RBC &

Erythropoiesis

Dr. K. Ambareesha., PhD (Med. Physio)

Assit. Professor, Department of Physiology

MNR Medical College & Hospital, Sangareddy, Telangana, India.

CONTENTS

• INTRODUCTION TO RBC –

• Structure, Functions, Normal count, Variations in size, shape and structure.

• HAEMOPOIESIS

• ERYTHROPOIESIS-

• Stages and its Regulation

ERYTHROCYTES

Surface area is 120 µ2.

Normal volume is 80-

94 µ3.

Normal life span of an

RBC is 120 days.

ERYTHROCYTES

Normal Erythrocyte Count

Males 5-5.5 million

cells/mm3

Females 4.5-5 million

cells/mm3

Infants 6 – 7 million

cells/mm3

STRUCTURE OF RBC

• Lipids: Cholesterol, phospholipid, and glycolipids

• Proteins: Spectrin, actin, ankyrin.

• The glycolipids:

constitute the ABO blood group substances (agglutinogens).

Metabolism Of RBC

It is met by the glucose

metabolism through the

anaerobic Embden-

Meyerhof (EMF) pathway

(90%) and the pentose

phosphate shunt (10%).

FUNCTIONS OF RBC

• Transport of oxygen

from lungs to tissues.

• Transport of Co2 from

tissues to lungs.

• Regulation of acid-base

balance.

ERYTHROPOIESIS

Erythropoiesis is the process of

formation of RBCs.

Till 3rd week of intrauterine life in the

mesoderm of the yolk sac.

From the third month erythropoiesis takes place

in the liver and spleen.

After the fifth intrauterine life, the fetal bone

marrow starts producing RBCs.

BONE MARROW

Red bone marrow

1. At birth, it is present in all the bones.

2. In adults, it is present in flat bones

(membranous bones) like cranial

bones, vertebrae, pelvic bones, ribs,

sternum, and upper ends of long

bones like femur and humerus.

Yellow bone marrow

1. is mainly made up of adipose

(fat) tissue

STAGES OF

ERYTHROPOIESIS

PLURIPOTENT STEM

CELLS

This differentiates to

form the committed

stem cell.

The committed stem

cell of the myeloid

series gives rise to all

blood cells except the

lymphocytes.*The committed stem cells for the erythrocyte

give rise to the progenitor cells.

PROGENITOR CELLS

BFU-E (burst-forming units)

The development of Large colonies requires the presence of factors called burst-promoting activity (BPA).

The cells are immature blast cells oval in shape with moderately basophilic cytoplasm, occasional pseudopods, fine chromatin, and nucleoli.

CFU-E (colony-forming units)

They form small colonies. They do not require BPA but require other factors like erythropoietin. CFU-E cells give rise blast cells.

CFU-E cells are more mature than BFU-E cells. Morphologically, they are similar to BFU-E cells.

ERYTHROPOIESIS -PROERYTHROBLAST

These cells develop from CFU-E.

They are large cells, 15-20 µ in diameter.

The nucleus is large containing basophilic nucleoli.

It occupies 80% of the cells.

Cytoplasm is scanty and basophilic.

These cells actively divide by mitosis.

They do not have hemoglobin.

ERYTHROPOIESIS - EARLY

NORMOBLAST •10-16 µ in diameter.

•They also show active

mitosis.

•The nucleus is large, the

cytoplasm is basophilic,

and hemoglobin

•begins to appear.

•The nucleoli disappear and

condensation of chromatin

begins in the stage.

ERYTHROPOIESIS - INTERMEDIATE

NORMOBLAST

• 10-14 µ in diameter.

• The nucleus becomes

small.

• Mitosis stops at this stage.

• Hemoglobin concentration

increases and cells become

acidophilic due to Hb.

• The condensation of

nuclear chromatin increase

in this stage.

ERYTHROPOIESIS -LATE

NORMOBLAST

8-10 µ in diameter.

The cytoplasm is

acidophilic.

The nucleus is very small,

becomes pyknotic (small),

and is lost by extrusion.

ERYTHROPOIESIS -

RETICULOCYTE• It is slightly basophilic.

• Hb content increases to

reach the level of the mature cell.

• The chromatin is organized in the

form of a network (reticulum);

hence, it is called a

reticulocyte.

• RBC attains maturity in 1-2 days

after the loss of the basophilic

material.

ERYTHROPOIESIS - ERYTHROCYTES

This is a mature cell, 7-2 µ in diameter, eosinophil, non-nucleated; it resembles a biconcave disk.

The process of erythropoiesis takes 7 days.

FACTORS AFFECTING ERYTHROPOIESIS-

Erythropoietin

• Glycoprotein hormone that stimulates

erythropoiesis. It increases RBC production.

• It has a molecular weight of 46,000. It is

made up of 74% protein and 26%

carbohydrate.

• Formation: It is mainly formed in the kidney

and partly in the liver. In the kidney it is

produced by the endothelial cells of the

peritubular capillaries.

Erythropoietin - Functions• Increases RBC production.

Enhances synthesis of Hb.

Hastens maturation of RBC.

• The basic stimulus for erythropoietin production is hypoxia.

Androgens increase erythropoietin production.

Estrogens depress erythropoietin production.

Products of RBC destruction increase erythropoietin production.

Vasoconstrictors produce renal hypoxia. They cause formation of

erythropoietin.

Erythropoietin is inactivated in the liver and is excreted through the kidneys.

Stimulus for Erythropoietin Androgens: Stimulate erythropoiesis. Therefore, men have a higher RBC

count compared to women. Androgens stimulate the production of

erythropoietin. In addition, they directly stimulate erythropoiesis.

Estrogens: They have inhibitory effect on the erythropoiesis by

suppression of erythropoietin production.

Hormones: Thyroxin, cortisol, and growth hormone are necessary for

RBC production. Interleukin 1,5, and 3, granulocyte macrophage colony-

stimulating factor (GM-CSF), and BPA all act as local hormones and

help in the conversion of stem cells to progenitor cells.

Stimulus for Erythropoietin

Stimulus for ErythropoietinDietary Factors: Iron is necessary for Hb synthesis. The

deficiency of iron leads to hypochromia and decrease in the size of

RBC.

Vitamin B12 and folic acid are necessary for maturation of RBC.

Vitamin B6 vitamin C, copper, and cobalt act as cofactors.

Applied Physiology

Conditions decrease RBC count

Physiological:

Conditions decrease RBC count

Anemia

This is a clinical condition wherein RBC count or

Hb% or both are decreased. In anemia, O2

carrying capacity of blood is reduced.

Pathological:

Conditions increase RBC count

Physiological:

Conditions increase RBC countPathological:

Conditions increase RBC countPathological:

Conditions increase RBC countPathological:

UNIVERSITY ASKED QUESTIONS

• Define erythropoiesis. Describe the stages of erythropoiesis and identify the factors influencing it 10m [1+7+2]

• Outline the steps of erythropoiesis. Explain the essential factors for it? [july-aug-2014].4m

• Erythropoiesis 4m [July; 2012]

• Erythropoietin 2m [july-2010]

Thank you