Blood Vessels and Hemodynamics

Blood Vessels and Hemodynamics

• Five main types of blood vessels exist: arteries, arterioles, capillaries, venules, and veins.
• All form a large interconnected loop.
• Arteries and arterioles carry blood away from the heart.
  • Large elastic arteries carry initial blood from the heart.
  • Branch into muscular, medium-sized arteries.
  • Small arteries branch into arterioles.
• Capillaries facilitate exchange between blood and tissues.
  • Arterioles branch into capillaries in tissues.
  • Thin walls facilitate exchange.
• Veins and venules return blood to the heart.
  • Capillaries merge into venules.
  • Venules merge into larger veins that return blood to the heart.

Blood Vessel Structure

• Blood vessels have three layers called tunics:
  • Tunica interna: innermost endothelial lining.
  • Tunica media: middle smooth muscle layer.
  • Tunica externa: outermost connective tissue layer.
• The tunica interna lines blood vessel walls.
  • Provides thin endothelial lining in direct contact with blood.
  • Facilitates exchange by diffusion.
  • Provides smooth surface for blood flow.
• The tunica media varies between vessel types.
  • Contains smooth muscle and elastic fibers.
  • Mediates vasoconstriction and vasodilation.
• The tunica externa varies between vessel types.
  • Mostly collagen and elastic fibers.
  • Contains many nerves.
  • Support larger blood vessels (vasa vasorum).

Capillary Beds

• Capillaries are the smallest blood vessels (5-10 μm diameter).
• Branch extensively, supplying all body cells with nutrients and removing waste.
• Three mechanisms of capillary exchange: diffusion, transcytosis, and bulk flow.
  • Diffusion: movement of substances due to concentration gradients.
  • Transcytosis: movement of large molecules through cells (e.g. hormones, antibodies).
  • Bulk flow: collective movement of large amounts of molecules from high pressure to low pressure.
• Capillary beds have a unique structure.
  • Lack both the tunica externa and media.
  • Only endothelium and basement membrane for rapid diffusion.
  • Many branches increase total surface area for exchange (capillary beds).
• Capillaries branch from metarterioles to 10-100 capillaries.
  • Through capillaries, or through a thoroughfare channel to venules.

Venules and Veins

• Venules are thin-walled vessels that lose shape easily.
• Muscular venules can stretch.
• Veins change shape as they merge into larger vessels, but all are thin-walled.
• Contain valves to prevent backflow.
• Accumulate large blood volumes.
• Venous return, movement of blood from capillaries to the heart depends on skeletal muscle pump.
• The respiratory pump helps to compress veins during inhalation to increase venous return.

Blood Pressure

• Blood pressure (BP) is the hydrostatic pressure exerted by blood on blood vessel walls.
• Measured in mmHg.
• Affected by cardiac output, blood volume, and resistance.
• Systolic blood pressure is highest during ventricular contraction, while diastolic blood pressure is lowest during ventricular relaxation.
• Blood flows from high to low pressure.

Blood Flow

• Blood flow is the volume of blood moving through a given tissue per unit of time.
• Measured in mL/min.
• Cardiac output (CO) is the total blood flow.
• Perfusion is the extent of blood flow to particular areas.
• Many factors modulate blood flow.
  • Resistance: friction between blood and vessel walls.
  • Viscosity (thickness of blood).
  • Length of blood vessels.
  • Total cross-sectional area.
• The net filtration pressure (NFP) determines whether fluid volume in tissues changes.

Homeostatic Control

• Many factors regulate blood pressure.
  • Hormones (e.g., ADH, ANP, epinephrine, norepinephrine).
  • Autonomic nervous system (vasoconstriction/vasodilation).
• Physical changes(e.g., temperature, stretching), can also affect blood vessel diameter/tone and modulate blood flow.

Shock

• Shock occurs when insufficient blood flow leads to cellular damage.
• Different types of shock exist, including hypovolemic, cardiogenic, anaphylactic, neurogenic, and obstructive shock.
• Shock causes the body's physiological responses to compensate.
• The body attempts to release ADH, stimulate the RAA pathway and sympathetic nervous system.

Hypertension

• Hypertension is persistently elevated blood pressure.
• Idiopathic hypertension: no identifiable cause.
• Physiological causes: increased blood volume, increased vascular resistance, or increased cardiac output.
• Systemic and pulmonary circulations are the two main circulatory routes.

Explore the five main types of blood vessels including arteries, veins, and capillaries. Learn about their structures and functions, including their roles in blood circulation. This quiz covers essential concepts related to blood flow and vessel anatomy.