White Blood Cells, Platelets, and Hemostasis

These vocabulary flashcards cover the characteristics and types of white blood cells, the structure and function of platelets, and the three phases of hemostasis as detailed in the lecture notes.

Leukocytes

Also known as white blood cells (WBCs); these cells have nuclei and other organelles, lack hemoglobin, and defend the body against pathogens, toxins, and wastes.

Diapedesis

The amoeboid movement used by all circulating white blood cells to migrate out of the bloodstream.

Positive chemotaxis

The mechanism by which white blood cells are attracted to specific chemical stimuli.

Neutrophils

Also called polymorphonuclear leukocytes, they make up $50-70$ percent of circulating WBCs and contain pale cytoplasmic granules with lysosomal enzymes and bactericidal compounds.

Eosinophils

Also known as acidophils, these make up $2-4$ percent of WBCs, release nitric oxide and cytotoxic enzymes to attack parasites, and are sensitive to allergens.

Basophils

WBCs representing less than $1$ percent of the population that release histamine to dilate blood vessels and heparin to prevent blood clotting.

Histamine

A chemical released by basophils that dilates blood vessels.

Heparin

A chemical released by basophils that prevents blood clotting.

Monocytes

Large, spherical cells making up $2-8$ percent of WBCs that enter peripheral tissues to become aggressive phagocytes called macrophages.

Lymphocytes

Cells comprising $20-40$ percent of circulating WBCs that are part of the body's specific defense system and continuously migrate in and out of the bloodstream.

T cells

A class of lymphocytes responsible for cell-mediated immunity, attacking foreign cells or controlling other lymphocytes.

B cells

A class of lymphocytes responsible for humoral immunity that differentiate into plasma cells to synthesize antibodies.

Natural killer (NK) cells

A class of lymphocytes that detect and destroy abnormal cells.

Leukopenia

A white blood cell disorder characterized by a low WBC count.

Leukocytosis

A white blood cell disorder characterized by a high WBC count.

Leukemia

A cancer of white blood cells indicated by extreme leukocytosis.

Hemocytoblasts

Hematopoietic stem cells that give rise to all formed elements in the blood.

Platelets

Also called thrombocytes, these are cell fragments involved in the clotting system that circulate for $9-12$ days.

Hemostasis

The process of the cessation of bleeding, consisting of three phases: vascular, platelet, and coagulation.

Vascular phase

The first step of hemostasis where a cut triggers a vascular spasm (contraction of smooth muscle) lasting about $30$ minutes.

Platelet phase

The second step of hemostasis involving platelet adhesion to sticky endothelial surfaces and aggregation to form a platelet plug.

Coagulation phase

The third step of hemostasis involving chain reactions of the extrinsic, intrinsic, and common pathways to convert fibrinogen into fibrin.

Fibrin

An insoluble protein that forms a network to trap blood cells and platelets, sealing off the damaged portion of a vessel.

Vitamin K

A fat-soluble vitamin essential to the clotting process because it is required for the synthesis of four clotting factors.

Clot retraction

A process occurring over $30-60$ minutes where platelets contract to pull the torn edges of a vessel together after the fibrin meshwork has formed.