Blood Cell Morphology Flashcards
Learning objectives
- Describe the morphological features of the
formed elements of blood (erythrocytes,
leukocytes and platelets) - Describe the relative abundance of each of
these elements in a sample of normal blood - Describe the formation (haemopoiesis) of
these elements of blood from stem cells
found in the bone marrow
What are the functions of blood?
o Delivery of nutrients and oxygen directly or indirectly to cells
o Transport of wastes and carbon dioxide away from cells
o Delivery of hormones and other regulatory substances to and from cells and tissues
o Maintenance of homeostasis by:
o acting as a buffer
o participating in coagulation
o Thermoregulation
o Transport of humoral agents and cells of the immune system that protect the body from pathogenic agents, foreign proteins, and transformed cells e.g. cancer cells
What are the features of an erythrocyte (RBC)?
-Biconcave disks
-Anucleate and lack
major organelles
-Contain haemoglobin
-Life span 120 days
-Formed in bone marrow
-Broken down in spleen,
liver
-45% of whole blood
Why are erythrocytes biconcave?
o ↑ Surface area – more
haemoglobin molecules closer to plasma membrane
o Less distance for O2 and CO2 to diffuse
o Anucleate
o Less likely to rupture
What happens in erythrocytes in sickle cell anaemia?
-Mutation in the haemoglobin gene (autosomal recessive)
-The altered haemoglobin (HbS) forms rigid
aggregates giving the erythrocyte a characteristic
sickle shape
- Adhere more readily to tunica intima of blood
vessels (inner lining of blood vessel, endothelial cells)
-Can accumulate in small capillaries and larger
vessels, depriving tissue of oxygen and nutrients
- Also break down more readily as they are very
fragile
What are the features of leukocytes?
- Possess a nucleus and most major organelles
-Formed in bone marrow & lymphoid organs
-Use vascular system for transportation but perform
their function in tissues and organs - Total WBCs < 1% of whole blood
-Life span of up to several years
How to classify leukocytes?
Granulocyte
• Cytoplasm packed with granules
• Nucleus has 2 or more lobes (polymorphonuclear)
• Neutrophils, Eosinophils & Basophils
Agranulocyte • Cytoplasm with few or no granules • Nucleus not lobed • Mononuclear • Lymphocytes & Monocytes
Features of neutrophils
- Most numerous of all WBCs (60-70%)
- Nucleus = 2-5 lobes
- Numerous cytoplasmic granules
- Respond most quickly to tissue destruction by bacteria or fungus
- Their numbers increase explosively during acute bacterial infections such as meningitis.
Features of eosinophils
- 2 - 4% of circulating WBCs
- Bilobed nucleus
- Large refractile granules (lysosomes)
- Regulate local inflammatory responses dues to allergic or parasitic action
Features of basophil
- Less than 1% of circulating WBCs
- Irregularly –lobed nucleus
- Numerous large overlying granules which often obscure the nucleus
- Granules contain heparin (anti-coagulant) and histamine (vasodilator)
- Associated with systemic inflammation and allergies
Features of lymphocyte
- 20-25% of circulating WBCs
- Nucleus is spherical and densely stained, no granules
- Usually present in tissues
- Involved in adaptive immune responses
- B-lymphocytes → plasma cells (produce antibodies)
- T-lymphocytes (cell mediated response)
Features of monocyte
- 3 – 8 % of circulating WBCs
- Kidney / U-shaped nucleus
- Large cell (12- 20um)
- Transform into a macrophage in tissues and organs (osteoclasts, Kupffer cells, alveolar macrophages)
Never Let Monkeys Eat Bananas-
The relative abundances of leukocytes
(Neutro, Lymph, Mono, Eosino, Baso)
Features of platelet (thrombocyte)
- Life span roughly 10 days
- Packets of cytoplasm budded from megakaryocyte (platelets are not cells)
- Possess granules containing growth factors
- Anucleate
- Involved in clot (thrombus) formation
Blood clotting (haemostasis)
o The body’s normal physiological response to preventing and stopping bleeding/haemorrhage
o When endothelial injury occurs, endothelial cells stop
secretion of coagulation and aggregation inhibitors and
instead secrete ‘von Willebrand factor’ (key clotting
protein)
o Platelets and fibrin(in blood plasma) bind together with cells to form platelet plug
o Three major steps involved:
1. Vasoconstriction of blood vessel wall
2. Temporary blockage of a break by a platelet plug - platelets attach to exposed collagen of vessel wall and release the contents of their granules, leading to aggregation of other platelets to the area
3.Blood coagulation, or formation of a fibrin clot – a fibrin mesh (from blood plasma) binds together with cells and platelets
What is the differential white cell count and what is its clinical relevance?
-Measure of the relative percentage of each type of WBCs
-Change in normal proportions may give indication for certain diseases and conditions, e.g. rise in neutrophils
may indicate presence of
acute bacterial infection
