Components of BloodRed Blood CellsWhite Blood CellsInflammatory processCoagulationBlood may be viewed as tissue—a sort of fluid transportation tissue, ofwhich the intercellular substance is the blood plasma (plasma). Thecellular components of this tissue are the red (erythrocytes) and white(leukocytes) blood cells and the platelets (thrombocytes (Fig. 6.1a, b).The proportion of the total blood volume occupied by all blood cells inpercent is called the hematocrit (see Fig. 6.3). It averages 45%, and is usuallya little higher in men (47%) than in women (43 %).
Functions of the BloodBlood has multiple functions closely connected with its components andwith the vascular system. While a function of the blood vessels is to distributethe blood overall (heat regulation and distribution of substances),the formed and unformed blood components have some very specificfunctions.The red blood cells, for instance, are responsible for the transport ofblood gases from the lung to the tissues (oxygen) and from the tissuesback to the lungs (carbon dioxide).White blood cells serve to defend against pathogens and foreign bodies(immunity). They perform these tasks most of the time outside theblood vessels, in the connective tissues. In this case the blood servessolely as a means of transportation from the site of cell formation (bonemarrow) to the site of action.The fluid portion of the blood, the plasma, subserves several differenttransportation tasks. For instance, it undertakes the transport of nutrients from where they are absorbed (intestinal villi) to where they are utilized (organs), of metabolic products to the excretory organs (kidneys),and of substances acting inside the body to their sites of activity(hormones). Simultaneously, blood transports heat from the metabolicallyactive organs to the surface.Another task of blood is coagulation. When blood vessels are injured,the clotting factors carried in the blood, such as fibrinogen and platelets,are of vital importance. In addition to water, blood plasma contains anumber of salts (electrolytes), proteins (albumins and globulins), lipids(fatty acids and cholesterol), and carbohydrates (blood glucose), andnumerous vitamins, trace elements, and enzymes. Other noteworthyfeatures of blood include its essentially constant composition, relativelyconstant osmotic pressure, and a pH value that varies only within narrowlimits (7.2−7.4) (the so-called “constant internal milieu”).
Genesis of white blood cells. The different cells of the myelocyte series are 1, myeloblast; 2, promyelocyte; 3,megakaryocyte; 4, neutrophil myelocyte; 5, young neutrophil metamyelocyte; 6, “band” neutrophil metamyelocyte;7, polymorphonuclear neutrophil; 8, eosinophil myelocyte; 9, eosinophil metamyelocyte; 10, polymorphonuclear eosinophil;11, basophil myelocyte; 12, polymorphonuclear basophil; 13–16, stages of monocyte formation.
Whenever a vessel is severed or ruptured, hemostasis is achieved by several mechanisms:1) vascular constriction, (2) formation of a platelet plug, (3) formation of a blood clot as a result of blood coagulation, and (4) eventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently.
Hematologic changes of pregnancy
Hematologic changes of pregnancy Berhanu Mohammed April 21, 2011
HematologyDefinition• Components of blood4/24/2011
Components of blood• Plasma Plasma Components – Transport mechanism • 90-92% water. Water 90% • 6-7% proteins • 2-3% – Fats – Carbohydrates (glucose) – Electrolytes – Gases (O2, CO2) – Chemical messengers Other Protein 3% 7%4/24/2011
Functions• responsible for the transport of blood gases from the lung to the tissues (oxygen) and from the tissues back to the lungs (carbon dioxide).• White blood cells serve to defend against pathogens and foreign bodies(immunity). They perform these tasks most of the time outside theblood vessels, in the connective tissues. In this case the blood serves solely as a means of transportation from the site of cell formation (bonemarrow) to the site of action.4/24/2011
Hemostasishemostasis is achieved by several mechanisms:1) vascular constriction,2) formation of a platelet plug,3) formation of a blood clot as a result of blood coagulation, and4) eventual growth of fibrous tissue into the blood clot to close the hole in the vessel permanently.4/24/2011
Fig. Clotting process in a traumatized blood vessel.4/24/2011
Schema for conversion of prothrombin to thrombin andpolymerizationof fibrinogen to form fibrin fibers4/24/2011
Plasma Volume Systemic vasodilatation Rise in vascular capacitance Underfilled vascular system Rise in plasma volume4/24/2011
Pregnancy-induced hypervolemia has important functions:• To meet the metabolic demands of the enlarged uterus & hypertrophied vascular system.• To provide an abundance of nutrients and elements to support the rapidly growing placenta and fetus.• To protect the mother and in turn the fetus, against the deleterious effects of impaired venous return in the supine and erect positions.• To safeguard the mother against the adverse effects of blood loss associated with parturition.4/24/2011
Plasma Volume during postpartum Decreases after delivery ,then increases again 2 to 5 days later 10 to 15% above at 3 weeks Nl at 6 wks4/24/2011
RED BLOOD CELLS• 20 to 30% (250 to 450 mL) above nonpregnant iron supplemented• 15 to 20% above nonpregnant not on iron supplement• Life span slightly decreased• Erythropoietin levels increase by 50 %4/24/2011
Fig. Erythropoietin levels in response to anemia4/24/2011
physiological or dilutional anemia of pregnancy• Observed in healthy pregnant woman• Greatest during late 2nd to early 3rd trimester lowest Hgb at 28 to 36wks• Nearer to term Hgb increases• Anemia cut off point: <11 g/dL 1st and 3rd trimesters and < 10.5 g/dL 2nd trimester, for black Americans 0.8g/dl less4/24/2011
Hemoglobin Values in Pregnancy MEAN FIFTH PERCENTILEWEEKS HEMOGLOBIN HEMOGLOBINGESTATION (G/DL) (G/DL)12 12.2 11.016 11.8 10.620 11.6 10.524 11.6 10.528 11.8 10.732 12.1 11.036 12.5 11.440 12.9 11.9From U.S. Department of Health and Human Services: Recommendations to 4/24/2011prevent and control iron deficiency in the United States. MMWR 47:1, 1998
PLATELET COUNT• Mean PLT slightly lower than healthy non pregnant woman due to the effects of hemodilution increased platelet consumption4/24/2011
Thrombocytopenia• most significant obstetrical consideration concerning platelet physiology in pregnancy• Gestational or incidental thrombocytopenia is characterized : mild asymptomatic occurring in the third trimester without any history not associated with maternal, fetal, or neonatal sequelae and spontaneously resolves postpartum Platelet counts are typically >70,000/microL, with about two-thirds being 130,000 to 150,000 microL4/24/2011
WHITE BLOOD CELLS• 1st trimester, the mean count is 8,000/mm3, Nl (5,110 to 9,900/mm)• 2nd & 3rd trimester, the mean is 8,500/mm3, Nl (5,600 to 12,200/mm3• In labor, rise to 20,000 to 30,000/mm3,• largely due to increases in circulating segmented neutrophils and granulocytes• caused by the elevated estrogen and cortisol levels• Returns to normal with in 1 to 2 weeks4/24/2011
Immunologic system• associated with suppression humoral and cell- mediated immunological functions• involve suppression of T-helper (Th) 1 and T- cytotoxic (Tc) 1 cells, which decreases secretion of interleukin-2 (IL-2), interferon- , and tumor necrosis factor- (TNF-)• upregulation of Th2 cells to increase secretion of IL- 4, IL-6, and IL-13.• In cervical mucus,immunoglobulins A and G (IgA and IgG) are significantly higher4/24/2011
COAGULATION FACTORS AND INHIBITORS• 5 to 6 fold increased risk for thromboembolic disease• venous stasis, vessel wall injury, and changes in the coagulation cascade• Fibrinogen, factors II, VII, VIII, X, XII, and XIII increase by 20 to 200 percent• Von Willebrand factor increases• Antithrombin, protein C, Factor V and Factor IX levels remain unchanged or increase slightly• return to baseline by six to eight weeks after delivery4/24/2011
Table 5-2. Changes in Measures ofHemostasis during Normal PregnancyParameter Nonpregnant Pregnant (35–40 weeks)Activated PTT (sec) 31.6 4.9 31.9 2.9Thrombin time (sec) 18.9 2.0 22.4 4.1aFibrinogen (mg/dL) 256 58 473 72aFactor VII (%) 99.3 19.4 181.4 48.0aFactor X (%) 97.7 15.4 144.5 20.1aPlasminogen (%) 105.5 14.1 136.2 19.5atPA (ng/mL) 5.7 3.6 5.0 1.5Antithrombin III (%) 98.9 13.2 97.5 33.3Protein C (%) 77.2 12.0 62.9 20.5aTotal Protein S (%) 75.6 14.0 49.9 10.2a 4/24/2011
Figure 3-11 The normal components of the coagulation cascade. (From Johnson RL: 4/24/2011Thromboembolic disease complicating pregnancy. In Foley MR, Strong TH [eds]:
Key points Maternal plasma volume increases 50 percent during pregnancy RBC volume increases approximately 18 to 30 percenthematocrit normally decreases during gestation but not below 30 percent Pregnancy is a hypercoagulable stateincreases in the levels of the majority of the procoagulant factors increase and fibrinolytic system decreases and in some of the natural inhibitors of coagulation4/24/2011
References• Guyton and Hall ,Text book of medical physiology , 11th edition• Williams Obstetrics,Cunningham, Leveno, Bloom, Hauth, Rouse, Spong, 23rd edition• Obstetrics normal and problem pregnancies, Steven G. Gabbe,Jennifer R.Niebyl, Joe leigh simpson, 5th Edition• Up to date , 18.24/24/2011