2C & 2D: Regulation of Cardiac Output via HR & Stroke volume

Question 0

What happens in the parasympathetic N. system?

Answer 0

The SA NODE, Atria, AV NODE, have vagal innervation. Neurotransitter= ACh (acts on muscarinic receptors)

Question 1

What factors are affecting HR?

Answer 1

In parasympathetic N. system–> Negative chronotropic effect

In Sympathetic N. system–> Positive chronotropic effect

Question 2

True or False ?SA node, atria, AV node and ventricles have sympathetic innervation (via T1-T4)

Answer 2

True

Question 3

What are other factors affecting HR?

Answer 3

Epinephrine/NE from adrenal medulla exert similar effects as SNS.

-Important during exercise, stress, & excitement

Question 4

What are other factors that affect HR?

Answer 4

1) thyroid hormones (T3 & T4); Elevates HR @ rest
2) Ions (Hyperkalemia & Hypokalemia can both DECREASE HR)
3) Age, gender, physical fitness, body temp

Question 5

Factors that affect Stroke Volume?

Answer 5

1) PRELOAD (via Frank-Starling Mechanism)*******
2) Isotropism (cardiac contractility)
3) AFTERLOAD

Question 6

What is preload ?

Answer 6

• “load or “stretch: on the ventricular muscle BEFORE it contracts
• Directly influenced by EDV
• ****Effects of preload are confirmed by the “Frank-Starling Law of the Heart”

-within physiological limits, the more the ventricles are filled during diastole, the more blood they eject during systole (i.e The greater the preload the greater the force of contraction)

Question 7

In regards to Preload what is this type of control of SV referred to ?

Answer 7

Heterometric regulation

Question 8

What is the Frank-Starling Law of Heart based on?

Answer 8

-Length-Tension relationship on the ventricle.

• Increases in EDV causes an increase in ventricular fiber length–> increase in developed tension
• May enhance the affinity of Troponin C for Ca++ & increase Ca++ uptake & release from the SR.
• This increases the contraction when the muscle fiber length increases

Question 9

What is Inotropism?

Answer 9

An increase in cardiac contractility is an increase in contractility strength that is independent of Starling’s Law

Question 10

The SNS has a __________ ionotropic effect on the heart

Answer 10

positive

*Causes an increase in SB at a constant preload. Lower ESV and greater SV = HOMOMETRIC REGULATION

Question 11

What is the AFTERLOAD?

Answer 11

The “load” the heart must overcome after (and while) it contracts

-The BACK PRESSURE exerted on the aortic & pulmonary semilunar valves by arterial blood in the aorta & pulmonary trunk.

Question 12

What happens during an Increase and decrease of afterload?

Answer 12

Increase: The ventricle must pump blood against a higher pressure, resulting in a Decrease in stroke volume .

Decrease: The venrticle pumps blood against a lower pressure, resulting in an increase stroke volume.

Question 13

What are example of increased afterload?

Answer 13

-Vasoconstriction (increases BP)
-Increased blood volume or viscosity (inc. BP)
-Vasodilators used to decrease afterload thereby decreasing myocardial oxygen demand.
EXAMPLE: Nitrostat

Question 14

What is cardiac out enchanced by?

Answer 14

1) Preload (increase)
2) Inotropy (increase)
3) HR (increase)
4) Afterload (decrease)

Question 15

Whereas cardiac output or performance is depressed by?

Answer 15

1) decrease preload
2) decreased inotropy
3) decreased HR
4) increase Afterload

Question 16

What does the Ventricular Pressure Volume Loops represent? 1–>2, 2–>3, 3—>4, 4–<1

Answer 16

1–> 2 isovolumetric contraction
2–>3 ventricualr ejection
3–>4 isovolumeteric relaxation
4–>1 Ventricular filling