6b Cardiac Cycle And Output

Question 1

What are the ways in which the heart is regulated?

Answer 1

By the intrinsic conducting system
By the nervous system: specifically the autonomic nervous system

Question 2

What effect does the autonomic nervous system have on heart activity?

Answer 2

Acts as a brake or accelerator to increase or decrease heart rate

Question 3

What is a cardiac cycle?

Answer 3

One complete heart beat in which both atria and ventricles contract AND relax

Question 4

What are the words used to describe contraction and relaxation in a cardiac cycle?

Answer 4

Systole: contraction
Diastole: relaxation

Question 5

What are the main events of a cardiac cycle?

Answer 5

1, atrial diastole
2, atrial systole
3, isovolumetric contraction
4, ventricular systole
5, isovolumetric relaxation

Question 6

Describe the first event in a cardiac cycle.

Answer 6

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

Question 7

Describe the second event of a cardiac cycle.

Answer 7

Atrial systole
Ventricles remain in diastole (relaxed)
Atria contract which forces the blood in the atrium to complete ventricular filling

Question 8

Describe the third step of a cardiac cycle.

Answer 8

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

Question 9

Describe the fourth event of a cardiac cycle.

Answer 9

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

Question 10

Describe the fifth event in a cardiac cycle.

Answer 10

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

Question 11

What is the difference between the isovolumetric contraction event and the ventricular systole event in a cardiac cycle?

Answer 11

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

Question 12

During what to phases/ events is the heart comprised of 4 separate chambers?

Answer 12

Isovolumetric contraction (3) and isovolumetric relaxation (5)

Question 13

Define the spikes found on a typical ECG.

Answer 13

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

Question 14

What is the flatline between P and Q on an ECG?

Answer 14

The delay between the SA and AV node activation

Question 15

What does the dip Q on an ECG represent?

Answer 15

Activation of the AV node

Question 16

What is cardiac output?

Answer 16

The amount of blood pumped by the blood in 1 minute

Question 17

What is the equation for cardiac output?

Answer 17

CO= stroke volume x heart rate

Question 18

What is stroke volume?

Answer 18

Teh volume of blood discharges from one ventricle with each contraction
Average for men is 70 mL

Question 19

What kind of factors can affect your cardiac output?

Answer 19

Increase or decrease in the following:
Physical or emotional trauma
Body temperature
Exercise
Blood pressure
Hemorrhage
Hormones
Crises

Question 20

What does Starlings law state?

Answer 20

More stretch in myocardial fibers= stronger contraction which directly affects stroke volume

Question 21

What is one way to increase stroke volume and cardiac output?

Answer 21

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

Question 22

Does stroke volume have any effect on resting heart rate?

Answer 22

Yes
Higher the stroke volume the lower the resting heart rate because more blood is being circulated per pump

Question 23

How do muscle contractions of skeletal muscle increase venous return?

Answer 23

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

Question 24

What role does the sympathetic nervous system play in the neural regulation of heart rate?

Answer 24

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

Question 25

What role does the parasympathetic nervous system play in neural regulation of heart rate?

Answer 25

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

Question 26

Where are the neurons that can control heart rate located and how do they detect it?

Answer 26

In the medulla oblongata Detect through baroreceptors/ pressorecetors/ stretch receptors

Question 27

Where are the receptors that detect changes in heart rate and report to the nervous system found?

Answer 27

Baroreceptors Carotid sinus and aorta Respond to the medulla

Question 28

Where is the cardioacceleratory center located and what does it do?

Answer 28

Medulla oblongata Stimulates the heart by sending impulses to the SA and AV nodes and the ventricular myocardium

Question 29

What effect does the cardioacceleratory center have on the nodes of the heart?

Answer 29

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

Question 30

What affect does the cardioacceleratory center have on the ventricular myocardium of the heart?

Answer 30

Increases contractility to increase force and consequently volume of contraction

Question 31

Where is the cardioinhibitory center located and what does it do?

Answer 31

Medulla Sends impulses via the right vagus nerve to the SA and AV nodes and the atrial myocardium

Question 32

What structure releases what substance onto the heart by order of the cardioinhibitory center?

Answer 32

Right vagus nerve Acetylcholine

Question 33

What affect does acetylcholine have on the heart?

Answer 33

It hyperpolarizes teh resting membrane potential (makes more negative) which decreases the probability of firing impulses

Question 34

What is the normal vagal tone?

Answer 34

Slow and regular rhythm set my you cardioinhibitory centre but more specifically your vagus nerve Resting HR

Question 35

What was vagusstoffs discovery?

Answer 35

That the heart was not strictly electrically controlled, there is also a chemical component

Question 36

Where is teh cardiac control center?

Answer 36

Medulla

Question 37

What effect can the hypothalamus have on the heart rate if it is stimulates with exciting news?

Answer 37

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

Question 38

What higher brain centers can input to the cardiovascular system?

Answer 38

Cerebral cortex Limbic system Hypothalamus

Question 39

What affect does epinephrine and ions have on heart rate?

Answer 39

Mimics sympathetic nerve action Increases heart rate

Question 40

What effect does thyroxin have on heart rate?

Answer 40

Thyroid hormone Increases heart rate by acting on cardiac muscle

Question 41

What effect does Ca2+ have on heart rate?

Answer 41

Too much: cardiac muscle stops contracting Too little: contractions are prolonged and heart could stop

Question 42

What effect do K+ and Na+ levels have on heart rate?

Answer 42

Must be regulated for Heart contractions Low k results in irregular and low rhythms

Question 43

What physical factors can affect regulation of heart rate?

Answer 43

Age, gender, exercise, body temperature

Question 44

Does higher body temperature raise or lower heart rate?

Answer 44

Raise

Question 45

What is the cardiac reserve?

Answer 45

Refers to teh hearts ability to quickly adjust to immediate demands The max % that the cardiac output can increase above normal

Question 46

What influences the cardiac reserve?

Answer 46

Increase in stroke volume AND inc in heart rate