3.5 Cardiac cycle

what happens in the P wave?

SA node fires, causes atrial depolarization

what happens in the QRS complex?

1. when atrial depolarization complete after P wave, the impulse is delayed at the AV node

2. at QRS complex, ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs

what happens after QRS complex but before T wave?

ventricular depolarization is complete

what happens during the T wave?

ventricular repolarization occurs which begins at apex

during ECG, what is the P-R interval?

time from beginning of atrial excitation to beginning of ventricular excitation

during ECG, what is the S-T segment?

entire ventricular myocardium is contracted because cardiomyocytes are in plateau phase of AP

during ECG, what is the Q-T interval?

time from beginning of ventricular depolarization through end of ventricular repolarization

ECG

pressure change: what happens in ventricular filling (mid-to-late ventricular diastole)?

blood flows passively from atria to ventricles

near the end of diastole, atria contract to maximize blood volume in ventricles

pressure change: what happens in isovolumic contraction (early vs. systole)?

period of rapid pressure increase between AV valve closure and semilunar valve opening as ventricles contract

pressure change: waht happens in ventricular ejection (mid-to-late v. systole)?

semilunar valves open and blood is ejected into aorta/pulmonary trunk

pressure change: what happens in isovolumic relaxation (early vs. diastole)

period of rapid pressure decrease between semilunar valve closure and AV valve opening as ventricles relax

Volume changes and stroke volume (SV): what is volume like at end-diastolic volume?

volume of blood is highest aat end of diastole

what is volume like at end-systolic volume?

volume of blood is lowest at end of systole

what is stroke volume (SV) and equation?

volume of blood ejected from a ventricle

SV = EDV - ESV

what is equation for ejection fraction?

SV/EDV x 100%

what is cardiac output (CO)?

volume of blood pumped out of each ventricle in one minute

equation for cardiac output CO

heart rate (beats/min) x stroke volume (volume/beat)

what is resting heart rate?

75 beats/min

what is resting stroke volume?

70 ml/beat

what is resting cardiac output CO?

75 beats/min x 70 ml/beat = 5250 ml/min or 5.25 L/min

approximate blood volume is what and that means entire blood passes though heart how fast?

adult blood volume is about 5 L so entire blood passes through heart in under 1 minute

what influences cardiac output?

changes in either SV, HR, or both

what system is major regulator of Heart Rate HR?

AUTONOMIC NERVOUS SYSTEM

what is released in sympathetic division and what does the release do?

releases norepinephrine as neurotransmitter

membrane potential is closer to threshold (more positive) so HR increases

what is released in parasympathetic division and what does that cause?

releases ACh as neurotransmitter where membrane potential is farther from threshold (more negative) so HR decreases

factors affecting HR: what releases epinephrine and what does that do to HR?

epinephrine is released by adrenal glands in response to sympathetic stimulation which increases HR

Factors affecting HR: what releases thyroxine and and does that do to HR?

thyroid gland releases thyroxine and increases HR

how does exercise impact HR?

Increases HR

how does heat impact HR?

increases HR

what is tachycardia?

abnormally fast resting heart rate (more than 100 beats/min)

what can cause tachycardia?

high body temp, stress, heart disease, or certain drugs

what is bradycardia?

abnormally slow resting heart rate (less than 60 beats/min)

what can cause bradycardia?

low body temp, high parasympathetic stimulation, or certain drugs

how can exercise cause bradycardia?

exercise-induced cardiovascular training due to hypertrophy of heart muscle

• greater force of contraction so increased SV

• slower HR maintains adequate CO with increased SV

affecting SV: what is preload?

degree to which cardiomyocytes are stretched just before contraction