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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.
slide7
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
slide8

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

  • acanthocytes
  • hemolysis
  • osmolarity(0.9%NaCl)
slide9

Red Blood Cells(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

slide10

Red Blood Cells(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
slide12

Red Blood Cells(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
white blood cells leukocytes
White Blood Cells(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(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
slide17

Basofils

contain heparin and histamine

slide18

B-lymphocytes

produce antibodies (= immunoglobulins, -globulins)

slide19

Platelets(thrombocytes)

participate in hemostasis

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