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Dr. Jitendra Patel (MBBS, MD)

Medical Educator & Researcher

Associate Professor, Department of Physiology

Email: dr.jrpatel84@gmail.com Web: www.esphys.weebly.com

OUTLINE

Introduction

Composition and Functions

Red cell membrane

Physiological characteristics

Fate of RBC

Applied Aspect

Summary

Key Terms & Concept 3

INTRODUCTION

• Shape : Biconcave

• Diameter :7.2 μm

• Thickness at periphery:2 μm

• Thickness at centre :1 μm

• Volume :90 μm3

• Surface area :140 μm2

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Advantages of biconcavity of red cells

• They do not easily lyses when

blood becomes hypotonic

• More surface area

• It can easily pass through the

narrow capillaries

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Intro…cont

• Non - nucleated

• Site of formation: BM

• Site of destruction: liver, spleen,

BM

• Development takes : 7–10 days

• Life span : 120 days

• Normal count:

M: 5-6 million/cumm

F: 4-5 million/cumm 6

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RED CELL COMPOSITION

Water : 62.5%

Hb : 35%

Other substances : 2.5%

(Glucose, lipids, proteins, enzymes)

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COMPOSITION: HAEMOGLOBIN

• Hb is a pigment (that is, it

is naturally coloured).

• Because of its iron

content, it appears

reddish when combined

with O2 and bluish when

deoxygenated

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Venous (darker) and arterial (brighter) blood

COMPOSITION: ENZYMES

The glycolytic enzymes are necessary for

generating the energy needed to fuel the active

transport mechanisms involved in maintaining

proper ionic concentrations within the cell.

Ironically, even though erythrocytes are the vehicles for

transporting O2 to all other tissues of the body, for energy

production they themselves cannot use the O2 they are

carrying.

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Enzyme…..cont

The other important enzyme within RBCs,

carbonic anhydrase, is critical in CO2 transport.

This enzyme catalyzes a key reaction that leads to

the conversion of metabolically produced CO2 into

bicarbonate ion (HCO3–), which is the primary

form in which CO2 is transported in the blood.

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G-6-PD Deficiency

• Inborn error of metabolism

• Causes hemolysis – hemolytic anemia

• These individuals are resistant to malaria

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Red cell membrane

• Most thoroughly studied biological membrane

• Three major structural elements: 1. lipid

bilayer 2. integral proteins 3. membrane

skeleton

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Element Physiological/Clinical significance

Phospholipid and

cholesterol

1. Provides an impermeable barrier 2. Slippery exterior – red cells do not stick to the

vascular endothelium

Band-3 protein (AE-I)

Chloride shift

Glycophorins (A to E)

1. Negative charge of membrane 2. Glycophorin-C – Stability and shape

(Eliptocytosis)

Spectrin It maintains cellular shape, provides structural support and regulate lateral mobility (Eliptocytosis and Poikilocytosis)

Ankyrin Provides primary linkage between membrane skeleton and lipid bilayer (Hereditary sherocytosis)

FUNCTIONS

• The functions of red cells

consist of oxygen and

carbon dioxide transport.

• Hb act as a buffer and

help in Regulation of

extracellular fluid pH.

• Red cells contribute to

50% of viscosity of blood

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Funct….cont

Antigen on red cell membrane helps in Blood group classification

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PHYSIOLOGICAL CHARACTERISTIC

1. Permeability

Semipermeable membrane, gas and urea freely

passing through, negative ions easily in or out of

RBC, and positive ions not.

There are Na-k ATPase as pump on the membrane

of RBC

RMP of RBC is : - 10 mV

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Characteristic…..cont

2. Plasticity and Metamorphose

Depend on:

1) Surface area-cubage ratio,

2) Viscosity of Hb,

3) Membrane elasticity and viscosity.

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Characteristic…..cont

3. Suspension stability

It cab be described by ESR which is RBC

descending distance per hour and suspension

stability is inverse proportion to ESR.

Normal value of ESR:

Male, 0~15 mm/h; Female, 0~20 mm/h.

Significance: ESR gives prognostic value rather

than diagnostic.

PCV is opposite to ESR 21

Characteristic…..cont

4. Osmotic fragility

Tendency to rupture.

Aged RBC are more fragile

Isotonic solution :Normal RBC

Hypertonic solution : Crenated RBC

Hypotonic : Swelling of RBC

Significance: congenital hereditary spherocytosis (Spectrin)

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Hypotonic Isotonic Hypertonic

FATE OF RBC

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APPLIED ASPECT: PHYSIOLOGICAL SIGNIFICANCE

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Physiological Variation In RBC Count

• Age : Inverse proportion.

• Sex : Male > Female

• High altitude : ++

• Exercise : ++

• Diurnal : Evening > Morning.

• Temperature : ++

• Excitement : ++

• Meals : ++

APPLIED ASPECT: CLINICAL SIGNIFICANCE

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Abnormal Count

Anaemia:

Decreased RBC count and / or Hb content

Polycythemia:

Increased RBC count

APPLIED ASPECT: CLINICAL SIGNIFICANCE

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Abnormal Shape & Size

Anisocytosis – Change in size

Microcytes – smaller RBCs

Macrocytes – Larger RBCs

Poikilocytosis – Change in shape

Spherical in spherocytosis

Sickle shape in sickle cell anemia

Sickle shape RBC

SUMMARY

• RBCs are biconcave discs without many cell organelles

• RBC are formed in bone marrow and destructed in tissue

macrophage system

• Clinically 5 million/cumm is taken as 100% RBC count

• l=Cumm

• The functions of red cells consist of oxygen transport, carbon

dioxide transport and regulation of extracellular fluid pH.

• Normal count can be altered in many physiological &

pathological conditions

• Source of energy for RBC: Glucose (Anaerobic metabolism)

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KEY TERMS & CONCEPT

Defo rmabil ity

An i so poikiloc ytosis

Sp ec t rin

Bo n e Ma rrow

Red cel l Fra g il ity

T i s su e Ma c ro p hage Sys tem

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“I honour, and shall always honour, To everyone who advances the noble science of physiology.“ — Charles Darwin