Lecture 18a: Heart Physiology ❤️⚡

What are the three main closed circuits that generate pressure for blood circulation?

systemic, pulmonary, coronary

What type of circulation has little resistance due to proportional myocardial thickness?

pulmonary circulation

Which type of circulation has higher pressures and lots of resistance to overcome?

systemic circulation

What are the three layers of the heart wall?

epicardium, myocardium, endocardium

What is myocardium?

thick muscular layer that allows for heart contraction

What are the main types of cells in the myocardium?

contractile, pacemaker/conducting

What are cardiac myocytes?

specialized muscle cells that make up the heart’s pumping function

How does myocardium act in syncytium?

branched cells connected by intercalated disks

What is the primary function of pacemaker cells?

Create and control heart rate

What is the primary function of contractile cells?

muscle cells that actually contract and pump blood

What is the primary function of conducting cells?

make up electrical pathways to ensure coordinated contraction

What part of the cardiac conduction system has the fastest depolarization rate?

SA node

What happens when the SA node generates an electrical signal?

signal travels through the internodal pathways

What is the effect of an electrical signal passing through the internodal pathways?

atrial myocardium contracts

What happens to an electrical signal at the AV node?

signal delays to allow atria to contract first

What is the role of purkinje fibers/ventricular myocardium in the conduction pathway?

cause ventricles to contract

What is the role of papillary muscle in the conduction pathway?

prevent AV valve prolapse and terminate signal

What is the pacemaker potential phase?

slow NA+ influx below threshold

What happens at the rapid depolarization phase of pacemaker physiology?

Ca++ voltage gated channels open at threshold

What happens at peak depolarization of pacemaker physiology?

voltage gated K+ channels open for outflux and repolarization

What is the effect of the sympathetic NS on pacemaker potential?

increases slope via NE/E opening Ca++ channels

What is the effect of the parasympathetic NS on pacemaker potential?

decreases slope via Ach opening K+ channels

What effect does NE have on pacemaker beta 1 receptors?

increases heart rate

What effect does NE have on ventricular myocardial beta 1 receptors?

increases force of contraction

What is the effect of Ach on muscarinic receptors of the heart?

decreases heart rate and contractibility

Which neural pathway is associated with sympathetic control of the heart?

cardiac nerve

Which neural pathway is associated with parasympathetic control of the heart?

vagus nerve

What causes the initial membrane depolarization in contractile cells?

fast Na+ channels open

What causes the plateau phase during excitation of contractile cells?

slow Ca++ channels open

What is the “pump” for coronary circulation?

aorta

What is the “pump” for pulmonary circulation?

pulmonary trunk/right ventricle

What is the “pump” for systemic circulation?

left ventricle

What is repolarization?

return of a cell to its negative resting membrane potential

What is hyperpolarization?

change in resting membrane potential to a more negative value

What is depolarization?

change in resting membrane potential to a less negative value

What is the effect of the plateau phase of contractile cell action potential?

prolonged depolarization (contraction/refractory period)

What causes the repolarization phase of contractile cell action potentials?

Ca++ and Na+ channels close while K+ exit the membrane

What are P waves in ECG?

atrial depolarization

What is the QRS complex in ECG?

ventricular depolarization

What are T waves in ECG?

ventricular repolarization

What is the Q-T interval in ECG?

entire duration of ventricular AP

How long is the Q-T interval in ECG?

0.36-0.44s

What is the S-T segment in ECG?

ventricular plateau phase

How long is the S-T segment in ECG?

0.12-0.2s