Blood 1.pdf

BLOOD Blood is the vital fluid that circulates within the cardiovascular system (CVS), and its volume is about 5-5.5 L in adults. Blood Composition: -Plasma (55%) -Cells (45%): RBCs, WBCs & Platelets Blood Functions: 1-Transport function (O2, CO2, glucose…)....

BLOOD Blood is the vital fluid that circulates within the cardiovascular system (CVS), and its volume is about 5-5.5 L in adults. Blood Composition: -Plasma (55%) -Cells (45%): RBCs, WBCs & Platelets Blood Functions: 1-Transport function (O2, CO2, glucose…). 2-Defensive function (WBCs and anti- bodies fight against pathogens). 3-Hemostatic function (Platelets and clotting factors help to stop bleeding). 4-Homeostatic function (Helps to keep the body internal environment constant as temperature, pH…). PLASMA Plasma is a clear yellow fluid composed of: -Water 90% -Organic substances as plasma proteins, glucose, lipid … -Inorganic substances as Na+, Cl- … -Gases O2, CO2 … PLASMA PROTEINS Concentration: 7.2–7.4 g/dL. Composition: 1-Albumin: 3.5-5 g/dL, (highest concentration & small molecular weight). 2-Globulins: α1, α2, β & γ globulins 2.5 g/dL, (larger molecular weight). 3-Other: Fibrinogen and Prothrombin. They are formed in liver except γ globulins which are the antibodies formed by immune system. Albumin/Globulin ratio (A/G ratio): Ratio between albumin & globulin concentration. Normally = 1.2–1.6. It decreases in liver & kidney diseases. 1 Functions of plasma proteins: 1-Osmotic function: The osmotic pressure of plasma proteins is called oncotic pressure. It is about 25 mmHg and is mainly due to albumin (has the highest concentration). Oncotic pressure is important for preventing excessive loss of plasma fluid from the capillaries into the interstitial fluid. (In capillaries, blood hydrostatic pressure pushes plasma fluid, causing its filtration though capillary pores to interstitial fluid. This fluid is pulled back from interstitial fluid to plasma by the oncotic pressure of plasma proteins). Decrease plasma proteins especially albumin as in liver & kidney diseases, leads to increase fluid filtration and swelling of tissues “edema”. 2-Transport function: Plasma proteins albumin, α1, α2, & β globulin act as carrier for important elements in blood (vitamins, mineral, hormones…). 3-Defensive function: Antibodies against pathogens are γ globulins. 4-Hemostatic function: Blood clotting needs fibrinogen & prothrombin. 5-Buffer function: Plasma proteins help to keep the pH of blood at 7.4. 6-Diet reserve: Plasma proteins act as a source of protein in starvation. ERYTHROCYTES RED BLOOD CORPUSCLES (RBCs) Hematocrit value (Hct) = Packed cell volume (PCV): It is the percentage of RBCs volume to total blood volume. It is about 45%. RBCs COUNT: In male = 5.5 million/mm3. In female = 5 million/mm3. RBCs SHAPE AND SIZE: Normal red blood corpuscles are small round biconcave discs. The average volume of RBC is around 90 fL. The biconcave shape of RBCs gives the maximum surface area (for diffusion of gases) with the least size, this allows RBCs to pass through narrow capillaries. RBC cytoplasm has no organelles and there is no nucleus allowing them to contain more hemoglobin to perform their function efficiently. 2 HEMOGLOBIN (Hb): Hemoglobin content (Hb%): In male = 15-16 gm/dl. In female = 13-14 gm/dl. Structure: Hb consists of a protein part (globin) and a non-protein part (heme). Globin consists of four polypeptide chains. To each chain is attached one heme molecule. Heme consists of protoporphyrin ring attached to iron atom in the ferrous state Fe2+. Functions: -Hb transports oxygen and carbon dioxide in the blood. -Hb has powerful buffer action keeping blood pH constant. BLOOD INDICES: -Mean corpuscular volume (MCV): Volume of a single RBC, it is 80-95 fL -Mean corpuscular hemoglobin (MCH): Amount of Hb in a single RBC, it is 26-32 pg -Mean corpuscular hemoglobin concentration (MCHC): Amount of Hb in 1dL RBCs, it is 31-36 g/dL ERYTHROPOIESIS PRODUCTION OF RBCs Site: In Fetus: it takes place in liver and spleen. In Children: it takes place in bone marrow of all bones. Above 20 years: it takes place in bone marrow of skull, sternum, ribs, vertebrae and hip bones. Steps: Hemopoietic stem cells differentiate into pro- erythroblasts→ erythroblasts→ normoblasts. Cells lose cytoplasm and nucleus becomes reticulocytes which finally mature into erythrocytes. 3 Factors affecting erythropoiesis: 1-Healthy bone marrow 2-Erythropoietin hormone: It is secreted by liver 15% and kidney 85%. Its secretion is stimulated mainly by hypoxia as in anemia. It stimulates all steps of erythropoiesis. 3-Nutrients: a-Iron: -Iron in diet is mainly ferric Fe3+. It is dissolved by gastric HCl and is reduced by Vitamin C from ferric Fe3+ to ferrous Fe2+, which is absorbed mainly in upper part of small intestine (duodenum). -Iron is transported in blood bound to transferrin, it is stored in the liver as ferritin. -Iron is essential for heme synthesis. b-Vitamin B12: -Vitamin B12 is combined in the stomach with a glycoprotein called intrinsic factor secreted from the gastric parietal cells, forming a complex, that is absorbed from lower part of small intestine (ileum). -It is transported in the blood bound to transcobalamine, it is stored in the liver. -Vitamin B12 is essential for synthesis of DNA and maturation of RBCs. It is also important for of synthesis of myelin sheath of nerves. c-Folic acid: -Folic acid is absorbed in the small intestine. -Folic acid is essential for synthesis of DNA and maturation of RBCs. d-Proteins: Proteins of high biological value (rich in essential amino acids) are important for the formation of globin part of hemoglobin. 4-Other factors: as Hormones: Thyroid hormones, glucocorticoids and androgens; Trace elements: Copper and cobalt. LIFE SPAN OF RBCs: RBCs life span is 120 days. Old RBCs are hemolyzed mainly in the spleen, hemoglobin is phagocytized by macrophages Amino acids & iron are reused. Porphyrin portion of hemoglobin is converted to bile pigment “bilirubin”, which is released into blood to be taken by the liver to be secreted in bile. 4  ANEMIA Anemia is decrease in RBCs count and hemoglobin content, leading to impaired oxygen delivery to tissues. Clinical picture of anemia: -Fatigue, -Weakness, -Rapid heartbeats, -Shortness of breath, -Pallor Classification of anemia: Anemia is classified according to blood indices into: 1-Normocytic anemia: Anemia with normal size RBCs. Causes: Aplastic anemia due to decrease RBCs synthesis due to bone marrow depression by chemicals, irradiation, malignancies… Hemolytic anemia due to acute hemolysis of RBCs due to infectious diseases (malaria), drugs, snake venom… Hemorrhagic anemia due to acute blood loss 2-Microcytic hypochromic anemia: Anemia with small size RBCs. Causes: Iron deficiency anemia Iron deficiency may occur in: -Decrease intake especially with increase need as in pregnancy. -Decrease iron absorption as in: Gastrectomy (due to lack of HCl) and Vitamin C deficiency, and disease of upper small intestine (duodenum) 3-Macrocytic (Megaloblastic) anemia: Anemia with large size RBCs. Causes: Vitamin B12 or Folic acid deficiency anemia Vitamin B12 deficiency may occur as result of decrease intake as in pure vegetarians, lack of intrinsic factor as in gastrectomy and in diseases of lower small intestine (ileum) decreasing absorption Folic acid deficiency may result from decrease intake, or due to some cytotoxic drugs POLYCYTHEMIA RBCs count and hemoglobin content above normal. It may be: Physiological as people living in high altitudes, or Pathological as in hypoxia due to heart or lung diseases. 5  BLOOD GROUPS I-ABO system: RBCs cell membranes contain mucopolysaccharide substances called antigens (agglutinogen), they are either: A antigen or B antigen. Plasma contains antibodies (agglutinins) against the absent antigen. Accordingly, people are classified into four groups as follow: Blood group A B AB O Agglutinogen A B A&B - Agglutinins Anti-B Anti-A - Anti-A & Anti-B Importance: 1-Medicolegal importance: Inheritance of blood groups is by two genes from both father and mother. The A & B antigens are dominant, while the O one is recessive. Blood group is a good negative test in disputed parenthood. 2-Blood transfusion: In incompatible blood transfusion, the donor RBCs is agglutinated by recipient plasma. -Group O is universal donor, because there is no agglutinogen. -Group AB is universal recipient, because there is no agglutinin. -Cross matching test: should be done before blood transfusion. II-Rh FACTOR: -85 % of people are Rh positive → have D antigen. -15 % of people are Rh negative → have no D antigen. -Normally Rh -ve have no anti-D, however they can form anti D if exposed to D antigen as in case of blood transfusion of Rh +ve blood. Importance: 1-Erythroblastosis Fetalis: (Rhesus hemolytic disease of newborn) The disease occurs if: - An Rh -ve female is married from an Rh +ve male & she carries an Rh +ve fetus - At delivery of this first baby, little fetal blood leaks into maternal circulation. Mother will produce anti-D agglutinins (IgG) In the next pregnancy, maternal agglutinins (IgG) cross placenta causing fetal hemolysis leading to severe anemia and jaundice of fetus. 2-Blood transfusion: If Rh -ve persons is transfused with Rh +ve blood, he will produce agglutinins against Rh factor (anti-D agglutinins). If this person is transfused later with Rh +ve blood, agglutination occurs. 6