Structure and Function of the Hematologic System

Flashcards covering the structure and function of the hematologic system, including blood composition, cellular components, lymphoid organs, blood cell development (hematopoiesis, erythropoiesis, myelopoiesis, lymphopoiesis), hemostasis mechanisms, and age-related changes.

Blood composition (adults)

91% water, 9% solutes; 6 quarts (5.5 L); functions include delivery of substances for cellular metabolism, removal of wastes, defense against microorganisms and injury, and maintenance of acid-base balance.

Plasma

50% to 55% of blood volume, liquid portion containing organic and inorganic elements.

Albumin

Plasma protein that functions as a carrier and controls plasma oncotic pressure.

Globulins

Plasma proteins that are carrier proteins and immunoglobulins.

Clotting factors/proteins

Plasma proteins that promote coagulation, mainly fibrinogen.

Erythrocytes

Red blood cells; most abundant cells in blood, responsible for tissue oxygenation, biconcave shape, reversible deformity, 100 to 120-day life cycle.

Leukocytes

White blood cells; defend against infection and remove debris, act in tissues but transported by circulation, classified as granulocytes or agranulocytes (by structure) or phagocytes or immunocytes (by function).

Granulocytes

Leukocytes with membrane-bound granules containing enzymes for destroying microorganisms; involved in inflammatory and immune functions; capable of ameboid movement (diapedesis).

Neutrophils

Polymorphonuclear neutrophils (PMN); phagocytes active in early inflammation.

Eosinophils

Granulocytes that ingest antigen-antibody complexes, induced by IgE hypersensitivity, and increase in parasitic infections.

Basophils

Granulocytes structurally and functionally similar to mast cells.

Agranulocytes

Leukocytes without membrane-bound granules, includes monocytes and lymphocytes.

Monocytes

Immature macrophages that mature to form the mononuclear phagocyte system (MPS).

Lymphocytes

Agranulocytes that mature to T cells, B cells, and plasma cells.

Natural killer (NK) cells

A type of lymphocyte.

Platelets (thrombocytes)

Irregularly-shaped cytoplasmic fragments essential for blood coagulation and control of bleeding.

Primary lymphoid organs

Include bone marrow and thymus.

Secondary lymphoid organs

Include spleen, lymph nodes, tonsils, Peyer patches; liver also has lymphoid function.

Spleen

Largest lymphoid organ involved in fetal hematopoiesis, cleansing blood, initiating immune response, destroying aged cells, and blood reservoir. Contains splenic pulp and venous sinuses.

Splenic pulp

Lymphoid tissue within the spleen containing macrophages, lymphocytes, and lymphoid follicles.

Venous sinuses (spleen)

Part of the spleen responsible for phagocytosis of old, damaged, and dead blood cells, and blood storage (300ml).

Lymph nodes

Structurally part of the lymphatic system, functionally part of hematologic and immune systems; transport lymphatic fluid back to circulation and cleanse it of microorganisms and foreign particles.

Red (active or hematopoietic) marrow

Found primarily in flat bones in adults; vascularized and responsible for blood cell production.

Yellow (inactive) marrow

Found in other bones, primarily adipose tissue.

Endosteal niches (osteoblastic niches)

Microenvironments in bone marrow involving osteoblasts and osteoclasts.

Perivascular niches

More active microenvironments in bone marrow.

Mesenchymal stem cells (MSCs)

Develop into osteoclasts, fibroblasts, chondrocytes, and adipocytes; maintain hematopoietic stem cells (HSCs).

Hematopoietic stem cells (HSCs)

Self-renewing stem cells from which all blood cells originate, differentiating further into hematopoietic progenitor cells.

Multipotent stem cells

Intermediate groups of stem cells with limited abilities to differentiate into many different types of cells.

Hematopoiesis

Process of blood cell production; occurs in liver and spleen in fetus, and in bone marrow (medullary hematopoiesis) after birth; involves proliferation and differentiation.

Colony-stimulating factors (CSFs or hematopoietic growth factors)

Factors that promote the production and differentiation of blood cells.

Erythropoietin

Hormone that controls the regulation of red blood cell development (erythropoiesis).

Erythropoiesis

Process of red blood cell development, from progenitor cell to erythrocyte; regulated by erythropoietin in response to tissue hypoxia.

Hemoglobin (Hb)

Oxygen-carrying protein of the erythrocyte, composed of two pairs of polypeptide chains (globulins) and four iron-protoporphyrin complexes (heme), each heme carrying one oxygen molecule.

Heme

Four colorful iron-protoporphyrin complexes in hemoglobin, each carrying one molecule of oxygen, bound to reduced ferrous iron (Fe2+).

Methemoglobulin

Form of hemoglobin where nonreduced ferrous iron (Fe3+) cannot bind oxygen.

Nutritional requirements for erythropoiesis

Includes proteins (amino acids), vitamins (B12, B6, B2, E, C, folic acid, pantothenic acid, niacin), and minerals (iron, copper).

Senescent erythrocytes

Old, increasingly fragile red blood cells that lose reversible deformability and are destroyed by macrophages of the MPS, primarily in the spleen.

Iron

Mineral essential for erythropoiesis, bound to heme, stored bound to ferritin or hemosiderin, or in mononuclear phagocytes.

Iron cycle

Process where iron from recycled erythrocytes is returned to the bloodstream, controlled by hepcidin.

Hepcidin

Regulator of the iron cycle.

Myelopoiesis

Development of granulocytes and monocytes, which mature in the bone marrow.

Lymphopoiesis

Development of lymphocytes, which are released into the bloodstream and mature in lymphoid organs.

Megakaryocyte

Large cell that undergoes DNA replication without dividing, and whose cell surface elongations fragment into thousands of platelets.

Thrombopoietin

Hormone that regulates platelet levels.

Hemostasis

Arrest of bleeding by formation of blood clots, involving vasoconstriction, platelet adherence and plug formation, and activation of the clotting system to form fibrin clots.

Endothelial cells (hemostasis)

Normally produce nitric oxide and prostacyclin to regulate blood flow and prevent clotting; damage exposes subendothelial matrix and releases platelet activators like von Willebrand factor (vWF).

von Willebrand factor (vWF or clotting factor VIII)

Platelet activator released by damaged endothelial cells, essential for platelet adhesion.

Platelets (hemostasis functions)

Regulate blood flow by vasoconstriction, form platelet plug, activate coagulation cascade, and initiate repair processes (clot retraction, clot dissolution).

Clotting factors

Proteins that form a meshwork of fibrin strands (blood clot) to stabilize the platelet plug.

Intrinsic pathway (coagulation)

Activated when factor XII (Hageman factor) contacts subendothelial substances exposed by vascular injury.

Extrinsic pathway (coagulation)

Activated when tissue thromboplastin is released by damaged endothelial cells.

Common pathway (coagulation)

Pathway where activation of factor X proceeds to clot formation, shared by both intrinsic and extrinsic pathways.

Thrombin inhibitors (antithrombin)

Factors in endothelial cell surface that prevent spontaneous hemostasis.

Tissue factor inhibitors (tissue factor pathway inhibitor)

Factors that prevent spontaneous hemostasis.

Protein C

Mechanism for degrading activated clotting factors, preventing spontaneous hemostasis.

Clot retraction

Process where fibrin strands shorten, become denser and stronger to approximate injured vessel edges, facilitated by platelets.

Lysis of blood clots (fibrinolytic system)

System involving plasminogen and plasmin that breaks down blood clots, producing fibrin degradation products.

Plasmin

Enzyme involved in the fibrinolytic system that degrades fibrin, leading to clot lysis.

Polycythemia (newborns)

Increased red blood cell count in newborns due to the hypoxic intrauterine environment stimulating erythropoietin production.

Newborn immune system

Newborns are at risk for impaired phagocytosis, bacterial infections, and delayed wound healing, but receive protection from disease via passive IgG antibody from the mother.

Hematologic system (older adults)

Erythrocyte life span is normal but replacement is slower due to iron depletion; lymphocyte function decreases with age and the humoral immune system is less responsive.