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					    Physiology

Cardiovascular System
                    Physiology

Circulatory System

   Heart
      Pump
      Separates the two circulations


   Systemic Circulation

   Pulmonic Circulation
                   Vessels


Each Circulatory System Consist of 3 types
of vessels:

1.   Arteries

2.   Veins

3.   Capillaries
                 Vessel Wall

Structure of vessel walls

The walls of arteries and veins contain three
distinct layers:

1.   Tunica interna

2.   Tunica media

3.   Tunica externa
                 Tunica Interna

Tunica Interna

    Innermost layer of a blood vessel

    Includes the endothelial lining and an
     underlying layer of connective tissue
     with a variable amount of elastic fibers.

    In arteries the outer margin of the
     Tunica Interna contains a thick layer of
     elastic fibers called the Internal Elastic
     Membrane.
               Tunica Media


Tunica Media

   Middle layer

   Contains concentric sheets of smooth muscle
    in a framework of loose connective tissue.
              Tunica Media


   Collagen fibers bind the tunica media to
    the tunica interna and tunica externa.

   The thickest layer in the wall of a small
    artery is the tunica media

   The tunica media is separated from the
    tunica externa by the External Elastic
    Membrane.
         Tunica Externa

Tunica Externa (tunica adventitia)

    Outermost layer

    Contains collagen fibers with scattered
     bands of elastic fibers.

    Blends into the connective tissue of
     adjacent tissue.

    In the veins it is thicker than the tunica
     media and contains networks of elastic
     fibers and bundles of smooth muscle
     cell.
                        Artery versus Vein
        Feature                  Typical Artery                 Typical Vein

General Appearance          Round with thick wall.        Collapsed or flattened with
in Sectional View                                         relatively thin wall.

Tunica Interna

Endothelium                 Usually rippled due to vessel Smooth
                            constriction.
Internal Elastic Membrane   Present                       Absent
Tunica Media                Thick dominated by smooth     Thin dominated by smooth
                            muscle and elastic fibers.    muscle and elastic fibers.
External Elastic Membrane   Present                       Absent.

                                                          Collagen, elastic and
Tunica Externa              Collagen and elastic fibers
                                                          smooth muscle fibers.
                      Artery


Properties of Arteries:

   Elasticity – allows passive changes in vessel
    diameter in response to changes in blood
    pressure.

   Contractility – gives them the ability to
    change diameter actively primarily under
    the control of the sympathetic division of
    the autonomic nervous system.
                       Contractility

                           SNS




Vasoconstriction   =                   =   Vasodilation
   Contractility

     Vasoconstriction




1. Afterload
2. Blood Pressure
3. Capillary blood flow
   Contractility

       Vasodilation




1. Afterload
2. Blood Pressure
3. Capillary blood flow
                    Artery


Type of Arteries:

   Elastic (conducting) arteries

   Muscular (distribution) arteries

   Arterioles (resistant vessels)
          Elastic Arteries


Elastic (conducting) arteries

   Diameter up to 2.5 cm

   Transport large volume of artery from
    the heart.
                Elastic Arteries



   Walls have high density of elastic fibers and
    few muscle fibers.

   Resilient wall.
             Elastic Arteries



   Tolerate pressure changes that occur during
    the cardiac cycle.

   Examples are the Pulmonary and aortic
    trunks and their branches.
Elastic Arteries

    Ventricular
      systole




     BP rises




                              Cushions the
                              Sudden rise in
                              pressure
                  Expansion
        Elastic Arteries

                             Ventricular
                              diastole




                              BP falls




Slows the drop
in pressure
                    Recoil
              Muscular Artery


Muscular (distribution) arteries

   Distribute blood to the skeletal muscle and
    internal organs

   Lumen diameter approximately 0.4 cm.
            Muscular Artery



   Thick tunica media containing more smooth
    muscle cell than that of Elastic artery.

   Examples are External Carotid arteries,
    Brachial arteries and Femoral arteries.
                 Arterioles

Arterioles (resistant vessels)

   Internal diameter < 30 micrometer

   Poorly defined tunica externa

   Tunica media in the larger arterioles consist
    of one or two layers of smooth muscle.

   The tunica media of the smallest arterioles
    contains scattered smooth muscle that do
    not form complete layers.
              Resistance


   The force opposing blood flow is called
    resistance (R).

   Arterioles are called resistance vessel.
           Resistance Vessels
           Smaller Muscular Arteries
                       &
                   Arterioles




                                       Resistance




Increase
  SNS
           Resistant Vessels
           Smaller Muscular Arteries
                       &
                   Arterioles



                                       Resistance




Decrease
  O2
              Capillaries

   Thin walled

   Permits exchange between blood and
    interstitial fluid.

   Slow blood flow allowing sufficient time for
    diffusion and active transport.
              Capillaries


   Consist of an endothelial tube inside a
    delicate basement membrane.

   There is no tunica media or externa

   Measures 8 micrometer in diameter.
              Capillaries


There are two types of capillaries

   Continuous capillaries

   Fenestrated capillaries.
    Continuous Capillaries

   Found in all tissues except epithelia and
    cartilage.

   Permits diffusion of water, small solutes and
    lipid soluble materials into the surrounding
    interstitial fluid.
    Continuous Capillaries



   Allow vesicular transport of substance.

   Prevents the loss of blood cells and plasma
    proteins.
    Fenestrated Capillaries

Fenestrated capillaries.

   Contains pores that span the endothelial
    lining.

   Permit rapid exchange of water and solutes
    as large as small peptides, between plasma
    and the interstitial tissue.
    Fenestrated Capillaries



   Found in choroid plexus of the brain and in
    endocrine organs (hypothalamus, pituitary,
    pineal and thyroid glands

   Located along absorptive areas of the
    intestinal tract and at filtration sites in the
    kidneys.
               Sinusoids


   Resembles fenestrated capillaries

   Have gaps between adjacent endothelial
    cells.

   Thin or absent basement membrane.

   Blood moves through them very slowly
    maximizing the time available for exchange
    across the sinusoidal walls.
            Capillary Bed

   Capillaries do not function as individual
    units.

   Function as part of an interconnected
    network called a capillary bed or capillary
    plexus.

   A single artery give rise to dozens of
    capillaries that empty into several venules.

   The entrance to each capillary is guarded by
    a band of smooth muscle called a pre-
    capillary sphincter.
                 Capillary Bed




Contraction of                    Relaxation of
 Pre-capillary                    Pre-capillary
  Sphincter                         Sphincter




         Reduced Flow     Increased flow
            Capillary Bed

Capillary bed contains

   Metarteriole – initial segment of passage
    way containing smooth muscles capable of
    changing diameter

   Thoroughfare channel – distal part of the
    passage way.

   Arteriovenous anastomosis – direct
    connections between arterioles and venules.
              Vasomotion



Cycling of contraction and relaxation of smooth
muscles that changes blood flow through
capillary bed.
              Vasomotion


Controlled by

    concentration of chemicals

    concentration of dissolved gasses

in the interstitial fluid.
                    Veins


   Veins collect blood from all tissues.

   Walls thinner than corresponding arteries.

   Larger in diameter than corresponding
    arteries.
                 Veins


   Pressure in veins are lower.

   Thinner wall and lower portion of smooth
    muscle – more distensible.

   Expand easy – Capacitance vessels.
    Types of Veins


   Venules

   Medium-Sized Veins

   Large Veins
              Types of Veins
Venules

   Collect blood from the capillaries

   Varying widely in size and character

   Average internal diameter is 20 µm

   Venules < 50 µm lacks a tunica media
         Types of Veins

Medium-Sized Veins

   Range from 2 to 9 mm

   Comparable in size to muscular arteries.

   Thin tunica media with few smooth muscle
    cells.

   Thickest layer is the tunica externa – contains
    longitudinal strands of elastic and collagen
    fibers.
         Types of Veins


Large Veins

   Includes SVC, IVC and their
    tributaries.

   All tunica layers are present.

   Slender tunica media is surrounded by
    a thick tunica externa.
               Valves


   Folds of the tunica interna

   Projects from the vessel wall

   Points in the direction of blood flow
                   Valves


   Permits blood flow in one direction.

   Prevents backflow of blood towards the capillary.

   Compartmentalize the blood – dividing the weight
    of the blood between the compartments.
                         Physiology

                                  Lungs
                                Capillaries


  Pulmonic Circulation                                Pulmonic Circulation
       Arterial                                            Venous




                           Heart           Heart
                         Right side       Left Side




Systemic Circulation              Body Tissue              Systemic Circulation
      Venous                       Capillaries                   Arterial
                        Pulmonic         Pulmonic     Systemic Circulation
Systemic Circulation
                       Circulation      Circulation        Left Side
     Right Side
                        RT Lung           LT Lung         Head, Neck
    Head, Neck
    Upper Limb                                            Upper Limb
      Thorax                                                Thorax




                         Systemic Circulation
                              Abdomen
                             Lower Limbs
                        Pulmonic       Pulmonic
Systemic Circulation   Circulation    Circulation   Systemic Circulation
     Right Side         RT Lung         LT Lung          Left Side
    Head, Neck                                          Head, Neck
    Upper Limb                                          Upper Limb




                          Systemic Circulation
                             Thorax, Body
                              Lower Limbs

				
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