Blood Disorders: Normal Structure, Function, and Pathophysiology

Vocabulary flashcards covering the formed elements of blood, the mechanisms of hematopoiesis and coagulation, and the pathophysiology of common blood disorders such as anemias, neutropenia, and hypercoagulable states.

Erythrocytes (Red Blood Cells)

The most common formed elements in the blood, responsible for carrying oxygen to tissues via the main component, hemoglobin.

Leukocytes (White Blood Cells)

Formed elements present at about $1/700\text{th}$ the number of erythrocytes that function as mediators of immune responses to infection or inflammation.

Platelets

Small, anuclear fragments of megakaryocytes that are crucial for normal blood clotting and coagulation.

Hematopoiesis

The developmental process by which all mature formed elements of blood develop from a common hematopoietic stem cell population in the bone marrow.

Cytokines

Peptides involved in regulating hematopoiesis, such as erythropoietin for red cells and thrombopoietin for platelets.

Erythropoietin (EPO)

A peptide hormone produced primarily by the kidneys that regulates red blood cell production via a feedback system sensitive to oxygen delivery.

Megakaryocytes

Large multinucleated cells in the bone marrow that produce platelets by fragmenting their cytoplasm.

Wright Stain

A common microscopic stain used to examine thin blood smears to detect abnormalities in formed elements.

Hematocrit

The percentage of total blood volume that is composed of erythrocytes (42\text{--}50\text{%} in male adults; 37\text{--}47\text{%} in female adults).

Mean Corpuscular Volume (MCV)

An automated measurement representing the average volume of a single red blood cell, with normal values between $80\text{--}100\text{ fL}$.

Reticulocytes

Young erythrocytes that appear more basophilic (blue) because they retain ribosomes and mitochondria for a few days after their nuclei are extruded.

Heme

The oxygen-binding portion of hemoglobin containing a central iron atom that binds oxygen in the lungs and releases it in tissues.

Neutrophils

The most abundant granulocytes and the first line of defense against bacterial pathogens, characterized by lobulated nuclei and enzymatic granules.

Bands

Less mature neutrophils with horseshoe-shaped nuclei; an increase in their circulating numbers is referred to as a "left shift."

Monocytes

The largest cells seen on a blood smear, which spend about 3 days in circulation before residing in tissues to phagocytose bacteria.

Primary Hemostasis

The initial phase of blood clotting involving vasoconstriction and platelet adhesion and activation at the site of endothelial injury.

Secondary Hemostasis

The process whereby fibrin is formed through the initiation, amplification, and propagation of the coagulation cascade.

Tenase Complex

A complex formed on the surface of platelets by factors VIIIa and IXa in the presence of phospholipids and calcium ($VIIIa\text{--}IXa\text{--}Ca^{2+}\text{--}PL$) that activates factor X.

Prothrombinase Complex

A complex of factors Xa and Va, phospholipids, and calcium ($Xa\text{--}Va\text{--}Ca^{2+}\text{--}PL$) that catalyzes the cleavage of prothrombin ($II$) to thrombin ($IIa$).

Fibrinolysis

The process of breaking down a fibrin clot into degradation products, primarily catalyzed by the enzyme plasmin.

International Normalized Ratio (INR)

A reporter test used alongside Prothrombin Time (PT) to remove the impact of different prothrombin batch purity, commonly used to monitor warfarin therapy.

Poikilocytosis

A medical term used to describe significant variation or nonuniformity in the shape of erythrocytes.

Anisocytosis

A medical term used to describe significant variation in the size of erythrocytes.

Hepcidin

A 25-amino acid peptide produced by the liver that inhibits iron export into plasma by inducing the degradation of ferroportin.

Ferritin

The combination of iron and the protein apoferritin; it is the primary storage form of iron within body cells.

Pica

An unexplained craving for nonnutritive substances, such as clay or dirt, often observed in patients with severe iron deficiency.

Pernicious Anemia

A megaloblastic anemia caused by autoimmune destruction of gastric parietal cells, leading to a deficiency of intrinsic factor and vitamin $B_{12}$.

Intrinsic Factor

A glycoprotein produced by gastric parietal cells that is required for the absorption of vitamin $B_{12}$ in the terminal ileum.

Subacute Combined Degeneration

A neurologic condition resulting from vitamin $B_{12}$ deficiency involving the demyelination of the posterolateral spinal columns.

Cyclic Neutropenia

A rare disorder characterized by regular 3-week oscillations in neutrophil counts, typically caused by mutations in the $ELANE$ gene.

Heparin-Induced Thrombocytopenia (HIT) Type II

An immune-mediated syndrome where IgG antibodies against the heparin-PF4 complex cause platelet destruction and a paradoxical prothrombotic state.

Factor V Leiden

The most common inherited hypercoagulable state, caused by a mutation replacing arginine with glutamine at position 506, making factor Va resistant to activated protein C (APC).

Antithrombin (AT)

A protease inhibitor that blocks thrombin and other serine proteases (IX, X, XI, XII); its activity is enhanced 2000-fold by heparin.

Virchow Triad

The three factors predisposing to thrombus formation: decreased blood flow (stasis), vessel injury/inflammation, and changes in the intrinsic properties of blood (hypercoagulability).