Comprehensive Notes on Body Fluids and Circulation

Overview of Body Fluids and Transport Mechanisms

• All living cells require a continuous supply of nutrients, $O_{2}$ , and other essential substances for survival.

• Harmful or waste substances produced by cellular metabolism must be removed continuously to ensure the healthy functioning of tissues.

• Efficient mechanisms are necessary for the movement of these substances to and from the cells.

• Simple organisms such as sponges and coelenterates facilitate substance exchange by circulating water from their surroundings through their body cavities directly to the cells.

More complex organisms utilize special fluids within their bodies for transport:

• Blood is the most common body fluid used by higher organisms, including humans.

• Lymph (tissue fluid) is another fluid used to transport certain substances, such as fats.

• Angiology is defined as the study of the blood vascular system.

• William Harvey is recognized as the Father of Angiology.

• Cardiology is defined as the study of the heart.

Composition and General Properties of Blood

• Blood is classified as a specialized/fluid connective tissue.

• It is categorized as a connective tissue because it consists of a ground substance called matrix (plasma) with cells (formed elements) suspended within it.

• Blood is considered a "false" connective tissue for three reasons:

  1. Cells of the blood lack the power of division.

  2. The matrix is devoid of fibers.

  3. The matrix is not secreted by the blood cells themselves.

• Haematology is the study of blood.

• Haemopoiesis is the process of blood formation, which occurs in the bone marrow.

• Physical and Chemical Properties:

  • Color: Red.

  • pH: $7.4$ (slightly alkaline).

  • Weight: Constitutes $7\text{ to }8\%$ of total body weight.

  • Volume: $5\text{--}6\,\text{litres}$ in males and $4\text{--}5\,\text{litres}$ in females.

• Heparin is the natural anticoagulant present in human blood.

• Total Composition:

  • Liquid Part: Plasma (matrix), constituting $55\%$ of the blood.

  • Solid Part: Blood corpuscles/Formed elements, constituting $45\%$ (RBCs, WBCs, and Platelets).

Plasma: Characteristics and Components

• Plasma is a straw-colored, viscous fluid that appears light yellow when separated from the rest of the blood.

• It consists of $90\text{ to }92\%$ water and $8\text{ to }10\%$ solids.

• Plasma Proteins:

  • Albumin ($4\%$): The smallest plasma protein; its primary function is maintaining Blood Colloidal Osmotic Pressure (BCOP).

  • Globulins ($2\text{--}2.5\%$): Primarily involved in the body's defense mechanisms; includes $\alpha$, $\beta$, and $\gamma$ (antibodies) types.

  • Fibrinogen and Prothrombin ($0.3\%$ each): Necessary for blood clotting. Fibrinogen is the largest plasma protein and is synthesized in the liver.

• Other Solids:

  • Inorganic Part: Ions such as $K^{+}$, $Na^{+}$, $Mg^{+2}$, $Cl^{-}$, $Ca^{+2}$, $HCO_{3}^{-}$, and $CO_{3}^{2-}$. Salts like $NaCl$ (maximum concentration), $KCl$, $MgCl_{2}$, and $NaHCO_{3}$.

  • Organic Part: Includes nutrients, vitamins, hormones, and excretory matter (e.g., $NH_{3}$, urea, uric acid).

  • Gases: Dissolved $O_{2}$, $CO_{2}$, and $N_{2}$.

Erythrocytes (Red Blood Cells): Morphology and Function

• Erythrocytes are the most abundant cells in the blood.

• RBC Counts:

  • Healthy Adult Male: $5\text{--}5.5\,\text{million/mm}^{3}$.

  • Healthy Adult Female: $4.5\text{--}5\,\text{million/mm}^{3}$.

  • Newborn Baby: $6.8\,\text{million/mm}^{3}$.

• Clinical Conditions:

  • Polycythemia: Increased RBC count, typically occurring at high altitudes (hill stations).

  • Anaemia: Decreased RBC count. Iron deficiency is the most common type.

  • Pernicious Anaemia: Caused by a lack of Vitamin $B_{12}$, which is essential for RBC maturation.

• Shape and Size:

  • Standard mammalian RBCs are biconcave, disc-shaped, and circular in cross-section to increase surface area. Size is approximately $7.5\,\mu\text{m}$ in diameter and $2.0\,\mu\text{m}$ in thickness.

  • Exceptions: Camel and Lama possess biconvex and oval-shaped RBCs.

• Response to Tonicity:

  • Poikilocytosis: The term for a change in the shape of RBCs.

  • Hypertonic solution: RBCs shrink (crenation).

  • Hypotonic solution: RBCs will burst.

  • Isotonic solutions: $0.8\text{--}1\%$ (standard $0.9\%$) $NaCl$ solution or $5.0\%\,w/v$ glucose solution.

• Structural Details:

  • Mature mammalian RBCs are enucleated (devoid of a nucleus).

  • They lack Endoplasmic Reticulum (ER), Golgi Complex (GC), Ribosomes, and Mitochondria. Because they lack mitochondria, they respire anaerobically.

  • Donnan's membrane is the specific name for the RBC plasma membrane.

  • Stomatin is a structural protein forming a spongy cytoskeleton.

  • Carbonic anhydrase is a zinc-containing enzyme (one of the fastest known) present in RBCs that aids in $CO_{2}$ transport.

• Haemoglobin (Hb):

  • An iron-containing complex protein and respiratory pigment that gives RBCs their red color and facilitates $O_{2}$ and $CO_{2}$ transport.

  • Each RBC contains approximately $26.5\text{ crores}$ ($2.65 \times 10^{8}$) molecules of Hb.

  • Healthy individual range: $12\text{--}16\,\text{gms per 100 ml}$ of blood.

  • Molecular weight: $67,200\,\text{Dalton}$.

  • Composition: Haem ($5\%$; iron in $Fe^{+2}$ ferrous state and porphyrin) and Globin protein ($95\%$; composed of $4$ polypeptide chains).

• Life Cycle:

  • Erythropoiesis: RBC formation. Stimulated by the hormone erythropoietin synthesized by the kidney.

  • Production sites: Yolk sac (first RBCs), Liver/Spleen/Placenta/Thymus (embryonic stage), Red Bone Marrow (adults).

  • Life span: $120\,\text{days}$ in adults; $100\,\text{days}$ in newborns.

  • Approximately $1\%$ of RBCs are destroyed daily and replaced.

  • Destruction occurs in the spleen, known as the "Graveyard of RBC." The spleen also acts as the "Blood Bank of the Body" by storing extra corpuscles.

Leucocytes (White Blood Cells): Classification and Roles

• Leucocytes are colorless due to the lack of haemoglobin and are nucleated cells.

• TLC (Total Leucocyte Count): $6000\text{--}8000/\text{mm}^{3}$.

• Diapedesis: The ability of leucocytes to squeeze through capillary walls to reach infection sites.

• DLC (Differential Leucocyte Count): Percentage distribution of various WBC types:

  • Neutrophils: $60\text{--}65\%$ (Maximum).

  • Lymphocytes: $20\text{--}25\%$.

  • Monocytes: $6\text{--}8\%$.

  • Acidophils/Eosinophils: $2\text{--}3\%$.

  • Basophils: $0.5\text{--}1\%$ (Minimum).

• Pathological States:

  • Leucocytosis: Increase in TLC.

  • Leucocytopenia: Decrease in TLC.

  • Leukemia: Abnormal increase in TLC (over $100,000$), referred to as blood cancer.

• Major Categories:

  • Granulocytes: Contain cytoplasmic granules and lobed nuclei (Polymorphonuclear).

    • Acidophils (Eosinophils): Stained by acidic dyes (Eosin). Bilobed nucleus. Protect against allergy and endoparasitic infections.

    • Basophils: Stained by basic dyes (Methylene Blue). S-shaped nucleus ($2\text{ to }3$ lobes). Transport and secrete heparin, histamine, and serotonin.

    • Neutrophils: Stained by a combination of acidic and basic dyes. Nucleus has $3\text{ to }5$ lobes. Known as "Micropolice man" of blood. Destroy pathogens via phagocytosis.

  • Agranulocytes: Clear cytoplasm and non-lobed nuclei (Mononuclear).

    • Monocytes: Kidney or bean-shaped nucleus. Phagocytic cells known as "Macropolice man" and scavenger cells.

    • Lymphocytes: Large spherical nucleus. Two types:

      • T-Lymphocytes: Produced in bone marrow, matured in the thymus. Stimulate B-cells.

      • B-Lymphocytes: Produced and matured in bone marrow. Produce and transport antibodies for immune response.

Platelets (Thrombocytes) and Hemostasis

• Platelets are cell fragments derived from megakaryocytes (special cells in the bone marrow).

• Characteristics: Disc-like, oval, or biconvex shape; size $2\text{--}3\,\mu\text{m}$; non-nucleated; unique to mammals.

• Normal Count: $1.5\text{--}3.5\,\text{lakh/mm}^{3}$ .

• Thrombocytopenia: Decrease in platelet count, leading to clotting disorders and excessive blood loss.

• Critical count: $40,000/\text{mm}^{3}$. Values below this lead to Purpura disease, characterized by red spots or rashes on the skin.

• Life span: $2\text{--}5\,\text{days}$.

• Functions:

  • Blood coagulation.

  • Synthesis of thromboplastin and serotonin.

  • Repairing endothelium by forming platelet plugs.

Blood Grouping Systems: ABO and Rh Factor

• Developed by Karl Landsteiner, based on antigens (agglutinogens) on the RBC surface and antibodies (agglutinins) in the plasma.

• Group A: Antigen A, Antibody-b.

• Group B: Antigen B, Antibody-a.

• Group AB: Antigens A and B, No antibodies. Universal Recipient.

• Group O: No antigens, Antibodies a and b. Universal Donor.

• Blood Transfusion Rules: Matching is critical to avoid clumping (agglutination). If donor antigens and recipient antibodies matches ($A+a$ or $B+b$), clumping leads to death.

• Rh Factor:

  • Discovered by Landsteiner and Weiner in Rhesus monkeys.

  • Found in nearly $80\%$ of humans ($Rh+$). Those without it are $Rh-$.

  • Erythroblastosis Foetalis (HDN): Occurs when an $Rh-$ mother carries an $Rh+$ fetus.

    • The first delivery is usually safe as blood is separated by the placenta, but fetal blood may leak during birth, causing maternal formation of Rh antibodies.

    • In subsequent pregnancies, maternal Rh antibodies leak into the fetus, destroying fetal RBCs. Results in severe anemia, jaundice, or death.

  • Treatment: Administration of Rhogam, Rholin, or Anti-D medicines post-delivery.

Coagulation of Blood (Blood Clotting)

• Bleeding time is $1\text{--}3\,\text{min}$; Clotting time is $2\text{--}8\,\text{min}$.

• Clot (Coagulum): A network of fibrin threads trapping dead and damaged formed elements.

• Mechanism (Cascade Process):

  1. Injury/Trauma stimulates platelets and local tissues to release Thromboplastin.

  2. This initiates a series of linked enzymatic reactions producing Thrombokinase.

  3. Prothrombin (inactive) is converted to Thrombin (active) by thrombokinase in the presence of $Ca^{+2}$ and Vitamin K.

  4. Fibrinogen (inactive) is converted to Fibrin (active) by Thrombin.

  5. Fibrin polymerizes to form a network that traps blood elements.

• Serum: Plasma minus fibrinogen and other clotting factors.

• Anticoagulants:

  • Natural: Heparin (vertebrates), Hirudin (leech), Anophelin (Anopheles), Lampredin (Petromyzon).

  • Artificial (Calcium binders): Sodium citrate, Sodium oxalate, and EDTA (Ethylene diamine tetra acetic acid).

Circulatory Pathways and Heart Anatomy

• Open Circulatory System: Blood/haemolymph pumps into sinuses; tissues are directly bathed. Examples: Arthropoda, Mollusca (except cephalopods), Echinodermata, Tunicates.

• Closed Circulatory System: Blood travels through a closed network of vessels (arteries, veins, capillaries). More efficient and precisely regulated. Examples: Annelida, Cephalopods, Chordates.

• Evolution of Vertebrate Heart:

  • Fishes: $2$ chambers ($1$ atrium, $1$ ventricle). Single circulation. Heart pumps deoxygenated blood (Venous heart).

  • Amphibians/Reptiles: $3$ chambers ($2$ atria, $1$ ventricle). Transitional/Incomplete double circulation (mixed blood in ventricle).

  • Crocodiles, Birds, Mammals: $4$ chambers ($2$ atria, $2$ ventricles). Complete double circulation (no mixing).

• Human Heart Anatomy:

  • Origin: Mesodermal. Size: $12 \times 9 \times 6\,\text{cm}$ (clenched fist). Weight: $300\,\text{gms}$ (male), $250\,\text{gms}$ (female).

  • Location: Mediastinum (between lungs), tilted to the left.

  • Covering: Pericardium (Fibrous and Serous). Pericardial fluid between parietal and visceral layers acts as a shock absorber and lubricant.

  • Walls: Outermost Epicardium, middle Myocardium (thickest, made of cardiac muscle), and innermost Endocardium.

  • Chambers: Two upper atria (thin-walled) and two lower ventricles (thick-walled). The left ventricle wall is the thickest because it pumps blood to the entire body.

  • Valves:

    • Tricuspid: Right atrium and right ventricle.

    • Bicuspid (Mitral): Left atrium and left ventricle.

    • Semilunar: Openings into the pulmonary artery and aorta.

  • Chordae Tendineae/Papillary Muscles: Prevent AV valves from flipping back into atria during ventricular contraction.

Conducting System and Cardiac Cycle

• Human heart is Myogenic (auto-excitable), meaning the impulse originates in specialized muscular tissue (Nodal tissue).

• Nodal Pathway:

  1. Sino-atrial Node (SAN): Located in the right upper corner of the right atrium. Known as the Pacemaker; generates $70\text{--}75$ action potentials/min.

  2. Atrio-ventricular Node (AVN): Lower left corner of the right atrium. Known as the Pacesetter; introduces a $0.1\,\text{sec}$ delay to allow atrial emptying.

  3. AV Bundle/Bundle of His: Arises from AVN, divides into right and left bundle branches.

  4. Purkinje Fibers: Minute fibers throughout the ventricular walls.

• Cardiac Cycle ($0.8\,\text{sec}$ total):

  • Atrial Systole ($0.1\,\text{sec}$): Increases ventricular filling by $30\%$.

  • Ventricular Systole ($0.3\,\text{sec}$): AV valves close (Lub sound); semilunar valves open.

  • Ventricular Diastole ($0.5\,\text{sec}$): Semilunar valves close (Dub sound); AV valves open.

  • Joint Diastole ($0.4\,\text{sec}$): All four chambers are relaxed.

• Hemodynamics:

  • Stroke Volume (SV): Amount of blood pumped by each ventricle per cycle; approximately $70\,\text{ml}$. ($SV = EDV - ESV = 120\,\text{ml} - 50\,\text{ml}$).

  • Cardiac Output: $SV \times \text{Heart Rate} \approx 5040\,\text{ml/min}$ ($5\,\text{litres}$).

• Heart Sounds:

  • Lub: First sound, dull, long, low pitch. Caused by closure of AV valves.

  • Dub: Second sound, sharp, short, high pitch. Caused by closure of semilunar valves.

  • Murmur: Defective sound indicating valve issues.

Regulation and Circulation Pathways

• Regulation:

  • Nervous: Medulla Oblongata contains the cardiac center. Sympathetic nerves increase rate/strength; Parasympathetic nerves (via acetylcholine) decrease rate/strength.

  • Hormonal: Adrenaline (Epinephrine), Nor-adrenaline, and Thyroxine increase cardiac output.

• Double Circulation:

  • Pulmonary: Right Ventricle $\rightarrow$ Pulmonary Arteries $\rightarrow$ Lungs $\rightarrow$ Pulmonary Veins $\rightarrow$ Left Atrium. Aids in oxygenation.

  • Systemic: Left Ventricle $\rightarrow$ Aorta $\rightarrow$ Arteries/Capillaries $\rightarrow$ Body Tissues $\rightarrow$ Veins/Vena Cava $\rightarrow$ Right Atrium. Provides nutrients/$O_{2}$.

• Specialized Circulations:

  • Hepatic Portal System: Vascular connection where blood from the digestive tract passes to the liver via the hepatic portal vein before entering systemic circulation.

  • Coronary Circulation: Specific blood vessel network for the cardiac musculature.

ECG, Blood Pressure, and Disorders

• Electrocardiograph (ECG): Developed by Willem Einthoven. Graphical recording of electrical activity.

  • P Wave: Atrial depolarization (systole).

  • QRS Complex: Ventricular depolarization (systole).

  • T Wave: Ventricular repolarization (relaxation). The end of the T wave marks the end of systole.

• Blood Pressure (BP): Measured with a Sphygmomanometer. Normal value is $120/80\,\text{mm Hg}$.

  • Systolic: $120\,\text{mm Hg}$.

  • Diastolic: $80\,\text{mm Hg}$.

• Disorders:

  • Hypertension (High BP): $140/90\,\text{mm Hg}$ or above. Leads to brain hemorrhage or kidney/eye damage.

  • Hypotension (Low BP): $110/70\,\text{mm Hg}$ or below. Causes dizziness and weakness.

  • Coronary Artery Disease (Atherosclerosis): Deposits of calcium, fat, and cholesterol narrow the arterial lumen.

  • Angina Pectoris: Acute chest pain due to inadequate oxygen reaching heart muscles.

  • Heart Failure: Heart cannot pump blood effectively to meet body needs.

  • Heart Attack (Myocardial Infarction): Sudden damage to heart muscle due to lack of blood supply.

  • Cardiac Arrest: Total stoppage of heart activity.

Questions & Discussion

• Why do we consider blood as a connective tissue? Blood contains a fluid matrix (plasma) and cells (formed elements) suspended within it, consistent with the definition of connective tissue consisting of ground substance and internal cells.

• What is the importance of plasma proteins? Albumin maintains osmotic pressure (BCOP); Globulins are for defense; Fibrinogen and Prothrombin are for blood clotting.

• Why is the heart called myogenic? The impulse for contraction is generated within the heart's own musculature (nodal tissue) rather than being initiated by external nervous stimuli.

• What is the significance of the AV Node and AV Bundle? The AV Node delays the impulse by $0.1\,\text{sec}$ to ensure atria empty fully before ventricular contraction starts. The AV Bundle then distributes the impulse to the ventricles via the Bundle of His and Purkinje fibers.

• What is the difference between lymph and blood? Blood is red and contains plasma and all formed elements for transport and immunity. Lymph is colorless, lacks RBCs and large proteins, is part of the lymphatic system, and focuses on defense and fat absorption.