum.
  • Role of Vitamin K: Essential for the synthesis of prothrombin in the liver.
  • Role of Calcium ions (Ca++): Very important in the clotting cascade.

5. Lymph (Tissue Fluid)

  • As blood passes through capillaries, some water along with small water-soluble substances move out into the spaces between cells, forming the interstitial fluid or tissue fluid.
  • Composition: Similar to plasma but has fewer proteins, no RBCs, fewer platelets, but more lymphocytes. It's essentially blood minus RBCs, platelets, and large plasma proteins.
  • Exchange of nutrients, gases, etc., between blood and cells occurs through this fluid.
  • Lymphatic System: An elaborate network of vessels collects this fluid and drains it back into the major veins.
    • Fluid within lymphatic vessels is called Lymph.
    • Lymphatic capillaries -> Lymphatic vessels -> Lymph nodes -> Larger ducts (Thoracic duct, Right lymphatic duct) -> Subclavian veins.
  • Functions of Lymph:
    • Carries nutrients, hormones, etc.
    • Important carrier for fats absorbed through lacteals present in the intestinal villi.
    • Contains lymphocytes and antibodies, playing a crucial role in the immune system. Lymph nodes filter lymph and trap microorganisms.

6. Circulatory Pathways

  • Open Circulatory System: Blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses. Found in arthropods and molluscs. Blood flows at low pressure.
  • Closed Circulatory System: Blood pumped by the heart is always circulated through a closed network of blood vessels (arteries, veins, capillaries). Found in annelids, cephalopod molluscs, echinoderms, and vertebrates. Blood flow is more precisely regulated, higher pressure.

7. Human Circulatory System (Blood Vascular System)

  • Consists of a muscular chambered Heart, a network of closed branching Blood Vessels, and Blood (the fluid).

    • A. Heart:

      • Mesodermally derived organ. Located in the thoracic cavity, between the lungs, slightly tilted to the left.
      • Size: Roughly of a clenched fist.
      • Protection: Enclosed in a double-walled membranous bag, Pericardium, containing pericardial fluid (reduces friction).
      • Chambers: Four chambers - two relatively small upper chambers called Atria (singular: Atrium) and two larger lower chambers called Ventricles.
      • Septa: Inter-atrial septum (thin, muscular) separates the right and left atria. Inter-ventricular septum (thick-walled) separates the right and left ventricles. Atrio-ventricular septum separates atria from ventricles.
      • Valves: Prevent backflow of blood.
        • Tricuspid Valve: Guards the opening between the right atrium and right ventricle (has 3 muscular flaps or cusps).
        • Bicuspid (Mitral) Valve: Guards the opening between the left atrium and left ventricle (has 2 cusps).
        • Semilunar Valves: Guard the openings of ventricles into the pulmonary artery (from right ventricle) and aorta (from left ventricle).
      • Chordae Tendineae: Fibrous cords attached to the flaps of AV valves and papillary muscles in the ventricles, preventing valve inversion during ventricular contraction.
      • Heart Wall: Epicardium (outer thin layer), Myocardium (middle thick muscular layer), Endocardium (inner thin layer lining the chambers).

    • B. Nodal Tissue (Specialised Cardiac Musculature):

      • Auto-excitable (can generate action potentials without external stimuli).
      • Sino-atrial Node (SA Node): Patch of nodal tissue in the upper right corner of the right atrium. Called the Pacemaker as it initiates and maintains the rhythmic contractile activity of the heart (generates max. number of action potentials, ~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.
      • Atrio-ventricular Bundle (AV Bundle / Bundle of His): Continues from the AV node, passes through the AV septum, and divides into right and left branches in the inter-ventricular septum.
      • Purkinje Fibres: Minute fibres arising from the bundle branches that spread throughout the ventricular musculature.
      • Conduction Pathway: SA node -> Atrial musculature -> AV node -> Bundle of His -> Bundle Branches -> Purkinje fibres -> Ventricular musculature.

    • C. Cardiac Cycle:

      • Sequential events in the heart which are cyclically repeated. Includes 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 from pulmonary veins and vena cava into the left and right atria respectively, and passively into the ventricles (AV valves open). Semilunar valves are closed.
        2. Atrial Systole (approx. 0.1 sec): SA node generates action potential, both atria contract simultaneously. Increases blood flow into ventricles by about 30%.
        3. Ventricular Systole (approx. 0.3 sec): Begins shortly after atrial systole. Impulse conducted via AV node and Bundle of His causes ventricular contraction.
          • Ventricular pressure increases, causing closure of AV valves ("LUB" sound - first heart sound).
          • Further rise in ventricular pressure forces open the semilunar valves. Blood is pumped into the pulmonary artery (from RV) and aorta (from LV).
        4. Ventricular Diastole: Ventricles relax. Ventricular pressure falls, causing closure of semilunar valves ("DUB" sound - second heart sound). As ventricular pressure falls below atrial pressure, AV valves open, initiating joint diastole again.
      • Stroke Volume (SV): Volume of blood pumped out by each ventricle per beat (approx. 70 mL).
      • Cardiac Output (CO): Volume of blood pumped out by each ventricle per minute. CO = Stroke Volume × Heart Rate. (e.g., 70 mL/beat × 72 beats/min ≈ 5040 mL/min or ~5 Litres/min). Can be altered by physiological demands.

    • D. Electrocardiogram (ECG):

      • Graphical representation of the electrical activity of the heart during a cardiac cycle. Obtained using an electrocardiograph machine. Patient connected via leads (typically 3 or 12).
      • Waves:
        • P-wave: Represents electrical excitation (depolarization) of the atria, leading to atrial contraction.
        • QRS Complex: Represents depolarization of the ventricles, initiating ventricular contraction. Q marks the beginning, S marks the end. (Atrial repolarization occurs during this phase but is masked).
        • T-wave: Represents repolarization of the ventricles (return to normal state), marking the end of systole.
      • Clinical Significance: Deviations from the normal ECG pattern indicate possible abnormalities or diseases. Counting QRS complexes in a given time period determines the heart rate.

    • E. Double Circulation:

      • Blood flows through the heart twice during each complete circuit through the body. Characteristic of birds and mammals.
      • Consists of two circuits:
        1. Pulmonary Circulation: Blood flow between the heart and the lungs. Right ventricle pumps deoxygenated blood -> Pulmonary artery -> Lungs (oxygenation) -> Pulmonary veins -> Left atrium.
        2. Systemic Circulation: Blood flow between the heart and the rest of the body. Left ventricle pumps oxygenated blood -> Aorta -> Arteries -> Arterioles -> Capillaries (in tissues, O2 supplied, CO2 picked up) -> Venules -> Veins -> Vena Cava -> Right atrium.
      • Significance: Prevents mixing of oxygenated and deoxygenated blood, allowing efficient supply of oxygen to body tissues. Essential for warm-blooded animals with high metabolic rates.
      • Hepatic Portal System: Unique vascular connection between the digestive tract (intestine) and the liver. Hepatic portal vein carries blood from the intestine to the liver before it enters the systemic circulation. Allows liver to process absorbed nutrients and detoxify substances.
      • Coronary Circulation: Blood vessels supplying the heart muscle itself.

    • F. Regulation of Cardiac Activity:

      • Intrinsic regulation: By nodal tissues (SA node).
      • Extrinsic regulation:
        • Neural Control: Medulla oblongata via Autonomic Nervous System (ANS).
          • Sympathetic nerves: Increase heart rate, strength of ventricular contraction, and cardiac output.
          • Parasympathetic nerves (Vagus nerve): Decrease heart rate, speed of conduction, and cardiac output.
        • Hormonal Control: Adrenal medullary hormones (epinephrine and norepinephrine) increase cardiac output.

8. Disorders of Circulatory System

  • Hypertension (High Blood Pressure): BP higher than normal (120/80 mmHg; Systolic/Diastolic). 140/90 or higher is hypertension. Can damage heart, brain, kidneys.
  • Coronary Artery Disease (CAD): Commonly called Atherosclerosis. Affects vessels supplying blood to the heart muscle. Caused by deposition of calcium, fat, cholesterol, and fibrous tissues, making the lumen of arteries narrower. Leads to reduced blood flow to the heart muscle.
  • Angina (Angina Pectoris): Symptom of acute chest pain, appearing when not enough oxygen is reaching the heart muscle. Often occurs due to conditions affecting blood flow (like CAD). More 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 by inadequate blood supply).

Multiple Choice Questions (MCQs)

  1. Which plasma protein is primarily involved in blood coagulation?
    a) Albumin
    b) Globulin
    c) Fibrinogen
    d) Prothrombin

  2. The 'graveyard of RBCs' is:
    a) Red Bone Marrow
    b) Spleen
    c) Liver
    d) Kidney

  3. Which of the following white blood cells are the most abundant phagocytic cells?
    a) Eosinophils
    b) Basophils
    c) Lymphocytes
    d) Neutrophils

  4. A person with blood group AB is considered a universal recipient because:
    a) They have both A and B antigens on RBCs.
    b) They have both anti-A and anti-B antibodies in plasma.
    c) They lack both A and B antigens on RBCs.
    d) They lack both anti-A and anti-B antibodies in plasma.

  5. The T-wave in a standard ECG represents:
    a) Depolarization of the atria
    b) Repolarization of the atria
    c) Depolarization of the ventricles
    d) Repolarization of the ventricles

  6. The first heart sound "LUB" is associated with the closure of:
    a) Semilunar valves
    b) Tricuspid and Bicuspid valves (AV valves)
    c) Pulmonary valve only
    d) Aortic valve only

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

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

  9. Which circulatory pathway involves blood flowing from the digestive tract to the liver before returning to the heart?
    a) Pulmonary circulation
    b) Systemic circulation
    c) Coronary circulation
    d) Hepatic portal system

  10. Atherosclerosis, a major cause of heart disease, refers to:
    a) Inflammation of the pericardium
    b) Narrowing of artery lumen due to deposition of cholesterol and fats
    c) Failure of heart valves to close properly
    d) Abnormally high heart rate

Answer Key for MCQs:

  1. c) Fibrinogen
  2. b) Spleen
  3. d) Neutrophils
  4. d) They lack both anti-A and anti-B antibodies in plasma.
  5. d) Repolarization of the ventricles
  6. b) Tricuspid and Bicuspid valves (AV valves)
  7. b) Mother is Rh-ve and fetus is Rh+ve
  8. d) SA node
  9. d) Hepatic portal system
  10. b) Narrowing of artery lumen due to deposition of cholesterol and fats

Study these notes thoroughly. Focus on the composition of blood, functions of each component, blood grouping principles, the cardiac cycle events, ECG interpretation, and the definitions of common disorders. Understanding the sequence of events in coagulation and heart conduction is also vital. Good luck with your preparation!

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