Editing Anatomy and Physiology (section)

== Hematologic and Immune Systems ==

Blood is about 55% plasma and 45% formed elements.

* '''Erythrocytes (red blood cells)''' carry oxygen bound to hemoglobin. Production is stimulated by '''erythropoietin''' from the kidney in response to hypoxia. Life span is about 120 days. Typical adult reference ranges are hemoglobin about 14 to 18 g/dL in men and 12 to 16 g/dL in women, with hematocrit about 42% to 52% in men and 37% to 47% in women.
* '''Leukocytes (white blood cells)''' defend against infection. A typical adult range is about 5,000 to 10,000 per cubic millimeter. Neutrophils are the first responders in bacterial infection; lymphocytes mediate adaptive immunity; eosinophils rise in allergy and parasitic infection.
* '''Thrombocytes (platelets)''' initiate clotting. A typical range is about 150,000 to 400,000 per cubic millimeter.

Hemostasis proceeds through vasoconstriction, platelet plug formation, and the coagulation cascade producing a fibrin clot. The liver synthesizes most clotting factors and requires vitamin K for factors II, VII, IX, and X.

'''Immunity''' is innate (skin, mucous membranes, inflammation, phagocytes, complement) or adaptive. Adaptive immunity includes humoral immunity by B lymphocytes producing antibodies and cell-mediated immunity by T lymphocytes. Active immunity is produced by infection or vaccination and is long lasting; passive immunity comes from transferred antibodies (placenta, breast milk, immune globulin) and is temporary.

'''Nursing application:'''
* Chronic kidney disease reduces erythropoietin production, which explains the anemia of chronic kidney disease.
* Neutropenia, not a low total white count alone, drives infection risk; neutropenic patients may not mount a fever or purulent drainage because the inflammatory response requires white cells. Any temperature elevation in a neutropenic patient is an emergency.
* Liver disease and warfarin therapy both prolong the prothrombin time and international normalized ratio because both interfere with vitamin K dependent factor production.
* Splenectomy increases lifelong risk of infection with encapsulated organisms, so vaccination status matters.