Comparative Vertebrate Physiology Regulation of cardiac output and blood pressure

Cardiac output Increasing preload pressure increases heart rate and stroke volume

Cardiac output Cardiac output = HR x SV e.g. Humans: 80 beats/min. x 0.07l/beat = 5.6 l/min

Cardiac output Most of the increase in C.O. is due to HR and not SV

Starling’s law Cardiac muscle is much shorter than its optimum length The great the filling of the heart, the greater the amount pumped by the heart

Control of cardiac output Heart is innervated by the ANS

Control of cardiac output Sympathetic Norepinephrine (Na+ and Ca+ + influx) Parasympathetic Acetylcholine (K+ efflux)

Blood pressure Determined by: Mean arterial pressure = CO x TPR cardiac output vascular resistance (TPR) blood volume Mean arterial pressure = CO x TPR

Changes in blood pressure

Blood pressure regulation Short term Control of heart rate Vascular resistance Altering blood flow Altering vessel diameter

Blood pressure regulation Vasodilation Blood pumped faster Venous return Muscle pump Respiratory pump

Blood pressure regulation Long term (days) Changes in blood volume (kidneys)

Blood pressure regulation Baroreceptors Nerve endings detect stretch Most important (aortic arch, carotid arteries) Information relayed to the brain

Blood pressure in divers Air breathing vertebrates Bradycardia Reduction in cardiac output

Blood pressure in divers

Blood pressure in divers Blood pressure unaffected Vasoconstriction and shunting