Blood Composition and Functions

Blood

• Specialized connective tissue, viscous fluid
• Found in blood vessels and bone marrow
• Originates from mesenchyme
• Volume: 5 liters in healthy adult human
• 1 cubic millimeter of blood is equivalent to a microliter
• Functions:
  • Transport of gases, nutrients, waste products, hormones
  • Regulation of pH and osmosis
  • Maintenance of body temperature
  • Protection against foreign substances
  • Clot formation

Blood Composition

• 55% plasma + 45% blood cells

Hematocrit

• Volume percentage of red blood cells in the blood
• Erythrocytes constitute about 43% of the blood volume after centrifugation
  • 47% ±5% in men
  • 42% ±5% in women
• Buffy coat: Thin layer of leukocytes and platelets located between the erythrocytes and plasma.

Blood Film

• Blood film procedure:
  • Clean slide
  • Prick finger
  • Put a drop of blood on a clean dry slide
  • Put another slide on top at 45° angle
  • Move backward to touch the blood drop
  • Move forward to spread the blood
  • Stain with Leishman stain (mixture of eosin, methylene blue, and azures)

Plasma

• Comprises 55% of the blood volume
• Yellowish fluid
• Aqueous solution, pH 7.4
• Composition:
  • Water (92%)
  • Plasma proteins (7%):
    • Albumin (osmotic pressure)
    • Globulin (antibodies)
    • Fibrinogen (coagulation)
  • Organic and inorganic substances (1%)

Blood Cells (Formed Elements)

• Red blood cells (RBCs) or Erythrocytes
• White blood cells (WBCs) or Leukocytes
• Platelets or Thrombocytes

Red Blood Cells (RBCs) or Erythrocytes

• Also known as red blood corpuscles
• Characteristics:
  • Rounded, biconcave discs
  • 7.5 µm diameter, 2.6 µm thick at the rim, 0.75 µm thick in the center
  • Non-nucleated, no organelles (not a true cell)
  • Non-motile
  • Suspended in an isotonic medium (plasma)
  • Soft and plastic, change shape in capillaries
  • Aggregated in small vessels, called Rouleaux
  • Life span is about 120 days

Abnormal Red Blood Cell Shapes (Poikilocytosis)

• Example: Sickle cell anemia, inherited disease where red blood cells are abnormally shaped (sickle shape)

Red Blood Cell Count

• Normal:
  • Male: 5-5.5 million/mm3
  • Female: 4.5-5 million/mm3
• Increase: Polycythemia (erythrocytosis)
  • Physiological: Individuals living at high altitudes (low O2 tension)
  • Pathological: Congenital heart and hypoxic lung
• Decrease: Anemia

Red Blood Cell Structure

• Cell membrane: 40% lipid, 10% carbohydrate, 50% protein
• Cytoskeletons maintain cell shape
• Antigens on the surface determine blood group (A, B, O, and Rh)

Red Blood Cell Size and Osmotic Pressure

• Isotonic solution (plasma): Osmotic pressure of plasma = in RBCs
• Hypertonic solution: Water flows from low solute inside the cell to high solute outside the cell, leading to cell shrinking (crenation)
• Hypotonic solution: Water accumulates inside the cell leading to swelling (hemolysis)

Red Blood Cell Size Variations

• Normocyte: 6-9 um (7.5)
• Macrocyte: Larger than 9 um
• Microcyte: Smaller than 6 um
• Anisocytosis: High percentage of erythrocytes with great variations in size

Hemoglobin (Hb)

• Protein found in the cytoplasm of red blood cells
• Haem (4%) + Globin (96%)
• Normal:
  • Male: 15.5 gm/L
  • Female: 14 gm/L
• Hb normal: Normochromic
• Less than normal: Hypochromic
• Hb more than normal: Hyperchromic
• Hemoglobin carries O2 from lungs to tissues of the body
• Heme contains iron, a pigment

Anemia

• Causes:
  • Decreased number of RBCs: Aplastic anemia, hemorrhagic anemia
  • Decreased Hb
  • Decreased hemopoietic factors (iron and vitamin B12)
  • Haemolysis (breakdown of RBCs)

Red Blood Cell Adaptations for Function

• Biconcave discs: Increased surface area for gas exchange
• Plastic: Compress in narrow capillaries
• No nuclei or organelles: More space for Hb
• Glucose metabolism enzymes: Energy production

Leukocytes, WBCs

• Names: Leukocytes, white blood cells, WBCs
• Characteristics:
  • True cells (with nucleus and organelles)
  • Originate in bone marrow
  • Spherical when suspended in blood plasma
  • Become amoeboid and motile after leaving blood vessels and invading tissues

Types of Leukocytes

• Agranulocytes (Mononuclear): Contains non-specific granules only
  • Lymphocytes
  • Monocytes
• Granulocytes (Polymorphonuclear): Contains specific and non-specific granules
  • Neutrophils
  • Eosinophils
  • Basophils

Granular Leukocytes

• Two types of granules:
  • Non-specific (azurophilic): Lysosomes, stain darkly, present in all leukocytes
  • Specific: Bind neutral, basic, or acidic stains and have specific functions
• Three types based on specific granule stain:
  • Neutrophils: Neutral
  • Eosinophils: Acidophilic
  • Basophils: Basophilic

Differential Leukocytic Count

• Percentage of each type of leukocyte

Leukemia

• Cancer that begins in the bone marrow, causing an abnormal increase of immature white blood cells (blasts or leukemia cells)
• These cells are not fully developed

Agranulocytes vs Granulocytes

• Agranulocytes:
  • Monocyte: 2-8% of WBCs, few days lifespan, 20 micrometers diameter, basophilic cytoplasm, kidney-shaped nucleus, phagocytic function
  • Lymphocyte: 20-40% of WBCs, 3 months to years lifespan, 7-8 micrometers diameter, basophilic cytoplasm, large rounded nucleus, immunity function
• Granulocytes:
  • Basophil: 0-0.5% of WBCs, few days (life span), 10-12 micrometers diameter, large basophilic specific granules, S-shaped bilobulated nucleus, allergy (Histamine and Heparin) function
  • Eosinophil: 1-4% of WBCs, 8-12 days lifespan, 10-12 micrometers diameter, larger acidophilic specific granules, horse-shoe shaped nucleus, cytotoxic and allergy function
  • Neutrophil: 50-70% of WBCs, 12-15 days lifespan, 10-12 micrometers diameter, small numerous specific granules, multilobulated nucleus, phagocytic function

Platelets (Thrombocytes)

• Non-nucleated (not a true cell), oval or disk-like cell
• 2-4 um in diameter
• Origin: Megakaryocytes (giant cells) in the bone marrow
• Normal platelet count: 200,000 to 400,000/mm3 of blood
• Life span: 5-10 days
• Structure:
  • Peripheral zone (hyalomere): Rich in GAGs and glycoproteins, involved in platelet adhesion, marginal bundle of microtubules and microfilaments (actin, myosin) for shape maintenance, two membranes:
    • Open canalicular system: Facilitates uptake of factors
    • Dense tubular system: Derived from ER and stores Ca2+ ions
  • Central zone (granulomere): Mitochondria, glycogen, and granules:
    • Alpha: Proteins (clot factors)
    • Delta: Calcium, enzymes (e.g. Serotonin)
    • Lambda: Lysosomes

Platelet Functions

• Control of hemorrhage
• Promote blood clotting
• Clot factors:
  • Fibrinogen
  • Plasminogen
  • Thromboplastin

Role of Platelets in Controlling Hemorrhage

• Primary platelet aggregation: Platelets adhere together forming a platelet plug
• Secondary platelet aggregation: Release of glycoproteins enhances plug size
• Blood coagulation: Release of coagulation factors produces fibrin protein, forming a network that traps blood cells, creating a blood clot
• Clot retraction: Clot contracts due to interaction of platelet actin and myosin
• Clot removal: Vessel wall is restored with new tissue, and the clot is removed by plasma proteolytic enzymes (plasmin, plasminogen) and lambda granules (lysosomal enzymes)

Hemophilia

• Severe hemorrhage after injury
• Inherited genetic X-chromosome disorder, transmitted by females
• People with hemophilia have little or no clotting factors

Explore the fascinating world of blood, a specialized connective tissue vital for numerous bodily functions. This quiz covers blood composition, hematocrit, and the essential roles blood plays in transport, regulation, and protection in the human body.