control of cardiac output

Question 1

what is cardiac output (CO)

Answer 1

its the volume of blood pumped by EACH ventricle per minute

Question 2

what is the CO equation

Answer 2

CO= HR (Heart rate) X SV (Stroke volume)

Question 3

what is stroke volume

Answer 3

the volume of blood (mL) ejected per contraction

Question 4

what is the SV equation

Answer 4

end-diastolic volume - end systolic volume

Question 5

how is CO controlled

Answer 5

control of HR and SV

Question 6

The strength of cardiac muscle contraction and, accordingly SV can be graded by:

Answer 6

1. Varying the initial length of the cardiac muscle fibres, which in turn depends upon EDV (intrinsic control)
2. Varying the extent of sympathetic stimulation (extrinsic control)

Question 7

The strength of cardiac muscle contraction and, accordingly SV can be graded by:

Answer 7

1. Varying the initial length of the cardiac muscle fibres, which in turn depends upon EDV (intrinsic control)
2. Varying the extent of sympathetic stimulation (extrinsic control)

Question 8

Intrinsic control of SV depends on the direct correlation between EDV and SV.

Answer 8

As more blood returns to the heart, the heart pumps out more

Question 9

what does intrinsic control depend on

Answer 9

the length-tension relationship of cardiac muscle, which is similar to that of skeletal muscle

Question 10

What causes cardiac muscle fibers to vary in length before contraction?

Answer 10

 Increased EDV, the more the heart is stretched.
 The more the heart is stretched, the longer the initial cardiac fiber length before contraction.
 The increased length results in a greater force on the subsequent cardiac contraction and thus in a greater stroke volume

Question 11

what does EDV stand for

Answer 11

end-diastolic volume

Question 12

what is the frank-starling law of the heart

Answer 12

The heart normally pumps out during systole the volume of blood returned to it during diastole; increased venous return results in increased stroke volume

Question 13

what are the two major advantages of intrinsic relationship matching SV with venous return

Answer 13

1) Equalising output between the left and right sides of the heart.
2) When a larger CO is required, e.g. during exercise, venous return is increased through the action of the sympathetic NS. The resulting increase in EDV automatically increases SV.
 Exercise also increases HR so these two factors act together to increase CO so more blood can be delivered to the exercising skeletal muscles.

Question 14

what are some cellular basis of the frank starling mechanism

Answer 14

1. Greater initial length increases the sensitivity of contractile proteins in the myofibrils to Ca2+
2. Increased initial fiber length may also increaseCa2+ release from the sarcoplasmic reticulum

Question 15

what allows for the semilunar valves to open and allow the ejection of blood

Answer 15

when the ventricles contract and they must generate sufficient pressure to exceed the blood pressure in the major arteries

Question 16

why is arterial blood pressure called the afterload

Answer 16

because it is the workload imposed on the heart after the contraction has begun