17.3 Cellular Defenses

Plasma is the liquid component of blood that suspends the blood cells and transports various substances throughout the body. It is the largest component of blood and plays a crucial role in both the circulatory and immune systems.

Erythrocytes: Red blood cells that carry oxygen and carbon dioxide throughout the body.

Leukocytes: White blood cells that are part of the body's immune defense system.

Thrombocytes: Also known as platelets, they are responsible for blood clotting and wound healing.

Formed elements are the cellular components of blood, including erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets). They play crucial roles in immune defense, oxygen transport, and clotting.

Phagocytosis: The process by which certain cells engulf and digest microorganisms and cellular debris.

Antigen Presentation: A process where immune cells display antigens on their surface to T-cells to initiate an immune response.

Cytokines: Small proteins released by cells that have a specific effect on cell-to-cell communication and behavior during immune responses.

Platelets, also known as thrombocytes, are small cell fragments in the blood that play a key role in clotting and wound repair. They are an essential component of the body's cellular defenses against injury.

Megakaryocytes: Large bone marrow cells that produce platelets through cytoplasmic fragmentation.

Clotting Factors: Proteins in blood plasma that work with platelets to form blood clots.

Hemostasis: The process that stops bleeding at the site of an injury involving vascular spasm, platelet plug formation, and coagulation.

Hematopoiesis is the process by which all blood cells are produced from hematopoietic stem cells in the bone marrow. It is essential for maintaining the body's immune and circulatory systems.

Cytokine: Small proteins that act as signaling molecules in the immune system.

Bone Marrow: The soft tissue inside bones where hematopoiesis takes place.

Multipotent Stem Cells: Stem cells capable of differentiating into multiple cell types within a specific lineage.

Leukocytes, also known as white blood cells, are immune cells that play a critical role in defending the body against infection and disease. They circulate in the blood and migrate to sites of infection or injury.

Phagocytosis: The process by which certain leukocytes engulf and digest microorganisms and cellular debris.

Antigen Presentation: The process by which macrophages or dendritic cells display foreign antigens on their surface to T cells.

Natural Killer Cells: A type of lymphocyte involved in recognizing and killing virus-infected cells or tumor cells without prior sensitization.

Neutrophils are a type of white blood cell that play a crucial role in the innate immune response. They are the first responders to microbial infection and are highly active in phagocytosis.

Phagocytosis: The process by which cells, like neutrophils, engulf and digest pathogens.

Chemotaxis: The movement of an organism or cell toward or away from a chemical stimulus.

Granulocytes: A category of white blood cells characterized by the presence of granules in their cytoplasm; includes neutrophils, eosinophils, and basophils.

Eosinophils are a type of white blood cell that plays a critical role in the immune system, particularly in combating parasitic infections and mediating allergic reactions. They are part of the body's innate nonspecific host defenses as well as involved in certain adaptive immune responses.

Neutrophils: A type of white blood cell that is the first responder to microbial infection.

Mast Cells: Cells that play a key role in inflammation and allergic reactions by releasing histamine.

Adaptive Immunity: A subsystem of the overall immune system that provides long-term immunity through memory cells.

Basophils are a type of white blood cell that play a role in immune responses, primarily by releasing histamine during allergic reactions and inflammatory processes. They are also involved in defense mechanisms against parasites.

Histamine: A compound released by cells in response to injury and allergic reactions, causing contraction of smooth muscle and dilation of capillaries.

IgE Antibodies: A class of antibodies produced by the immune system that function mainly to combat parasitic infections and play a significant role in allergic diseases.

Mast Cells: Cells found in connective tissues that release histamine and other substances during inflammatory and allergic responses.

Monocytes are a type of white blood cell that plays a crucial role in the innate immune system by differentiating into macrophages and dendritic cells upon entering tissues. They are essential for phagocytosis and pathogen recognition.

Macrophage: A large phagocytic cell derived from monocytes that engulfs pathogens and dead cells.

Dendritic Cell: An antigen-presenting cell derived from monocytes that activates T-cells.

Phagocytosis: The process by which certain living cells called phagocytes ingest or engulf other cells or particles.

Lymphocytes are a type of white blood cell that play a crucial role in the body's immune response. They are responsible for recognizing and responding to foreign invaders, such as bacteria, viruses, and other pathogens, as well as abnormal cells within the body.

T Cells: A type of lymphocyte that matures in the thymus gland and is responsible for cell-mediated immunity, directly attacking infected or cancerous cells.

B Cells: A type of lymphocyte that matures in the bone marrow and is responsible for humoral immunity, producing antibodies to neutralize and eliminate pathogens.

Natural Killer Cells: A type of lymphocyte that can directly kill infected or cancerous cells without the need for prior activation or recognition.

Thrombocytes, also known as platelets, are small blood components that play a crucial role in blood clotting and wound healing. They are produced in the bone marrow and are essential for preventing excessive bleeding.

Megakaryocytes: Large bone marrow cells that produce thrombocytes through cytoplasmic fragmentation.

Hemostasis: The process of stopping bleeding, which involves vascular spasm, platelet plug formation, and coagulation.

Granules: Small packets within platelets that contain proteins and molecules essential for blood clotting and wound repair.

Hemostasis is the process by which the body stops bleeding and maintains blood flow within the vascular system. It is a critical physiological mechanism that prevents excessive blood loss following injury or trauma to blood vessels.

Platelet Activation: The process by which platelets become activated and aggregate at the site of a blood vessel injury to form a temporary plug and initiate the clotting cascade.

Coagulation Cascade: A series of enzymatic reactions that lead to the formation of a fibrin clot, which strengthens and stabilizes the initial platelet plug.

Fibrinolysis: The process of breaking down and dissolving a blood clot once the injury has healed, restoring normal blood flow.

Cytokines are small proteins released by cells, especially those of the immune system, that have a specific effect on interactions and communications between cells. They play crucial roles in regulating immune responses and inflammation.

Interleukins: A group of cytokines that were first seen to be expressed by white blood cells (leukocytes).

Chemokines: A subset of cytokines responsible for inducing chemotaxis in nearby responsive cells.

Tumor Necrosis Factor (TNF): A type of cytokine involved in systemic inflammation and stimulation of the acute phase reaction.

Inflammation is a complex biological response of the body's immune system to various stimuli, such as pathogens, damaged cells, or irritants. It is a protective mechanism that helps the body eliminate harmful agents and initiate the healing process.

Acute Inflammation: A short-term response characterized by redness, swelling, heat, and pain, often caused by an infection or injury.

Chronic Inflammation: A long-term, persistent inflammation that can lead to tissue damage and the development of various diseases.

Inflammatory Mediators: Chemical signals, such as histamine, prostaglandins, and leukotrienes, that regulate the inflammatory response.

Hematopoiesis is the process by which all blood cells are produced from hematopoietic stem cells in the bone marrow. It is essential for maintaining the body's immune and circulatory systems.

Cytokine: Small proteins that act as signaling molecules in the immune system.

Bone Marrow: The soft tissue inside bones where hematopoiesis takes place.

Multipotent Stem Cells: Stem cells capable of differentiating into multiple cell types within a specific lineage.

Hematopoietic stem cells (HSCs) are multipotent stem cells that give rise to all the blood cell types, including both myeloid and lymphoid lineages. They play a crucial role in the body's immune response and regeneration of blood cells.

Myeloid Cells: Blood cells derived from HSCs that include granulocytes, monocytes, erythrocytes, and platelets.

Lymphoid Cells: Blood cells derived from HSCs that include T cells, B cells, and natural killer (NK) cells.

Bone Marrow: The primary site of new blood cell production where HSCs reside.

Myeloid progenitors are a group of undifferentiated cells in the bone marrow that give rise to various types of myeloid cells, including granulocytes, monocytes, macrophages, and dendritic cells. These progenitor cells are essential for the cellular defenses of the immune system, as they are responsible for producing the key effector cells that combat pathogens and maintain homeostasis.

Hematopoietic Stem Cells: Multipotent stem cells found in the bone marrow that can differentiate into all types of blood cells, including myeloid progenitors.

Granulocytes: A type of white blood cell that includes neutrophils, eosinophils, and basophils, which play crucial roles in the innate immune response.

Monocytes: A type of white blood cell that can differentiate into macrophages and dendritic cells, which are responsible for phagocytosis, antigen presentation, and cytokine production.

Lymphoid progenitors are immature, undifferentiated cells that have the potential to develop into various types of lymphocytes, including T cells, B cells, and natural killer cells. These progenitor cells are crucial for the maintenance and replenishment of the body's lymphoid cell populations, which are essential components of the adaptive immune system.

Hematopoietic Stem Cells: Multipotent stem cells that can give rise to all types of blood cells, including lymphoid progenitors.

Lymphocytes: White blood cells that play a central role in the adaptive immune response, including T cells, B cells, and natural killer cells.

Adaptive Immune System: The part of the immune system that adapts to specific pathogens and provides long-lasting, targeted immunity.

B cells, also known as B lymphocytes, are a type of white blood cell that play a crucial role in the adaptive immune response. They are responsible for the production of antibodies, which recognize and bind to specific foreign antigens, neutralizing them or marking them for destruction by other immune cells.

Antibodies: Proteins produced by B cells that recognize and bind to specific foreign antigens, neutralizing them or marking them for destruction by other immune cells.

Plasma Cells: Specialized B cells that are responsible for the production and secretion of large quantities of antibodies.

Memory B Cells: B cells that remain in the body after an initial immune response, allowing for a faster and more robust response upon subsequent exposure to the same antigen.

T cells, also known as T lymphocytes, are a type of white blood cell that play a crucial role in the adaptive immune response. They originate from stem cells in the bone marrow and mature in the thymus gland, developing specialized functions to recognize and eliminate threats to the body.

Cytotoxic T Cells: A subtype of T cells that directly kill infected or cancerous cells by releasing cytotoxic granules and triggering apoptosis.

Helper T Cells: A subtype of T cells that coordinate the immune response by secreting cytokines that activate and regulate other immune cells.

Regulatory T Cells: A subtype of T cells that suppress immune responses to prevent autoimmunity and maintain tolerance to self-antigens.

NK (Natural Killer) cells are a type of lymphocyte, a white blood cell, that plays a crucial role in the body's innate immune response. They are called 'natural killer' cells because they can identify and destroy infected or cancerous cells without prior sensitization.

Lymphocytes: A type of white blood cell that is essential for the adaptive immune response, including T cells and B cells.

Innate Immunity: The body's first line of defense against pathogens, which includes physical barriers, chemical defenses, and cells like NK cells.

Cytotoxicity: The ability of certain cells, like NK cells, to induce the death of target cells through the release of cytotoxic granules.

Neutrophils are a type of white blood cell that play a crucial role in the innate immune response. They are the first responders to microbial infection and are highly active in phagocytosis.

Phagocytosis: The process by which cells, like neutrophils, engulf and digest pathogens.

Chemotaxis: The movement of an organism or cell toward or away from a chemical stimulus.

Granulocytes: A category of white blood cells characterized by the presence of granules in their cytoplasm; includes neutrophils, eosinophils, and basophils.

Eosinophils are a type of white blood cell that plays a critical role in the immune system, particularly in combating parasitic infections and mediating allergic reactions. They are part of the body's innate nonspecific host defenses as well as involved in certain adaptive immune responses.

Neutrophils: A type of white blood cell that is the first responder to microbial infection.

Mast Cells: Cells that play a key role in inflammation and allergic reactions by releasing histamine.

Adaptive Immunity: A subsystem of the overall immune system that provides long-term immunity through memory cells.

Cytotoxic granules are specialized secretory vesicles found in certain immune cells, such as natural killer (NK) cells and cytotoxic T lymphocytes (CTLs). These granules contain a variety of potent cytotoxic proteins that can induce apoptosis, or programmed cell death, in target cells that are infected or transformed.

Perforin: A pore-forming protein found in cytotoxic granules that can create holes in the target cell membrane, allowing other cytotoxic proteins to enter and induce cell death.

Granzymes: Serine proteases stored within cytotoxic granules that can activate caspase enzymes, leading to apoptosis in the target cell.

Degranulation: The process by which cytotoxic cells release the contents of their cytotoxic granules towards a target cell, triggering its destruction.

Basophils are a type of white blood cell that play a role in immune responses, primarily by releasing histamine during allergic reactions and inflammatory processes. They are also involved in defense mechanisms against parasites.

Histamine: A compound released by cells in response to injury and allergic reactions, causing contraction of smooth muscle and dilation of capillaries.

IgE Antibodies: A class of antibodies produced by the immune system that function mainly to combat parasitic infections and play a significant role in allergic diseases.

Mast Cells: Cells found in connective tissues that release histamine and other substances during inflammatory and allergic responses.

Histamine is a biologically active amine involved in local immune responses. It plays a key role in inflammation and allergic reactions.

Mast Cells: Immune cells that release histamine and other chemicals during inflammatory and allergic reactions.

Basophils: A type of white blood cell that releases histamine and heparin as part of the body's immune response.

Anaphylaxis: A severe, potentially life-threatening allergic reaction caused by excessive release of histamine.

Vasodilation is the widening of blood vessels resulting from relaxation of the muscular walls of the vessels. It increases blood flow to tissues and helps in thermoregulation and immune response.

Inflammation: A biological response to harmful stimuli, characterized by redness, swelling, heat, pain, and loss of function.

Nitric oxide: A signaling molecule that promotes vasodilation by relaxing smooth muscles in blood vessels.

Endothelial cells: Cells lining the interior surface of blood vessels, playing a crucial role in vascular functions including vasodilation.

Monocytes are a type of white blood cell that plays a crucial role in the innate immune system by differentiating into macrophages and dendritic cells upon entering tissues. They are essential for phagocytosis and pathogen recognition.

Macrophage: A large phagocytic cell derived from monocytes that engulfs pathogens and dead cells.

Dendritic Cell: An antigen-presenting cell derived from monocytes that activates T-cells.

Phagocytosis: The process by which certain living cells called phagocytes ingest or engulf other cells or particles.

Macrophages are large phagocytic cells derived from monocytes that play a crucial role in both innate and adaptive immunity. They engulf and digest pathogens, dead cells, and cellular debris.

Phagocytosis: The process by which a cell engulfs particles such as bacteria or cellular debris.

Antigen-Presenting Cells (APCs): Cells that display antigens to T cells, initiating an adaptive immune response.

Cytokines: Signaling proteins released by cells that affect the behavior of other cells, particularly in immune responses.

Dendritic cells are specialized antigen-presenting cells that play a crucial role in the initiation of the immune response. They capture, process, and present antigens to T cells, thereby bridging innate and adaptive immunity.

Macrophages: Phagocytic white blood cells that engulf pathogens and present antigens to T cells.

T Cells: A type of lymphocyte that plays a central role in cell-mediated immunity.

Major Histocompatibility Complex (MHC): A set of cell surface proteins essential for acquired immune system's recognition of foreign molecules.

Adaptive immunity is a specialized immune response that develops over time, involving the activation and clonal expansion of lymphocytes. It provides long-lasting protection and memory against specific pathogens.

Antigen: A substance that induces an immune response, often by binding to a receptor on B or T cells.

Antibody: A protein produced by B cells that binds specifically to an antigen to neutralize it or mark it for destruction.

Cytokines: Small signaling proteins released by T cells that regulate the intensity and duration of the immune response.

Apoptosis is a form of programmed cell death that occurs in multicellular organisms. It plays a crucial role in regulating immune responses and maintaining cellular homeostasis.

Necrosis: A form of traumatic cell death that results from acute cellular injury and often leads to inflammation.

Caspases: A family of protease enzymes that play essential roles in programmed cell death (apoptosis) and inflammation.

Autoimmunity: A condition where the immune system mistakenly attacks the body's own tissues.

Cytokines are small proteins released by cells, especially those of the immune system, that have a specific effect on interactions and communications between cells. They play crucial roles in regulating immune responses and inflammation.

Interleukins: A group of cytokines that were first seen to be expressed by white blood cells (leukocytes).

Chemokines: A subset of cytokines responsible for inducing chemotaxis in nearby responsive cells.

Tumor Necrosis Factor (TNF): A type of cytokine involved in systemic inflammation and stimulation of the acute phase reaction.

Interferon-γ (IFN-γ) is a cytokine that plays a crucial role in the cellular immune response. It is primarily produced by T cells and natural killer (NK) cells, and acts as a key regulator of various immune functions, including the activation and differentiation of immune cells, the inhibition of viral replication, and the enhancement of antigen presentation.

Cytokine: Small proteins secreted by various cells, including immune cells, that act as signaling molecules to coordinate and regulate immune responses.

T cells: A type of lymphocyte that plays a central role in cell-mediated immunity, recognizing and responding to specific antigens.

Natural Killer (NK) cells: A type of cytotoxic lymphocyte that plays a key role in the innate immune response, capable of recognizing and destroying infected or cancerous cells.

Innate immunity refers to the body's natural, non-specific defense mechanisms that provide immediate protection against pathogens. It is the first line of defense against infectious agents and plays a crucial role in maintaining overall immune function.

Physical Defenses: Physical barriers, such as the skin, mucous membranes, and cilia, that prevent the entry of pathogens into the body.

Cellular Defenses: Immune cells, like phagocytes and natural killer cells, that directly attack and destroy invading microorganisms.

Pathogen Recognition: The process by which the immune system identifies and responds to the presence of foreign substances or pathogens.

Adaptive immunity is a specialized immune response that develops over time, involving the activation and clonal expansion of lymphocytes. It provides long-lasting protection and memory against specific pathogens.

Antigen: A substance that induces an immune response, often by binding to a receptor on B or T cells.

Antibody: A protein produced by B cells that binds specifically to an antigen to neutralize it or mark it for destruction.

Cytokines: Small signaling proteins released by T cells that regulate the intensity and duration of the immune response.

The complement system is a group of proteins that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism. It forms part of the innate immune response and also helps bridge innate and adaptive immunity.

Opsonization: The process by which pathogens are marked for ingestion and destruction by phagocytes.

Membrane Attack Complex (MAC): A structure formed on the surface of pathogenic bacterial cells as a result of the activation of the host's complement system.

Phagocytosis: The process by which cells ingest and destroy foreign particles or microorganisms.