Vascular System

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Cardiovascular Physiology

• Vascular System

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Components of Circulatory System

• Cardiovascular System (CVS)
• Heart
• Blood vessels
• Lymphatic System

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Cardiovascular System (CVS)

• Cardiac
• (heart)

Vascular

• Arteries
• Arterioles
• Capillaries
• Venules
• Veins

• Right sided
• (volume pump)

• Left sided
• (Pressure pump)

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Major function of Systemic Circulation
? To direct the flow of blood from the heart to
capillaries, back to the heart.

• 1. Transportation
• ? O2 CO2.
• ? digestion products.
• ? wastes.
• ? distribution of body fluids.
• 2. Regulation
• ? Hormonal.
• ? Immune.
• ? Protection.
• ? Temperature.

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Blood Vessels

• Walls composed of 3 tunicas
• Tunica externa
• Outer layer of connective tissue.
• Tunica media
• Middle layer of smooth muscle.
• Tunica interna
• Innermost simple squamous endothelium.
• Layer of elastin.

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Classification of the vascular system

• 1. Aorta (elastic recoil)
• Numerous layers of elastin fibers b/w
  smooth ms.
• Expand when the pressure of the bl rises.
• Act as recoil system when ventricles relax.
• 2. Arteries (muscular, low resistance vessels)
• Less elastic have a thicker layer of smooth ms.
• Diameter changes slightly as BP raises falls.
• 3. Arterioles (high resistance vessels)
• Contain highest smooth muscle.
• Expand less under pressure (less compliance).
• Called resistance vessels (greatest resistance to
  flow).

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Classification of the vascular system (continued)

• Capillaries (exchange vessels)
• Smallest blood vessels.
• 1 endothelial cell thick.
• Provide direct access to cells.
• Permits exchange of nutrients wastes.
• Venules
• Formed when capillaries unite.
• Very porous.

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Classification of the vascular system (continued)

• 6. Veins (capacitance vessels)
• Contain little smooth muscle or elastin.
• Capacitance vessels (blood reservoirs).
• Contain 1-way valves that ensure blood flow to
  the heart.
• ? 2/3 of total blood volume is located in
  veins (? 70).

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Distribution of blood within the circulatory
system at rest
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Mean Arterial and Venous pressure (continued)

• Mean arterial pressure
• 90 100 mmHg.
• Mean venous pressure
• Is only 2 mmHg (low).
• Due to
• 1. Pressure drop b/w arteries
  capillaries.
• 2. High venous compliance.
• N.B. Venous pressure is highest in venules (10
  mmHg), lowest at junction of venae cavae w Rt
  atrium (0 mmHg).

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Arteries
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Structure of an arteriole
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Exchange of Fluid between Capillaries and Tissues
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Capillaries
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Fluid Movement (continued)
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Exchange of Fluid between Capillaries and Tissues

• Distribution of ECF between plasma and
  interstitial compartments is in state of dynamic
  equilibrium.
• Balance between tissue fluid and blood plasma.
• Hydrostatic pressure
• Exerted against the inner capillary wall.
• Promotes formation of tissue fluid.
• Net filtration pressure.
• Colloid osmotic pressure
• Exerted by plasma proteins.
• Promotes fluid reabsorption into circulatory
  system.

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Net Filtration Pressure

• Hydrostatic pressure of blood capillaries
  minus the hydrostatic pressure in the
  interstitial fluid.
• Blood hydrostatic pressure (arteriolar pressure)
  37 mm Hg.
• Blood hydrostatic pressure (venular end) 17 mm
  Hg.
• Interstitial hydrostatic pressure 1 mm Hg.

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Colloid Osmotic Pressure

• Pressure exerted by plasma proteins or
  interstitial proteins.
• Difference between plasma osmotic pressure and
  interstitial osmotic pressure is called oncotic
  pressure.
• Plasma osmotic pressure 25 mm Hg.
• Interstitial osmotic pressure 0 mm Hg.

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Arterioles, Capillaries, Venules
Capillary
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Lymphatic System

• Lymphatic vessels present b/w capillaries.
• 3 basic functions
• Drain excess interstitial (tissue) fluid back to
  the bl, in order to maintain original bl volume.
• Transports absorbed fat from small intestine to
  the bl.
• Helps provide immunological defenses against
  pathogens.

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Lymphatic System (continued)

• Lymphatic capillaries
• Closed-end tubules that form vast networks in
  intercellular spaces.
• Lymph
• Fluid that enters the lymphatic capillaries.
• Lymph carried from lymph capillaries, to lymph
  ducts, and then to lymph nodes.
• Lymph nodes filter the lymph before returning it
  to the veins.

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