Lecture #73: Histology: Histology of Blood

What are the major components of blood?

Blood consists of plasma, erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets).

What are the granulocytes?

Neutrophils, eosinophils, and basophils are granulocytes.

What are the agranulocytes?

Lymphocytes and monocytes are agranulocytes.

What is hematocrit?

Hematocrit is the volume of packed erythrocytes after centrifugation of anticoagulated blood.

What is the buffy coat?

The buffy coat contains leukocytes and platelets and represents about 1% of centrifuged blood volume.

What is plasma primarily composed of?

Plasma is approximately 90% water and serves as the solvent for blood components.

What is the most abundant plasma protein?

Albumin is the most abundant plasma protein.

What are the major functions of albumin?

Albumin maintains colloid osmotic pressure and serves as a carrier protein for hormones, metabolites, and drugs.

What are globulins?

Globulins include immunoglobulins and nonimmune globulins, which help maintain osmotic pressure and function as carrier proteins.

What is the function of fibrinogen?

Fibrinogen is synthesized in the liver and is essential for blood clotting.

What is serum?

Serum is plasma with the clotting factors removed.

What is the morphology of erythrocytes?

Erythrocytes are anucleate, biconcave discs with a shape that maximizes surface area for gas exchange.

What are the primary functions of erythrocytes?

They transport oxygen to tissues and carbon dioxide from tissues.

What is the lifespan of a normal erythrocyte?

Approximately 120 days.

Which membrane proteins help maintain RBC structure?

Glycophorins, Band 3 proteins, spectrin, ankyrin, actin, and tropomyosin.

What is the function of Glycophorin C?

It attaches the underlying cytoskeleton to the erythrocyte membrane.

What is the function of Band 3 protein?

It binds hemoglobin and anchors cytoskeletal proteins to the membrane.

What provides erythrocytes with flexibility?

The spectrin-based cytoskeletal network anchored by ankyrin provides membrane stability and elasticity.

What is the major adult hemoglobin?

HbA, composed of two alpha and two beta globin chains.

What is HbA2?

HbA2 contains two alpha and two delta chains and accounts for about 2% of adult hemoglobin.

What is fetal hemoglobin?

HbF contains two alpha and two gamma chains and is the predominant fetal hemoglobin.

What stimulates erythropoietin production?

Reduced oxygen delivery to the kidney stimulates erythropoietin production.

What are normal adult RBC indices?

MCV 82–98 fL, MCH 26–34 pg, MCHC 32–36 g/dL, and reticulocyte count 0.5–1.5%.

Which leukocyte is the most abundant?

Neutrophils comprise approximately 40–70% of circulating leukocytes.

What type of nucleus do neutrophils have?

A multilobed nucleus with 2–4 lobes.

What are the three types of neutrophil granules?

Primary (azurophilic), secondary (specific), and tertiary granules.

What do primary neutrophil granules contain?

Lysosomes, myeloperoxidase, and defensins.

What do secondary neutrophil granules contain?

Type IV collagenase, phospholipase, complement activators, and lysozyme.

What do tertiary neutrophil granules contain?

Phosphatases and metalloproteinases that aid migration.

What clinical setting is associated with neutrophils?

Acute inflammation and bacterial infections.

What are the steps of neutrophil migration?

Margination, rolling via selectins, adhesion via integrins, transmigration, opsonization, and phagocytosis.

What is opsonization?

Coating pathogens with antibodies or complement to enhance neutrophil recognition and phagocytosis.

What cytokine released by neutrophils causes fever?

IL-1 stimulates prostaglandin synthesis in the hypothalamus, producing fever.

Which leukocytes are associated with chronic inflammation and viral infections?

Lymphocytes.

What are the three major lymphocyte types?

T lymphocytes, B lymphocytes, and natural killer (NK) cells.

What is the primary function of T lymphocytes?

Cell-mediated immunity.

Where do T lymphocytes mature?

In the thymus.

What are the major CD markers for T cells?

CD4 and CD8.

What is the function of B lymphocytes?

B lymphocytes differentiate into plasma cells that produce antibodies.

What CD markers identify B cells?

CD19, CD20, and CD21.

What is the function of NK cells?

NK cells destroy virus-infected and transformed (tumor) cells.

What CD markers identify NK cells?

CD16 and CD56.

What is a cluster of differentiation (CD)?

A cell surface molecule used to classify leukocytes by immunophenotyping.

How can T cells and B cells be definitively distinguished?

By immunohistochemistry or flow cytometry using CD markers.

What do cytotoxic CD8+ T cells recognize?

Antigens presented on MHC class I molecules.

How do CD8+ T cells kill target cells?

They release perforins and lymphokines that lyse infected or neoplastic cells.

What do helper CD4+ T cells recognize?

Antigens presented on MHC class II molecules by antigen-presenting cells.

What cytokine is primarily secreted by activated helper CD4+ T cells?

IL-2, which stimulates proliferation and differentiation of immune cells.

What is the largest leukocyte in peripheral blood?

The monocyte.

What is the morphology of a monocyte?

It has a large indented or horseshoe-shaped nucleus with azurophilic granules.

What is the function of monocytes?

They migrate into tissues, become macrophages, perform phagocytosis, and present antigen.

How long do circulating monocytes typically survive?

Approximately 3 days.

What are tissue macrophages called in the skin?

Langerhans cells.

What are tissue macrophages called in the CNS?

Microglia.

What are tissue macrophages called in bone?

Osteoclasts.

What are tissue macrophages called in the liver?

Kupffer cells.

What are tissue macrophages called in the lung?

Alveolar macrophages.

What are the major functions of eosinophils?

Defense against parasites and participation in allergic reactions and chronic inflammation.

What is the morphology of eosinophils?

A bilobed nucleus with large eosinophilic granules.

What toxic proteins are found in eosinophil specific granules?

Major basic protein, eosinophil peroxidase, eosinophil-derived neurotoxin, and eosinophilic cationic protein.

How do eosinophils reduce allergic responses?

They contain histaminase and arylsulfatase, which neutralize histamine and leukotrienes.

Which leukocyte is least numerous?

The basophil.

What receptors are abundant on basophils?

Fc receptors that bind IgE.

What substances are found in basophil granules?

Histamine, heparin, heparan sulfate, and leukotrienes.

What are basophils functionally related to?

Mast cells.

What are basophils primarily associated with?

Immediate hypersensitivity and allergic reactions.

What are platelets?

Small anucleate cytoplasmic fragments derived from megakaryocytes.

What is the normal platelet lifespan?

Approximately 10 days.

What is the normal platelet count?

Approximately 150,000–400,000/µL.

What do platelet alpha granules contain?

PDGF, fibrinogen, coagulation factors, plasminogen, and plasminogen activator inhibitor.

What is the function of alpha granules?

Vessel repair, platelet aggregation, and coagulation.

What do platelet delta granules contain?

Serotonin, ADP, ATP, and histamine.

What is the function of delta granules?

Promote platelet adhesion, aggregation, and vasoconstriction.

What do gamma (lambda) granules contain?

Lysosomal hydrolytic enzymes involved in clot resorption.

What is the primary function of platelets?

Hemostasis.

How do platelets initiate hemostasis?

They adhere to exposed connective tissue, degranulate, release serotonin, ADP, and thromboxane A2, and form the primary platelet plug.

What is the role of thromboxane A2?

It promotes platelet aggregation and formation of the primary hemostatic plug.

What is the role of serotonin released by platelets?

It causes vasoconstriction to reduce blood flow at the site of injury.