Circulatory & Respiration Flashcards
Increase in venous return results in an increase in _____, which lengthens cardiac fibers, which improves the force of contractility, resulting in an increase in _____.
- End-Diastolic BP
2. Stroke Volume
End-Diastolic Volume
(Preload)
How much blood is in the left ventricle before it squeezes
Factors of Venous Return
- Venoconstriction
- Muscle Pump
- Respiratory Pump
Venoconstriction
Reduces the volume capacity of the veins to store blood –> blood moves toward heart
Muscle Pump
When muscles contract during exercise, they compress veins & push blood back toward the heart
Respiratory Pump
During inspiration, pressure in the thorax decreases & the abdominal pressure increases. This creates a flow of venous blood from the abdominal region into the thorax = venous return
Predominant factor of venous return.
Stroke Volume
Volume per beat
Stroke Volume is regulated by?
- End-Diastolic Volume
- Afterload (Aortic BP)
- Strength of ventricular contraction (Contractility)
Preload
The pressure on the wall of the heart
**more blood = more pressure
Afterload
The pressure on the aortic semilunar valve (Diastolic BP)
Overcoming the pressure to open the semilunar valves
Stroke Volume in relation to Afterload
SV is inversely proportional to the Afterload; increase in aortic pressure produces a decrease in SV
Contractility
How hard the heart squeezes
Mechanisms of Contractility
- the effect of epinephrine & norepinephrine
- direct sympathetic stimulation by cardiac accelerator nerves
Both increase the Calcium available to the myocardial cell
Ejection Fraction
The percentage of blood pumped out of a filled ventricle during contraction.
The greater the EF, the greater the Stroke Volume which increases Cardiac Output.
Cardiac Output
Volume of blood pumped to the body per minute
Q= HR * SV
Heart Rate
Beats per minute
Isovolumic Contraction
The pressure increases while volume stays the same
Surfactant
Lowers the surface tension of the alveoli & prevents its collapse