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Cardiovascular system physiology (Introduction - COP - conductive system)




Cardiovascular

                                                                   
 Introduction  :

The main function of the heart is to supply the body with blood. This activity can be assessed with measurable parameters, including heart ratestroke volume, and cardiac output.


very important term must be define :

1.  Heart rate:
The number of heart contractions per minute. 
The normal heart rate atrest: 60–100 beat/minute. 
2.  Stroke volume (SV): 
the volume of blood pumped by the left or right ventricle in a single heartbeat
SV = end-diastolic volume (EDV) − end-systolic volume (ESV
3.  Ejection fraction:  
the proportion of EDV ejected from the ventricle
4.  Venous return
the rate at which blood flows back to the heart, which typically  equals cardiac output

Cardiac output

the volume of blood the heart pumps through the circulatory system per minute
                                              ( ∼ 5 L/min at rest)

  • (Cardiac output (CO) = heart rate (HR) × stroke volume (SV)

                                                                                                                                  Measurement:
    • Via Fick principleCardiac output is proportional to the quotient of the total body oxygen consumption and the difference in oxygen content of arterial blood and mixed venous blood.
      • Cardiac output (CO) = oxygen consumption rate/arteriovenous oxygen difference (O2 consumption)/(arterial O2 content − venous O2 content) 
    • Via mean arterial pressure (MAP): MAP = cardiac output (CO) × total peripheral resistance (TPR)
      • Mean arterial pressure (MAP) = 1⁄3 systolic blood pressure (SP) + ⅔ diastolic blood pressure (DP) = (SP + 2 x DP)/3
  • As HR increases, diastole is shortened, which decreases CO due to less filling time.

5. Volumetric flow rate
the volume of blood that flows across a valve per second 




     Conduction system of the heart  :  


Definition: the collection of nodes and specialized conduction cells that initiate and coordinate contraction of the heart muscle

 Sinoatrial node  : 

Found on  Upper wall of the right atrium at the junction where the SVC enters    
     Characteristics: 
              Natural pacemaker center of the heart with specialized pacemaker cells  
          
  • Spontaneously generates electrical impulses that intiate heart


  •   Influenced by autonomic nervous system 
  •   Supplied by sinus node artery (branch of the right coronary artery)

Atrioventricular node: 

 Found within the AV septum (superior and medial to the opening of the coronary sinus in the right atrium)

   Characteristics  :

  •  Receives impulses from the SA node and passes these impulses to the bundle of His

  •  Has the slowest conduction velocity
  •  Delays conduction for 60–120 ms (allowing the ventricles to fill with blood; without this delay, the atria and ventricles would contract at the same time)
  •  Supplied by the AV nodal artery (posterior descending artery of right coronary artery)

   Bundle of His:

 Found directly below the cardiac skeleton, within the membranous part of the interventricular septum.
  


     Characteristics:


  •  Receives impulses from the AV node
  •  Splits into left and right bundle branches (Tawara branches) → the right bundle travels to the right ventricle; the left bundle splits into an anterior and a posterior branch to supply the left ventricle → terminate into terminal conducting fibers (Purkinje fibers) of the left and right ventricle
  •   Prevents retrograde conduction
  •  Filters high-frequency action potentials so that high atrial rates (e.g., in atrial fibrillation) are not conducted to the myocardium


Purkinje fibers:

Terminal conducting fibers in the subendocardium .

Characteristics 

  •  Conduct cardiac AP faster than any other cardiac cells
  •  Ensure synchronized contraction of the ventricles
  • Purkinje fibers have a long refractory period 
  •  Form functional syncytium: forward incoming stimuli very quickly via gap junctions to allow coordinated contraction.


     

 







                                                                                       

                                
                             

                     

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