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Cardiovascular control mechanism

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									Cardiovascular control
     mechanism

        黃基礎
  Introduction
• Control of blood volume and
  arterial pressure results in
  that all of the organs receive
  sufficient blood flow.
                  Central
                 controller
 Sensory nerve                Sympathetic nerve
                              Parasympathetic n



  Sensor                         Effector

Changes in BP                 Heart and arteriole
Circulatory control system
   Sensors
• The animal body employs a variety of
  receptors for monitoring the status of
  the cardiovascular system.
• There are two main baroreceptors
  aortic baroreceptor via vagus nerve
  carotid baroreptor via sinus nerve
An increase in blood pressure stretches
the wall of the carotid sinus, causing an
increase in discharge frequency from the
baroreceptors.
 Chemoreceptors
Increase   +
               Chemorecpeotr
 in CO2

               vasoconstriction


           A rise in arterial pressure
   Cardiac receptors
• Atrial receptors

                          Increase in          Increase in
       Increase in BP                          atrail filling
                        venous pressure




                                                Stimulate the
                                               atrial receptors




         Reduction in                          Inhibition of
         blood volume      Leasd to diuresis   ADH release
   Cardiac receptors
• Atrial receptors

                          Increase in           Increase in
       Increase in BP                           atrail filling
                        venous pressure




                                                   Strtch
                                              the the atrial wall



                         Cause an increase
         Reduction in   In urine production   Cause atial myocytes
         blood volume       and sodium          to secrete ANP
                             excretuib
                    ANP
    _



Renin      ADH      Reduce    Reduce   Antagonize the
                                       pressor effect of
release   release   Cardiac     BP       angiotensin
                    Output
 Central nervous system
• Medullaray CV center
  1. Pressor and depressor center
  2. Cardioaccerator center
  3. Cardioinhibitory center
 Central nervous system
• Autonomic nervous system (ANS)
  1. Sympathetic preganglionic
  fibers arise from cell bodies in
  the IML of the spinal cord of the
  thoracodorsal regions
• Autonomic nervous system (ANS)
  2. The stellate ganglion supplies
  postganglionic sympathetic fibers
 to the heart
 3. All of preganglionic sympathetic
 fibers are cholinergic but the
 postganglionic sympathetic fibers
 are adrenergic or cholinergic
• Parasympathetic nervous system
  1. The primary effect of the
  parasym. n. s. on CV function
  is to slow the heart rate.
  2. Impulses conducted by the
  vagus nerve affect the S-A node,
  A-V node and reduce artial
  contractivitility
Neural
pathways for
thr BP control
NTS: nucleus
tractus of the
solitarius
Medullary cardiovascular center
Control of microcirculation
• Capillary blood flow has to be
  adjusted to meet the demands of
  the tissue.
• Two control mechanisms
  1. Neural control
  2. Local control
Neural control of capillary blood flow

• Sympathetic stimulation and catcholamine
    Stimulation of
    alpha receptors      vasodilatation

    Stimulation of
    beta receptors        vasoconstriction

    Vasoconstriction activated by  -adrenergic
    receptors would override vasodilatation by  -
    adrenergic receptors
• Neuropeptide Y
  1. co-localized with norepinephrine within
  sympathetic ganglion and adrenergic nerve
  2. nerve endings that surrounded the atrial and
  ventricular myocytes and the coronary arteries
  contain neuropeptide Y
  3. NPY decrease coronary blood flow and the
  contraction of cardiac muscle by reducing the
  level of IP3
• Parasympathetic stimulation cause to
  vasodilation in arterioles
Local control of capillary blood flow

 • Endothelium-produced compounds
   endothelium can produce NO, endothelin,
   and prostacyclin to affect the activity of the
   smooth muscle and hence, to regulate the
   capillary blood flow
 Endothelium-derived
    relacing factor                      Muscle
                         cGMP
   (now known NO)                       relaxation
Local control of capillary blood flow

 • Endothelin can produce vasoconstriction
   prostacyclin can initiate vasodilation and
   act as an anticoagulant. Prostacyclin
   functions as an antagonist of the
   thromboxane A2 ,which promotes blood
   clotting and causes vasoconstriction.
   Influammators and other mediators
   thromboxane A2 cause vasoconstriction
   histamine and kinin produce vasodilatation
• Histamine, bradykinin, and serotonin cause an
  increase in capillary permeability

• Metabolic condition associated with activity
  decrease in O2, increase in CO2, and H+, a
  variety of metabolites (adenosine) , heart, rise
  in extracellular K+ , NO, prostacyclin
  all of the above substances produce
  vasodilation and a local increase in capillary
  blood flow.

								
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