Lecture Notes on Blood Vessels

Importance of Blood Pressure

• High blood pressure (hypertension) can lead to:
  • Kidney problems
  • Aneurysms
  • Increased risk of strokes
  • Silent killer, often undetected without symptoms
• Low blood pressure can cause:
  • Faintness

Types of Blood Vessels

• Arteries: Vessels carrying blood away from the heart.
• Veins: Vessels returning blood to the heart.
• Capillaries: Smallest blood vessels, site of nutrient and gas exchange with tissues.
• Arterioles: Small branches of arteries leading to capillaries.
• Venules: Small vessels collecting blood from capillaries to veins.

Capillary Beds

• Networks of capillaries in tissues, providing nutrients and oxygen.
• Precapillary sphincters regulate blood flow into capillaries based on the body's needs (e.g., during fight or flight).
• Thoroughfare channels allow blood to bypass capillary beds.

Blood Flow and Pressure

• Blood pressure is influenced by vessel size and resistance.
• Tunics of Blood Vessels:
  • Tunica Intima: Innermost layer with simple squamous epithelium.
  • Tunica Media: Middle layer, contains smooth muscle for vasoconstriction/dilation.
  • Tunica Externa: Outermost layer, connective tissue providing support.

Mechanisms of Blood Return to the Heart

• Veins have one-way valves preventing backflow.
• Muscle contractions and breathing help push blood back to the heart.

Arteries vs. Veins

• Elastic Arteries: Large, elastic, and act as pressure reservoirs (e.g., aorta).
• Muscular Arteries: More smooth muscle, active in vasoconstriction/dilation.
• Veins: Larger lumens, thinner walls, contain more blood volume (reservoir function).

Varicose Veins

• Caused by incompetent valves and pooling of blood.
• Risk factors include standing for long periods, pregnancy, and obesity.

Types of Capillaries

• Continuous Capillaries: Tight junctions, found in skin, muscles, CNS.
• Fenestrated Capillaries: Have pores, found in kidneys, allow more filtration.
• Sinusoidal Capillaries: Large openings, found in liver, spleen, bone marrow.

Vascular Anastomoses

• Collateral channels providing alternate pathways for blood flow.
• Common in joints, heart, and brain to prevent blood flow interruptions.

Additional Notes

• Veins hold 60-65% of total blood volume.
• Veins are under low pressure and can store more blood without bursting.