essay 26 - anemias - definition, etiology, pathogenesis, classification

what is anemia

• abnormally low level of circulating red blood cells, haemoglobin or both, resulting in reduced oxygen carrying capacity of the blood.

• clinical symptoms = fatigue, weakness, dizziness, fainting, tachycardia, cold hands and feet

the levels of rbc and haemoglobin in men and women

etiology of anemia

• blood loss e.g heavy menstrual bleeding or trauma

• impaired red blood cell production e.g bone marrow failure or nutritional deficiencies

• increased destruction of red blood cells e.g autoimmune haemolytic anaemia

• genetic defects e.g sickle cell disease

hemorrhagic anemia - blood loss

1. acute

• due to sudden loss of intravascular volume e.g trauma

• immediate effect = decreased circulating RBC → hypovolemia and risk of shock

• the body compensated by increasing HR, vasoconstriction and erythropoiesis

2. chronic

• progressive bleeding e.g ulcers, menstrual loss

• slow continuous bleeding leads to depletion of iron stores causing impaired hemoglobin synthesis

• leads to iron deficiency anaemia (microcytic, hypochromic RBC)

hemolytic anemia - increased RBC destruction

• premature destruction of red blood cells (earlier than 120 days)

• bone marrow compensates by increasing reticulocytes, but is often insufficient

• increased haemolysis causing increased bilirubin levels which can lead to jaundice or sphenomegaly

• intrinsic causes = sickle cell anemia, thalassemia

• extrinsic causes = malaria, poisons

iron deficiency anemia - decreased iron

• caused by dietary deficiency, chronic blood loss or pregnancy (increased demand)

• iron is reacquired for hemoglobin synthesis, so when it is depleted it causes a reduction in the amount of hemoglobin per cell, making the RBC microcytic and hypochromic

megaloblastic anemia - B12 and folate deficiency

• B12 and folate are used for DNA synthesis , when they are reduced it causes delayed nuclear maturation while the cytoplasm develops normally. this leaves the RBC large, fragile and red

• this causes ineffective erythropoeisis and intramedullary hemolysis

• common causes= vegetarian, gastric atrophy and pernicious anemia

pernicious anemia - special type of b12 deficiency

• destruction of gastric parietal cells causing loss of intrinsic factor leading to impaired B12, absorption

• common causes = chronic atrophic gastritis, autoimmune

aplastic anemia - bone marrow failure

• destruction/suppression of the hematopoietcic stem cells in bone marrow causing pancytopenia (decreased red blood cells, platelets and WBC)

• common causes = radiation, chemotherapy, idiopathic

sickle cell anemia - genetic mutation in beta-globin gene

• changes normal hemoglobin (HbA) into hemoglobin S (HbS)

• when oxygen levels drop HbS molecules stick together making them change shape to a crescent shape

• sickle cells are stiff and fragile

• complications = blockage of small vessels causing severe pain crisis and tissue ischemia, hemolysis, leg ulcers