The Heart as a Pump

Question 1

What are the functions of circulation?

Answer 1

Transport nutrients to body tissues
Waste away from the body
Hormones throughout the body
Homeostasis

Question 2

What is the difference between syncytium and gap junctions?

Answer 2

Syncytium cells joining electrical gap junctions-cytosol is continuous
Gap junctions (intercalated discs) specially fused cell membranes

Question 3

What is the purpose of the transmission of electrical signals by gap junctions and syncytium?

Answer 3

Forming a coordinated contraction of the ventricular tissue

Question 4

What are the two major difference between cardiac muscle and skeletal muscle?

Answer 4

Cardiac t-tubules have a diameter 5x that of muscle (increased volume)
Cardiac SR less developed than skeletal muscle

Question 5

Are gap junctions located between the atria and ventricles?

Answer 5

No, otherwise they would contract at the same time

Question 6

What is the importance of the chorda tendineae and papillary muscles?

Answer 6

Prevent bulging backwards during ventricular systole

Question 7

What is a benefit of the cardiac muscle’s ability to use Lactate as an energy source?

Answer 7

During brief ischemic conditions, the cardiac muscle can use lactate for energy

Question 8

When are the coronary arteries best perfused?

Answer 8

During diastole, the arteries can become compressed during systole

Question 9

How does the SNS affect the coronary arteries?

Answer 9

B2 outweighs A1 resulting in vasodilation (remember local responses can overrule neural responses)

Question 10

Why do we give CV patients B1 specific beta blockers?

Answer 10

If its non selective it can affect B2 (vasodilation thus alpha would win out and the vessels would constrict) B1 prolongs diastole thus perfusing the coronary arteries longer

Question 11

The period of time when the pressure is rising in the ventricle yet no volume is exiting

Answer 11

Isovolumic contraction, tension is increasing but little or no shortening of the muscle fibers is occurring

Question 12

There is no change in the volume of blood in the ventricle but there is a decrease in pressure

Answer 12

Isovolumic relaxation, eventually the pressure in the ventricle is less than that in the atria and thus AV valves open

Question 13

What causes the aortic valve to open?

Answer 13

The pressure in the ventricle exceeds the pressure in the aorta (90ish)

Question 14

What is the difference between isometric and isotonic muscles?

Answer 14

Isometric means the muscle length remains constant

Isotonic means the muscle tension remains constant

Question 15

Why does kinetic work increase in stenosis?

Answer 15

The cross sectional area through the aorta decreases meaning the velocity of ejection with be much higher for a given flow rate

Question 16

In a cardiac function curve what do lines I, II, III and IV indicate?

Answer 16

I: ventricular filling
II: isovolumic contration
III: ejection of blood from the ventricle to the aorta
IV: isvolumic relaxation

Question 17

The work required to move blood from veins to arteries?

Answer 17

External work (volume-pressure work)

Question 18

The work required to accelerate blood to the velocity of ejection

Answer 18

Kinetic energy

Question 19

What is the difference between skeletal muscle and cardiac muscle in the length/tension relationship?

Answer 19

There is a finite limit to the cardiac muscle, if you stretch the myocytes too much you will get diminished ventricular pressure (fibrous tissue of the pericardium)

Question 20

How do you calculate ejection fraction?

Answer 20

stroke volume/preload

Question 21

What does the area inside the cardiac function curves represent?

Answer 21

External work, the product of volume moved against a given pressure

Question 22

Define the Frank Starling mechanism.

Answer 22

Length/tension relationship, if preload increased the heart is able to pump the extra blood out (with greater cross bridge formation) and return to the same end systolic blood volume. There is however a limit to this mechanism

Question 23

Why is more oxygen used when systolic b/p is elevated?

Answer 23

O2 consumption is nearly proportional to the tension that occurs in the heart muscles during contraction