Zhikal O. Khudhur/Assist lecturer_____________________________________________Hematology– 3rd Stage /1st Semester

zhikal.omer@tiu.edu.iq https://tiu.edu.iq/

2021 - 2022

TIU - Faculty of ScienceMedical Analysis Department

Lec. 3: Hematology

ERYTHROCYTEStructure, Function, Production &

Destruction

Erythrocyte properties• Biconcave discs huge

surface area relative tovolume, anucleate, noorganelles

Filled with hemoglobin, aprotein gas transport

•

• Contain the plasmamembrane proteinspectrin and otherproteins Giveerythrocytes theirflexibilitychange shape as needed

Erythrocyte properties• Erythrocytes account for

slightly less than half theblood volume, and 99.9%of the formed elements.

• the ratio of the volume of red

blood cells to the total volume of blood.

Erythrocyte properties• ATP is generated

anaerobically, so theerythrocytes do notconsume the oxygen theytransport

Hb gives the red color of•blood Why?

Individual erythrocytes areorange yellow

•

• Erythrocytes are non motilecells, but toleratedeformation, pass thoughsmallest capillaries andvenules and are remarkablyelastic

Erythrocyte differentiation (Erythropoiesis)

In the process of red blood corpuscle maturation, a cell undergoes a series of

differentiation. The following stages of development all occur within the bone marrow:

A hemocytoblast, a multipotent hematopoietic stem cell, becomes a common myeloid

progenitor or a multipotent stem cell, and then a unipotent stem cell, then a pronormoblast,

also commonly called a proerythroblast or a rubriblast. This becomes a basophilic or early

normoblast, also commonly called an erythroblast, then a polychromatophilic or

intermediate normoblast, then an orthochromatic or late normoblast. At this stage, the

nucleus is expelled before the cell becomes a reticulocyte. The cell is released from the bone

marrow after Stage 7, and so in newly circulating red blood cells, there are about 1%

reticulocytes. After one to two days, these ultimately become "erythrocytes" or mature red

blood cells.

Essential for the maturation of red blood cells are Vitamin B12 (cobalamin) and Vitamin

B9 (Folic acid). Lack of either causes maturation failure in the process of erythropoiesis,

which manifests clinically as reticulocytopenia, an abnormally low amount of reticulocytes.

Characteristics seen in erythrocytes during erythropoiesis

As they mature, a number of erythrocyte characteristics change: Theoverall size of the erythroid precursor cell reduces with thecytoplasmic to nucleus (C:N) ratio increasing. The nuclear diameterdecreases and chromatin condenses with the staining reactionprogressing from purplish red to dark blue at the final nuclear stageof orthochromatic erythroblast, prior to nuclear ejection. The colorof the cytoplasm changes from blue at pro-erythroblast andbasophilic stages to a pinkish red as a result of the increasedexpression of hemoglobin as the cell develops. Initially, the nucleus islarge in size and contains open chromatin. But, as red blood cellsmature, the size of the nucleus decreases, until it finally disappearswith the condensation of the chromatin material.

Regulation of erythropoiesis

- Too few RBC's leads to tissue hypoxia (low oxygen)

- Too many RBC's increases blood viscosity (too thick)

- two million red blood cells are made per second

- The balance between RBC production and destruction

depends on hormonal controls, and adequate supplies of

iron, amino acids, and B vitamins

Balance between RBC production and destruction depends on

-hormonal controls and adequate supplies of iron, amino acids, and B vitamins

Hormonal control

- Hormone erythropoietin

- The direct stimulus for erythropoiesis, always small amount in blood to maintain the basal rate

- (high RBC or O2 levels depress production)

Hypoxia

Deficiency in the amount of oxygen reaching the tissues

Causes of hypoxia

- decreased RBC numbers due to hemorrhage or increased destruction

- Insufficient hemoglobin per RBC (ex. iron deficiency)

- reduced availability of O2 (ex, high altitudes)

Effects of EPO

- The rapid maturation of committed marrow cells and Increased circulating reticulocyte count in

1-2 days

- Testosterone enhances EPO production, resulting in higher RBC counts in male

•RBC cytoplasmiccontentsRBC has certain proteins and lipids

RBC has Hb; (1) globin, a protein and (2) iron containing heme pigment

Old RBCs are sequestered in the spleen and bone marrow by phagocytes

Heme iron is captured for re-use

Blood volume is 6–8 % of bodyweight

•

•

•

•

•

• PCV depends on numbersize of cells and plasmavolume RBC staining(affinity for Hb) may be

&

•

•

•

normal (normochromasia)lower (hypochromasia)

higher Hb (hyperchromasia) than normal. Differences may be in sizes (anisocytosis), shapes (poikilocytosis) and number (hypererythrocytosis) Lower than normal counts is oligoerythrocytosis or anemia

• RBC plasmalemma is trilaminar Erythrocytemembrane• Outermost layer: glycolipids,

glycoproteinsCentral layer: cholesterol,phospholipidsInner layer: cytoskeleton

•

•

• spectrin•

•

Composed of alpha & beta chainsJoin to form a matrix which strengthens themembrane against sheer force and controlsbiconcave shape

ankyrin•

• membrane proteinsFunction of plasmalemma

• ShapeProvides the optimum surface to volume ratio for respiratory exchange and is essential to deformability

Provide deformability, elasticity• Allows for passage through

microvessels

•

• Provides permeability• Allows water and electrolytes to

exchange• RBC controls volume and H2O

content primarily through controlsodium and potassium content

of

Erythrocyte membrane

•

•

•

Cell membrane selectively permeable Na and K

Potassium prevents escape of Hb and other cell material

RBC contain 60% H20, 40% conjugated proteins globin andheme pigment (4%) to form (hemoglobin)

RBC membrane is permeable to H20, electrolytes,polysaccharides impermeable to Hb.

•

Erythrocyte Function

•Erythrocytes are adopted to respiratory gas transport

Hemoglobin oxygen in the blood is bound to hemoglobin

Hemoglobin is composed ofthe protein globin, made upof two alpha and two beta

•

•

chains, each bound to aheme group

Each heme group bears an atom of iron, which can bind to one oxygen molecule

•

• Each hemoglobin molecule can transport four moleculesof oxygen

Importance of Hb within RBC• Intra RBC environment is a little more acidic than

plasma for capable respiration

Hb is removed from metabolic pool, preventing turn over.

• its rapid

•

•

•

Half-Life for Hb in

Half-Life for Hb in

Hb chemical stateabsolutely.

RBC is months,

plasma is only 3 hrs.

is required for O2 transport

• Each Saturated gram of Hb can carries 1.3 ml oxygen

Metabolism of erythrocytes

• Tricarboxylic acid (TCA) cycleor Krebs cycle• Embden – Meyerhof (EM)pathway or glycolysis• Pentose cycle (Hexosemonophosphate shunt) or HMS

mature erythrocyte lacks TCA cycle and c apacity for oxidative phosphorylation because of lack of organelles mitochondria, ribosomes and endoplasmic reticulum

Destruction of erythrocytesCell decrease deformability in microcirculationassociated with;

* increase in red cell rigidity

is

* increase in blood viscosity,

* impeded blood flow

* cell fragmentation

The changes inMaintenance ofNormal internal

deformability depends oncell geometry or biconcave shapeor hemoglobin fluidity Intrinsic

membrane deformability or visco-elastic properties

�-Macrophage Aged. abnormal,

120 daysIn <,pleen .,.-- - - --...... or

damago<:tor ltver

\erytnrocytos

He i \ . . n

GIOlllnHeme

Rea t,onemarrow

Bilirubin excreted

Into Intestine as

part ol blle

Bdlrub ,n convertedinto plgmonts that

are pan ot tecos

•

• When red blood cells are delivered from thebone marrow into the circulatory system,they normally circulate an average of 120days before being destroyed.

• Even though mature red cells do not havenucleus, mitochondria, or endoplasmic

a

reticulum, they do have cytoplasmic enzymesthat are capable of metabolizing glucose andforming small amounts of adenosinetriphosphate.

•

•

•

•

These enzymes also:

(1)

(2)

(3)

maintain

maintain

keep the

pliability of the cell membrane.

membrane transport of ions.

iron of the cells’ hemoglobin inthe ferrous form rather than ferric form(Which causes the formation ofmethemoglobin that will not carry oxygen)

(4) prevent oxidation of the proteins in thered cells.

•