structure and function of the hematologic system chapter 19

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