This document provides an outline and objectives for a lecture on erythrocytes (red blood cells). The outline covers the structure, function, formation, variations and fate of red blood cells. The objectives are for learners to understand red blood cell counts, the difference between packed cell volume and erythrocyte sedimentation rate, how to calculate red blood cell indices, and distinguish between polycythemia and anemia. Key points covered in the document include the biconcave shape of red blood cells, hemoglobin function, erythropoiesis controlled by erythropoietin from the kidneys, and the lifespan and breakdown of aged red blood cells.

1. The Erythrocytes

2. Outline…
1) Structure of RBCs
2) Normal counts and variations
3) Functions of RBCs
4) Formation of RBCs and requirements
5) Variations in size of RBCs
6) Fate of aged RBCs
7) Packed cell volume and ESR
8) Anemia and polycythemia
9) Review questions

3. Objectives…
By the end of the lecture, learners should be
able to;
i. State the normal RBC count
ii. Distinguish between PCV and ESR
iii. Calculate the RBC indices
iv. Explain the fate of aged RBCs
v. Distinguish between polycythemia and
anemia
vi. Elaborate the usefulness of regulating
RBC count

4. RBCs?
• Non-nucleated formed elements in the blood
• Also known as erythrocytes (erythros = red)
• Red color is due to hemoglobin
• Most abundant type of blood cell
• About 2-3million new erythrocytes are
produced per second.

5. Normal counts and longevity
• Normal count varies with sex,
males>females
• Avg is 5million cells/mm3 of blood
• Circulate for abt 120 days in the body
• Cover about 700 miles in the 120 days
• RBC count increase or decrease as per
health conditions

6. Structure of RBC
• Mature RBCs are oval
biconcave disks and
flexible.
• Each RBC is abt 7.8µm in
diameter and abt 2µm
thick at ends
• Lacks a cell nucleus and
most organelles ;-
accommodates maximum
space for Hb
• Membrane is elastic.
why?

7. Is the biconcave shape of RBC
useful?
1) Allows equal and rapid diffusion of oxygen and
other substances into the interior of the cell.
2) Large surface area is provided for absorption
or removal of different substances.
3) Minimal tension is offered on the membrane
when the volume of cell alters.
4) RBCs squeeze through the minute capillaries
very easily without getting damaged.

8. How useful are RBCs?
RBCs serve the following functions;-
1. Mainly transports Hb, which in turn
transports respiratory gases (O2 and CO2)
2. Hb is a useful intracellular acid-base buffer
3. Blood group determination (carry antigen)

9. Fate of Old RBCs…
• After abt 120 days, RBC membrane is weak
• Old RBCs are immediately phagocytized by
macrophages of the body, particularly
macrophages present in liver (Kupffer cells),
spleen and bone marrow.
• The spleen (red pulp) is called ‘graveyard of
RBCs’.
• Hb is degraded into iron, globin and porphyrin.
• Iron is stored in the body and reused later.
• Globin enters the protein depot for later use.
• Porphyrin is degraded into bilirubin; excreted by liver
through bile.

10. Variation is size of
RBCs
• Under physiological conditions, the size
of RBCs in venous blood is slightly larger
than those in arterial blood.
• In pathological conditions, the variations
in size of RBCs are:
1. Microcytes (smaller cells)
2. Macrocytes (larger cells)
3. Anisocytes (cells with different sizes)

11. Variations in
shape
• Shape of RBCs is altered in many conditions
including different types of anemia.
1. Crenation: Shrinkage as in hypertonic
conditions.
2. Spherocytosis: Globular form as in hypotonic
conditions.
3. Elliptocytosis: Elliptical shape as in certain types
of anemia.
4. Sickle cell: Crescentic shape as in sickle cell
anemia.
5. Poikilocytosis: Unusual shapes due to deformed
cell membrane. The shape will be of flask,
hammer or any other unusual shape.

12. Variation in structure of
RBCs
1. Punctate basophilsm; RBCs are striated in
appearance due to presence of dots
2. Ring in RBCs; in certain types of anemia,
3. Howell-Jolly bodies;
• Presence of nuclear fragments in cytoplasm
of RBCs

13. Properties of
RBCs
1. Are capable of synthesizing
bicarbonate which acts as a buffer.
(carbonic anhydrase)
2. RBCs are capable of piling up one on
top of the other like a stack of coins
(rouleaux formation).This enables
them to sediment (ESR)
3. Suspension stability (flowing freely in
blood)
4. Specific gravity of RBC is 1.092 to
1.101.
5. Average Lifespan is about 120 days

14. Origin of
cells…
• The process of origin, development and
maturation of all blood cells;-
hemopoeisis or hematopoiesis.

15. Formation of
RBCs
• The process of origin, development and
maturation of red cells is erythropoiesis.
• The process begins in the embryonic yolk
sac and is continued in the liver, spleen
and lymph nodes in the maturing fetus.
By the end of pregnancy and after birth,
however, the process is restricted to red
bone marrow

16. 16

17. Summary of events in
erythropoiesis
Stage of
erythropoiesis
Important event
Proerythroblast Synthesis of Hb starts
Early normoblast Nucleoli disappear
Intermediate
normoblast
Hemoglobin starts
appearing
Late normoblast Nucleus disappears
Reticulocyte Reticulum is formed.
Cell enters capillary from
site of production
Matured RBC Reticulum disappears

18. Control of
erythropoiesis
• Erythropoiesis is controlled by the kidney,
which releases a hormone known as
erythropoietin if the delivery of O₂ to renal
cells falls below normal.
• It occurs if circulating [Hb] is reduced, i.e.,
during anemia.
• The bone marrow responds by increasing
red cell production, thus increasing the Hb
content back to normal.

19. • Since this control loop is sensitive to tissue O₂
levels rather than the actual Hb concn, other
conditions which reduce the O₂ content of blood
will also stimulate erythropoiesis, even if the Hb
concn is normal.
• This is seen at high altitudes, where the partial
pressures of O₂ in the lungs and blood are
reduced.
• Over a period of weeks at high altitudes,
erythropoietin stimulates an increase in the Hb
concn, with a rise in PCV and red cell count
(compensatory polycythemia).
• It is for this reason that athletes wishing to increase
the O₂-carrying capacity of their blood often train at
high altitudes

20. 20

22. Requirements for
Erythropoiesis
In addition to erythropoietin;
1. Vit B12 and folic acid are required for DNA
formation at early stages
Deficiency of either leads to maturation
failure
2. Iron is for Hb formation; deficiency leads to
hypochromic anemia
3. Intrinsic factor is required for absorption of
Vit B12 from GIT

23. Hemoglobin (Hb)
• Hb is the iron containing coloring matter of
RBC
-[Hb] is 15g/dL (14-18) in adult males
-[Hb] is 14g/dL (12-16) in adult females
-[Hb] is 14-20g/dL in infants
• In fetus it is HbF and in adults its HbA
• HbF has a higher affinity for oxygen
compared to HbA.

24. Erythrocyte sedimentation rate
(ESR)
• ESR is also called sedimentation rate, sed
rate or Biernacki reaction
• ESR is the rate at which the RBCs settle
down.
• Normally, RBCs remain suspended uniformly
in circulation
• If blood is mixed with an anticoagulant and
allowed to stand on a vertical tube, the red
cells settle down due to gravity with a
supernatant layer of clear plasma.
• Can be determined using a Westergren or
Wintrobe tube.

25. Factors affecting
ESR…..
Factors increaseing ESR
1. Specific Gravity of RBC
2. Rouleaux Formation
Globulin and fibrinogen
accelerate the rouleaux
formation.
3. Increase in size of RBC.
When the size of RBC
increases (macrocyte), ESR
also increases.
4. Anemia except sickle cell
anemia
Factors decreasing ESR
1. Increased viscosity of
Blood
Viscosity offers more
resistance for settling of
RBCs.
2. RBC count
When RBC count increases,
the viscosity of blood is
increased and ESR
decreases. And when the
RBC count decreases, ESR
increases
3. Sickle cell anemia

26. Packed cell volume
(PCV)
• Also called hematocrit value
or erythrocyte volume
fraction (EVF).
• It is the proportion of blood
occupied by cells.
• Its expressed as a
percentage.
• It is the volume of RBCs
packed at the bottom of a
hematocrit tube when the
blood is centrifuged.
• Normal PCV:males= 40%-
45% ; females= 38% - 42%

27. Variations in
PCV…
• Low PCV values can be indicative of anemia
while high PCV values can be indicative of
polycythemia.
• The hematocrit is decreased in a variety of
common conditions including chronic and recent
acute blood loss, some cancers, kidney and liver
diseases, malnutrition, vitamin B 12 and folic acid
deficiencies, iron deficiency, pregnancy, systemic
lupus erythematosus, rheumatoid arthritis and
peptic ulcer disease.
• An elevated hematocrit is most often associated
with severe burns, diarrhea, and dehydration

28. RBC indices…
• Are calculations derived from RBC count, Hb
content of blood and PCV.
• Help in diagnosis of the type of anemia
1. Mean corpuscular volume; Is the average
volume of a single RBC; MCV=
𝑃𝐶𝑉 𝑥10
𝑅𝐵𝐶(10⁶/µL)
fL
1. Mean corpuscular hemoglobin: Is the quantity
of Hb present in one RBC; MCH=
𝐻𝑏𝑥10
𝑅𝐵𝐶(10⁶/µL)
pg
2. Mean corpuscular Hemoglobin concn; Is the
concentration of Hb in one RBC
MCHC=
𝐻𝑏𝑥100
𝑃𝐶𝑉
g/dL
Side work
If pcv is 39%,
Hb is 14g/dL
and total
RBC is 4.5x
10⁶/mm3
MCV=??/
MCH=??
MCHC=??

29. Review questions
1. Control loop for erythropoiesis directly responds
to..
2. Normal PCV is about……
3. Normal RBC count is about…………….
4. The two proteins that promote rouleaux
formation…
5. ESR is high in all anemia except in……..
6. Most red cell meet their demise in …………
7. ESR increases with …………….. In viscosity of
blood
8. The main hormone for erythropoiesis is …… and
mainly produced by ………..

30. References…
1) Guyton and Hall (2015): Textbook of
Medical Physiology. 13th Edition.
2) Sembulingam (2012): Essentials of Medical
Physiology. 6th Edition.
3) Sherwood, L. (2015). Human physiology:
from cells to systems, Cengage learning.
4) William F. Ganong (2003): Review of
Medical Physiology. 23rd Edition.

31. Thank you