Blood Composition and Volume Quiz

Blood Composition and Volume

• Blood makes up approximately 8% of total body weight.
• Average blood volume is 5 liters in women and 5.5 liters in men.
• Hematocrit is the percentage of red blood cells in the blood. Average hematocrit is 42% for women and 45% for men.
• Venous blood is darker red than arterial blood.
• Blood is composed of three main components:
  • Erythrocytes (red blood cells): responsible for oxygen transport.
  • Leukocytes (white blood cells): defend the body against infections.
  • Platelets (thrombocytes): fragments important for blood clotting (hemostasis).
• The buffy coat is a thin layer between plasma and formed elements containing white blood cells and platelets.

Physiological Role of Blood

• Transports oxygen, nutrients, hormones, metabolic wastes and heat.
• Regulates body temperature and pH.
• Protects the body through clotting and immune responses (immunoglobulins).

Plasma

• Plasma is the liquid portion of blood.
• Mostly composed of water.
• Contains electrolytes, nutrients, wastes, gases and hormones.

Plasma Proteins

• Exert osmotic pressure which helps distribute fluid between the vascular and interstitial compartments.
• Prevent excessive loss of plasma from capillaries into interstitial fluid.
• Buffer pH changes.
• Synthesized in the liver except for gamma globulins.

Albumins

• Most abundant plasma protein.
• Transport various substances.
• Contribute significantly to colloid osmotic pressure.
• Non-specific in terms of transport.

Globulins

• Alpha and beta globulins transport specific water-insoluble substances like cholesterol, iron, and complement.
• Involved in the blood-clotting process.
• Gamma globulins are antibodies (immunoglobulins) produced by immune cells.

Fibrinogen

• Inactive precursor of fibrin meshwork involved in blood clotting.
• Activated during blood clotting.
• Serum is plasma minus fibrinogen.

Erythrocytes (Red Blood Cells)

• Contain hemoglobin, a pigment responsible for oxygen transport.
• Red blood cells are shaped like biconcave discs to increase surface area and maximize gas exchange.
• Packed with over 250 billion hemoglobin molecules each carrying >100 million oxygen molecules.
• In the absence of a nucleus, organelles, and ribosomes, erythrocytes focus on carrying oxygen, hydrogen and carbon dioxide.
• Erythrocytes have a lifespan of 120 days.
• Spleen removes old erythrocytes from circulation.
• Dead red blood cells are recycled in the spleen.

Erythropoiesis (Red Blood Cell Production)

• The process of producing new red blood cells to replenish dying ones.
• Occurs in bone marrow.
• Pluripotent stem cells differentiate into erythrocytes through various stages:
  • Erythroblast: last stage with a nucleus.
  • Reticulocyte: organelle degradation is ongoing.
  • Erythrocyte: mature red blood cell released into circulation.

Hemoglobin

• Located in red blood cells.
• Iron-containing pigment.
• Appears reddish when oxygenated, bluish when deoxygenated.
• Each hemoglobin molecule can bind four oxygen molecules.
• Hemoglobin also binds to carbon dioxide, acidic hydrogen ions, and carbon monoxide.

Significance of No Nucleus in Erythrocytes

• No nucleus allows for increased space for hemoglobin molecules.
• The absence of organelles allows for a more efficient oxygen carrying capacity.
• However, it also results in a limited lifespan.
• Fragile cell structure.

Blood Groups

• Blood types are determined by surface antigens on red blood cells (RBCs).
• Antigens are large, complex molecules triggering specific immune responses.
• Antigens are found on the surface of RBCs, protruding outwards for identification.
• Over 100 types of antigens exist on RBCs.
• Most antigens are proteins.
• Immune cells initially did not evolve to combat transplants.
• The immune system destroys organs that do not match the recipient's blood type.
• Transfusion reactions occur when mismatched blood types are mixed.
• Antibodies in the recipient's blood bind to the donor's RBC antigens, causing the cells to rupture.
• This can lead to blood clots, blocking blood vessels.

Rhesus (Rh) Blood Group

• The Rh blood group is characterized by the CDE system, with 50 blood group antigens and 5 primary antigen groups (D, C, E, c, e).
• The D antigen determines whether someone is Rh-positive (D present) or Rh-negative (D absent).
• The 'd' notation is a placeholder for the absence of the D antigen, not a separate antigen.
• The D antigen is the most prevalent and antigenic, making it crucial for blood compatibility.
• Rh-positive individuals possess the D antigen.
• Rh-negative individuals lack the D antigen.
• People with the Rh factor have Rh-positive blood (D present).
• Individuals without the Rh factor are Rh-negative (d absent).
• Naturally occurring antibodies against the Rh factor do not typically develop.
• Rh-negative individuals only produce anti-Rh antibodies after exposure to Rh-positive blood, either through transfusion or pregnancy.
• Rh-positive individuals never produce antibodies against the Rh-negative factor they possess.
• Therefore, Rh-negative individuals should only receive Rh-negative blood transfusions.

Leukocytes

• Leukocytes are white blood cells (WBCs) found in the blood.
• They are the mobile units of the body's immune system, responsible for defending against pathogens.
• Leukocytes are comprised of various cell types, their derivatives, and plasma proteins.
• They are involved in immune responses, including producing defending substances and communicating with other cells.
• Leukocytes have diverse shapes and functions.
• Plasma proteins, such as complement proteins and globulins, contribute to the immune system.
• Complement proteins are produced by the liver but have immune functions.
• Globulins are produced by immune cells.

Polymorphonuclear Granulocytes (PMNs)

• PMNs are characterized by their multi-shaped nucleus, despite having only one nucleus.
• They are granulocytes, meaning they contain granules.
• One type of PMN is the neutrophil, known for its acidic granules, which bind to acidic molecules .
• Neutrophils are phagocytic specialists, engulfing and destroying bacteria intracellularly.
• They are typically the first responders to pathogen detection in tissues, with many dying during their initial defense.
• Neutrophils release neutrophil extracellular traps (NETs), a sticky web of extracellular fibers containing bacteria-killing chemicals, to trap pathogens.

Polymorphonuclear Granulocytes: Eosinophils

• Eosinophils are a type of granulocyte with acidic granules (staining red).
• They are primarily involved in fighting and killing parasites and capturing and releasing granules to eliminate them.
• Eosinophils kill antibody-coated parasites by releasing the contents of their granules.
• An increase in circulating eosinophils (eosinophilia) is associated with:
  • Allergic conditions like asthma and hay fever, often due to eosinophils degranulating on harmless substances.
  • Internal parasitic infestations, like worms.
  • Eosinophils attach to worms and secrete substances to kill them.
• Eosinophils lack the specificity to distinguish between parasites and harmless substances, potentially attacking the latter.

Polymorphonuclear Granulocytes: Basophils

• Basophils are the least abundant and least understood leukocytes.
• They bind to basic dyes, staining blue, and are involved in immune responses to parasites.
• Basophils produce and store:
  • Histamine, crucial for allergic reactions.
  • Heparin, which accelerates the removal of fat particles from the blood after a fatty meal and prevents blood clotting.

Mononuclear Agranulocytes: Monocytes

• Monocytes are characterized by a single (simple-shaped) nucleus and lack granules.
• They are larger than other leukocytes and can engulf more material.
• Their main functions include:
  • Phagocytosis, ingesting foreign material.
  • Antigen presentation, displaying antigens to other immune cells.
  • Cytokine production, releasing signaling proteins.
  • Cytotoxicity, directly killing cells.
• Monocytes are released from the bone marrow in an immature state, circulating for 1-2 days before settling in various tissues.
• They mature and enlarge in resident tissues, becoming macrophages.
• Macrophages have a lifespan ranging from months to years, but they die sooner during phagocytosis.
• They communicate with other cells by producing cytokines and chemokines, a subgroup of cytokines that attract other cells.
• Tissue-resident macrophages are the first to detect invading microorganisms, secreting cytokines/chemokines to recruit neutrophils and other leukocytes.
• They engulf dead neutrophils, contributing to tissue repair.

Mononuclear Agranulocytes: Lymphocytes

• Lymphocytes recognize antigens and produce antibodies against them.
• Antibodies bind to specific antigens, leading to the antigen's destruction by various mechanisms.
• The immune system learns to tolerate self-antigens, but may react to foreign antigens.
• This can lead to allergic reactions to food antigens.
• There are varying responses to pathogens.
• Lymphocytes produce antibodies, essential for immunity.
• COVID-19 vaccines contain antigens, prompting the body to recognize and generate antibodies.
• Upon subsequent exposure to the virus, the body can mount a faster and more effective response.
• Antibodies bind to specific antigens, leading to their destruction.
• Pathogens can evolve, changing their antigens, which can render existing antibodies ineffective.
• The immune system has learned to tolerate our own antigens, but can react to foreign antigens.
• Foods contain antigens, and some individuals develop allergic reactions.
• Different pathogens trigger varying immune responses.

How Leukocytes Work (Generally)

• The immune system recognizes and destroys or neutralizes foreign materials in the body.
• It utilizes receptors to identify threats.
• The immune system defends against invading microbes (e.g., eosinophils, basophils).
• Other important immune cells not primarily circulating in the blood are involved in immune responses.
• Various immune cell types, including neutrophils, basophils, monocytes, and lymphocytes, are involved in the immune response.
• When different blood types mix, antibodies in the recipient's blood bind to the donor's RBC antigens causing the cells to rupture.

Large Granular Lymphocytes (NK Cells)

• Large granular lymphocytes, also known as natural killer (NK) cells, are effector cells of the innate immune response.
• They are highly effective against virally infected cells.
• NK cells release lytic granules to kill infected cells.
• They produce cytokines to limit viral replication.
• Cells display markers indicating their health or infection status.
• NK cells attack infected cells, even if the virus evolves to hide infection markers.
• This suggests NK cells have learned to detect subtle abnormalities even when conventional markers are masked.

Immune System: Overview

• Immunity is the body's ability to defend itself against foreign invaders like bacteria, viruses, and abnormal cells.
• Most immune cells reside in tissues, not the bloodstream.

Immune System: Pathogenic Microbes

• Bacteria: Non-nucleated, single-celled organisms that damage tissues by releasing enzymes or toxins. Examples include chlamydia, Streptococcus, E.coli, and Salmonella.
• Viruses: Consists of DNA or RNA enclosed in a protein coat. They cannot reproduce without invading a host cell. Examples include SARS-CoV-2, HIV, HCV, Influenza, Ebola, and Polio.
• Fungi: Examples include aspergillus and Candida.
• Parasites: Include protozoan parasites like plasmodium malaria and helminth parasites (worms).
• Virulence: The inherent ability of a pathogen to cause disease. Pathogens vary in their virulence, with some being more potent than others.

Immunity: External Defenses

• Mechanical defenses: Prevent pathogens from entering the body. Examples include cilia in the nasal passages trapping bacteria and skin acting as a barrier.
• Chemical defenses: Antimicrobial peptides produced by epithelial cells directly fight pathogens.
• Microbiological defenses: Microbiota (bacteria) found in the gut and skin compete with harmful pathogens for resources.

Immunity: Internal Defenses

• Lymphoid tissue: Sites where immune cells are produced, stored, or processed.
  • Bone marrow: Produces and divides immune cells. Mature cells then circulate in the blood or lymphatic vessels.
  • Thymus: Where T cells mature.
• Lymph nodes: Checkpoints where lymph and its cells are examined for foreign antigens. B and T cells circulate through lymph nodes.
• Spleen: Has patches of white pulp containing immune cells.
• Tonsils and adenoids: Smaller lymph nodes that act as entry points in the mouth and pharynx.
• Appendix: Contributes to immune function.
• Peyer's patches (GALT): Lymphoid tissue found in the gut and lungs.

Immunity: Functions of Lymphoid Tissue

• Bone Marrow: Produces and divides immune cells.
• Thymus: Where T cells mature.
• Lymph Nodes: Checkpoints that filter lymph and its cells ensuring they are not infected.
• Spleen: Houses immune cells and filters blood.
• Tonsils and Adenoids: Smaller lymph nodes in the mouth and throat, acting as entry points.
• Appendix: Contributes to immune function.
• Peyer's Patches (GALT): Located in the gut and lungs to combat pathogens.

Immunity: Immune Responses

• Innate Immune Response: Non-specific and rapid, providing the first line of defense against foreign material. Includes:
  • Inflammation: A localized response to injury or infection.
  • Interferons: Anti-viral proteins.
  • Natural Killer cells (NK): Kill virus-infected and cancer cells.
  • Complement system: A cascade of proteins that work together to kill pathogens.
  • Dendritic cells: Resident in tissues like lungs, liver, and skin. They engulf pathogens and activate T cells.
• Adaptive Immune Response: Selective targeting of specific invaders. Includes:
  • Antibody-mediated immunity (humoral): Production of antibodies by plasma cells (B lymphocyte derivatives).
  • Cell-mediated immunity: Production of activated T lymphocytes that directly attack unwanted cells.

Inflammation

• Innate, nonspecific response to tissue injury, characterized by redness, swelling, pain, and heat.
• Begins locally, but can become systemic if not stopped.
• Goal: repair tissue damage and remove pathogens.
• Triggered by tissue damage, like a twisted ankle, or by pathogens.
• Resident tissue macrophages activate the inflammatory response by releasing cytokines and histamine.

Macrophages

• First line of defense against pathogens.
• Engulf pathogens.
• Release cytokines and chemokines to activate other cells and recruit more immune cells.

Mast cells

• Release histamine, which dilates blood vessels and increases capillary permeability.

Neutrophils and monocytes

• Recruited to the site of inflammation.
• Perform phagocytosis (engulf and destroy pathogens).
• Monocytes differentiate into macrophages.

Cytokines

• Potent signaling molecules that regulate and coordinate the immune response.
• Produced by leukocytes.
• Include interleukin-1, interleukin-6, and Tumor Necrosis Factor Alpha (TNF-α).
• Induce fever (endogenous pyrogens).
• Decrease plasma iron levels.
• Stimulate release of acute phase proteins.
• Trigger clotting and anticlotting systems.

Complement System

• Nonspecific response.
• Composed of plasma proteins produced by the liver.
• Three mechanisms of activation:
  • Spontaneous activation on microbial surfaces.
  • Binding to carbohydrates on microbial surfaces.
  • Activation by antibody binding to antigens on pathogens.
• Destroys pathogens by:
  • Forming Membrane Attack Complexes (MACs), which punch holes in the pathogen.
  • Enhancing phagocytosis (opsonization).

Dendritic Cells (DCs)

• Bridge between innate and adaptive immunity.
• Resident tissue cells with star-shaped morphology.
• Immature DCs actively internalize antigens via micropinocytosis.
• Encounter with pathogen causes them to mature.
• Professional antigen-presenting cells.
• Migrate to lymphoid organs to present antigens to T cells.

Adaptive Immunity

• Two branches of adaptive immunity: antibody-mediated (humoral) and cell-mediated
• Antibody-mediated immunity involves B lymphocytes, which differentiate into plasma cells to produce antibodies
• Antibodies are released into the blood and circulate to infection sites, but also remain in lymph tissue
• Cell-mediated immunity involves T lymphocytes, which directly attack unwanted cells
• Two types of T cell attacks: direct killing of infected cells and instructing other immune cells

Antigens

• Large, foreign, unique complex molecules
• Elicit an immune response
• More complex molecules generally have higher antigenicity (ability to elicit an immune response)
• Most proteins in nature are highly antigenic

Functions of Adaptive Immunity

• Specificity: billions of lymphocytes recognize different antigens, forming memory T and B cells
• Clonal expansion: lymphocytes with receptors that recognize a specific antigen proliferate, with the ability to fight infection
• Clonal selection: only lymphocytes that can recognize the antigen are selected for expansion
• Immunological memory: some lymphocytes are preserved as memory cells to provide a faster immune response during subsequent infections

B Lymphocytes

• Secrete antibodies
• Have membrane-bound antibodies on their surface that function as antigen receptors
• B cell activation leads to proliferation, differentiation into plasma cells, and secretion of soluble antibodies with the same specificity

Basic Functions of Antibodies

• Binding to antigens
• Fc (fragment, crystallizable) region of antibody allows for:
  • Activation of the complement system
  • Neutralization: blocking pathogens from entering cells, binding and neutralizing bacteria, and preventing toxins from reaching cells
  • Enhancing phagocytosis (opsonization): coating pathogens facilitates their engulfment by phagocytes

T Lymphocytes

• Recognize peptides of pathogens
• Carry out cell-mediated immunity
• Do not secrete antibodies but directly bind to targets
• Killer T cells release chemicals (granules) that destroy targeted cells within seconds, triggering apoptosis
• Clonal and antigen-specific
• Mature in the thymus and are activated only when they encounter a foreign antigen presented on the surface of a cell

T Cells and Their Targets

• T cell receptors (TCRs) recognize peptide fragments bound to MHC (Major Histocompatibility Complex) proteins on the surface of antigen presenting cells (APCs, like dendritic cells)
• Two T cell states: inactive/naïve and active
• Inactive T cells are activated by APCs in lymph tissues, leading to proliferation and differentiation
• Active T cells leave the lymph nodes to attack infected cells at the site of infection

Two Types of T Cells

• CD4 cells (helper T cells):
  • Act as generals, modulating the activity of other immune cells and secreting chemicals to amplify their functions
• CD8 cells (cytotoxic/killer T cells):
  • Directly kill infected cells by releasing granules, targeting viral-infected and cancerous cells
  • Bind to viral antigens and self-antigens on the surface of infected cells
  • Can kill cells directly or through enzymes that induce self-destruction

Test your knowledge on the components and physiological roles of blood. This quiz covers topics such as blood volume, hematocrit levels, and the functions of different blood cells. Perfect for anyone studying human biology or anatomy.