Blood Cells Overview

Blood Cells

• Red Blood Cells (RBCs or Erythrocytes)
  • Shape: Biconcave discs
  • Size: 6-9 microns in diameter (average 7.5 µm)
    • Normocytes: Normal size RBCs
    • Macrocytes: RBCs larger than 9 µm (e.g., macrocytic anemia)
    • Microcytes: RBCs smaller than 6 µm (e.g., microcytic anemia)
  • Number: 4.5-5.5 million/mm3 of blood
  • Structure:
    • Lack nuclei and organelles
    • Contain hemoglobin (Hb) enclosed by cell membrane
  • Reticulocytes: Immature RBCs (1% of circulating RBCs)
    • Slightly larger than mature RBCs
    • Contain free ribosomes and a few mitochondria

White Blood Cells (WBCs or Leukocytes)

• Total Leukocytic Count: 4,000 – 11,000/mm3 of blood
• Differential Leukocytic Count: Percentage of each type of WBC in total WBC count

Granular Leukocytes

• Neutrophils (Polymorphs or Polymorphonuclear Leukocytes): 50-70% of WBCs

  • Nucleus: Segmented (lobulated) with 2-5 lobes (usually 3)
  • Cytoplasm: Contains specific granules (small, numerous) and non-specific (azurophilic) granules (large, less numerous, lysosomes)
  • Function: Antibacterial, crucial for acute inflammation

• Eosinophils: 1-4% of WBCs

  • Nucleus: Bilobed, horse-shoe shaped
  • Cytoplasm:
    • Specific eosinophilic granules: Contain antiparasitic and histaminase
    • Non-specific granules: Lysosomes containing hydrolytic enzymes
  • Functions: Antiallergic, antiparasitic

• Basophils: 0-0.5% of WBCs

  • Nucleus: S-shaped
  • Cytoplasm:
    • Specific granules: Contain heparin (anticoagulant) and histamine (allergy)
    • Non-specific granules: Lysosomes containing hydrolytic enzymes
  • Functions: Secretion of heparin and histamine

Non-Granular Leukocytes

• Lymphocytes: 20-40% of WBCs

  • Small lymphocytes:
    • Nucleus: Large, rounded, condensed chromatin
    • Cytoplasm: Scanty, few organelles
  • Large lymphocytes:
    • Nucleus: Large, rounded with indentation, less condensed chromatin
    • Cytoplasm: Basophilic (due to increased ribosomes)
  • Functions:
    • Humoral immunity (B-lymphocytes)
    • Cellular immunity (T-lymphocytes)

• Monocytes: 2-8% of WBCs

  • Nucleus: Oval or kidney-shaped, eccentrically placed
  • Cytoplasm: Contains lysosomes
  • Functions: Phagocytosis, production of mononuclear phagocytic system (MPS)

Blood Platelets (Thrombocytes)

• Light Microscopy (L/M):
  • Peripheral hyalomere (pale)
  • Central granulomere (granular)
• Electron Microscopy (EM):
  • Hyalomere: Contains microtubules, actin, and myosin filaments
  • Granulomere: Contains:
    • Dense granules:
      • Alpha granules: Fibrinogen
      • Delta granules: ADP, ATP, epinephrine, and serotonin
      • Lambda granules: Lysosomes

Blood Vessels

• Cardiovascular System: Heart + blood vessels
  • Arteries: Carry blood from the heart to tissues
  • Veins: Carry blood from tissues to the heart
  • Capillaries: Arterio-venous connections for exchange

General Structure of Blood Vessels

• Tunica Intima (Innermost):

  • Endothelium: Simple squamous cells
  • Subendothelium: Loose connective tissue

• Tunica Media (Middle):

  • Smooth muscle cells: Circular arrangement
  • Elastic fibers: Variable amounts

• Tunica Adventitia (Outermost):

  • Loose connective tissue
  • Vasa vasorum: Small blood vessels that supply the outer part of the vessel wall

Arteries

• Large (Elastic) Arteries: Aorta and its major branches

  • Specific Features:
    • Tunica media: Concentric layers of elastic laminae with circular smooth muscle between them
    • Tunica adventitia: Relatively thin

• Medium Sized (Muscular) Arteries:

  • Specific Features:
    • Tunica media: Predominantly smooth muscle
    • Tunica adventitia: Thicker than in large arteries

• Arterioles: Smallest arteries

  • Specific Features:
    • Tunica media: One or two layers of smooth muscle
    • Tunica adventitia: Thin

• Metarterioles: Connect arterioles to capillaries

  • Specific Features:
    • Precapillary sphincters: Regulate blood flow into capillaries

Veins

• Large veins:

  • Specific Features:
    • Tunica media: Thin with few layers of smooth muscle
    • Tunica adventitia: Thickest layer, contains longitudinal smooth muscle
    • Valves: Prevent backflow of blood

• Medium sized veins:

  • Specific Features:
    • Tunica media: Thinner than arteries of similar size

• Venules: Smallest veins

Capillaries

• Smallest channels in the circulatory system
• Arise from metarterioles or directly from arterioles
• Re-collect to form venules

Structure of Capillaries

• Light Microscopy (L/M):
  • Endothelial cells: Single layer (1-3 cells)
  • Basal lamina:
  • Pericytes: Partly surround endothelial cells with long cytoplasmic processes, contain actin and myosin (contractile function), produce new smooth muscle cells after injury

Types of Blood Capillaries

• Continuous capillary: No fenestrae (pores)

  • Location: Brain

• Fenestrated capillary: Large fenestrae in endothelial cells, continuous basal lamina

  • Location: Renal glomeruli, endocrine glands

• Sinusoidal capillary: Tortuous, wide lumen, multiple fenestrae, discontinuous basal lamina

  • Location: Liver, bone marrow, spleen

This quiz covers the essential characteristics of red and white blood cells, including their structure, types, and functions. Learn about the differences between normocytes, macrocytes, and microcytes, along with the various types of leukocytes and their percentages in blood. Test your understanding of hematology with this informative quiz.