Chapter 19 last part

Coronary circulation vs. systemic circuit

Coronary circulation is part of the systemic circuit; the other main division is the pulmonary circuit

One-way valves and atrial systole

There are no valves at the openings of the venae cavae or pulmonary veins

Blood entry into ventricles

About two-thirds of ventricular filling happens before atrial contraction; atria add ~31% more

Vagus nerve effects

Vagus nerves reduce heart rate but do not affect ventricular contraction strength

Carbon dioxide (CO₂; Carbon Dioxide) and pH effects on heart rate

High carbon dioxide (CO₂) and low pH increase heart rate

First heart sound timing

The first heart sound occurs during the QRS complex, not the P wave

Nerve severance effect

The heart has its own pacemaker and will continue beating; nerves only modify heart rate

Pulmonary arteries clamped

Pulmonary edema results from clamping pulmonary veins, not arteries

Cardiomyocyte resting potential

Cardiomyocytes have a stable resting membrane potential when at rest

Electrocardiogram (ECG; Electrocardiogram) meaning

An electrocardiogram (ECG) is a composite record of electrical activity from the whole myocardium, not a single action potential

Verapamil (calcium channel blocker) effect

Blocks slow calcium channels; reduces calcium ion (Ca²⁺; Calcium Ion) influx into cardiomyocytes; leads to negative inotropic effect (weaker contractions) because calcium ion (Ca²⁺) is essential for contraction strength

Carotid artery massage for tachycardia

Stimulates baroreceptors in the carotid sinus; increases vagal (parasympathetic) output to heart; lowers heart rate and helps restore normal sinus rhythm

Ventricular septal defect (VSD; Ventricular Septal Defect) effects

Left-to-right shunt due to higher left ventricular pressure; increases pulmonary blood pressure (more blood pushed to lungs); slightly lowers systemic blood pressure; long-term: right ventricular hypertrophy due to increased pulmonary resistance

Ventricular systole timing difference

Left ventricle has thicker, stronger walls → takes longer to build pressure; right ventricle has thinner walls → reaches expulsion pressure faster; pulmonary valve opens sooner than aortic valve because of lower pulmonary pressure

Dilated cardiomyopathy and mitral regurgitation

Enlarged left ventricle stretches the mitral valve ring; valve cusps cannot close tightly during systole; causes blood regurgitation from left ventricle back into left atrium during contraction