Blood #2, RBCs - Physiology

RBC’sDefinition:

RBC’s is a flexibile, biconcave, non-nucleated cell that have an average life span of about 120 days

Flexible

Biconcave

RBC’s• Circular

• Biconcave7.2 m in diameter

2.2 m in thickness

RBC’s is not true cell as it lack nucleus, ribosomes and mitochondria

• Main content of RBC’s is Hb.

• Main function is to carry O2 and CO2

Water shift

Biconcave shape results in minimal tension on the RBC’s membrane when the volume increases

RBC’s Biconcave

Biconcave shape is caused by ankyrin and spectrin proteins

“Absent in spherocytosis”

Biconcave shape increase the surface area of the RBC’s up to 140 2

Erythrocytic count (Average)

5.4 mill / mm3

4.8 mill / mm3

increase due to relative

intrauterine hypoxia

decreaseIncrease due

to decrease O2

tension

Increase due to relative hypoxia

decrease

RBC’sIs flexible and not stretchable

الفرق بين األستك و RBC’s can be deformed into almostالبالستيك

any shape and passes through narrow channels

O2 carriage

CO2 carriage

2 chains 2 chains

Hemoglobin: Red O2 carrying respiratory pigment

TypeChains

A 2 296 – 98 % of Hb in adult

F 2 2Fetal Hb changed to Hb A, a process that is completed by the age of 4 months

Types of hemoglobin

Hb F has more affinity to O2 allowing more extraction of O2 from the mother

Chemical reactions of hemoglobin

O2 carriage

CO2 carriage

Affinity of O2 to Hb is decreased By:

H+ ion concentration

Temperature

2,3 DPG

O2 “ Oxygenation”

CO2 carriage

Hemoglobin content

14 – 18 gm/dl 12 – 16 gm/dl

may reach 19 gm/dl due to

relative intrauterine

hypoxia

10.5 – 12 gm/dl

Functions of RBC’s

1- Blood viscosity.

2- O2 and CO2 carriage.

3- Buffering function.

4- RBC’s membrane keep Hb inside RBC’s protecting the renal tubules from the hazardous effects of Hb.

RBC’s

Fibrinogen

Viscosity is important in the production of the peripheral resistance and maintenance of diastolic blood pressure.

1 -Blood viscosity.

2- O2 and CO2 carriage.

O2 carriage

CO2 carriage

2 chains 2 chains

• C.A. increases the reaction thousands times

• C.A. present inside RBC’s and not outside it

3 -Buffering function.

Hb HbO2

H.Hb HHbO2

CO2 + H2O HCO3- + H + C.A.

HCO3-H2O

CL- CL-

Why Hb buffering power is six times more than plasma proteins

• The concentration of Hb is about 16 gm/dl while that of plasma proteins is 7.3 gm/dl.

• Each Hb molecule contains 38 histidine residues, which have the imidazole groups responsible for the buffering power of Hb.

4- RBC’s membrane

keep Hb inside

RBC’s protecting

the renal tubules

from the hazardous

effects of Hb.

• The activity of the glycolytic pathway in the RBC’s decreases as soon as the RBC’s gets older

• The RBC’s membrane becomes fragile and they rupture as they passes through tight spots especially splenic sinsoids.

• The released Hb is picked up by macrophages where it is broken into heme and globin.

Life span of RBC’sAfter about 120 days:

HB

Heme Globin

Fe++ Protoporphyrin

B.M

Formation of new RBC’s

Stored in the liver and spleen as

ferritin

Bilirubin

Secreted by the liver in bile

Protein pool