#08 Heart III

Question 1

Cardiac Cycle

Answer 1

• A cardiac cycle is the time from the start of one heartbeat to the initiation of the next.

Question 2

Systole vs. Diastole

Answer 2

• Systole is contraction of a heart chamber.
• Diastole is relaxation of a heart chamber.

Question 3

How Is Cardiac Cycle Driven?

Answer 3

• Cardiac cycle is driven by pressure, traveling from area of high pressure to low pressure.

Question 4

Step 1 of Cardiac Cycle: Atrial Systole

Answer 4

○ A brief contraction of atrial myocardium initiated by SA node. Before this, ventricles were being passively filled with blood to 70% of full volume. Atrial contraction “tops off” ventricles and fills it up to EDV.

Question 5

End Dialostic Value

Answer 5

§ EDV means end diastolic volume, 130 mL. It is the total volume of the ventricle.

Question 6

Importance Of Ventricles Being Able To Be Passively Filled

Answer 6

§ The passive filling of the ventricle makes it possible for the heart to be able to function without contraction of the atria, though not as much blood would be pumped.

Question 7

Step 2 of Cardiac Cycle: Early Ventricular Systole

Answer 7

○ As you push blood into ventricle, pressure inside ventricle climbs up. Increased pressure will cause it to start contracting. But the semilunar valve remains close, so these are isolvolumic contractions. Ventricles contract, but volume isn’t changing.
○ Atria are in diastole and are passively filling with blood.

Question 8

• Step 3 of Cardiac Cycle: Late Ventricular Systole

Answer 8

○ When pressure in ventricle surpasses pressure in atrium, that is the signal to open up the semilunar valves. Now ventricle produces isotonic contraction, contracting AND pushing out blood.

Question 9

Stroke Volume

Answer 9

○ The blood being ejected by the ventricle during step 3 of cardiac cycle is called the stroke volume.

Question 10

End Systolic Volume

Answer 10

○ Not all the blood is pushed out of ventricle during late ventricular systole and the volume of blood remaining in the ventricle is called the end systolic volume.

Question 11

How To Calculate Stroke Volume

Answer 11

• Stroke Volume is calculated by the difference between End Diastolic Volume (EDV, amount of blood in ventricle following atrial systole) and End Systolic Volume (ESV, blood remaining in ventricle following isotonic contraction).

Question 12

Step 4 of Cardiac Cycle: Early Ventricular Diastole

Answer 12

○ Still have ESV inside blood. We now have isolvolumic relaxation, which is going to lower the pressure. When pressure in ventricle is lower than pressure in artery, the semilunar valves will close. Atria are still filling.

Question 13

Step 5 of Cardiac Cycle: Late Ventricular Diastole

Answer 13

○ Pressure has fallen very low in ventricle, while atria continuously fills with blood and increases pressure. Ventricle fills passively back to 70% EDV when the AV valves open.

Question 14

Cardiac Output

Answer 14

• Cardiac Output is the Stroke Volume (mL/beat) multiplied by Heart Rate (beats/min), numerical representation of amount of blood pumped a minute. Normal number is 6L per min in humans.

Question 15

How Is Cardiac Output Controlled?

Answer 15

It is regulated by the autonomic innervation, although the conductive cells are autorhythmic so they produce electrical signals automatically. The RATE is what is being controlled.

Question 16

Regulating Cardiac Output: SNS

Answer 16

○ Sympathetic Nervous System: From the cervical and thoracic ganglia we have the cardiac nerve coming off. The signals themselves are coming from the brain, in the medulla there is a cardioacceleratory center. The catecholamines like epinephrine and norepinephrine are from fight or flight response of sympathetic nervous system, and they generally serve to increase rate of heart beat.

Question 17

Regulating Cardiac Output: PNS

Answer 17

○ Parasympathetic Nervous System: Acetylcholine is the main neurotransmitter. They have a cardioinhibitory center, and use the vagus nerve as pathway from it to the heart. Innervates heart and releases acetylcholine onto the myocytes.

Question 18

Cardioacceleration: Cateholamines

Answer 18

○ Catecholamines: Epinephrine and norepinephrine. They bind to beta-adrenergic receptors G-protein coupled receptors.

Question 19

Cardioacceleration Process

Answer 19

○ So catecholamines bind to beta-adrenergic receptors, increasing catalayse cyclase activity, bringing up levels of cyclic AMP. The increased cAMP brings about activation of protiein Kinase A, PKA. It modulates every step in pathway of this process. Can increase amount of calcium coming in from L-type calcium channel, increase amount coming out through RyR, can change sensitivity of myofilaments altering interaction between calcium and troponin, and change how quickly calcium can travel back into the SR. Getting calcium back into SR is just as important as increasing calcium at the beginning so another contraction can occur.

○ All types of myocytes have these beta-adrenergic receptors and they will respond to the catecholamines.

Question 20

Cardioacceleration: Targets

Answer 20

○ Targets
§ LTCC –> More Calcium Entry
§ Ryanodine Receptor –> More Calcium Release
§ Phospholamban –> Increases SERCA (SR) Activity

Question 21

Cardioinhibitory Process

Answer 21

○ The parasympathetic nervous system lowers levels of cAMP, or open up potassium channels, making potassium come out of cell. So when trying to fire action potentials, need to depolarize, but the open potassium channels makes it harder to depolarize. Both contractile and conductive cells.