Histology - Blood

Question 1

Constituents of blood

Answer 1

Plasma = 56%
Erythrocytes = 43%
Leucocytes = 1%

Question 2

Serum

Answer 2

Plasma minus clotting factors.

Question 3

Plasma

Answer 3

Blood minus cells.

• Water.
• Salt + minerals.
• Plasma proteins (albumins, globulins, fibrinogen).
• Hormones/signal molecules.
• Other clotting factors.

Question 4

Erythrocytes

Answer 4

• 4 to 6 million per mL of blood.
• Lifespan = 120 days.
• 6.5 to 8.5 micrometres diameter.
• Enucleate, biconcave discs.
• Haemoglobin - major protein.
• Destroyed in liver and spleen.
• Cell membrane attached to endoskeleton (spectrin protein) - maintains cell shape.

Question 5

3 groups of leucocytes

Answer 5

1) Granulocytes = visible fibres
- 40 to 75% = neutrophils.
- 5% = eosinophils.
- 0.5% = basophils.
2) Agranulocytes = no visible fibres.
- 20 to 50% = lymphocytes.
- 1 to 5% = monocytes.
3) Platelets = cell fragments.

Question 6

Neutrophils/ polymorphonuclear leucocytes

Answer 6

• Commonest WBC.
• Commonest granulocyte.
• 12 to 14 micrometres diameter.
• Multi-lobed nucleus.
• Faint granular cytoplasm.
• Phagocytes = engulf and destroy bacteria, using respiratory burst (myeloperoxidase).

Question 7

Types of granules in neutrophils (3)

Answer 7

1) Primary granules = lyzosomes (contain myeloperoxidase and acid hydrolase).
2) Secondary granules = secrete substances that mobilize inflammatory mediators.
3) Tertiary granules = gelatinases (break down proteins). adhesion molecules.

Question 8

Eosinophils

Answer 8

• Number increases during parasitic infections.
• 12 to 17 micrometres diameter.
• Bi-lobed nucleus.
• Large red/pink cytoplasmic granules with crystalline inclusions.
• Lozenge - shaped granules.
• Phagocytosis - affinity for antigen/antibody complexes.
• Antagonistic in action to basophils and mast cells as they neutralize histamines so restrict inflammatory response.
• Receptors for Immunoglobin E.

Question 9

Basophils

Answer 9

• Circulating form of mast cell.
• 14 to 16 micrometres diameter.
• Bi-lobed nucleus.
• Prominent dark staining cytoplasmic granules.
• Granules contain histamines involved in inflammatory reactions + prevent coagulation/agglutination.
• Histamines and other vaso-active agents released in response to allergens –> immediate type 1 hypersensitivity reaction = anaphylaxis.
• Receptors for Immunoglobin E.

Question 10

Lymphocytes

Answer 10

• 2 functional sub-types:
• B cells = develop in bone marrow, become plasma cells and secrete antibodies.
• T cells = develop in thymus, cell-mediated immunity.
• 10 micrometres diameter.
• T Helper cell = helps B cells, activate macrophages.
• T Cytotoxic cell = kill previously marked cells.
• T Suppressor cell = suppress TH cells/ immune response.
• Natural Killer cell = mainly kill virus infected cells.
• Almost all nucleus surrounded by thin layer of cytoplasm.
• Clear blue/grey cytoplasm with few organelles in it.
• All look the same with H+E stain.
• Only mature WBC capable of cell division.

Question 11

Monocytes

Answer 11

• Immature cells.
• Circulate in blood for a few hours.
• Reniform nucleus.
• 15 to 20 micrometres diametre.
• Phagocytic + defensive role.
• Small cytoplasmic granules (mostly lysosomes) despite classification of agranulocytes.
• Differentiate to:
• Tissue macrophages = everywhere.
• Kupffer cells = liver.
• Osteoclasts = bone.
• Antigen presenting cells = everywhere.
• Aveolar macrophages = lung.

Question 12

Platelets

Answer 12

• Blood clotting.
• Fragments of cells derived from large multi-nucleated megakaryocytes in bone marrow.
• 1 to 3 micrometres in diameter.
• Contain vesicles with coagulation factors.

Question 13

Haematopoiesis

Answer 13

Formation of blood cells.

• All blood cells from a multi-potential haematopoeitic stem cell (haemocytoblast).
• Haemocytoblast divide to form 2 different types of daughter cell:
  1) Common myeloid progenitor.
• Platelets, erythrocytes, mast cells, basophils, neutrophils, eosinophils, monocytes.
  2) Common lymphoid progenitor.
• Lymphocytes.

Question 14

Haomatopoiesis (cells)

Answer 14

• All produced in bone marrow in adults.
• All produced in liver in foetus.
  1) Myelon series = lies next to bone trabeculae.
• Give rise to WBC.
  2) Erythron series = lies between bony trabeculae.
• Give rise to RBC.
  3) Megakaryotypes = lies between bony trabeculae.
• Give rise to platelets.
• Multi-nucleated and larger than erythron series.

Question 15

Erythropoesis

Answer 15

Proerythroblast –> reticulocyte –> RBC.

• Early precursors are basophilic but change to eosinophilic as Hb increases.
• Mediated by hormone erythropoietin (EPO) - made in kidneys.
• As cells mature:
• Reduction in cell size.
• Hb production.
• Reduction and loss of organelles.
• Nucleus lost at final stage.

Question 16

Granulopoeisis

Answer 16

Morphology similar for neutrophils, eosinophils and basophils.

• Increasing number of granules.
• Increasingly complex nucleus shape.
• Large pod of stored mature neutrophils in bone marrow - released during infection.