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BLOOD CELLS METABOLISM. Objectives of the Lecture. 1- Understanding the general structural & functional features of red blood cells (RBCs). 2- Recognizing the main metabolic pathways occurring in RBCs with reference to their relations to functions of RBCs.

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Objectives of the lecture
Objectives of the Lecture

1- Understanding the general structural & functional features of red blood cells (RBCs).

2- Recognizing the main metabolic pathways occurring in RBCs with reference to their relations to functions of RBCs.

3- Identifying some of the main & common diseases of RBCs as implication of defects of RBCs metabolism.

4- Understanding the relation of characteristic features of structure of membrane of RBCs.

5-Recognizing the main functions of other blood cells and their metabolism


Rbcs metabolism functions
RBCs Metabolism & Functions

Introduction:

  • RBCs contain nomitochondria, so there is norespiratory chain, nocitric acid cycle, and nooxidation of fatty acids or ketone bodies.

  • Energy in the form of ATP is obtained ONLYfrom the glycolytic breakdown of glucose with the production of lactate (anaerobic glycolysis).

  • ATP produced being used for keeping the biconcave shape of RBCs & in the regulation of transport of ions & water in and out of RBCs.


Red blood cells erythrocytes
Red Blood Cells(erythrocytes)

  • Function

    erythrocyte as a bag forhemoglobin

    • O2→ transport, reactive oxygen species (ROS)

    • CO2→ transport, formation of HCO3-

    • H+→ transport, maintaining pH(35% of blood buffering capacity)

  • Structure

    • large surface(for diffusion of gases)

    • cytoskeletal proteins (for elasticity)

    • membrane as an osmometer(Na+/K+-ATPase)


Rbcs membrane structure
RBCs membrane structure

  • RBCs must be able to squeeze through tight spots in microcirculation (capillaries). For that RBCs must be easily & reversibly deformable. Its membrane must be both fluid & flexible .

  • About 50% of membrane is protein, 40% is fat & up to 10% is carbohydrate.

  • RBCs membrane comprises a lipid bilayer (which determine the membrane fluidity), proteins(which is responsible for flexibility) that are either peripheral or integral penetrating the lipid bilayer & carbohydrates that occur only on the external surface.

  • Defects of proteins may explain some of the abnormalities of shape of RBCs membrane as hereditary spherocytosis & elliptocytosis.


The membrane skeleton is four structural proteins that include  &  spectrin, ankyrin, protein 4.1 & actin

  • Spectrinis major protein of the cytoskeleton & its two chains ( & ) are aligned in an antiparallel manner .  &  chains are loosely interconnected forming a dimer, one dimer interact with another, forming a head to head tetramer.

  • Ankyrinbinds spectrin& in turn binds tightly to band 3 securing attachment of spectrin to membrane.

  • band 3is anion exchange protein permits exchanges of Cl- for HCO3+.

  • Actin binds to the tail of spectrin& to protein 4.1which in turn binds to integral proteins, glycophorins A, B & C.

  • GlycophorinsA,B,C are transmembrane glycoproteins


What happens to red blood cells when placed in hypotonic, hypertonic, and isotonic solutions?

  • acanthocytes

  • hemolysis

  • osmolarity(0.9%NaCl)


Red Blood Cells hypertonic, and isotonic solutions?(erythrocytes)

  • membrane transporters

    • Na+/K+-ATPase (active transport)

    • GLUT-1 (insulin independent)

    • anion exchanger = band 3 protein (Cl-/HCO3-)

  • membrane antigens

    • blood groups: ABO system

      Differ in antigen (glycoprotein)

      Over the surface of RBCs


Red Blood Cells hypertonic, and isotonic solutions?(erythrocytes)

  • metabolism

    • glucose is the main fuel

    • 90% anaerobic glycolysis(ATP, lactate: Cori cycle; 2,3-BPG)

    • 10% hexose monophosphate pathway(NADPH)

    • enzyme defects : * glucose-6-P dehydrogenase * pyruvate kinase→ hemolytic anemia ???

  • ATP is generated by anaerobic glycolysis→ ATP is used for ion transport across the cell membrane

  • glycolysis produces 2,3-BPGand lactate

  • approx. 5 to 10% of Glc is metabolized by hexose monophosphate pathway → production of NADPH → it is used to maintain glutathione in the reduced state


Red Blood Cells hypertonic, and isotonic solutions?(erythrocytes)

6. Enzymes

  • carbonate dehydratase (= carbonic anhydrase, CA) CO2 + H2O  HCO3- + H+

  • The red cell also contain rhodanaseresponsible for the detoxication of cyanides.

  • methemoglobin reductase

  • superoxide dismutase

  • catalase antioxidative enzyme system

  • glutathione peroxidase

  • glutathione reductase


Red Blood Cells hypertonic, and isotonic solutions?(erythrocytes)

  • Erythropioesis


White blood cells leukocytes
White Blood Cells hypertonic, and isotonic solutions?(leukocytes)

Classification

  • granulocytes

    • neutrophils (phagocytosis)

    • eosinophils (allergy, parasites)

    • basophils (allergy)

  • agranulocytes

    • monocytes→ macrophages

    • lymphocytes (B, T)→ immunity

  • Reactive oxygen ROS and nitrogen RNS speciesin blood elements

    ERYTHROCYTES: enzymes for deactivation of ROS formed from high content of oxygen found in the cells

    PHAGOCYTES:enzymes for production of ROS and RNS to destroy particles in phagosomes


    White blood cells leukocytes1
    White Blood Cells hypertonic, and isotonic solutions?(leukocytes)

    Neutrophils (microphages)

    • high content of lysosomes (hydrolytic enzymes)

    • few mitochondria

    • glucosedependent: NADPH production

    • NADPH is used for production of reactive oxygen species → they kill bacteria


    Basofils hypertonic, and isotonic solutions?

    contain heparin and histamine


    B-lymphocytes hypertonic, and isotonic solutions?

    produce antibodies (= immunoglobulins, -globulins)


    Platelets hypertonic, and isotonic solutions?(thrombocytes)

    participate in hemostasis


    Platelets hypertonic, and isotonic solutions?(thrombocytes)


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