Blood II: Leukocytes, Platelets, and Hemostasis

Comprehensive vocabulary flashcards covering leukocytes, granulocytes and agranulocytes, thrombocytes, hemostasis phases, clotting cascades, and related hematologic pathologies.

Leukocytes

The white blood cells of the body's immune defense; they are the only formed elements that are complete cells with nuclei and organelles, and they routinely leave the bloodstream to operate in tissues.

Diapedesis

The process by which leukocytes squeeze between endothelial cells of capillary walls to exit the bloodstream into surrounding tissues (derived from Greek dia- meaning "through" and -pedan meaning "to leap").

Positive Chemotaxis

The movement of leukocytes toward a chemical attractant emitted by damaged or infected tissues and nearby leukocytes, directing them to the site of infection or injury.

Leukocytosis

A white blood cell count exceeding $11{,}000\text{ per }\mu\text{l}$, which serves as a normal protective response to bacterial or viral infection.

Granulocytes

A category of leukocytes that contain visible, membrane-bound cytoplasmic granules and lobed nuclei; includes neutrophils, eosinophils, and basophils.

Agranulocytes

A category of leukocytes that lack visible cytoplasmic granules and possess spherical or kidney-shaped nuclei; includes lymphocytes and monocytes.

Neutrophils

The most abundant white blood cells ($50\text{--}70\%$ of leukocytes) with multilobed nuclei; act as first responders that target bacteria and fungi using defensins and respiratory burst.

Respiratory Burst

A pathogen-killing metabolic process in neutrophils where the cell synthesizes potent oxidizing substances, such as hydrogen peroxide or bleach, to destroy ingested microbes.

Defensins

Antimicrobial proteins found in neutrophil granules that merge with the phagosome to form spearlike structures that puncture the membranes of ingested microbes.

Eosinophils

Granulocytes accounting for $2\text{--}4\%$ of leukocytes, distinguished by a bilobed nucleus and red-staining granules containing digestive enzymes that attack large parasitic worms and modulate allergic responses.

Basophils

The rarest leukocytes ($0.5\text{--}1\%$ of WBCs) with large, purplish-black granules containing histamine; functionally similar to mast cells and responsible for intensifying inflammatory responses.

Histamine

An inflammatory chemical stored in basophil granules that functions as a vasodilator and attracts other leukocytes to inflamed tissue sites.

Lymphocytes

Agranulocytes comprising approximately $25\%$ of leukocytes that arise from lymphoid stem cells; predominantly located in lymphoid tissues to direct adaptive and non-specific immunity.

Natural Killer (NK) Cells

Lymphocytes that provide generalized, non-specific immunity by recognizing and destroying cells lacking "self" cell-surface proteins, such as cancer cells and virus-infected cells.

T Lymphocytes (T Cells)

Lymphocytes that mature in the thymus and directly attack virus-infected cells and tumor cells, as well as release cytokines to coordinate other immune responses.

B Lymphocytes (B Cells)

Lymphocytes that mature in the bone marrow and differentiate into plasma cells, which secrete antigen-specific antibodies (immunoglobulins).

Memory Cells

Long-lived varieties of B or T lymphocytes that form after initial antigen encounter and mount rapid, heightened defenses upon subsequent exposures.

Cytokines

Biochemical signaling molecules secreted by T lymphocytes and other white blood cells to stimulate and regulate immune responses and capillary permeability.

Monocytes

The largest leukocytes ($3\text{--}8\%$ of WBCs) featuring a kidney-shaped nucleus; they leave circulation to differentiate into actively phagocytic macrophages in tissues.

Macrophages

Tissue-resident phagocytes derived from monocytes that engulf pathogens, cellular debris, and old red blood cells, while releasing chemicals to attract leukocytes and activate lymphocytes.

Leukopenia

An abnormally low total white blood cell count, frequently induced by medical treatments such as glucocorticoids or anticancer chemotherapy.

Leukemia

A group of cancerous conditions marked by the uncontrolled proliferation of abnormal, nonfunctional white blood cell clones that crowd out normal bone marrow cell lines.

Acute Leukemia

A rapidly progressing leukemia deriving from early blast or stem cells that primarily affects children and requires immediate aggressive treatment.

Chronic Leukemia

A slowly progressing leukemia involving the proliferation and accumulation of later-stage leukocyte descendants, more common in elderly populations.

Infectious Mononucleosis

A contagious viral disease caused by the Epstein-Barr virus, characterized by fever, sore throat, fatigue, and an excess of atypical, enlarged lymphocytes.

Megakaryocytes

Enormous polyploid precursor cells that remain in the red bone marrow and pinch off cytoplasmic fragments into the bloodstream to produce platelets.

Platelets

Small, anucleate cytoplasmic fragments of megakaryocytes packed with enzymes and chemical factors necessary for the blood clotting cascade.

Hemostasis

The fast, localized physiological response that halts bleeding through three orderly steps: vascular spasm, platelet plug formation, and coagulation.

Vascular Spasm

The initial step of hemostasis wherein smooth muscle in the damaged vessel wall constricts to immediately reduce blood flow and blood loss.

Platelet Plug Formation

The second step of hemostasis occurring within $30\text{--}60\text{ seconds}$, where platelets adhere to exposed collagen fibers, become activated, and aggregate into a temporary seal.

Coagulation

The multi-step process wherein blood is transformed from a liquid to a gel through a cascade of procoagulants, generating a stabilizing fibrin meshwork.

Thrombin

An active enzyme formed from prothrombin via prothrombin activator that acts as molecular scissors to convert soluble fibrinogen into insoluble fibrin.

Fibrin

An insoluble, thread-like protein polymer derived from fibrinogen that forms an interwoven meshwork to trap formed elements and seal vascular defects.

Thrombus

A stationary blood clot that abnormally develops and persists on the wall of an unbroken, intact blood vessel.

Embolus

A thrombus or piece of clot material that detaches from the vessel wall and floats freely within the bloodstream.

Embolism

The sudden mechanical occlusion of an arterial or venous vessel by a traveling embolus (e.g., pulmonary or cerebral embolism).

Aspirin

An antiprostaglandin pharmaceutical agent that inhibits thromboxane $A_2$ synthesis to limit platelet aggregation, reducing myocardial infarction risk by $50\%$.

Heparin

A naturally occurring and clinically administered anticoagulant used during cardiac surgery and post-operatively to prevent venous thrombosis.

Warfarin

An oral anticoagulant medication that reduces stroke risk in atrial fibrillation patients by antagonizing vitamin K, thereby impairing clotting factor synthesis.

Thrombocytopenia

A hemostatic disorder characterized by an abnormally low platelet count caused by bone marrow destruction, resulting in widespread spontaneous microhemorrhages.

Petechiae

Small, purplish or reddish pinpoint skin spots resulting from spontaneous capillary hemorrhages typical of thrombocytopenia.

Hemophilia A

The most common hereditary bleeding disorder ($77\%$ of cases), caused by an X-linked deficiency of clotting factor VIII and resulting in prolonged bleeding into joint spaces.

Packed Red Blood Cells (PRBCs)

A blood transfusion preparation consisting of concentrated erythrocytes with plasma and leukocytes removed, holding a shelf life of approximately $35\text{ days}$.

Septic Shock (Sepsis)

A life-threatening condition caused by severe infection where uncontrolled cytokine release leads to excessive capillary permeability, fluid depletion, severe hypotension, and organ failure, carrying a $50\%$ mortality rate.