Blood Composition, Formed Elements, and Hematopoiesis

Comprehensive vocabulary flashcards covering the components of blood, plasma proteins, formed elements, leukocyte subtypes, blood clotting, hematologic disorders, and hematopoiesis.

Blood

A fluid connective tissue that circulates through the heart and blood vessels, consisting of plasma ($\approx 55\%$) and formed elements ($\approx 45\%$). An average adult has about $5\text{--}6\,\text{liters}$ ($\approx 7\text{--}8\%$ of body weight), a normal pH of $7.35\text{--}7.45$, and a temperature of about $38\,^\circ\text{C}$ ($100.4\,^\circ\text{F}$).

Plasma

The liquid portion of blood that makes up approximately $55\%$ of total blood volume. It is composed of $90\text{--}92\%$ water, $6\text{--}8\%$ plasma proteins, and $1\text{--}2\%$ solutes, functioning to dissolve substances, distribute heat, maintain blood volume and pressure, and transport cells.

Formed Elements

The cellular components and cell fragments suspended in plasma that account for approximately $45\%$ of whole blood volume, consisting of erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets).

Hematocrit

The percentage of whole blood volume occupied by red blood cells (for example, a hematocrit of $45\%$ indicates that erythrocytes make up $45\%$ of the blood volume).

Buffy Coat

The thin intermediate layer of a centrifuged blood sample that contains white blood cells and platelets, constituting less than $1\%$ ($< 1\%$) of total blood volume.

Albumin

The most abundant plasma protein; its primary function is maintaining blood osmotic (oncotic) pressure to keep water in the bloodstream, while also transporting fatty acids, bilirubin, hormones, and certain medications.

Globulins

A major group of plasma proteins categorized into alpha and beta globulins (which transport lipids, iron, and hormones) and gamma globulins (antibodies that function in immune defense).

Fibrinogen

A plasma protein essential for blood clotting that is enzymatically converted into insoluble fibrin during clot formation to build a meshwork that stabilizes the clot.

Blood Clotting Process

The physiological mechanism preventing blood loss after vascular injury, progressing through: 1) Injury, 2) Platelet plug formation as platelets adhere together, and 3) Fibrin mesh formation over the plug to stabilize the seal.

Erythrocytes (Red Blood Cells)

Biconcave, anucleated cells with a lifespan of approximately $120\,\text{days}$ that contain hemoglobin and function to transport oxygen from the lungs to peripheral tissues and return carbon dioxide to the lungs.

Hemoglobin

An iron-containing protein within erythrocytes responsible for binding oxygen in the lungs, transporting it through systemic circulation, and releasing it into body tissues.

Leukocytes (White Blood Cells)

Nucleated immune cells that protect the body against infectious diseases, phagocytize foreign pathogens and debris, mediate inflammatory responses, and provide immune memory.

Thrombocytes (Platelets)

Anucleated cytoplasmic cell fragments produced in red bone marrow from megakaryocytes, exhibiting a lifespan of $7\text{--}10\,\text{days}$ and a normal concentration of $150{,}000\text{--}400{,}000\,\mu\text{L}^{-1}$; they function in hemostasis by forming platelet plugs.

Granulocytes

A category of white blood cells characterized by visible secretory granules in their cytoplasm, comprising neutrophils, eosinophils, and basophils.

Agranulocytes

A category of white blood cells lacking visible cytoplasmic granules under light microscopy, comprising lymphocytes and monocytes.

Neutrophils

The most abundant leukocyte type ($50\text{--}70\%$ of circulating WBCs), possessing a $2\text{--}5$ lobed nucleus and pale granules; they act as primary cellular first responders that destroy bacteria and fungi through phagocytosis.

Phagocytosis

The cellular process wherein a specialized leukocyte surrounds, engulfs, and digests harmful particles through four distinct stages: entrapment, formation of a phagosome, degradation via lysosomes, and exocytosis of remnants.

Eosinophils

Granulocytes that constitute $1\text{--}4\%$ of circulating leukocytes, distinguished by a bilobed nucleus and large red-orange granules containing toxic proteins (such as major basic protein) used to destroy parasitic worms (helminths) and mediate allergic reactions.

Basophils

The least abundant leukocyte type ($< 1\%$ of WBCs), containing large dark purple granules that release histamine and heparin during inflammation and allergic responses.

Histamine

A vasoactive chemical released by basophils that induces vasodilation and enhances vascular permeability, contributing to clinical symptoms of redness, swelling, itching, and tissue inflammation.

Heparin

An anticoagulant substance produced and released by basophils that inhibits the blood clotting cascade.

Lymphocytes

Agranulocytes with a large, spherical nucleus and narrow cytoplasmic rim that constitute $20\text{--}40\%$ of circulating leukocytes in adults, serving as primary mediators of adaptive immunity and pathogen-specific defense.

B Lymphocytes (B Cells)

Lymphocytes that mediate humoral immunity by differentiating into plasma cells that synthesize and secrete pathogen-specific antibodies.

T Lymphocytes (T Cells)

Lymphocytes that mediate cell-mediated immunity; major subsets include Helper T cells ($\text{CD4}$), which activate and assist other immune cells, and Cytotoxic T cells ($\text{CD8}$), which directly kill infected and abnormal host cells.

Natural Killer (NK) Cells

Innate lymphoid cells that directly identify and induce apoptosis in virus-infected cells and neoplastic (cancerous) cells.

Monocytes

The largest circulating leukocytes ($2\text{--}8\%$ of WBCs), possessing a characteristic kidney-shaped nucleus; they circulate for $1\text{--}3\,\text{days}$ before migrating into tissues to differentiate into macrophages or dendritic cells.

Macrophages

Large tissue-resident phagocytic cells derived from extravasated monocytes that engulf pathogens, apoptotic cells, and cellular debris (e.g., alveolar macrophages in the lungs and Kupffer cells in the liver).

Anemia

A clinical hematologic condition defined by a deficiency in red blood cell count or insufficient functional hemoglobin, causing impaired oxygen transport to tissues and resulting in fatigue, weakness, pale skin, and dizziness.

Iron Deficiency Anemia

A form of anemia caused by inadequate iron supplies, characterized pathologically by red blood cells that are smaller (microcytic), paler (hypochromic), and more fragile than normal erythrocytes.

Sickle Cell Disease

An inherited hemoglobinopathy where abnormal hemoglobin causes erythrocytes to become rigid and crescent-shaped, leading to vaso-occlusion, early hemolysis (shortened RBC lifespan), and severe ischemic episodes.

Leukemia

A hematologic malignancy arising in the bone marrow characterized by the uncontrolled proliferation of abnormal, immature white blood cells that crowd out normal hematopoietic lines, causing anemia, infections, and bleeding.

Leukopenia

A clinical condition characterized by an abnormally low total circulating white blood cell count.

Leukocytosis

A clinical condition characterized by an abnormally elevated total circulating white blood cell count, frequently secondary to infection or acute inflammation.

Hematopoiesis

The continuous developmental process of generating new blood cells occurring primarily within adult red bone marrow (located in the sternum, ribs, vertebrae, pelvis, and proximal ends of the humerus and femur).

Hematopoietic Stem Cell (HSC)

A multipotent stem cell resident in the red bone marrow capable of perpetual self-renewal and lineage-specific differentiation into all mature blood cell types.

Myeloid Lineage

The developmental pathway descending from the common myeloid progenitor (CMP) that gives rise to erythrocytes, thrombocytes (via megakaryocytes), granulocytes, and monocytes.

Lymphoid Lineage

The developmental pathway descending from the common lymphoid progenitor (CLP) that produces B lymphocytes, T lymphocytes, and natural killer (NK) cells.

Erythropoiesis

The specific hematopoietic lineage pathway responsible for the differentiation and production of mature red blood cells (erythrocytes).

Leukopoiesis

The specific hematopoietic process responsible for the differentiation, maturation, and production of white blood cells (leukocytes).

Thrombopoiesis

The specific hematopoietic production pathway through which bone marrow megakaryocytes differentiate and fragment to produce circulating platelets.

Cytokines

Signaling proteins and growth factors (including hormones such as erythropoietin) that stimulate stem cell differentiation and regulate blood cell production during hematopoiesis.