Lecture 4 unit 1

Question 1

how does ventricular systole start?

Answer 1

when depolarized cardiac muscle fibers in the ventricles begin to contract, causing an increase in pressure within the ventricles and a rapid closing of the AV valves

Question 2

what is the result of ventricular systole?

Answer 2

ejection of blood into circulation

Question 3

what happens in ventricular diastole?

Answer 3

starts when depolarized ventricular muscle reduces contraction to the point that blood is no longer ejected into circulation, causing a rapid closing of the semilunar valves

Question 4

what is the result of ventricular diastole?

Answer 4

passive filling of the ventricles

Question 5

what is atrial systole?

Answer 5

very brief 
(ventricular filling is largely passive)

Question 6

what happens in atrial diastole?

Answer 6

begins when ventricular systole begins

Question 7

what is CO (cardiac output)?

Answer 7

the volume of blood pumped by the ventricles in a given unit of time

Question 8

was is the formula for Cardiac Output?

Answer 8

CO (L/min) = stroke volume (L/beat) x heart rate (beats/min)

Question 9

what is the stroke volume (SV) at rest?

Answer 9

0.07 L/beat

Question 10

what is the heart rate (HR) at rest?

Answer 10

75 beats/min

Question 11

what is cardiac output at rest?

Answer 11

5.25 L/min

Question 12

what are the determinants of stroke volume (SV)?

Answer 12

1. aortic (or pulmonary artery) blood pressure. AKA the “after load”
2. end diastolic volume or “preload”
3. active or passive contractility

Question 13

the ventricles can’t eject blood into thee aorta or pulmonary artery until what?

Answer 13

the pressure in the ventricle exceeds the pressure in the artery

Question 14

What does an increase in pressure have a major impact on?

Answer 14

the work of the heart and on the stroke volume

Question 15

What kind of pumps are the cardiac chambers?

Answer 15

mechanical pumps

Question 16

what do the cardiac chambers pump?

Answer 16

only what is delivered to them

Question 17

what is “preload” slang for?

Answer 17

“end-diastolic volume”

Question 18

what does the “preload” or “end-diastolic volume” have a major impact on?

Answer 18

stroke volume

Question 19

stroke volume cannot increase unless what?

Answer 19

the rate of cardiac filling also increases

Question 20

what is contractility?

Answer 20

the strength of cardiac muscle contraction

Question 21

is contractility active or passive?

Answer 21

both

Question 22

what is active contractility

Answer 22

stimulation of the sympathetic nerves to the heart

Question 23

what is passive contractility

Answer 23

the result of changing the length of the cardiac muscle fibers (“Frank-Starling mechanism”)

Question 24

what is the result of the action of norepinephrine or epinephrine?

Answer 24

• increased rate of pacemaker activity

- increased force fo cardiac muscle contraction

Question 25

what happens in active contractility

Answer 25

-the AP invades the t-tubules, and calcium is released from the sarcoplasmic reticulum

Question 26

what else does norepinephrine increase?

Answer 26

the calcium permeability of the plasma membrane (the sarcolemma) in cardiac muscle, letting in more Ca2+

Question 27

what is the result of active contractility?

Answer 27

the number of actin/myosin cross bridge interactions is increased

Question 28

sympathetic nerve endings release norepinephrine which initiates what?

Answer 28

a cyclic AMP second messenger system inside cardiac muscle cells in order to increase contractility

Question 29

what does the "Frank-Starling" mechanism refer to?

Answer 29

the relationship between the rise in stroke volume and the rise in preload

Question 30

what happens if the preload is increased

Answer 30

EVEN IN A HEART WITH NO NERVE SUPPLY, the stroke volume will increase systematically

Question 31

what is the typical cardiac sarcomere length?

Answer 31

1.9 micrometers