Body Fluids and Circulation Comprehensive Study Guide

Need for Transport Mechanisms in Living Organisms

• All living cells require continuous provision of nutrients, oxygen ($O_2$), and other essential substances to maintain cellular health and metabolism.
• Waste or harmful substances generated by cellular activities must be removed continuously to ensure the normal functioning of tissues.
• Transport mechanisms vary across different animal groups:
  • Simple organisms such as sponges and coelenterates circulate water from their surroundings through their body cavities, enabling cells to exchange nutrients and wastes directly.
  • Complex organisms utilize specialized internal body fluids to transport materials efficiently throughout their bodies.
• Primary body fluids utilized for circulation in higher organisms:
  • Blood: The primary and most commonly used body fluid in higher organisms, including humans.
  • Lymph (tissue fluid): A secondary fluid that assists in the transport of specific substances.

Blood Composition and Components

• Blood is a special connective tissue comprising a fluid matrix called plasma and suspended cellular elements called formed elements.

Plasma

• Plasma is a straw-colored, viscous fluid constituting approximately $55\%$ of total blood volume.
• Chemical composition of plasma:
  • Water: Constitutes $90\text{--}92\%$ of plasma.
  • Proteins: Contribute $6\text{--}8\%$ of plasma volume.
• Major plasma proteins and their functional roles:
  • Fibrinogen: Essential for blood clotting and coagulation processes.
  • Globulins: Primarily involved in defense mechanisms and immune responses of the body.
  • Albumins: Major contributors to maintaining osmotic balance in blood.
• Inorganic minerals present in small amounts:
  • Sodium ions ($Na^+$)
  • Calcium ions ($Ca^{++}$)
  • Magnesium ions ($Mg^{++}$)
  • Bicarbonate ions ($HCO_3^-$)
  • Chloride ions ($Cl^-$)
• Organic substances in transit:
  • Glucose, amino acids, lipids, and other nutrients are constantly present in plasma as they are transported across tissues.
• Clotting Factors:
  • Factors required for blood coagulation are present in plasma in an inactive form.
• Definition of Serum:
  • Serum is defined as plasma from which clotting factors have been removed ($\text{Serum} = \text{Plasma} - \text{Clotting Factors}$).

Formed Elements

• Formed elements comprise erythrocytes, leucocytes, and platelets, constituting approximately $45\%$ of the total blood volume.

Erythrocytes (Red Blood Cells / RBCs)

• Abundance: The most abundant of all blood cells.
• Cell Count: A healthy adult man averages $5\text{ millions}$ to $5.5\text{ millions}$ of RBCs per $mm^{-3}$ of blood.
• Site of Formation: Produced in the red bone marrow in adult humans.
• Morphological Features:
  • Devoid of a nucleus in most mammals upon maturity.
  • Biconcave shape.
• Hemoglobin Content:
  • Contains a red-colored, iron-containing complex protein called hemoglobin, which imparts color and name to these cells.
  • A healthy individual contains $12\text{--}16\,g$ of hemoglobin per $100\,mL$ of blood.
  • Functions critically in the transport of respiratory gases.
• Lifespan and Destruction:
  • Average lifespan is $120\text{ days}$.
  • Destroyed in the spleen, which is termed the "graveyard of RBCs".

Leucocytes (White Blood Cells / WBCs)

• General Characteristics:
  • Colorless due to the complete lack of hemoglobin.
  • Nucleated structures.
• Cell Count: Relatively lesser in number compared to RBCs, averaging $6000\text{--}8000\,mm^{-3}$ of blood.
• Lifespan: Generally short-lived.
• Structural Categorization:
  • Granulocytes: Neutrophils, Eosinophils, and Basophils.
  • Agranulocytes: Lymphocytes and Monocytes.
• Granulocyte Subtypes:
  • Neutrophils:
  • Proportion: Most abundant WBC type, constituting $60\text{--}65\%$ of total WBCs.
  • Function: Phagocytic cells that engulf and destroy foreign organisms entering the body.
  • Eosinophils:
  • Proportion: Constitute $2\text{--}3\%$ of total WBCs.
  • Function: Resist infections and are associated with allergic reactions.
  • Basophils:
  • Proportion: Least abundant WBC type, constituting $0.5\text{--}1\%$ of total WBCs.
  • Function: Secrete active substances including histamine, serotonin, and heparin; involved in inflammatory reactions.
• Agranulocyte Subtypes:
  • Monocytes:
  • Proportion: Constitute $6\text{--}8\%$ of total WBCs.
  • Function: Phagocytic cells that destroy foreign pathogens.
  • Lymphocytes:
  • Proportion: Constitute $20\text{--}25\%$ of total WBCs.
  • Subtypes: $B$ forms and $T$ forms.
  • Function: Both $B$ and $T$ lymphocytes are responsible for the immune responses of the body.

Platelets (Thrombocytes)

• Origin: Cell fragments produced from megakaryocytes, which are specialized cells in the bone marrow.
• Cell Count: Normal blood contains $1,50,000\text{--}3,50,000$ platelets per $mm^{-3}$.
• Function: Release a variety of substances, most of which are involved in the coagulation or clotting of blood.
• Pathological Effect: A reduction in platelet count leads to clotting disorders, causing excessive loss of blood from the body.

Human Blood Groups

• Human blood exhibits individual differences based on specific surface molecules, requiring rigorous grouping prior to transfusion.

ABO Blood Grouping System

• Basis: Presence or absence of two surface antigens (immunogenic chemicals) on the RBC membrane, designated as antigen $A$ and antigen $B$.
• Antibodies: Plasma naturally contains antibodies (proteins produced in response to antigens), designated as anti-A and anti-B.
• Distribution of Antigens and Antibodies across Blood Groups:
  • Group A:
  • Antigens on RBCs: $A$
  • Antibodies in Plasma: anti-B
  • Compatible Donors: $A$, $O$
  • Group B:
  • Antigens on RBCs: $B$
  • Antibodies in Plasma: anti-A
  • Compatible Donors: $B$, $O$
  • Group AB:
  • Antigens on RBCs: $A$, $B$
  • Antibodies in Plasma: Nil
  • Compatible Donors: $AB$, $A$, $B$, $O$
  • Group O:
  • Antigens on RBCs: Nil
  • Antibodies in Plasma: anti-A, anti-B
  • Compatible Donors: $O$
• Blood Transfusion Rules:
  • Random blood cannot be used during transfusion; donor blood must be carefully matched with recipient blood to prevent severe clumping (destruction of RBCs).
  • Universal Donors: Individuals with Group $O$ blood can donate blood to persons with any other blood group because their RBCs lack surface antigens $A$ and B$.\n - Universal Recipients: Individuals with Group AB$blood can accept blood from persons with Group$AB as well as all other blood groups because their plasma lacks anti-A and anti-B antibodies.\n\n## Rh Blood Grouping System\n\n- Basis: Presence or absence of the Rh antigen, similar to an antigen present in Rhesus monkeys, on the surface of RBCs.\n- Prevalence: Observed in nearly 80\%$of humans, who are classified as Rh positive ($Rh^{+ve}$). Individuals lacking this antigen are classified as Rh negative ($Rh^{-ve}).\n- Exposure Effects: An Rh^{-ve}$person exposed to$Rh^{+ve} blood will synthesize specific antibodies against Rh antigens; therefore, Rh matching is necessary prior to blood transfusions.\n- Erythroblastosis Foetalis (Rh Incompatibility):\n - Occurs when an Rh^{-ve}$pregnant mother carries an$Rh^{+ve} foetus.\n - First Pregnancy: Maternal and foetal blood systems are separated by the placenta, preventing exposure of maternal blood to foetal Rh antigens.\n - Delivery of First Child: Potential exposure of maternal blood to small amounts of Rh^{+ve} foetal blood occurs during delivery.\n - Sensitization: The mother initiates the synthesis of anti-Rh antibodies in her bloodstream.\n - Subsequent Pregnancies: Anti-Rh antibodies from the Rh^{-ve}$mother leak into the circulation of an$Rh^{+ve} foetus, destroying foetal RBCs.\n - Clinical Outcomes: Can be fatal to the foetus or cause severe anemia and jaundice in the newborn.\n - Prevention: Administration of anti-Rh antibodies to the mother immediately following the delivery of the first child.\n\n# Mechanism of Blood Coagulation\n\n- Coagulation or clotting is a homeostatic mechanism to prevent excessive blood loss from the body in response to injury or trauma.\n- Clot (Coagulum) Composition:\n - Forms as a dark reddish-brown scum at the site of injury over time.\n - Consists of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.\n- Biochemical Enzymatic Cascade:\n - Active fibrins are formed by the conversion of inactive fibrinogens in plasma by the enzyme thrombin.\n - Thrombin is formed from an inactive precursor in plasma called prothrombin.\n - The conversion of prothrombin to thrombin requires an enzyme complex called thrombokinase.\n - Thrombokinase is produced through a linked series of enzymatic reactions (cascade process) involving multiple inactive plasma factors.\n- Initiation and Role of Calcium:\n - Trauma or injury stimulates platelets to release specific factors that activate coagulation.\n - Factors released by damaged tissues at the site of injury can also initiate clotting.\n - Calcium ions (Ca^{++}) play an essential role in multiple steps of the blood clotting process.\n\n# Lymph and Tissue Fluid\n\n- Formation of Interstitial Fluid:\n - As blood flows through tissue capillaries, water along with small water-soluble substances filter out into the spaces between tissue cells.\n - Larger proteins and most formed elements remain inside the blood vessels.\n- Properties of Interstitial (Tissue) Fluid:\n - Has the same mineral distribution as plasma.\n - Serves as the continuous medium for the exchange of nutrients, gases, and substances between blood and cells.\n- Lymphatic System and Lymph:\n - An elaborate network of vessels called the lymphatic system collects interstitial fluid and drains it back into major veins.\n - The fluid inside the lymphatic system is called lymph.\n - Lymph is a colorless fluid containing specialized lymphocytes responsible for body immune responses.\n - Lymph acts as a carrier for nutrients, hormones, and other vital substances.\n - Dietary fats are absorbed through lymph in specialized lymphatic capillaries called lacteals located in intestinal villi.\n\n# Circulatory Pathways in Animals\n\n- Animal circulatory systems are categorized into open and closed circulatory patterns.\n\n## Types of Circulatory Systems\n\n- Open Circulatory System:\n - Present in arthropods and molluscs.\n - Blood pumped by the heart passes through large vessels into open spaces or body cavities called sinuses.\n- Closed Circulatory System:\n - Present in annelids and chordates.\n - Blood pumped by the heart is circulated through a closed network of blood vessels.\n - Advantage: Provides precise regulation of fluid flow and tissue perfusion.\n\n## Comparative Anatomy of Vertebrate Hearts\n\n- All vertebrates possess a muscular, chambered heart.\n- Two-Chambered Heart (Fishes):\n - Consists of one atrium and one ventricle.\n - Single Circulation: Heart pumps deoxygenated blood \rightarrow$oxygenated by gills$\rightarrow$supplied to body parts$\rightarrow$$ deoxygenated blood returns to the heart.
• Three-Chambered Heart (Amphibians and Reptiles, except Crocodiles):
  • Consists of two atria and a single ventricle.
  • Incomplete Double Circulation: Left atrium receives oxygenated blood from gills/lungs/skin; right atrium receives deoxygenated blood from body parts. Both blood streams mix in the single ventricle, which pumps out mixed blood.
• Four-Chambered Heart (Crocodiles, Birds, and Mammals):
  • Consists of two atria and two ventricles.
  • Double Circulation: Oxygenated blood enters the left atrium and passes to the left ventricle; deoxygenated blood enters the right atrium and passes to the right ventricle. Ventricles pump blood without mixing, maintaining two distinct circulatory pathways.

Human Cardiovascular System Architecture

• The human circulatory system (blood vascular system) consists of a muscular chambered heart, a network of closed branching blood vessels, and blood.

Location and Protective Structure of the Heart

• Embryological Origin: Mesodermally derived organ.
• Anatomic Position: Situated in the thoracic cavity between the two lungs, slightly tilted to the left.
• Dimensions: Approximately the size of a clenched fist.
• Protection: Enclosed by a double-walled membranous bag called the pericardium, which encloses pericardial fluid.

Internal Chambers and Septa

• Four Internal Chambers:
  • Two smaller upper chambers called atria (right atrium and left atrium).
  • Two larger lower chambers called ventricles (right ventricle and left ventricle).
• Internal Septa:
  • Inter-atrial Septum: A thin, muscular wall separating the right and left atria.
  • Inter-ventricular Septum: A thick-walled partition separating the right and left ventricles.
  • Atrio-ventricular Septum: A thick fibrous tissue separating the atrium and ventricle on the same side.

Cardiac Valves and Openings

• Atrioventricular Openings:
  • Each atrio-ventricular septum contains an opening connecting the atrium and ventricle of the same side.
  • Tricuspid Valve: Guards the opening between the right atrium and right ventricle; consists of three muscular flaps or cusps.
  • Bicuspid Valve (Mitral Valve): Guards the opening between the left atrium and left ventricle; consists of two muscular cusps.