Hema - Module 3, Unit 1

What are the five criteria used to identify RBC precursors?

Nuclear chromatin pattern, nuclear diameter, N:C ratio, presence or absence of nucleoli, and cytoplasmic colour.

What does CFU:E stand for in RBC maturation?

Colony Forming Unit: Erythrocytic.

How long does it take for a BFU-E to mature into a CFU-E?

About 1 week.

How long does it take for a CFU-E to become a pronormoblast?

About 1 week.

How long does the entire process take from a BFU-E to a mature RBC?

About 18-21 days.

What is the size range of a pronormoblast?

14-18 u.

What is the N:C ratio of a pronormoblast?

8:1.

How many nucleoli does a pronormoblast have?

1-2.

What is the cytoplasm like in a pronormoblast?

Deeply basophilic, scanty, and has no granules.

Where are pronormoblasts found in healthy states?

Only in the bone marrow.

What is the size range of a basophilic normoblast?

10-15 u

What is the N:C ratio of a basophilic normoblast?

6:1.

Are nucleoli present in a basophilic normoblast?

No.

• chromatin begins to condense, stains deep purple

What key process begins at the basophilic normoblast stage?

Hemoglobin production.

What is a distinct feature of the cytoplasm in a basophilic normoblast?

A perinuclear halo may be seen

• present only in BM in healthy states

What is the size range of a polychromatophilic normoblast?

8-14 u.

What is the N:C ratio of a polychromatophilic normoblast?

4:1 to 1:1.

What is the chromatin like in a polychromatophilic normoblast?

Coarse and clumped.

Why does the cytoplasm of a polychromatophilic normoblast show wide color variation (blue-gray to pink-gray)?

Due to rapid hemoglobin production.

What is the key defining characteristic of the polychromatophilic normoblast stage?

its the last stage of mitosis.

What is the size range of an orthochromatic normoblast?

8-10 u.

What is the N:C ratio of an orthochromatic normoblast?

1:2.

What is the nucleus like in an orthochromatic normoblast?

Pyknotic (homogeneous), round, small, and eccentric.

What key event happens at the end of the orthochromatic normoblast stage?

The nucleus is extruded

What is the cytoplasm like in an orthochromatic normoblast?

PINK - reflecting nearly complete hemoglobin synthesis

• Present only in BM in normal states

What is the size range of a polychromatic erythrocyte?

8-10 u.

Does a polychromatic erythrocyte have a nucleus?

No.

Why does a polychromatic erythrocyte have a slight bluish tinge?

Due to residual ribosomes and RNA.

What is a polychromatic erythrocyte called on a Wright's stained smear?

Polychromasia

What is a polychromatic erythrocyte called on a vital stain?

Retic

How long does a polychromatic erythrocyte stay in the bone marrow before moving to peripheral blood?

1-2 days.

How long does a polychromatic erythrocyte stay in the peripheral blood before reaching maturity?

About 1 day.

What is the size range of a mature RBC?

6-8 u.

what is round, non-nucleated and biconcave disc?

mature RBC

• deformable to pass thru microcirculation

What is the average diameter of a mature RBC?

7.2 u.

What is the average thickness of a mature RBC?

2.1 u.

What is the reference range for the MCV of a mature RBC?

80-100 fL.

What is the lifespan of a mature RBC?

120 days.

What is the main function of a mature RBC?

O2 transport to tissues.

What is the central pallor of a mature RBC?

An area of central pallor occupying 1/3 of the diameter.

What type of charge does the surface of a mature RBC carry?

Negative charge.

What is the process of removing senescent or damaged RBCs by macrophages in the spleen called?

Extravascular hemolysis.

where does extravascular hemolysis occur?

outside of the vascular system - veins, arteries, capillaries

What are the three areas of RBC metabolism crucial for survival and function?

1. red cell membrane

2. hemoglobin structure and function

3. RBC metabolic pathways.

What is the primary composition of the RBC membrane?

Lipids, proteins, and carbohydrates

what do lipids, proteins and carbohydrates do together?

1. Maintain RBC shape

2. regulate movement of substances in and out of cell

3. provide flexibility

what are the 3 major RBC membrane functions?

1. regulates movement of ions and molecules into and out of cell

2. maintains membrane integrity and cell shape

3. provides deformability = allows RBC to pass thru microcirculation

What are the three major structural components of the RBC membrane?

1. Membrane proteins and carbohydrates

2. lipid bilayer

3. membrane cytoskeleton.

what makes up the outer surface of RBC?

glycoproteins

glycolipids

membrane proteins

What are glycophorins?

Major RBC membrane glycoproteins

What do glycophorins contain that contributes to the RBC's negative surface charge?

Sialic acid

Where are many important RBC blood group antigens located?

On membrane glycoproteins and glycolipids.

what helps connects the lipid bilayer to the cytoskeleton?

membrane proteins = contributes to membrane stability

What is the primary composition of the lipid bilayer in RBCs?

Phospholipids and cholesterol

• selective barrier, controls substance movements in and out of RBC

What ion distribution do membrane proteins and energy-dependent pumps maintain in RBCs?

High intracellular K+ and low intracellular Na+.

What effect does excess cholesterol have on RBCs?

Changes RBC shape and decreases RBC survival.

What are the three major proteins of the RBC cytoskeleton (inner surface)?

Spectrin, ankyrin, and actin.

What protein attaches spectrin to the RBC membrane?

Ankyrin

What is the function of the RBC membrane cytoskeleton?

Provides strength, stability, and flexibility while helping the RBC maintain its biconcave shape.

What happens if cytoskeletal proteins are abnormal?

Altered RBC shape, decreased deformability, and shortened RBC survival.

why are RBC deformable?

to pass thru narrow capillaries and the splenic microcirculation

• dec deformability = premature removal of RBC from circulation and reduced RBC survival

how does RBC balance water and cell volume?

membrane permeability and active cation transport

what happens if you inc membrane permeability?

disrupt Na and K transport = changes cell volume, dec RBC survival and hemolysis

do mature RBC have mitochondria and what does it depend on for energy?

No

depends on glucose metabolism for energy

why are RBC metabolism necessary?

• maintain membrane integrity and deformability

• maintain cell volume and ion balance

• protect agaisnt oxidative damage

• keep hgb functional

• regulate O2 delivery

What is the main pathway of glucose metabolism in the RBC?

Embden-Meyerhof pathway.

What percentage of RBC glucose is used by the Embden-Meyerhof pathway?

About 90%.

What is the major product of the Embden-Meyerhof pathway?

ATP.

why is ATP required?

• maintains membrane integrity, deformability and cell shape

• matins normal Na;K balance

What happens to RBCs if ATP production decreases?

Membrane dysfunction, decreased RBC survival, and hemolysis = anemia

whats the purpose of HMP shunt?

protects RBC from oxidative damage

What does the HMP Shunt / Pentose Phosphate Pathway produce?

NADPH

What does NADPH maintain?

Reduced glutathione (GSH).

What is the function of GSH?

Protects hemoglobin and the RBC membrane from oxidants.

What is the result of oxidative stress?

Denatured Hgb, Heinz bodies, membrane damage, and hemolysis.

What stain is required to see Heinz bodies?

supravital stain

What can splenic removal of Heinz bodies produce?

Bite cells

What is the normal form of iron in hemoglobin?

Ferrous (Fe2+)

What happens when Fe2+ (ferrous) is oxidized to Fe3+ (ferric)?

It forms methemoglobin, which cannot bind oxygen normally.

What enzyme restores Fe2+ in hemoglobin?

Methemoglobin reductase.

what is rapoport-luebering shunt?

produces 2,3-DPG which regulates hgb affinity for oxygen

inc 2,3-DPG results in?

dec hgb affinity for O2 → inc O2 released to tissues

dec 2,3-DPG results in?

inc hgb affinity to O2 → hgb holds O2 more tightly

What is the function of 2,3-DPG in the RBC?

Regulates oxygen delivery to tissues (helps Hb release O2).

what happens as RBC age?

• dec enzyme activity and ATP production

• dec membrane flexibility/deformability

• inc susceptibility to membrane damage

how are aging RBCs removed?

splenic macrophages

What percentage of circulating RBCs are removed and replaced each day?

Approximately 1%.

What is the primary organ that produces erythropoietin (EPO)?

kidneys

What stimulates the production of erythropoietin?

Hypoxia (decreased tissue oxygenation).

What is the function of erythropoietin?

Stimulates erythroid progenitor cells, increases RBC proliferation/maturation, and increases RBC production.

What type of molecule is erythropoietin?

A glycoprotein hormone produced by the kidneys

what is required for normal erythropoiesis?

• nutrients for hgb production

• DNA synthesis

• RBC maturation

What is iron required for in erythropoiesis?

Heme synthesis.

In what form is iron incorporated into heme?

Ferrous (Fe2+) form

• essential for oxygen-carrying function of hgb

What combines with Fe2+ to form heme?

Protoporphyrin

• heme combines with globin chains to form hgb

What is required for the production of globin chains?

Amino acids

• globin chains combine with heme to form hgb

What is Vitamin B12 required for?

Normal DNA synthesis, cell division, and normal RBC maturation.

What other function does Vitamin B12 serve besides RBC maturation?

Maintenance of myelin and normal neurological function.

What is Folate (folic acid) required for?

Normal DNA synthesis and cell division.

What vitamin does Folate work closely with?

Vitamin B12.