Cardiac Cycle Flashcards
Cardiac cycle
Consists of a series of mechanical events, pressures & volume changes in the hearty during a heartbeat
Systole
Contraction phase of the cardiac cycle
When the heart muscle is squeezing
Diastole
Relaxation phase of the cardiac cycle
When the chambers of the heart open like they’re dilating
Ventricular filling
Occurs during mid-to-late ventricular diastole
- atrioventricular valves open
- semi lunar valves are closed
- Atria contract during the end of ventricular diastole, propelling final blood volume into the ventricles
End diastolic volume
The volume of blood in each ventricle at the end of ventricular diastole
Ventricular systole
Atria relax and ventricles contract.
atrioventricular valves close and semilunar valves open
- Isovolumetric contraction (all valves are closed)
- ventricular ejection (semilunar valves open due to high ventricular pressure)
- End systolic volume (volume remaining in each ventricle after systole)
Isovolumetric relaxation
Occurs during early diastole, ventricular pressure drops, semilunar valves close then atrioventricular valves open.
- Dicrotic notch: a brief rise in blood pressure due to back flow of blood in the aorta and pulmonary trunk
Heart sounds
First lub: closure of the atrioventricular valves during ventricular systole
S1: sound of the tri/bicuspid valves closing
Second dub: closure of the aortic and pulmonary semilunar valves during ventricular diastole
S2: sound of the pulmonary and aortic semilunar valves closing
Heart murmurs
Extraneous heart sounds due to turbulent back flow of blood through a valve that doesn’t fully close (an incompetent valve) or doesn’t fully open (stenotic valve)
Cardiac output
The amount of blood pumped out of a ventricle per minute
- Product of strocke volume and heart rate
** CO = HR x SV **
HR - number of heart per minute
Normal resting cardiac output = 5.25 L/min
Maximal CO in nonathletic people (20-25L/min)
in athletic people ( 35L/min)
Stroke volume
Volume of blood pumped out by one ventricle in each heart beat, roughly = 70mL
- Represents the difference between the end diastolic volume and the end systolic volume
Cardiac reserve
Difference between the resting & maximal cardiac output
Average adult heart rate = 75 BPM
Frank-Starling law of the heart
The critical factor controlling stroke volume is preload - the degree of stretch of cardiac muscle cells immediately before they contract
- venous return to the heart ios the most important facto determining the degree of cardiac muscles stretch
End diastolic volume
The amount of blood in the ventricle during diastole
- Affected by the length of ventricular diastole & venous blood pressure (120mL/ beat)
End systolic volume
The volume of blood remains in in the ventricle after contraction is complete
- Is affected bu arterial blood pressure & the force of ventricular contraction (50mL/ beat)
Normal SV = 120mL (EDV) - 50mL (ESV) = 70mL/beat
Contractility
The contractile strength of a muscle
Increasing cytoplasmic [Ca2+] leads to more myosin-actin cross-bridge formations & increases muscle contractility
After load
The ventricular pressure that must be overcome before blood can be ejected from the heart.
Doesn’t become a signification factor for stroke volume except in hypertensive individuals
What does increased contractility do?
This lowers end systolic volume
- Positive inotropic agents (thyroxine, epinephrine, digitalis etc) increase heart contractility
Heart rate regulation
- Sympathetic stimulation of pacemaker cells increased heart rate & contractility by increasing Ca2+ movement into the cell
- Parasympartheticinhibition of cardiac pacemaker cells decreases heart rate by increasing membrane permeability to K+
Congestive heart failure
Occurs when the pumping efficiency of the heart is so low that blood circulation cora not meet tissue needs
Pulmonary congestion
- Occurs when the left side of the heart fails but the right side continues to pump blood into the lungs.
- Blood isn’t taken back into the left side of the hear and accumulated int he lungs = pulmonary edema & can lead to suffocation
Pulmonary edema
Excess fluid in body cavities/tissues
also called dropsy short for hydropsy
