Leukocytes Flashcards
explain leukocytes
Leukocytes, commonly known as white blood cells, play a crucial role in the immune system’s defense mechanisms. They are complete, colorless cells found in various body compartments, including bone marrow, blood, and lymphatic tissues. White blood cells are responsible for a range of essential functions, which include:
Fighting Against Infections: White blood cells are the primary defenders against infectious agents, such as bacteria, viruses, fungi, and parasites. They actively participate in the immune response to combat these invaders.
Participating in Immune Responses: Leukocytes, particularly lymphocytes, are key players in the adaptive immune system. They help recognize specific pathogens and mount immune responses, including the production of antibodies and memory responses.
Removing Old Cells, Debris, and Foreign Objects: White blood cells are involved in the process of phagocytosis, where they engulf and digest cellular debris, aging cells, and foreign substances, including virally infected or cancerous cells.
Leukocytes can be classified into two main groups based on their characteristics:
Granulocytes: Granulocytes are so named because they contain visible granules in their cytoplasm, which can be seen when the cells are stained. These cells often have lobulated (polymorphous) nuclei, which means their nuclei have irregular shapes. Granulocytes, also known as “polymorphs,” are primarily found in tissues rather than in the blood. They are subdivided into three main types: neutrophils, eosinophils, and basophils.
Agranulocytes: Agranulocytes have fewer, less visible granules in their cytoplasm. The granules in agranulocytes are not as easily distinguished under a microscope. Agranulocytes include two major cell types: lymphocytes and monocytes. These cells play crucial roles in immune responses, with lymphocytes involved in adaptive immunity, while monocytes can differentiate into macrophages and dendritic cells, contributing to immune defense and antigen presentation.
explain neutrophils
Neutrophils are a type of granulocyte and a key component of the innate immune system. They play a vital role in the body’s defense against infections and inflammation. Here’s a closer look at the behavior of neutrophils in response to infection or tissue damage:
Circulating Blood: Neutrophils are typically found in the bloodstream, where they have a relatively short lifespan. They spend approximately 3 to 12 hours circulating in the blood, with a mean lifespan of around 7 hours.
Migration to Tissues: When an infection, inflammation, or tissue damage occurs, the body responds by releasing chemical signals known as chemotactic stimuli. Neutrophils can sense and respond to these chemical signals, prompting them to migrate to the affected sites.
Rolling, Adhering, and Diapedesis: Neutrophils follow a series of steps to reach the site of infection or inflammation. This process involves “rolling,” where they interact with the endothelial cells lining blood vessels. They then adhere or “stick” to the vessel walls and eventually undergo diapedesis, which is the process of squeezing through the vessel walls to enter the tissues.
Once in the affected tissues, neutrophils actively participate in the immune response. They are equipped to phagocytose (engulf and digest) bacteria, fungi, and other foreign invaders, effectively removing them from the body. Neutrophils are also involved in releasing various antimicrobial substances to combat pathogens.
The migration and activation of neutrophils are integral components of the innate immune response, which provides rapid and immediate defense against infections. While neutrophils have a relatively short lifespan in the circulation, they can extend their activity to around 30 hours in the tissues, allowing them to contribute significantly to the body’s immune defenses during the early stages of infection or inflammation.
explain the process of neutrophils migrating from the bloodstream to the site of infection or inflammation
Floating: Neutrophils are initially found in the bloodstream, where they circulate freely.
Chemo-Detection: Neutrophils detect chemical signals (chemotactic stimuli) released by cells at the site of infection or inflammation. These signals act as a beacon to guide neutrophils toward the affected area.
Margination: Neutrophils move closer to the inner wall of the blood vessels (endothelium), preparing for the next steps.
Rolling: Neutrophils interact with the endothelial cells lining the blood vessels in a rolling motion. This initial contact allows neutrophils to “sample” the endothelial cells.
Tethering: Neutrophils briefly adhere to the vessel wall, slowing down their movement.
Deceleration: Neutrophils further slow their movement and make stronger connections with the endothelial cells.
Activation: Neutrophils become activated in response to the chemotactic signals and adhere more firmly to the endothelium.
Adhesion/Arrest: Neutrophils firmly adhere to the vessel wall, coming to a complete stop.
Diapedesis (Extravasation): Neutrophils undergo diapedesis, which is the process of squeezing between the endothelial cells and crossing the vessel wall to enter the surrounding tissues.
Transversing Basal Membrane: Neutrophils move through the basement membrane, which separates the endothelium from the underlying tissue.
Migration Through ECM (Extracellular Matrix): Neutrophils navigate through the extracellular matrix of the tissues to reach the specific site of infection or inflammation.
Chemotaxis: Neutrophils follow the gradient of chemotactic signals to reach the precise location of the pathogen or injury.
Recognition and Attachment (+- Opsonization): Neutrophils recognize and attach to the foreign invader (pathogen) or damaged cells. Opsonization, which involves the binding of opsonins (proteins that enhance phagocytosis), can enhance this process.
Phagocytosis: Neutrophils engulf and ingest the pathogen or foreign material, enclosing it within a phagosome. The neutrophil will then proceed to destroy the ingested material.
explain the lifecycle and functions of neutrophils
Circulating Blood:
Neutrophils spend approximately 7 hours in the circulating blood, patrolling the system for any signs of infection or inflammation.
Migration to Sites of Infection and Inflammation: In response to chemotactic stimuli released by cells at sites of infection, inflammation, or cell death, neutrophils migrate to these affected areas.
During this process, neutrophils undergo a series of steps, including rolling, adhering, and diapedesis, allowing them to exit the blood vessels and enter the surrounding tissues.
Tissue Activity: Once in the tissues, neutrophils become highly phagocytic, meaning they can engulf and digest foreign invaders such as bacteria.
Neutrophils use pseudopodia (temporary extensions of the cell membrane) to surround and engulf bacteria, encapsulating them in phagocytic vacuoles.
Bacterial Killing: Within the phagocytic vacuoles, neutrophils release proteolytic enzymes and myeloperoxidases from their granules.
These enzymes and myeloperoxidases work together to break down and destroy the ingested bacteria.
Neutrophils generate hydrogen peroxide (H2O2) and other reactive oxygen species (ROS), which are toxic to microbes. These ROS contribute to killing the bacteria within the phagocytic vacuoles.
explain the several distinctive features of neutrophils
Size: Neutrophils typically have a diameter ranging from 10 to 14 micrometers (µm).
Nuclear Structure: The nuclei of neutrophils are multi-lobed, with these lobes connected by fine chromatin threads. This multi-lobed appearance gives them the name “polymorphonuclear leucocytes.”
Nuclear Shape: In immature neutrophils, the nucleus can appear horseshoe-shaped. As they mature, the nucleus becomes more multi-lobed.
Granules: Neutrophils have small granules within their cytoplasm that can be seen when stained. These granules contain various enzymes and antimicrobial proteins, which play a crucial role in their phagocytic and antimicrobial functions.
Staining: Neutrophil granules typically stain lilac or light purple.
explain several important functions of neutrophils
Phagocytosis: Neutrophils are highly phagocytic cells, meaning they have the ability to engulf and digest foreign invaders, such as bacteria. They use pseudopodia to surround and internalize pathogens, subsequently destroying them within phagocytic vacuoles.
Inflammatory Response: Neutrophils play a key role in the inflammatory response. When they are activated, they release inflammatory mediators, including leukotrienes, prostaglandins, and thromboxanes. These signaling molecules contribute to the inflammatory process by increasing blood flow, making blood vessels more permeable, and recruiting other immune cells to the site of infection or injury.
Febrile Response: Neutrophils can contribute to the febrile (fever) response during infection. When neutrophils are activated, they release endogenous pyrogens, which are substances that can induce a fever response in the body. Fever is part of the body’s defense mechanisms against infections, as it can help limit the growth of some pathogens.
explain some situations and conditions that can lead to physiological and pathological increases in the number of neutrophils (neutrophilia)
Physiological Increases:
After Exercise: Physical activity can lead to a temporary increase in the number of circulating neutrophils. This is part of the body’s response to the stress of exercise and is generally a normal and expected reaction.
After Injection with Adrenaline: The release of adrenaline, which is a stress hormone, can stimulate the mobilization of neutrophils from the bone marrow into the bloodstream.
During Pregnancy, Menstruation, Parturition, and Lactation: Hormonal changes associated with pregnancy, menstruation, childbirth, and lactation can lead to an increase in neutrophil counts.
After Meals: Neutrophil counts can temporarily increase after eating. This is thought to be related to the postprandial inflammatory response.
Mental or Emotional Stress: Stressful situations, both acute and chronic, can lead to the release of stress hormones that affect neutrophil counts.
Pathological Increases:
After Pus-Forming Bacterial Infections: In response to bacterial infections, especially those associated with pus formation, the body may increase neutrophil production and release to combat the infection.
Acute Rheumatic Fever: Certain inflammatory conditions, such as acute rheumatic fever, can lead to an elevated neutrophil count as part of the immune response to the condition.
Gout: Gout is an inflammatory arthritis caused by the deposition of urate crystals in joints. Inflammation associated with gout can lead to neutrophilia.
Tissue Destruction: Various forms of tissue damage, such as burns, significant hemorrhage, myocardial infarction (heart attack), or poisoning by heavy metals like mercury or lead, can trigger an increase in neutrophils as part of the body’s response to injury and inflammation.
explain neutropenia
Neutropenia is a condition characterized by a lower than normal number of neutrophils in the bloodstream. Neutrophils are a type of white blood cell, and they play a crucial role in the body’s immune response, particularly in defending against bacterial infections. Neutropenia can occur for various reasons, including both physiological and pathological factors:
Physiological Causes:
Being a Child: It’s not uncommon for infants and very young children to have lower neutrophil counts than adults. This is often a normal part of early development.
Pathological Causes:
Typhoid Fever: Typhoid fever is a bacterial infection caused by Salmonella typhi. It can lead to neutropenia, among other complications.
Viral Infections: Certain viral infections, such as HIV, hepatitis, or Epstein-Barr virus (EBV), can suppress bone marrow function and lead to neutropenia.
Malaria: Malaria is a parasitic infection transmitted by mosquitoes. Severe cases of malaria can result in neutropenia as part of the body’s response to the infection.
Aplasia of Bone Marrow: Aplasia of the bone marrow, also known as aplastic anemia, is a condition where the bone marrow fails to produce an adequate number of blood cells, including neutrophils.
Bone Marrow Depression: Various factors can lead to bone marrow depression, which can result in reduced neutrophil production. This can be caused by chemotherapy or radiation therapy, exposure to certain toxins, or some medications.
explain eosinophils
Size: Eosinophils are typically 10 to 14 micrometers (µm) in diameter.
Function Against Parasites: The major function of eosinophils is the defense against parasitic infections. They play a crucial role in combating parasitic invaders, such as helminths (worm-like parasites).
Antibacterial Activity: Eosinophils can also attack bacteria, although they are not as effective in this role as neutrophils, another type of white blood cell.
Phagocytic: Eosinophils are phagocytic cells, meaning they can engulf and digest particles, including parasites and cellular debris.
Granule Characteristics: Eosinophils have characteristic granules within their cytoplasm. These granules are brightly colored with eosin dye, giving the cells a distinctive light pink appearance after staining.
Cell Morphology: Most eosinophils have bilobed nuclei that resemble a pair of spectacles, although some variations in nuclear shape can occur.
Granule Contents: Eosinophil granules contain enzymes, such as lysozymes, as well as a high content of histaminase, which is an enzyme involved in breaking down histamine. This histaminase content helps regulate allergic responses.
Role in Allergic Reactions: Eosinophils are known to be involved in allergic reactions. They can release their granule contents, including histaminase, in response to allergens, which can help modulate the allergic response.
explain eosinophilia and eosinopenia
Eosinophilia (Elevated Eosinophil Count):
Allergic Conditions: Eosinophilia can be seen in individuals with allergic conditions such as asthma, hay fever, or allergic rhinitis. Allergic reactions can trigger an increase in eosinophils as part of the immune response.
Parasitic Infestation: Eosinophils play a significant role in defending the body against parasitic infections. In response to parasitic invaders like trichinosis, schistosomiasis, or various worms, eosinophil counts can rise as the body’s defense mechanism is activated.
Skin Disease: Some skin conditions, such as urticaria (hives), can be associated with eosinophilia. Skin allergies or inflammatory reactions may contribute to increased eosinophil levels.
Eosinopenia (Reduced Eosinophil Count):
Steroid Therapy: Eosinopenia can result from the use of corticosteroid medications. Steroids are potent anti-inflammatory drugs that can suppress the immune system, leading to a decrease in eosinophil numbers.
Stressful Situations: Eosinopenia can occur during stressful situations. Stress can activate the body’s “fight or flight” response, which may temporarily shift the distribution of white blood cells, reducing eosinophils in the bloodstream.
Acute Pyogenic Infections: Acute bacterial infections, especially those associated with the formation of pus (pyogenic infections), can cause eosinopenia. In response to a bacterial infection, the body may prioritize the release of other white blood cells like neutrophils.
explain basophils
Size: Basophils are typically 10 to 14 micrometers (µm) in diameter.
Function: Basophils play a limited role in directly fighting against infectious agents. Their primary function is related to chemical signaling and immune response modulation.
Nuclear Characteristics: Basophils have a nucleus with a shape and boundary that are not always clear when viewed under a microscope. This can be due to overcrowding of the nucleus with coarse granules.
Cytoplasm Appearance: The cytoplasm of basophils is slightly basophilic, which means it appears slightly blue when stained. It is filled with granules that stain a deep blue or purple color.
Granule Contents: The granules within basophils contain various substances, including heparin, histamine, and serotonin (5HT). These substances are involved in the body’s immune and inflammatory responses.
Basophils are part of the immune system and play a role in mediating allergic reactions and hypersensitivity responses. When they are activated, basophils release histamine and other chemical mediators that can contribute to the inflammatory response. These mediators are important in the context of allergic conditions, as they can lead to symptoms such as swelling, itching, and bronchoconstriction in response to allergens.
explain the main functions of basophils
Release of Histamine: Basophils release histamine, a key chemical mediator in allergic responses. Histamine plays a central role in increasing blood vessel permeability, leading to swelling, and in bronchoconstriction, which can cause difficulty in breathing.
Release of Other Mediators: Basophils also release other chemical mediators, such as bradykinin and serotonin, which contribute to local vascular and tissue reactions during allergic responses. These mediators can further enhance the inflammatory process.
Preventing Allergic Inflammation Spread: Basophils help prevent the spread of allergic inflammatory processes in the body. By releasing these mediators and modulating the immune response, they play a role in containing the allergic reaction to the site of exposure.
Heparin Release: Basophils liberate heparin, an anticoagulant substance. Heparin prevents blood clotting by inhibiting blood coagulation factors. It also activates lipoprotein lipase, an enzyme responsible for the removal of fat particles (triglycerides) from the bloodstream after a fatty meal.
explain basophilia and basopenia
Basophilia (Elevated Basophil Count):
Viral Infections: Some viral infections, such as influenza (flu), smallpox, and chickenpox, can lead to an increase in basophil counts. Basophils may play a role in the body’s immune response to these infections.
Allergic Diseases: Basophilia can be seen in individuals with allergic diseases, as basophils play a central role in allergic and hypersensitivity reactions. Allergic responses trigger the release of histamine and other mediators by basophils.
Chronic Myeloid Leukemia: Basophilia can be a feature of chronic myeloid leukemia (CML), a type of blood cancer. In CML, there is an overproduction of white blood cells, including basophils.
Basopenia (Reduced Basophil Count):
Steroids: The use of corticosteroid medications, such as prednisone, can lead to basopenia. Steroids can suppress the immune system and reduce the number of circulating basophils.
Drug-Induced Reactions: Some medications may cause basopenia as an adverse reaction. Monitoring basophil counts is important when certain drugs are being used to detect potential side effects.
Acute Pyogenic Infections: Basopenia can occur during acute bacterial infections, especially those associated with the formation of pus (pyogenic infections). In response to bacterial infections, the body may prioritize the release of other white blood cells like neutrophils.
explain mast cells
Characteristics of mast cells include:
Resemblance to Basophils: Mast cells have similarities in function and appearance to basophils. Both cell types are involved in allergic and hypersensitivity responses and play a role in releasing histamine and other mediators during allergic reactions.
Tissue Localization: Unlike basophils, mast cells do not circulate in the bloodstream. Instead, they are primarily found in tissues throughout the body. Mast cells are abundant beneath epithelial surfaces (the outermost layers of skin and mucous membranes) and are commonly located in connective tissue.
Role in Allergic Reactions: Mast cells are key players in allergic reactions and hypersensitivity responses. When exposed to allergens or specific triggers, mast cells release histamine and other chemical mediators, initiating the inflammatory and immune responses associated with allergies.
Immediate Environment: Mast cells are strategically positioned near environmental interfaces, such as the skin and mucosal linings, making them poised to respond to potential allergens or pathogens that come into contact with these surfaces.
explain monocytes
Here are the key features of monocytes based on the description:
Size: Monocytes are relatively large, with a diameter typically ranging from 18 to 20 micrometers (µm).
Nuclear Characteristics: Monocytes have a single nucleus that is often indented or kidney-shaped. The nucleus is relatively large and is usually located on one side of the cell.
Cytoplasm Appearance: Monocytes have abundant, clear cytoplasm. Unlike other white blood cells like neutrophils, monocytes do not typically have visible granules in their cytoplasm. The cytoplasm of monocytes tends to stain pale blue, but it can sometimes appear to have fine purple dust-like specks.
Monocytes are part of the mononuclear phagocyte system and have several essential roles in the immune response. They can migrate to tissues where they differentiate into macrophages, which are specialized phagocytic cells responsible for engulfing and digesting pathogens, dead cells, and cellular debris. Monocytes are also involved in antigen presentation, which is a crucial step in the initiation of specific immune responses.
