The Cardiac Cycle Flashcards
The Cardiac Cycle
all of the events associated with one heart beat
Systole
Contraction (muscles contract; squeeze on blood)
-Depolarization (membrane potential gets +, action potential occurs) triggers systole
Diastole
Relaxation
-Repolarization (action potential goes away) triggers diastole
Length of the Cardiac Cycle
- 8 seconds (75 beats per minute
- 5 liters per minute
3 Main Periods of the Cardiac Cycle
- Atrial Systole
- Ventricular Systole
- Relaxation Period
Period of the Cardiac Cycle: Atrial Systole
How Long? What do the atria and ventricles do?
length: 0.1 seconds
Atria- systole (contract)
Ventricles- diastole (relax)
Period of the Cardiac Cycle: Ventricular Systole
How Long? What do the atria and ventricles do?
length: 0.3 seconds
Atria- Diastole (relax)
Ventricles- Systole (contract)
Period of the Cardiac Cycle: Relaxation Period
How long? What do the atria and ventricles do?
length: 0.4 seconds
Atria- diastole (relax)
Ventricles- diastole (relax)
Atrial Systole
Atria contract (no heart sound)
- both contract shortly after P wave
- AV valves remain open
- SL valves remain closed
- ventricles continue filling
Ventricular Systole
blood pumped out of the heart
- both ventricles contract shortly after QRS wave
- AV valves close (1st heart sound)
- Isovolumetric contraction period occurs in beginning
- SL valves open
- blood enters aorta and pulmonary arteries
Relaxation Period
ventricles fill with blood
- ventricles relax shortly after T wave
- SL valves close (2nd heart sound)
- Isovolumetric relaxation period occurs in beginning
- AV valves open in middle of period
- blood fills ventricles
Isovolumetric
constant volume of blood in ventricles; all 4 valves closed
- isovolumetric contraction
- isovolumetric relaxation
Isovolumetric Contraction
brief period at beginning of Ventricular Systole
-ventricles contract while valves closed
Isovolumetric Relaxation
brief period at the beginning of relaxation period
-ventricles relax while valves closed
Venous Return
blood is returned, continuously pumped into the atria (L + R atria)
-causes AV valves to open
Cardiac Output
amount of blood pumped out of each ventricle per minute
-CO = HR X SV
HR= heart rate
SV= stroke volume
Factors affecting HR (heart rate)
- Parasympathetic Division- decreases HR to resting conditions; slows down HR, “rest + digest”
- Sympathetic Division- increases HR and stimulates adrenal medulla to release epinephrine & norepinephrine; speeds up HR, “fight or flight”
Parasympathetic Division
- decreases heartrate to resting conditions
- decreases cardiac output
- “rest + digest”
Sympathetic Division
- increases heart rate
- stimulates adrenal medulla to release epinephrine & norepinephrine
- increase cardiac output
Stroke Volume
amount of blood pumped out of each ventricle per heart beat
Factors affecting Stroke Volume
- Preload
- Contractility
- Afterload
Factor affecting Stroke Volume: Preload
degree of stretch of heart muscle
- Frank-Starling law of the heart
- when heart muscle is stretched more, heart contracts more forcefully and more blood will be pumped
- increase preload, increase stroke volume, increase cardiac output
Factor affecting Stroke Volume: Contractility
increase in contractile strength over and above preload
(increase in contractility strength independent on muscle strength)
-sympathetic increase contractility, increase stroke volume, increase cardiac output
Factor affecting Stroke Volume: Afterload
back pressure exerted on SL valves by arterial blood
- increase afterload, decrease stroke volume, decrease cardiac output
- hypertension (high blood pressure, pressure in arteries to high)
The Cardiovascular Centers are located in the?
Medulla Oblongata
