18.4 Leukocytes and Platelets
4 min read•june 18, 2024
, or white blood cells, are the body's defense squad. They fight off invaders like bacteria and viruses, keeping us healthy. Each type of has a unique role in the , from that gobble up pathogens to that remember past infections.
are tiny cell fragments that spring into action when we're injured. They stick together to form clots, stopping bleeding and helping wounds heal. Understanding how work is key to grasping how our bodies protect themselves and repair damage.
Leukocytes
Characteristics and functions of leukocytes
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- Leukocytes, or white blood cells (WBCs), are essential components of the immune system that defend the body against infectious agents (bacteria, viruses) and foreign substances
- Leukocytes can exit the bloodstream and migrate to tissues where they are needed to fight infections or
- Leukocytes are categorized into (, , ) which contain granules in their cytoplasm, and (lymphocytes, ) which lack granules
- Leukocytes are produced in the through , where they originate from and differentiate into specific types based on the presence of and growth factors
Types of leukocytes in immune response
- Neutrophils (50-70% of leukocytes)
- Possess a multilobed nucleus and fine, pale pink granules in the cytoplasm
- Primary role is of bacteria and fungi, serving as the first responders to sites of infection or inflammation
- (2-4% of leukocytes)
- Have a bilobed nucleus and large, coarse, reddish-orange granules in the cytoplasm
- Involved in allergic reactions, defense against parasites, and release enzymes that neutralize inflammatory chemicals
- (0.5-1% of leukocytes)
- Contain a lobed nucleus and large, dark blue-purple granules in the cytoplasm
- Release and other inflammatory mediators during allergic reactions, contributing to the inflammatory response
- Lymphocytes (25-35% of leukocytes)
- Characterized by a large, round nucleus with a thin rim of cytoplasm
- Two main types: for cell-mediated immunity (direct attack on infected or cancerous cells) and for humoral immunity (antibody production)
- Play a crucial role in recognizing and responding to specific
- (3-8% of leukocytes)
- Feature a large, kidney-shaped nucleus and abundant pale-blue cytoplasm
- Migrate into tissues and differentiate into and
- Phagocytose pathogens, cellular debris, and foreign substances, and present antigens to lymphocytes to initiate specific immune responses
Immune System and Inflammation
- The immune system is a complex network of cells, tissues, and organs that work together to defend the body against pathogens and foreign substances
- Inflammation is a protective response of the immune system to injury or infection, characterized by redness, swelling, heat, and pain
- Bone marrow plays a crucial role in the immune system by producing and maturing various types of immune cells
Platelets and Hemostasis
Structure and function of platelets
- Platelets () are small, disc-shaped cell fragments derived from in the bone marrow through a process of fragmentation
- Platelets lack a nucleus but contain organelles, granules, and enzymes essential for their function in (stopping bleeding and repairing damaged blood vessels)
- involves three main stages:
- Vascular spasm
- Platelet plug formation
- Coagulation (blood clotting)
- When a blood vessel is injured, platelets adhere to the damaged , become activated, and release granules containing clotting factors and growth factors
- Activated platelets change shape and aggregate to form a platelet plug, sealing the damaged vessel
- Platelets also contribute to the coagulation cascade by providing a surface for the assembly of clotting factors which convert into , forming a mesh-like network that stabilizes the platelet plug and creates a solid clot
Disorders of leukocytes and platelets
- Leukocyte disorders:
- Leukopenia: low leukocyte count, increases susceptibility to infections, caused by medications, autoimmune disorders, or bone marrow disorders
- : high leukocyte count, often a sign of infection, inflammation, or , caused by stress, smoking, or certain medications
- : blood cancer, uncontrolled production of abnormal leukocytes, impairs normal blood cell production and function, leads to anemia, infections, and bleeding disorders
- Platelet disorders:
- : low platelet count, increases risk of bleeding and impairs clotting, caused by autoimmune disorders, medications, or bone marrow disorders
- : high platelet count, increases risk of blood clots and thrombosis, caused by , iron deficiency, or certain cancers
- Platelet dysfunction: impaired platelet function despite normal count, can be inherited or acquired, leads to prolonged bleeding time and impaired clot formation, caused by medications (aspirin, NSAIDs)
Key Terms to Review (65)
Agranular leukocytes: Agranular leukocytes are a type of white blood cell that lack visible granules in their cytoplasm. They play crucial roles in the immune system, including lymphocytes and monocytes, which help fight infection and disease.
Agranulocytes: Agranulocytes, also known as mononuclear leukocytes, are a type of white blood cell that lack the characteristic granules found in granulocytes. They play a crucial role in the body's immune response and are an important component of the leukocyte and platelet systems.
Antigens: Antigens are molecules, usually proteins or polysaccharides, that are recognized by the immune system as foreign or different from the body's own cells. They trigger an immune response, leading to the production of antibodies and the activation of other immune defenses to neutralize or eliminate the perceived threat.
Antithrombin: Antithrombin is a protein in the blood that helps regulate blood clotting by inhibiting several enzymes of the coagulation system. It plays a crucial role in preventing the formation of dangerous clots that can block blood vessels.
B lymphocytes: B lymphocytes, also known as B cells, are a type of white blood cell crucial for the immune response by producing antibodies that neutralize pathogens. They develop in bone marrow and play a key role in the humoral immunity component of the adaptive immune system.
B Lymphocytes: B lymphocytes, also known as B cells, are a type of white blood cell that play a crucial role in the adaptive immune response. They are responsible for producing antibodies, which are proteins that recognize and bind to specific foreign substances, known as antigens, in order to neutralize them or mark them for destruction by other immune cells.
Basophils: Basophils are a type of white blood cell that plays a critical role in the body's immune response by releasing chemicals such as histamine and heparin during allergic reactions and inflammation. They represent less than 1% of the total white blood cell count but are vital for mounting a protective response against pathogens.
Basophils: Basophils are a type of white blood cell that play a crucial role in the body's immune response and inflammatory processes. They are the least common type of leukocyte, accounting for only about 0.5-1% of all white blood cells in the body.
Bone Marrow: Bone marrow is the soft, spongy tissue found inside the cavities of bones. It is responsible for the production of various blood cells, including red blood cells, white blood cells, and platelets, making it a crucial component of the skeletal, circulatory, and immune systems.
Bone marrow biopsy: A bone marrow biopsy is a medical procedure in which a small amount of bone marrow tissue is removed from the body for examination, typically to diagnose blood disorders or diseases. This procedure helps in understanding the production and health of formed elements in the blood, such as red blood cells, white blood cells, and platelets.
Chronic inflammation: Chronic inflammation is a prolonged inflammatory response in the body that can last for months or years, often resulting from failure to eliminate the cause of an acute inflammation or due to persistent irritants. Unlike acute inflammation, which is a healthy and necessary response for healing, chronic inflammation can lead to tissue damage and contribute to various diseases.
Cytokines: Cytokines are small proteins released by cells, particularly those of the immune system, that have an effect on the interactions and communications between cells. They play a crucial role in the body's response to infection, inflammation, and trauma.
Cytokines: Cytokines are a broad category of small proteins that are secreted by various cells in the body, including immune cells, endothelial cells, and fibroblasts. These signaling molecules play a crucial role in regulating the immune response, inflammation, and various other physiological processes across multiple systems, including the integumentary, immune, and inflammatory systems.
Defensins: Defensins are small antimicrobial peptides produced by leukocytes and epithelial cells that play a crucial role in the body's innate immune defense against pathogens. They act by disrupting the membrane integrity of bacteria, fungi, and viruses, leading to their destruction.
Dendritic Cells: Dendritic cells are a type of antigen-presenting immune cell that play a crucial role in the body's innate and adaptive immune responses. They act as sentinels, patrolling the body for foreign substances and initiating the appropriate immune reactions against potential threats.
Diapedesis: Diapedesis is the process by which white blood cells (leukocytes) move through the walls of capillaries and enter the tissues to reach sites of infection or injury. It involves squeezing between endothelial cells that line the blood vessels, allowing these immune cells to exit the bloodstream and participate in immune response.
Emigration: Emigration is the process by which leukocytes move out of the bloodstream and into the tissues to reach sites of infection or injury. This movement involves passing through the blood vessel wall in response to chemical signals at the site of damage or infection.
Endothelium: The endothelium is a thin layer of simple squamous epithelial cells that lines the interior surface of blood vessels and lymphatic vessels, as well as the heart's inner chambers. It serves as a barrier and regulator for substances entering and exiting the bloodstream and plays a key role in vascular function and blood pressure regulation.
Endothelium: The endothelium is a thin, delicate layer of cells that lines the interior surface of blood vessels, including arteries, veins, and capillaries. It serves as a critical interface between the bloodstream and the surrounding tissues, playing a vital role in various physiological processes within the body.
Eosinophils: Eosinophils are a type of white blood cell that play a crucial role in the body's immune response, particularly in combating parasitic infections and participating in allergic reactions. They contain granules rich in enzymes that help reduce inflammation and fight off pathogens.
Eosinophils: Eosinophils are a type of white blood cell that play a key role in the immune response, particularly against parasitic infections and in allergic reactions. They are characterized by the presence of granules containing cytotoxic proteins that can damage or destroy foreign invaders.
Fibrin: Fibrin is a protein that plays a crucial role in blood clotting, forming a fibrous mesh that impedes blood flow at the site of injury. It is created by the action of the enzyme thrombin on fibrinogen, a soluble protein found in blood plasma.
Fibrin: Fibrin is an insoluble protein that is formed during the blood clotting process. It acts as a mesh-like network that traps blood cells, platelets, and other clotting factors to form a stable blood clot and stop bleeding. Fibrin plays a crucial role in the body's hemostatic response to tissue injury and in the overall process of blood coagulation.
Fibrinogen: Fibrinogen is a soluble plasma glycoprotein, produced by the liver, that plays a crucial role in blood clot formation. When activated, it converts into fibrin, forming a mesh that helps to stabilize the blood clot.
Fibrinogen: Fibrinogen is a large, soluble glycoprotein found in the blood plasma that plays a crucial role in the blood clotting process known as hemostasis. It is synthesized in the liver and circulates in the bloodstream, ready to be converted into insoluble fibrin during an injury or trauma to the blood vessels.
Granulocytes: Granulocytes are a type of white blood cell that contain granules in their cytoplasm. They are a crucial component of the immune system, responsible for defending the body against pathogens and infections.
Hematopoiesis: Hematopoiesis is the process by which the body produces blood cells and platelets, occurring primarily in the bone marrow. It involves the differentiation of multipotent stem cells into various types of blood cells, including red blood cells, white blood cells, and platelets.
Hematopoiesis: Hematopoiesis is the process by which blood cells are produced and replenished in the body. It is a crucial function that occurs within the connective tissue of the skeletal system, ensuring the continuous supply of various blood components essential for the body's health and function.
Hematopoietic Stem Cells: Hematopoietic stem cells are a type of multipotent stem cell that can differentiate into various blood cell types, including red blood cells, white blood cells, and platelets. These stem cells are responsible for the continuous production and replenishment of the body's blood and immune system components.
Hemostasis: Hemostasis is the process by which the body stops bleeding at the site of an injury, involving blood vessel constriction, platelet plug formation, and blood clotting. It's a critical mechanism for preventing excessive blood loss and facilitating wound healing.
Hemostasis: Hemostasis is the physiological process that stops bleeding and maintains the integrity of the circulatory system. It is a crucial mechanism that prevents excessive blood loss following tissue injury or damage to blood vessels.
Histamine: Histamine is a compound released by cells in response to injury and in allergic and inflammatory reactions, serving as a mediator of itching, sneezing, and vasodilation. It plays a significant role in the body's immune response by signaling the surrounding tissue to react accordingly.
Histamine: Histamine is a biogenic amine that acts as a chemical mediator in the body, playing a crucial role in various physiological processes and pathological conditions. It is involved in the body's immune response, inflammatory reactions, and the regulation of certain bodily functions.
Immune System: The immune system is a complex network of cells, tissues, and organs that work together to defend the body against infections, diseases, and other harmful agents. It is responsible for recognizing and eliminating foreign substances, pathogens, and abnormal cells to maintain the body's health and well-being.
Inflammation: Inflammation is the body's natural response to injury, infection, or irritation. It is a protective mechanism that aims to remove harmful stimuli and initiate the healing process. Inflammation is a critical component in various physiological processes, including tissue repair, immune system function, and the body's defense against pathogens.
Leukemia: Leukemia is a type of cancer that affects the blood and bone marrow, characterized by the overproduction of abnormal white blood cells. This excessive growth can impede the body's ability to fight infection and impair the production of red blood cells and platelets.
Leukemia: Leukemia is a type of cancer that affects the blood and bone marrow, characterized by the uncontrolled production and accumulation of abnormal white blood cells. This disrupts the normal function of the blood and immune system, leading to various health complications.
Leukocyte: Leukocytes, also known as white blood cells, are cells of the immune system involved in defending the body against both infectious disease and foreign materials. They are produced and derived from multipotent cells in the bone marrow known as hematopoietic stem cells.
Leukocytes: Leukocytes, also known as white blood cells, are a vital component of the body's immune system. They play a crucial role in defending the body against infections, diseases, and foreign substances by detecting and destroying pathogens, clearing cellular debris, and coordinating the overall immune response.
Leukocytes and Platelets: Leukocytes, also known as white blood cells, are a type of blood cell primarily involved in the body's immune response to identify and combat infections, diseases, and foreign invaders. They vary in function and appearance, playing critical roles from producing antibodies to directly attacking pathogens.
Leukocytosis: Leukocytosis is a condition characterized by an increased number of white blood cells (leukocytes) in the bloodstream, often indicating an immune response to infection, inflammation, or other stimuli. It can be detected through a complete blood count (CBC) test, showing levels above the normal range for leukocytes.
Leukocytosis: Leukocytosis is a condition characterized by an abnormally high number of white blood cells (leukocytes) in the bloodstream. It is often a sign of an underlying health issue, such as infection, inflammation, or other medical conditions, and can provide important insights into the body's immune response.
Lymphocytes: 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 eliminating foreign pathogens, such as bacteria, viruses, and cancer cells, through a complex network of interactions and signaling pathways. Lymphocytes are central to the functioning of both the innate and adaptive immune systems.
Lysozyme: Lysozyme is an enzyme found in the secretions of leukocytes (white blood cells) and platelets that destroys the cell walls of certain bacteria, contributing to the body's defense system against infection. It acts by breaking down the polysaccharides present in bacterial cell walls, leading to osmotic imbalance and cell lysis.
Macrophages: Macrophages are a type of large white blood cell that play a crucial role in the body's immune response. They are responsible for engulfing and digesting pathogens, cellular debris, and other foreign materials, serving as the first line of defense against infection and disease.
Megakaryocyte: A megakaryocyte is a large bone marrow cell responsible for the production of blood thrombocytes (platelets), which are crucial for blood clotting. These cells undergo a process called endomitosis, where they replicate their DNA without cell division, leading to an increase in cell size and nuclear content.
Megakaryocytes: Megakaryocytes are large, polyploid cells found in the bone marrow that are responsible for the production of platelets, which are essential for blood clotting and wound healing.
Memory cell: Memory cells are a type of white blood cell, specifically a component of the adaptive immune system, that remain in the body after an initial infection and provide immunity by quickly responding to subsequent infections by the same pathogen. They "remember" the pathogen, allowing for a faster and more effective immune response upon re-exposure.
Monocytes: Monocytes are a type of white blood cell that plays a crucial role in the immune system by engulfing and destroying pathogens and debris. They are the largest type of leukocyte and can differentiate into macrophages and dendritic cells, which further participate in the body's defense mechanisms.
Monocytes: Monocytes are a type of white blood cell that play a crucial role in the immune system. They are the largest of the leukocytes and serve as precursors to macrophages and dendritic cells, which are responsible for engulfing and destroying pathogens, as well as presenting antigens to other immune cells.
Neutrophils: Neutrophils are a type of white blood cell that play a crucial role in the body's immune response by engulfing and destroying pathogens, such as bacteria and fungi. They are the most abundant type of leukocytes in human blood and are among the first responders to microbial infection.
Neutrophils: Neutrophils are a type of white blood cell that play a crucial role in the body's innate immune response. They are the most abundant type of leukocyte and are the first responders to sites of infection or injury, acting as the body's primary defense against invading pathogens and damaged tissue.
Phagocytosis: Phagocytosis is the process by which certain living cells called phagocytes engulf and digest particles or other cells, often to fight off pathogens or to clear debris in the body. It involves the cell membrane wrapping around the particle and forming a vesicle known as a phagosome that encloses the material to be broken down.
Phagocytosis: Phagocytosis is the process by which certain cells, called phagocytes, engulf and digest foreign particles, pathogens, or cellular debris. It is a crucial mechanism in the body's immune response and plays a vital role in cellular homeostasis, tissue repair, and the innate immune system.
Platelets: Platelets, also known as thrombocytes, are small, irregularly shaped cell fragments found in the bloodstream that play a crucial role in blood clotting and hemostasis. They are produced in the bone marrow and are essential for maintaining the integrity of blood vessels and preventing excessive bleeding.
Polymorphonuclear: A polymorphonuclear cell is a type of white blood cell characterized by the presence of granules in its cytoplasm and a nucleus that is divided into multiple lobes. These cells are crucial in the body's immune response, particularly in fighting bacterial infections.
Positive chemotaxis: Positive chemotaxis is the movement of an organism or cell towards higher concentrations of a specific chemical stimulus. In the context of leukocytes within the cardiovascular system, it refers to their movement towards areas of infection or injury signaled by chemicals released from those sites.
T lymphocytes: T lymphocytes are a type of white blood cell that play a central role in cell-mediated immunity, part of the adaptive immune system. They originate from stem cells in the bone marrow but mature in the thymus, which is how they get their "T" designation.
T Lymphocytes: T lymphocytes, also known as T cells, are a type of white blood cell that play a crucial role in the adaptive immune response. They are responsible for cell-mediated immunity, recognizing and destroying infected or cancerous cells, and regulating the overall immune system function.
The Adaptive Immune Response: T lymphocytes and Their Functional Types: The adaptive immune response is a specific defense mechanism in the body involving T lymphocytes (T cells), which adapt to recognize and eliminate specific pathogens or infected cells. T cells come in various functional types, including helper T cells, cytotoxic T cells, and regulatory T cells, each playing unique roles in immune defense.
Thrombin: Thrombin is a serine protease enzyme that plays a crucial role in the blood clotting process, known as hemostasis. It is a key component in the coagulation cascade, responsible for converting fibrinogen into fibrin, which forms the backbone of a blood clot.
Thrombocytes: Thrombocytes, commonly known as platelets, are small, colorless cell fragments in the blood that form clots to stop or prevent bleeding. They play a crucial role in the repair of damaged blood vessels.
Thrombocytes: Thrombocytes, also known as platelets, are small, disc-shaped cell fragments found in the blood that play a crucial role in blood clotting and hemostasis. They are derived from the fragmentation of large cells called megakaryocytes in the bone marrow and circulate in the bloodstream, ready to respond to vascular injury.
Thrombocytopenia: Thrombocytopenia is a condition characterized by an abnormally low number of platelets in the blood, which can impair the body's ability to form clots and stop bleeding. Platelets play a crucial role in hemostasis, and their deficiency can lead to increased bleeding and bruising.
Thrombocytosis: Thrombocytosis is a condition characterized by an abnormally high number of platelets, also known as thrombocytes, in the bloodstream. This term is particularly relevant in the context of the topics covered in Chapter 18.4, which focuses on leukocytes and platelets.