Blood Vessels Overview

Blood Vessels

• Types: Arteries, veins, arterio-venous connections
• Large Arteries:
  • Example: Aorta
• Large Veins:
  • Example: Inferior vena cava
  • Wide lumen with numerous valves
  • Thin, flat wall
  • Tunica intima: similar to medium-sized veins
  • Tunica media: thin with only smooth muscle fibers
  • Tunica adventitia: thick layer of loose connective tissue (CT) containing collagenous fibers, CT cells, vasa vasorum, and nerves; also contains longitudinally arranged bundles of smooth muscle fibers
• Medium-Sized Arteries:
• Medium-Sized Veins:
• Arterioles:
• Venules:
• Blood Capillaries:
  • Thin-walled, tubular blood channels connecting terminal arterioles to venules
  • Diameter: 8-10 μm
  • Network of capillaries called a capillary bed
  • Histological Structure:
    • Single layer of endothelial cells resting on a basal lamina
    • Pericytes lie between the endothelium and basal lamina
    • Endothelial cell cytoplasm contains:
      • Usual organelles
      • Numerous microfilaments
      • Intermediate filaments
      • Pinocytotic vesicles
    • Cells held together by zona occludens and gap junctions
  • After tissue injury: Pericytes proliferate and differentiate to form new blood vessels and CT cells

Types of Blood Capillaries

• Continuous Capillaries:
  • No fenestrae present
  • Location: All kinds of muscle tissue, CT, exocrine glands, and nervous tissue
• Fenestrated Capillaries:
  • Large fenestrae present in the cytoplasm of endothelial cells
  • Fenestrae closed by diaphragms that are thinner than a cell membrane
  • Continuous basal lamina present
  • Location: Kidney, intestine, and endocrine glands
• Fenestrated Capillaries Without Diaphragm:
  • Have a very thick basal lamina
  • Location: Renal glomerulus capillary
• Discontinuous Sinusoidal Capillaries:
  • Discontinuous basal lamina and endothelial cells
  • Multiple fenestrae without diaphragm found in the endothelial cells

Arterio-Venous Connection

• Blood Sinusoids:
  • Dilated, irregular blood spaces (5-30 μm in diameter)
  • Location: Bone marrow, spleen, liver, and endocrine glands
  • Histological Structure:
    • Lined by fenestrated endothelial cells (simple squamous epithelium)
    • Walls contain pores that are not covered by diaphragms
    • Endothelium rests on a thin layer of reticular CT
    • No basement membrane present
    • Macrophages present outside the sinusoidal wall, extending pseudopodia inside the wall to phagocytose any foreign body

Capillary vs Sinusoid

• Diameter:
  • Capillaries: Uniform 8-10 μm
  • Sinusoids: Irregular 5-30 μm
• Lumen:
  • Capillaries: Narrow
  • Sinusoids: Wide
• Sites:
  • Capillaries: Present everywhere in the body
  • Sinusoids: Present in certain sites: bone marrow, spleen, liver, and endocrine glands
• Structure:
  • Lining Endothelium:
    • Capillaries: Fenestrated or continuous
    • Sinusoids: Fenestrated, not covered with diaphragm
  • Basement Membrane:
    • Capillaries: Well developed
    • Sinusoids: Absent
  • Pericytes:
    • Capillaries: Absent
    • Sinusoids: Present
  • Macrophages:
    • Capillaries: Absent
    • Sinusoids: Present

Arterio-venous Anastomosis (A-V Shunts)

• Function:
  • Capillaries: Gas and nutrient exchange
  • Sinusoids: Function according to their location (e.g., blood cell production, filtration, etc.)

Explore the fascinating world of blood vessels in this quiz. Learn about the types of arteries and veins, their structures, and functions. Test your knowledge on key components like capillaries and arterioles.