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.
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
Introduction:
• RBCs contain no mitochondria, so there is no
respiratory chain, no citric acid cycle, and no oxidation
of fatty acids or ketone bodies.
• Energy in the form of ATP is obtained ONLY from 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)
1.
Function
erythrocyte as a bag for hemoglobin
2.

O2 → transport, reactive oxygen species (ROS)

CO2 → transport, formation of HCO3-

H+ → transport, maintaining pH
(35% of blood buffering capacity)
Structure

large surface

cytoskeletal proteins

membrane as an osmometer
(for diffusion of gases)
(for elasticity)
(Na+/K+-ATPase)
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
•
•
•
•
•
Spectrin is 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.
Ankyrin binds spectrin & in turn binds tightly to band 3 securing
attachment of spectrin to membrane.
band 3 is anion exchange protein permits exchanges of Cl- for HCO3+.
Actin binds to the tail of spectrin & to protein 4.1 which in turn binds to
integral proteins, glycophorins A, B & C.
Glycophorins A,B,C are transmembrane glycoproteins
What happens to red blood cells when placed in hypotonic,
hypertonic, and isotonic solutions?
• osmolarity
(0.9%NaCl)
• acanthocytes
• hemolysis
Red Blood Cells (erythrocytes)
3.
membrane transporters
 Na+/K+-ATPase (active transport)
 GLUT-1 (insulin independent)
 anion exchanger = band 3 protein (Cl-/HCO3-)
4.
membrane antigens
 blood groups: ABO system
Differ in antigen (glycoprotein)
Over the surface of RBCs
Red Blood Cells (erythrocytes)
5.
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-BPG and 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 (erythrocytes)
6. Enzymes
 carbonate dehydratase (= carbonic anhydrase, CA)
CO2 + H2O  HCO3- + H+
 The red cell also contain rhodanase responsible for the detoxication of
cyanides.
 methemoglobin reductase
 superoxide dismutase
 catalase
 glutathione peroxidase
 glutathione reductase
antioxidative enzyme system
Red Blood Cells (erythrocytes)
6. Erythropioesis
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 species in 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 (leukocytes)
Neutrophils (microphages)
 high content of lysosomes (hydrolytic
enzymes)
 few mitochondria
 glucose dependent: NADPH production
 NADPH is used for production of reactive
oxygen species → they kill bacteria
Basofils
contain heparin and histamine
B-lymphocytes
produce antibodies (= immunoglobulins, -globulins)
Platelets(thrombocytes)
participate in hemostasis
Platelets(thrombocytes)