Circulatory System

• Erythrocytes last for 123 days before degradation
• Erythrocytes: Lack of nucleus and organelles

  Red blood cells contain no nucleus or organelles
• Erythrocyte enzymes; Only a few crucial, non-renewable enzymes remain within a mature erythrocyte Glycolytic enzymes and carbonic anhydrase
• Pluripotent stem cell ->Myeloid stem cell ->Erythroblast-> Reticulocyte->Erythrocyte
• Erythropoiesis: Bone marrow generation of new red blood cells
• Erythropoiesis is Controlled by Erythropoietin from the Kidneys Reduced O₂ delivery to kidneys stimulates them to secrete erythropoietin into the blood In turn stimulates erythropoiesis by the red marrow
• Reticulocytes: immature erythrocytes Synthetic erythropoietin: often used to boost RBC production in patients with suppressed erythropoietic activity
• 1.Kidneys detect reduced O₂-carrying capacity of blood. 2.When less O₂ is delivered to the kidneys, they secrete erythropoietin into blood. 3.Erythropoietin stimulates erythropoiesis by red bone marrow. 4.Additional circulating erythrocytes increase O₂-carrying capacity of blood. 5. Increased O₂-carrying capacity relieves initial stimulus that triggered erythropoietin secretion.
• Anaemia can be Caused by a Variety of Disorders; Nutritional anaemia, Pernicious anaemia, Aplastic anaemia, Renal anaemia, Haemorrhagic anaemia, Haemolytic anaemia Malaria and sickle cell disease
• Polycythemia is an Excess of Circulating Erythrocytes: -Too many circulating RBCs and an elevated hematocrit -Two general types, depending on what causes the excess RBC production 1.Primary polycythaemia 2.Secondary polycythaemia
• Diagnosis according to hamatocrit levels:

  
• ABO blood types: -Type A blood contains A antigens -Type B blood contains B antigens -Type AB blood has both A and B antigens -Type O blood does not have any A or B red blood cell surface antigens
• Transfusion reaction; -Agglutination and haemolysis of donor RBCs by antibodies in plasma; can be fatal
• Universal blood donors and recipients: -Type O blood can be transfused into people of any blood type Type O individuals can receive only type O blood
• Rh blood-group system: -People who have the Rh factor are said to have Rh-positive blood Those lacking the Rh factor are considered Rh-negative
• Leukocytes: mobile units of the body's immune defense system

  Immunity: the body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells

  
  

  Immune system: internal defence system that recognizes and either destroys or neutralizes foreign materials
• There are five types of leukocytes Neutrophils, eosinophils, basophils, monocytes, and lymphocytes
• Granulocytes and agranulocytes The five types of leukocytes fall into these main categories Depending on appearance of their nuclel and presence or absence of granules in their cytoplasm when viewed microscopically
• Granulocyte colony-stimulating factor stimulates increased replication and release of granulocytes
• Granulocyte colony-stimulating factor stimulates increased replication and release of granulocytes, Especially neutrophils from bone marrow Abnormalities in leukocyte production Too few or too many WBCs can be produced • Leukemia: cancerous condition involving uncontrolled proliferation of WBC
• •Intrinsic and extrinsic pathways:

  •Intrinsic pathway precipitates clotting within damaged vessels, and clotting of blood samples in test tubes

  •Extrinsic pathway initiates clotting of blood that has escaped into the tissues
• •Clot retraction:

  •Platelets trapped within the clot contract and shrink the fibrin mesh, pulling the edges of the damaged vessel closer together
• •Vessel repair: fibroblasts form a scar at the vessel defect

  •Clot dissolution: plasmin becomes trapped in the clot and later dissolves it by slowly breaking down the fibrin meshwork

  •Preventing inappropriate clot formation: plasmin functions continually to prevent clots from forming inappropriately
• •Inappropriate clotting produces thromboembolism

  •Thrombus: abnormal intravascular clot attached to a vessel wall

  •Emboli: freely floating clots

  •Haemophilia is the primary condition that produces excessive bleeding: Deficiency of one of the clotting cascade factors
• •Blood flow through a vessel depends on4)

  :•The pressure gradient and the Vascular resistance (r
• •Pressure gradient:•The difference in pressure between the beginning and end of a vessel
• •Resistance:

  •Hindrance to blood flow through a vessel

  •Viscosity: friction developed between molecules of a fluid as they slide over each other during fluid flow
• •Poiseuille’s Law: Integrates factors affecting flow rate through a vessel
• F = ΔP/R

  •F = flow rate of blood through a vessel

  •ΔP = pressure gradient

  •R = resistance of blood vessels