structure and function of the hematologic system chapter 19
TRANSCRIPT
Structure and Function of the Hematologic System
Chapter 19
Components of the Hematologic System
• Composition of blood– 90% water and 10% solutes– 6 quarts (5.5 L)– Plasma• 55% to 60% of the blood volume• Organic and inorganic elements
Components of the Hematologic System
• Chief function– Delivery of substances needed for cellular
metabolism– Removal of wastes– Defense against microorganisms and injury– Maintenance of acid-base balance
Components of the Hematologic System
• Composition of blood– Plasma proteins• Albumins
– Function as carriers and control the plasma oncotic pressure
• Globulins– Carrier proteins and immunoglobulins (antibodies)
• Clotting factors– Mainly fibrinogen
Components of the Hematologic System
• Composition of blood– Cellular components• Erythrocytes
– Most abundant cell in the body– Responsible for tissue oxygenation– Biconcavity and reversible deformity– 120-day life cycle
Composition of Blood
• Cellular components– Leukocytes (white blood cells)• Defend the body against infection and remove
debris• Granulocytes
– Membrane-bound granules in their cytoplasm– The granules contain enzymes capable of destroying
microorganisms– Inflammatory and immune functions
Composition of Blood
• Granulocytes– Neutrophils ( think bacterial infection)• Polymorphonuclear neutrophil (PMN)• Phagocytes in early inflammation• Segs-Mature neutrophils• Bands –immature cells and if they are up you have
serious rapid infection going on( shift tot the left)
– Eosinophils• Eosinophils ingest antigen-antibody complexes• Induced by IgE hypersensitivity• Increase in parasitic infections
Composition of Blood
• Granulocytes– Mast cells• Central cell in inflammation• Found in vascularized connective tissue
– Basophils• Structurally and functionally similar to mast cells
Composition of Blood
• Agranulocytes– Monocytes and macrophages make up the
mononuclear phagocyte system (MPS)– Monocytes– Macrophages– Lymphocytes– Natural killer (NK) cells
Composition of Blood
• Platelets– Disk-shaped cytoplasmic fragments– Essential for blood coagulation and control of
bleeding– Thrombopoietin• Main regulator of platelets
Lymphoid Organs
• Spleen– Largest secondary lymphoid organ– Splenic pulp• Masses of lymphoid tissue containing
macrophages and lymphoid tissue
– Venous sinuses• Phagocytosis of old, damaged, and dead blood
cells• Blood storage
Lymphoid Organs
• Lymph nodes– Part of the immune and hematologic systems• Facilitates maturation of lymphocytes• Transports lymphatic fluid back to the circulation• Cleanses the lymphatic fluid of microorganisms and
foreign particles
Lymphoid Organs
Mononuclear Phagocyte System (MPS)
• The MPS consists of a line of cells that originate in the bone marrow, are transported into the bloodstream, differentiate into monocytes, and settle in the tissues as mature macrophages
• Cells of the MPS ingest and destroy microorganisms and foreign material
• The MPS is mostly the liver and spleen
Hematopoiesis
• Hematopoiesis is the process of blood cell production
• Two stages– Mitosis• Mitosis stops before the cell enters the
peripheral blood
– Maturation and differentiation
Hematopoiesis
• Stem cell system– Pluripotent stem cells-can become any type
of cell– Colony-stimulating factors
• Bone marrow– Also called myeloid tissue– Red and yellow bone marrow– Adult active bone marrow• Pelvic bones, vertebrae, cranium and mandible,
sternum and ribs, humerus, and femur
Erythropoiesis
• Erythrocytes are derived from erythroblasts (normoblasts)
• Maturation is stimulated by erythropoietin
Erythropoiesis
• Sequence– Uncommitted pluripotent stem cell,
committed proerythroblast, normoblast, basophilic normoblast, polychromatophilic normoblast, orthochromic normoblast, reticulocyte (nucleus is lost), erythrocyte
– In each step the quantity of hemoglobin increases and the nucleus decreases in size
Erythropoiesis
Hemoglobin Synthesis
• Oxygen-carrying protein of the erythrocyte
• A single erythrocyte contains as many as 300 hemoglobin molecules
• Two pairs of polypeptide chains– Globins
Hemoglobin Synthesis
• Four colorful iron-protoporphyrin complexes
• Adult hemoglobin– Two alpha chains and two beta chains
Hemoglobin Synthesis
Hemoglobin Synthesis
• Nutritional requirements– Building blocks• Proteins
– Amino acids
• Vitamins– Vitamins B12, B6, B2, E, and C; folic acid; pantothenic
acid; and niacin
• Minerals– Iron and copper
• Folate
Hemoglobin Synthesis
• Iron cycle– Total body iron is bound to heme or stored
bound to ferritin or hemosiderin mononuclear phagocytes and hepatic parenchymal cells
– Less than 1 mg per day is lost in the urine, sweat, epithelial cells, or from the gut
– Transferrin– Apotransferrin
Iron Cycle
Regulation of Erythropoiesis
• Numbers of circulating red cells in healthy individuals remain constant
• The peritubular cells of the kidney produce erythropoietin
• Hypoxia stimulates the production and release of erythropoietin
Regulation of Erythropoiesis
• Erythropoietin causes an increase in red cell production and release from bone marrow
Regulation of Erythropoiesis
Normal Destruction of Senescent Erythrocytes
• Aged red cells are sequestered and destroyed by macrophages of the MPS, primarily in the spleen
• The liver takes over if the spleen is absent• Globin chains are broken down into amino
acids
Normal Destruction of Senescent Erythrocytes
• Porphyrin is reduced to bilirubin, transported to the liver, and secreted in the bile
Development of Leukocytes
• Leukocytes arise from stem cells in the bone marrow
• Granulocytes mature in the bone marrow
• Agranulocytes and monocytes are released into the bloodstream before they fully mature
Development of Leukocytes
• Growth factors and colony-simulating factors encourage production and maturation of leukocytes
Development of Platelets
• Endomitosis– The megakaryocyte undergoes the nuclear
phase of cell division but fails to undergo cytokinesis
– The megakaryocyte expands due to the doubling of the DNA and breaks up into fragments
Development of Platelets
• Platelet levels are maintained by thrombopoietin and IL-11
• Platelets circulate for 10 days before losing their functional capacity
Hemostasis
• Hemostasis means arrest of bleeding• Requirements– Platelets– Clotting factors– Blood flow and shear forces– Endothelial cells– Fibrinolysis
Hemostasis
Hemostasis
• Platelet plug formation– Activation– Adhesion• von Willebrand factor (vWF)
– Aggregation– Secretion
Hemostasis
• Function of clotting factors– Intrinsic pathway• Activated when factor XII contacts
subendothelial substances exposed by vascular injury
– Extrinsic pathway• Activated when tissue factor (TF) (tissue
thromboplastin) is released by damaged endothelial cells
Coagulation Cascade
Control of Hemostatic Mechanisms
• Clot retraction – Fibrin strands shorten; become denser and
stronger to approximate the edges of the injured vessel and site of injury
– Facilitated by large numbers of platelets within the clot and actin-like contractile proteins in the platelets
Control of Hemostatic Mechanisms
• Lysis of blood clots– Fibrinolytic system• Plasminogen and plasmin• Fibrin degradation products
– D-dimers
Fibrinolytic System
Evaluation of the Hematologic System
• Tests of bone marrow function– Bone marrow aspiration– Bone marrow biopsy– Measurement of bone marrow iron stores– Differential cell count
• Blood tests– Large variety of tests
Pediatrics and the Hematologic System
• Blood cell counts increase above adult levels at birth– Trauma of birth and cutting the umbilical
cord
• The hypoxic intrauterine environment stimulates erythropoietin production– Results in polycythemia
Pediatrics and the Hematologic System
• Children tend to have more atypical lymphocytes as a result of frequent viral infections
Aging and the Hematologic System
• Erythrocyte life span is normal but erythrocytes are replaced more slowly– Possible causes• Iron depletion• Decreased total serum iron, iron-binding
capacity, and intestinal iron absorption
• Lymphocyte function decreases with age• The humoral immune system is less responsive