6b Cardiac Cycle And Output Flashcards
What are the ways in which the heart is regulated?
By the intrinsic conducting system
By the nervous system: specifically the autonomic nervous system
What effect does the autonomic nervous system have on heart activity?
Acts as a brake or accelerator to increase or decrease heart rate
What is a cardiac cycle?
One complete heart beat in which both atria and ventricles contract AND relax
What are the words used to describe contraction and relaxation in a cardiac cycle?
Systole: contraction
Diastole: relaxation
What are the main events of a cardiac cycle?
1, atrial diastole
2, atrial systole
3, isovolumetric contraction
4, ventricular systole
5, isovolumetric relaxation
Describe the first event in a cardiac cycle.
Atrial diastole
Heart and all chambers are relaxed
Pressure is low
Blood flows passively into atria and ventricles
AV valves are open
Semilunar valves are closed
Describe the second event of a cardiac cycle.
Atrial systole
Ventricles remain in diastole (relaxed)
Atria contract which forces the blood in the atrium to complete ventricular filling
Describe the third step of a cardiac cycle.
Isovolumetric contraction
Atrial systole ends
Ventricular systole begins
Intraventricular pressure rises
AV valve closes
In this step, in this moment, all the valves are closed and the blood is trapped, causing great pressure
Describe the fourth event of a cardiac cycle.
Ventricular systole/ ejection phase
Ventricles continue to contract because the intra ventricular pressure surpasses the pressure in the major arteries
Semilunar valves open
Blood leaves the ventricles
Atria are relaxed and filling with blood
Describe the fifth event in a cardiac cycle.
Isovolumetric relaxation
Ventricular diastole begins causing the pressure to fall below that of major arteries
Semilunar valves close
In this moment in this event, all chambers are closed
AV valves are still open
What is the difference between the isovolumetric contraction event and the ventricular systole event in a cardiac cycle?
Isovolumetric contraction defines the instance where ventricular systole BEGINS and where the ventricles are completely closed chambers
Ventricular systole defines the process at which the ventricles continue contracting to EJECT the blood from the ventricles
During what to phases/ events is the heart comprised of 4 separate chambers?
Isovolumetric contraction (3) and isovolumetric relaxation (5)
Define the spikes found on a typical ECG.
First peak: P, marks atrial depolarization (contraction/systole). Triggered by the SA node.
Second peak: QRS complex, ventricular depolarization (contraction/systole),
Third peak: T, relaxing/ repolarization of the ventricles
What is the flatline between P and Q on an ECG?
The delay between the SA and AV node activation
What does the dip Q on an ECG represent?
Activation of the AV node
What is cardiac output?
The amount of blood pumped by the blood in 1 minute
What is the equation for cardiac output?
CO= stroke volume x heart rate
What is stroke volume?
Teh volume of blood discharges from one ventricle with each contraction
Average for men is 70 mL
What kind of factors can affect your cardiac output?
Increase or decrease in the following:
Physical or emotional trauma
Body temperature
Exercise
Blood pressure
Hemorrhage
Hormones
Crises
What does Starlings law state?
More stretch in myocardial fibers= stronger contraction which directly affects stroke volume
What is one way to increase stroke volume and cardiac output?
Exercise or any activity that will increase venous return will leads to a volume increase in the heart during diastole
This added stretch results in a stronger contraction (starlings law) and consequently an increased stroke volume and cardiac output
Does stroke volume have any effect on resting heart rate?
Yes
Higher the stroke volume the lower the resting heart rate because more blood is being circulated per pump
How do muscle contractions of skeletal muscle increase venous return?
The contractions put pressure on the veins which directs blood down its path faster
It can only go one way due to teh valves
When relaxed, there isn’t as much pressure affecting the vein and blood
What role does the sympathetic nervous system play in the neural regulation of heart rate?
Nerves stimulate the SA and AV nodes and cardiac muscle to increase HR during physical activity or emotional stress
Role: they control the rate, even if they dont control the beating itself
What role does the parasympathetic nervous system play in neural regulation of heart rate?
Right vagus nerve acts on SA node to slow and steady the heart when not in a crisis
Again, affects rate of beats, not teh fact that it beats
Where are the neurons that can control heart rate located and how do they detect it?
In the medulla oblongata
Detect through baroreceptors/ pressorecetors/ stretch receptors
Where are the receptors that detect changes in heart rate and report to the nervous system found?
Baroreceptors
Carotid sinus and aorta
Respond to the medulla
Where is the cardioacceleratory center located and what does it do?
Medulla oblongata
Stimulates the heart by sending impulses to the SA and AV nodes and the ventricular myocardium
What effect does the cardioacceleratory center have on the nodes of the heart?
It sends impulses to the AV and SA nodes that result in a depolarization of the nodes
This means that they are less negative and are more likely to fire an impulse
What affect does the cardioacceleratory center have on the ventricular myocardium of the heart?
Increases contractility to increase force and consequently volume of contraction
Where is the cardioinhibitory center located and what does it do?
Medulla
Sends impulses via the right vagus nerve to the SA and AV nodes and the atrial myocardium
What structure releases what substance onto the heart by order of the cardioinhibitory center?
Right vagus nerve
Acetylcholine
What affect does acetylcholine have on the heart?
It hyperpolarizes teh resting membrane potential (makes more negative) which decreases the probability of firing impulses
What is the normal vagal tone?
Slow and regular rhythm set my you cardioinhibitory centre but more specifically your vagus nerve
Resting HR
What was vagusstoffs discovery?
That the heart was not strictly electrically controlled, there is also a chemical component
Where is teh cardiac control center?
Medulla
What effect can the hypothalamus have on the heart rate if it is stimulates with exciting news?
Strong emotion allows for teh hypothalamus to override that medulla temporarily
This increases rate of depolarization of SA and AV nodes and increases the contractility of the heart muscle
What higher brain centers can input to the cardiovascular system?
Cerebral cortex
Limbic system
Hypothalamus
What affect does epinephrine and ions have on heart rate?
Mimics sympathetic nerve action
Increases heart rate
What effect does thyroxin have on heart rate?
Thyroid hormone
Increases heart rate by acting on cardiac muscle
What effect does Ca2+ have on heart rate?
Too much: cardiac muscle stops contracting
Too little: contractions are prolonged and heart could stop
What effect do K+ and Na+ levels have on heart rate?
Must be regulated for Heart contractions
Low k results in irregular and low rhythms
What physical factors can affect regulation of heart rate?
Age, gender, exercise, body temperature
Does higher body temperature raise or lower heart rate?
Raise
What is the cardiac reserve?
Refers to teh hearts ability to quickly adjust to immediate demands
The max % that the cardiac output can increase above normal
What influences the cardiac reserve?
Increase in stroke volume AND inc in heart rate
