Blood Composition and Function

Study Notes

Plasma: Comprises 55% of blood volume
- Primarily water (91%)
- Contains proteins like Albumin, Globulins, Fibrinogen, and other solutes (ions, nutrients, waste products, gases, regulatory substances)
Formed Elements: Constitute 45% of blood volume
- Platelets: Between 250,000-400,000 per cubic mm
- White Blood Cells (WBCs): Between 5,000-10,000 per cubic mm
  - Neutrophils: 60%-70%
  - Lymphocytes: 20%-25%
  - Monocytes: 3%-8%
  - Eosinophils: 2%-4%
  - Basophils: 0.5%-1%
- Red Blood Cells (RBCs): Between 4.2-6.2 million per cubic mm

Albumin:
- Highest concentration protein in plasma
- Contributes significantly to osmotic pressure
- Transports certain substances
Globulin (α, β, γ):
- Gamma globulins primarily contribute to defense mechanisms
- Transports various substances
Fibrinogen:
- Essential for blood clotting
- Elongated shape contributes to blood viscosity
Prothrombin:
- Crucial for blood clotting

Red Blood Corpuscles (RBCs):
- About 5 million per cubic mm
- Decrease leads to anemia, increase leads to polycythemia
White Blood Corpuscles (WBCs):
- 4,000-11,000 per cubic mm
- Decrease leads to leukopenia, increase leads to leukocytosis
Platelets:
- Between 250,000-500,000 per cubic mm
- Decrease leads to thrombocytopenia, increase leads to thrombocytosis

Arteries:
- Carry blood away from the heart
- Generally located deeper within the body
- Thick walls and narrow lumens provide strength and resilience
- Less distensible (change in volume/change in pressure) due to strong walls
Veins:
- Carry blood to the heart for oxygenation
- Generally positioned closer to or beneath the skin surface
- Thinner walls and wider lumens allow for blood storage
- Highly distensible, accommodating 0.5-1 liters of blood with slight pressure increase

Venous Sample (preferred for clinical tests):
- Collected via venipuncture (direct puncture of superficial vein)
- Used for routine laboratory tests (hematological and biochemical investigations)
Arterial Sample:
- Collected by puncturing an artery (radial or femoral)
- Used for analyzing arterial blood gases and blood pH
Capillary Sample:
- Collected from a dermal puncture (fingertip or heel)
- Used for Hb estimation, cell counts, bleeding and coagulation time, blood films, micro chemical tests, and blood group detection
- More prone to contamination due to tissue fluid dilution

Clotted Samples: Presence of even small clots can affect test results
Hemolysed Samples: Damaged red blood cells release Hb, rendering the sample unusable

Whole Blood:
- Blood drawn from a vein is transferred to a container with an anticoagulant
- Sample is ready for testing after mixing
- Plasma can be obtained by centrifuging the anticoagulated blood
Plasma:
- Supernatant plasma collected after centrifuging anticoagulated blood
Serum:
- Blood collected in a container without anticoagulant clots naturally
- Serum is the supernatant liquid after clot shrinkage
- Further centrifugation removes remaining red blood cells