1. Structure and Function of the Hematologic System
Chapter 19

2. 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

3. 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

5. 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

6. 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

8. 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
Capable of ameboid movement (diapedesis)

9. Composition of Blood Granulocytes Neutrophils Eosinophils
Polymorphonuclear neutrophil (PMN)
Phagocytes in early inflammation
Eosinophils
Eosinophils ingest antigen-antibody complexes
Induced by IgE hypersensitivity
Increase in parasitic infections

10. Composition of Blood Granulocytes Mast cells Basophils
Central cell in inflammation
Found in vascularized connective tissue
Basophils
Structurally and functionally similar to mast cells

11. Composition of Blood Agranulocytes
Monocytes and macrophages make up the mononuclear phagocyte system (MPS)
Monocytes
Macrophages
Lymphocytes
Natural killer (NK) cells

13. Composition of Blood Platelets Disk-shaped cytoplasmic fragments
Essential for blood coagulation and control of bleeding
Thrombopoietin
Main regulator of platelets

15. 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

16. 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

17. Lymphoid Organs

18. 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

19. Hematopoiesis Hematopoiesis is the process of blood cell production
Two stages
Mitosis
Mitosis stops before the cell enters the peripheral blood
Maturation and differentiation

20. Hematopoiesis Stem cell system Bone marrow Pluripotent stem cells
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

23. Erythropoiesis
Erythrocytes are derived from erythroblasts (normoblasts)
Maturation is stimulated by erythropoietin

24. 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

25. Erythropoiesis

27. 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

28. Regulation of Erythropoiesis
Erythropoietin causes an increase in red cell production and release from bone marrow

29. Hemoglobin Synthesis Oxygen-carrying protein of the erythrocyte
A single erythrocyte contains as many as 300 hemoglobin molecules
Two pairs of polypeptide chains
Globulins

30. Hemoglobin Synthesis Four colorful iron-protoporphyrin complexes
Adult hemoglobin
Two alpha chains and two beta chains

31. Hemoglobin Synthesis

32. 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

33. 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

34. Iron Cycle

36. 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

37. Normal Destruction of Senescent Erythrocytes
Porphyrin is reduced to bilirubin, transported to the liver, and secreted in the bile

38. Iron Cycle

39. 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

40. Development of Leukocytes
Growth factors and colony-simulating factors encourage production and maturation of leukocytes

41. 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

42. Development of Platelets
Platelet levels are maintained by thrombopoietin and IL-11
Platelets circulate for 10 days before losing their functional capacity

43. Hemostasis Hemostasis means arrest of bleeding Requirements Platelets
Clotting factors
Blood flow and shear forces
Endothelial cells
Fibrinolysis

44. Platelet’s Role
1. Vasospasm Plug Activate coagulation cascade Initiate repair

45. Hemostasis

46. Hemostasis Platelet plug formation Activation Adhesion Aggregation
von Willebrand factor (vWF)
Aggregation
Secretion

47. 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

48. Coagulation Cascade

49. 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

50. Control of Hemostatic Mechanisms
Lysis of blood clots
Fibrinolytic system
Plasminogen and plasmin
Fibrin degradation products
D-dimers

51. Fibrinolytic System

52. 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

53. 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

54. Pediatrics and the Hematologic System
Children tend to have more atypical lymphocytes as a result of frequent viral infections

55. 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