Red blood cells, or erythrocytes, are biconcave discs that carry oxygen and carbon dioxide throughout the body. They are small, circular cells that lack a nucleus. The red blood cell membrane is composed of lipids and proteins that facilitate gas exchange and allow the cells to deform to pass through narrow capillaries. The cell also contains hemoglobin, which carries oxygen, as well as enzymes and ions. Red blood cells have a lifespan of around 120 days before being destroyed and recycled by the spleen and liver.

1. THE RED BLOOD CELL
Erythrocytes -RBCs

2. RED BLOOD CELL
• 90 cubic microns in
volume
• 7.5 mm x 2 mm diameter
• 2.5 microns thickness in
edges & 1 m in center
• Has no nucleus
Size

3. BICONCAVE DISCS
(So, the center appears paler than
periphery due to the biconcavity).
Shape
small, circular, biconcave, non-nucleated discs

4. Structure
1) Red cell membrane: Composed of lipid bilayer.
Proteins traverse the lipid bilayer and responsible for:
- Antigenic property of red cells. e.g blood grouping. - Ion
channels e.g. Na+, K+, Cl-
- Binding of submembranous cytoskeleton
It is a flexible plastic to allow RBCs passage in narrow capillaries.
2) Submembranous cytoskeleton:
It is a protein network of two types of proteins (spectrin and actin) under
the cell membrane to give RBCs its shape and its ability of deformation.

5. Contents of RBCs:
a- Haemoglobin: red pigments give the RBCs
Its eosinophilic appearance and carry oxygen.
b- Carbonic anhydrase enzyme:
which catalyze reactions of Co2 transport.
c-Cytoplasmic enzymes: as glucose-6-phosphate dehydrogenase &
pyruvate kinase required for cell metabolism
d- Ions: K+, Na+, Mg++, Cl-, HCO3- & phosphate.
e- RBCs don’t contain normal cellular organelles.

6. * Functions of RBCs:
1) Function related to cell membrane:
a- The great surface area of the biconcave discs facilitate:
- Gas exchange - deformation in narrow capillaries
- Give the RBCs its characteristic shape and in case
of hydration the cell swell without rupture.
b- Through the ion channels the normal ionic composition,
osmotic pressure, Cl—shift phenomenon occurs
c- It contains blood groups antigens.
d- It keeps Hb and enzymes inside RBCs to prevent
the bad effects of escape of HB in the plasma

7. 2) Functions related to contents:
- O2 carriage:
1 molecule of Hb carries 4 O2 molecule and each gram of Hb
carries 1.33 ml of oxygen
- Co2 carriage
- by carbonic anhydrase enzyme, Co2  HCO3.
- Acid – base buffer: by Hemoglobin
- bl. Viscosity: RBCs & plasma proteins are responsible for bl.
Viscosity and blood pressure regulation.

8. PRINCIPLE FUNCTION
• Gas Exchange
• O2
• CO2

10. * Metabolism of RBCs:
 In premature RBCs: the metabolism is required to form Hb.
 In mature RBCs: the metabolism is required for:
Energy production by anaerobic glycolysis and pentose phosphate pathway
required for membrane pumps and for production of NADH & NADPH
from reducing substance called glutathions in RBCs.
These substances have antioxidant action to prevent oxidation of Hb to
methemoglobin and oxidation of lipoproteins of membrane with
destruction of the red cells.

11. Red Blood
Cells
Production
Erythropoetin
+
Bone
Marrow
Destruction
Spleen
Age,
morphology
of RBC
Polycythemia
–
+

12. Destruction of RBCs
• The life span of RBCs is 120 days
• old RBCs destroyed in narrow capillaries and spleen
 Hb released and splits by the cells of the
reticuloendothelial system into globin & haem
• Globin used in protein metabolism
•  Haem loss its iron to be stored as ferritin.
• The protoporphyrin part of haem  bile pigments

13. Fate of RBCs
Old RBCs are removed by
macrophages in spleen, liver
and the bone marrow.
( Tissue macrophage system)

14. Heme fate

15. Heme fate
• After extrusion of iron, the rest of the heme
is finally converted into unconjugated
bilirubin , bound to plasma albumin and
transported to the liver.
• In liver: it is conjugated with glucuronic
acid, making it water soluble for excretion
in the bile.

16. Heme fate
The conjugated bilirubin is delivered into the small
intestine and excreted as urobilinogen in urine or
stercobilinogen in feces.
The iron is transported in blood by transferrin and stored
mainly in the liver as ferritin (65%) and hemosiderin.
Excessive hemolysis increases bilirubin in blood
resulting in jaundice.