Introduction
- 7-8% body weight in mammals |
- Consists of: |
+ Plasma:
- 45-65% of blood volume
- Alkaline
- Contain dissolved gases, electrolytes, proteins, CHOs, lipids, hormones. |
+ Formed elements:
- Erythrocytes
- Leukocytes
- Thrombocytes |
Erythrocytes
- Highly specialised
Contains hemoglobin
-->Carries O2 and Co2
Maintains cell shape |
- Round, biconcave, enucleate (in mammals), 4 -8 Um |
-** Acidophilic cytoplasm: 60% water, 40% Hb |
- Plastic-like, can conform to capillaries |
- Most abundant, 120-days life span |
- Mammals: anucleate
- Other animals: nucleate |
- In bloodstream as immature form 1st: Reticulocyte
+ Slightly larger
+ Methylene blue staining
+ Proportion is clinically important |
Leukocytes
- Responsible for body's immune response |
- Migrate to other tissues:
+ Variable cell number
+ Clinical importance: infection, inflammation |
- Classified into 2 groups: |
+ Granular leukocytes:
- Basophils (blue)
- Neutrophils (white)
- Eosinophils (red) |
+ Non-granular leukocytes:
- Lymphocytes
- Monocytes |
Neutrophils
- Most numerous granulocytes
Most abundant types of leukocyte in carnivores |
- Large: 10 -12 Um |
- Lightly stained granules (hardly visible, white) |
- Nucleus:
- Mature: multilobed
- Immature: "U" or "S" shape
- Proportion of immature to mature cells is clinically important |
- Barr body in female = inactive X chromosome |
FUNCTION: |
- Phagocytosis of external microorganisms and particles: enzymes contained with granules inside degrade them |
- Go in large number to deal with infection;
Main constituent of pus |
- 5-day life span in circulation |
Eosinophils
Characteristics |
- Relatively infrequent ( 2-8% of leukocytes) |
- 10 - 15 Um |
- Large, acidophilic granules (stained red) |
- Bilobed nucleus |
- Granules contain hydrolytic enzymes and perioxidases |
FUNCTION |
- Phagocytose antigen/antibody complexes
--> Kill helminth parasites: rest against their body, release contents of granules onto them |
- Implicated in hypersensitivity reactions
Ex: a blood smear from an animal with flea allergy dermatitis will show eosinophilia |
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Basophils
CHARACTERISTICS |
- Rarely encountered (1,5% of leukocytes) |
- 10 -15 Um |
- Precursor for tissues' mast cells |
- Large, darkly basophilic granules (blue) |
- Granules mostly contain histamine, heparin and serotonin |
- Bilobed nucleus obscured by granules |
FUNCTIONS |
- Also involved in response to helminth parasites |
- Play a role in activation of a subset of T cells (T lymphocytes) |
- Implicated in hypersensitivity reactions (asthma, hayfever, anaphalytic shock) |
Lymphocytes
CHARACTERISTICS |
- Found in blood and lymph |
- Concentrated in lymphoid tissue
--> Lymph nodes, nodules, spleen, Peyer's patches in intestine |
- Second most abundant types of leukocytes |
- Ovoid to kidney-shaped nucleus that is almost proportionally large as cytoplasm |
- 2 forms:
- Small: 6-9 Um
- Large: 12-15 Um |
FUNCTIONS |
- Frontline for immunological defense system |
-Based on functional grounds, 3 classes:
+ T Cells: responsible for cell - mediated immune response --> release granules that kill virus-infected and tumour cells; Small lymphocytes
+ B Cells: produce antibodies (humoural immune response)
*Subset of B cells are Plasma cells; Small lymphocytes
+ Natural killer: also do cell-mediated immune response
--> release granules that kill virus-infected and tumor cells; Large lymphocytes |
Monocytes
CHARACTERISTICS |
- 5% of leukocytes |
- Largest: 15 - 20 Um |
- Large, eccentric nucleus: pale -staining |
- Nuclear shape is variable:
- Immature: indented
- Mature: horseshoe-like |
- May have 2 or more nucleoli |
FUNCTIONS |
- Have little function in circulating blood |
- Highly motile and phagocytic |
- Leave blood after 3 days
--> Macrophage (free roaming in tissues)
--> Histiocytes (fixed in tissues) |
- Respond to: necrotic tissue, microorganisms, inflammination |
- Also in pus with neutrophils |
- Multinucleate giant cells form by fusion of macrophages (reminiscent of osteoclasts) |
Thrombocytes
- Also called Platelets |
- Involved in formation of blood clots |
- Cytoplasmic fragments of megakaryocyte |
- 2 -4 Um |
- Often appear in clumps on blood smear |
FUNCTIONS |
- Respond to damaged endothelium in 2 stages: |
+ Stage 1: aggregate to form an immediate plug --> stop hemorrhage |
+Stage 2: catalyse formation of fibrin clot --> forms a more permanent seal |
Thrombocytes
- Also called Platelets |
- Involved in formation of blood clots |
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