Cardiovascular Physiology Flashcards
Cardiac Output
Blood volume pumped in one minute → how efficiently the heart can meet the body’s demand for maintenance of adequate tissue perfusion.
4-6 L/min at rest.
Q = SV x HR → 70mL x 70 beats (min-1) = 4900mL
SV: Stroke volume
HR: Heart rate
If HR increases, SV will decrease to compensate.
Factors Affecting Heart Rate
Autonomic innervation
Hormones
Fitness level
Age
Factors Affecting Stroke Volume
Heart size Fitness level Gender Contractility Duration of contraction Preload (EDV) Afterload (resistance)
End Systolic Volume
Remaining blood after systole: 50 mL
Systolic stroke exerts 70 mL of blood out of the heart.
Afterload problem: too much blood left in LV after stroke (70 mL).
End Diastolic Volume
Remaining blood after diastole: 120 mL (heart is full)
Preload problem: not 120 mL in LV.
Ejection Fraction
Measure of pumping efficiency, used to classify heart failure.
Fraction of total blood volume ejected from LV during each contraction.
Stroke volume / end diastolic volume
70mL / 120mL = 0,58 = 58%
Frank Sterling’s Law
Correlation between filling and ejection fraction of the heart.
Increased venous return → increased filling of atria and ventricle → increased stretch of cardiac muscles → increased force of contraction → increased stroke volume.
Cardiac Changes in Physical Activity
Stroke volume: 50 to 70 mL Volume per minute from 5 to 20-25L/min Heart rate until 200 strokes/min Increase perfusion of skeletal and heart muscle. Vasoconstriction in inactive organs.
Drug Effects on Cardiovascular System
Chronotropic drugs: change heart frequency
Inotropic drugs: Change heart strength
Dromotropic drugs: Change electrical conduction
Cardiac Muscle Fibers
Striated, organized unto sarcomeres. Usually only contain one nucleus (in center of cell).
Many mitochondria and myoglobin.
ATP primarily produced through aerobic metabolism.
Cells extensively branched and connected to one another by intercalated discs (allows wave-like contraction → heart works like a pump).
Vagus Nerve
Parasympathetic.
Decreases heart rate.
Sympathetic Cardiac Nerve
Increases heart rate and force of contraction.
Timing of Excitation (SA node)
SA node - Action potential every 0.6 sec = 100b/min-1
At rest: SA node under influence of parasympathetic division via acetylcholine. AP every 0.8 sec = 75b/min-1
Exercise: SA node under influence of sympathetic division via adrenaline. AP up to maximal heart rate.
Lymph
Water, metabolic waste, electrolytes.
Circulation of lymphocytes, takes immune cells to target spot.
Veins
20 mmHg blood pressure All vessels that come to the heart. Return transport of low-oxygenated blood from the periphery back to the heart muscle pump (against gravity) venous valves: prevent backflow.
