Blood as a tissue
- Specialised form of CT
- Liquid intercellular substance – plasma
- Formed elements of blood (blood cells):
- Erythrocytes (RBC) (96%)
- Leukocytes (WBC) (3%)
- Thrombocytes (Platelets) (1%)
Functions of blood:
- 1. Transports nutrients, gases, hormones and waste products of metabolism
- 2. Removes toxins from the body
- 3. Maintain body temperature
- 4. Buffer – pH control and homeostasis
- 5. Defence – leukocytes and antibodies
- 6. Blood clotting – prevention of haemorrhage
Composition of blood:
- 4.6 litres in man (7-8% of body weight)
- Plasma 55%
- Blood cells 45%
Haematocrit:
- 0.4-0.5 in men
- 0.35-0.45 in women
Blood plasma
- 55% of whole blood
Composition:
- 92% water
- 7-8% proteins
- 1-2% electrolytes
- nutrients (glucose, amino acids, fatty acids, vitamins, gases, metabolites)
- Osmotic pressure – 0.85% NaCl
- pH: 7.35-7.45
Serum = plasma – fibrinogen
- Plasma proteins:
- Albumins (60% - maintain osmotic pressure)
- Globulins - α, β, γ (20%)
- Fibrinogen – blood clotting
- Lipoproteins – LDL, HDL
- Complement proteins
Erythrocytes (RBC)
- Total number – 25 × 10¹²/L blood (~4–6 million/mm³)
- Size: 7.5 ± 0.5 μm
- Diameter: 0.8 μm in centre; 2.6 μm at rim
- Total surface: 140 μm² (≈ 2500 m² total)
- Life cycle in blood – 120 days (140 in men; 109 in females)
- Flexible, biconcave discs, allowing movement through capillaries
- Lack nucleus
- Haemoglobin makes up 90% of dry content: 120–180 g/L
- Haemoglobin types:
- HbA1 (96–97%)
- HbA2 (2%)
- HbF (1–2% in newborns; 80% in adults)
- HbS – sickle cell anaemia
- Plastic plasmalemma (membrane):
- 40% lipids – including phospholipids, glycolipids, and cholesterol
- 50% proteins – most are integral membrane proteins
- 10% carbohydrates
- Main function:
- O₂ – oxyhaemoglobin
- CO – carboxyhaemoglobin
- CO₂ – carbaminohaemoglobin
Reticulocytes
- Young erythrocytes = polychromatophilic erythrocytes
- Morphological characteristics:
- Reticular network of rRNA polyribosomes
- Basophilic nuclear fragments of DNA
- Mitotic spindle remnants