Hematology Lecture 2

The development and maturation of white blood cells from pluripotential stem cells.

What is leukopoiesis?

usually interleukins.

What growth factors typically stimulate leukopoiesis?

Commitment is driven by growth factors that provide the stimulus.

How do hematopoietic stem cells commit to specific lineages in leukopoiesis?

In the bone marrow.

Where do WBCs mature before entering peripheral blood?

Through slits between endothelial cells of the sinuses.

How are mature WBCs released into the blood from the bone marrow?

About 25 times more in the bone marrow.

How much more numerous are WBCs in the bone marrow compared with circulating WBCs?

WBCs that line inside blood vessels and wait for inflammation.

What is the marginated pool of white cells?

They diapedese into the tissues.

What happens to marginated WBCs during inflammation?

No; they do not return to blood.

Do diapedesed WBCs typically re-enter the bloodstream?

Approximately 1–2 days.

After entering tissue, how long do WBCs usually live?

The reticuloendothelial (RES) system.

Which system removes WBCs after their tissue life?

Cell size decreases as cells mature.

What is a general maturation trend regarding cell size?

Basophilia decreases; cells become less blue.

How does basophilia change as cells mature?

Nucleus becomes more condensed and nucleoli disappear.

What happens to the nucleus during maturation?

It decreases.

How does the N:C ratio change during maturation?

Primary granules first (promyelocyte), then secondary granules (myelocyte), then tertiary granules later.

What are the three granule types in myeloid cells and their appearance order?

Purple-red; appear in promyelocytes.

What color do primary granules stain and when do they appear?

In the myelocyte stage and increase with maturation.

When do secondary granules begin to appear?

They decrease in number.

What happens to primary granules as cells mature?

No; they develop later and do not readily stain.

Do tertiary granules stain readily?

Eosinophilic: red (acid); Basophilic: blue (alkaline); Neutrophilic: purple (acid and alkaline).

How are granules colored by type (eosinophilic, basophilic, neutrophilic)?

Chromatin condenses; nucleoli disappear; nucleus changes shape; N:C ratio decreases.

What are key features of nuclear maturation in granulopoiesis?

7–11 days.

How long does granulopoiesis take?

Phagocytosis of bacteria.

What is the main function of mature neutrophils?

In the bone marrow; may be seen in peripheral blood in leukemia.

Where is the myeloblast normally observed?

2–5 nucleoli.

How many nucleoli does a myeloblast typically have?

Sparse, basophilic blue-gray cytoplasm; no granules.

Describe the cytoplasm of a myeloblast.

Presence of primary granules that are large red/purple non-specific granules.

What are promyelocytes notable for regarding granules?

In the bone marrow; may be in blood in leukemia or severe infection.

Where are promyelocytes typically found?

1–2 nucleoli.

How many nucleoli may promyelocytes have?

More evident than blast; primary granules visible.

What is notable about promyelocyte cytoplasm?

Primary (non-specific) granules.

What granules do promyelocytes contain?

Primary and secondary granules; specific granules containing lysozymes.

What granules are present in myelocytes?

First stage to differentiate into eosinophil, basophil, or neutrophil.

Why is the myelocyte stage significant for lineage?

Kidney-bean shaped nucleus with coarser chromatin.

What nucleus feature appears in metamyelocytes?

Bone marrow or peripheral blood during infections.

Where can metamyelocytes be observed?

Horse-shoe shaped neutrophil precursor with clumped ends (C or S shaped).

What is a neutrophilic band?

Greater than 5%.

What percentage of bands in peripheral blood is abnormal?

Nucleus with 3–5 lobes; coarse chromatin; pink cytoplasm with secondary granules.

What defines a segmented neutrophil (Seg)?

50–70%.

What percentage of neutrophils typically circulate as Seg neutrophils?

If a filament is not seen, call the cell a band rather than a seg.

What is the Band–Seg controversy about?

3–5 lobes.

How many lobes does a Seg neutrophil typically have?

Humoral and cellular immunity.

What is the primary function of lymphocytes?

Round to oval; high N/C ratio; chromatin evenly coarse with dark clumping.

What is notable about the lymphocyte nucleus?

Blue.

What is the cytoplasm color of lymphocytes on Wright stain?

Nucleoli may be seen; not abnormal.

Are nucleoli usually seen in mature lymphocytes?

No.

Can B and T lymphocytes be distinguished on a peripheral smear?

20–40%.

What percentage of peripheral blood do lymphocytes comprise?

Lymphoblasts and prolymphocytes; lymphoblasts resemble myeloblasts but are not typically seen in peripheral blood.

From which precursors do lymphocytes arise?

Processing antigens for presentation to lymphocytes; scavenging; leave blood to tissues and become macrophages.

What is the main function of monocytes?

Indented, folded brain-like convolutions; pale chromatin.

What is the appearance of the monocyte nucleus?

Light gray or gray-blue with pseudopods; may contain vacuoles.

Describe the cytoplasm of monocytes.

Monoblast to promonocyte; derived from the same stem cell as granulocytes.

What are monocyte precursors?

Less than 10%.

What percentage of monocytes circulate in peripheral blood?

Monocytes have blue-gray cytoplasm.

How can you distinguish monocytes from bands by cytoplasm color?

To make platelets for clotting.

What is the main function of megakaryocytes?

Platelets pinch off cytoplasm as cytoplasmic fragments; they have no nucleus.

How do platelets form from megakaryocytes?

Very large cell with a multiform nucleus and abundant cytoplasm.

What is distinctive about the megakaryocyte nucleus?

A B cell that has differentiated to produce antibodies; mature plasma cell.

What is a plasma cell?

Plasmablast -> proplasma cell -> plasmacyte -> mature plasma cell.

What is the maturation sequence from B cell to plasma cell?

Round and eccentric with clumped chromatin.

How is the plasma cell nucleus described?

Cornflower blue with a pale perinuclear zone.

What color describes plasma cell cytoplasm on Wright stain?

Antibody production.

What is the main function of plasma cells?

Immunity, phagocytosis, and storage of iron.

What is the function of macrophages/histiocytes?

In bone marrow and tissues.

Where are macrophages/histiocytes typically found?

Abundant cytoplasm with a small nucleus and often vacuoles.

What is a key cytoplasmic feature of macrophages?

Osteoclasts destroy bone; osteoblasts form bone.

What are osteoclasts and osteoblasts?

Wright-Giemsa, a Romanovsky stain.

What is Wright stain?

Acidic cellular structures including nuclear DNA and cytoplasmic RNA.

What does alkaline methylene blue stain?

RBCs pink; WBC nuclei blue/purple; cytoplasm pink.

What colors do Wright stain components typically produce for RBCs and WBC nuclei?

Red/orange.

What color do eosinophilic granules stain?

Blue.

What color do basophilic granules stain?

Issues with buffer pH, stain duration, staining time, and stain age.

What causes staining deviations with Wright stain?

Within 5–6 hours; 3–4 hours preferred.

What is the recommended time window for preparing a peripheral blood smear?

Vaculated/broken WBCs and crenated erythrocytes (echinocytes).

What type of artifacts are associated with blood films of WBCs and RBCs?

Segments, lymphocytes, monocytes, eosinophils, basophils.

Which cells are normally present in peripheral blood smear to identify?

To identify and distinguish white blood cells on a smear.

What is the basic purpose of a Wright stain in hematology?

Large orange-red granules.

What is the typical appearance of eosinophil granules on Wright stain?

Huge dark blue or black granules that may obscure the nucleus.

What is the typical appearance of basophil granules on Wright stain?

Bone marrow.

What is the tissue origin of megakaryocytes?

Approximately 1–2 days (before RES removal).

What is the typical lifespan of a mature neutrophil in tissue?

Eosinophils.

Which WBC type is most associated with parasitic infections and allergies?

Basophils.

Which WBC type is most closely associated with IgE and histamine release?

About 50% circulate and 50% marginated.

What is the general composition of circulating vs marginated neutrophils?

Myelocyte.

Which stage is first to differentiate into eosinophil, basophil, or neutrophil?

Myeloblast.

Which stage is normally absent in peripheral blood of healthy individuals but may appear in leukemia?

Promyelocytes.

Which stage may be observed in blood during severe infection or leukemia?

Multiple lobes (3–5) connected by thin filaments.

What is the hallmark of a segmented neutrophil’s nucleus on a smear?

Monocytes have blue-gray cytoplasm and a large, indented nucleus; lymphocytes have round nuclei and blue cytoplasm.

What histologic feature helps distinguish monocytes from lymphocytes on a smear?

Neutrophils.

What cell type acts as the first line of defense against bacteria by phagocytosis?

Megakaryocytes.

Which cells in marrow give rise to platelets?

Humoral immune response and antigen-specific antibody production.

What is the functional consequence of plasma cells producing antibodies?

Clumped chromatin with a round eccentric nucleus.

What is the chromatin appearance of a mature plasma cell?

Secondary granules containing enzymes; they stain pink with Wright stain.

What specific granules are characteristic of neutrophils?

Kidney-bean shaped nucleus with coarser chromatin.

What is the morphological feature of a metamyelocyte’s nucleus?

Myelocyte.

Which stage is described as the last cell to divide during granulopoiesis?

Plasmablast, proplasma cell, plasmacyte, mature plasma cell.

What are the three steps in the maturation of B cells to plasma cells called in order?

In the bone marrow.

Where are structural bone marrow cells like reticular and fat cells mentioned to be located?

May contain vacuoles.

What is the typical content of a monocyte’s cytoplasm regarding vacuoles?

Cytoplasm may become pinker (less blue) as myelocytes mature into neutrophils.

What is the immediate color change expected in granulopoiesis as cells mature toward neutrophils?