Chapter 25 (Test #3)

Question 1

During Phase 0 of cardiac action potentials, how do the myocytes in the heart become stimulated to depolarize? is it slow or rapid?

Answer 1

The myocytes are stimulated to depolarize by sodium entering into the cell, this is a fast response action potential.

Question 2

During Phase 0 of cardiac action potentials, how do the SA and AV nodal cells get stimulated to depolarize? IS this a fast or slow process?

Answer 2

These cells are stimulated to depolarize when calcium enters the cells. This is a slow response action potential.

Question 3

What happens during Phase 0 of the cardiac action potential?

Answer 3

Positive ions influx into the cells, causing depolarization.

Question 4

What happens during Phase 1?

Answer 4

Early cellular repolarization begins as potassium exits the intracellular space.

Question 5

What happens during phase 2?

Answer 5

The plateau phase occurs

Rate of repolarization slows, calcium ions enter the cell.

Question 6

What happens during phase 3?

Answer 6

This is when the completion of repolarization occurs and the cell enters its resting state again. (potassium and sodium leave the cell)

Question 7

What happens during phase 4?

Answer 7

This is the resting phase before another depolarization occurs. (potassium enters cell again)

Question 8

`Describe automaticity.

Answer 8

This is the ability to generate an electrical impulse.

Question 9

Describe excitability.

Answer 9

This is an ability to respond to an electrical impulse.

Question 10

Describe conductivity.

Answer 10

This is the ability to transmit an electrical impulse from one cell to another.

Question 11

At what rate does the SA node fire? What is another name for the SA node?

Answer 11

60-100

primary pacemaker

Question 12

At what rate does the AV node fire? What is another name for the AV node?

Answer 12

40-60

Secondary pacemaker

Question 13

At what rate does the bundle of his, bundle branches, and purkinje fibers conduct impulses?

Answer 13

30-40

Question 14

Why is there a slight delay between the time the AV node receives the impulse from the SA node, and the time it relays the impulse to the ventricles?

Answer 14

This slight delay allows time for the atrias to contract to complete ventricular filling.

Question 15

Does is special about the left bundle branch?

Answer 15

The left bundle branch has to stimulate the largest chamber of the heart to contract, so it actually branch again into the left anterior and left posterior bundle branches.

Question 16

What is the terminal point of the cardiac conduction system? What does it specialize in?

Answer 16

The terminal point is the purkinje fibers, these purkinje cells rapidly conduct impulses through the walls of the ventricles to allow for an almost synchronous contraction.

Question 17

Does atrial systole account for most of the ventricular filling?

Answer 17

NO, it only accounts for 15-25%

passive ventricular filling is where its at

Question 18

Describe the the cardiac cycle (in detail!), starting with diastole.

Answer 18

The atrias are now filling the ventricles with blood through the AV valves that is returning through the vena cavae and the pulmonary vein, as this is happening the pressure inside the ventricles is increasing. At the end of passive filling the atrias will contract due to the transfer of an impulse from the SA to the AV node. After the last of the blood is filled into the ventricles the ventricles will begin to contract, as the pressure increases in the ventricles the AV valves will close, preventing regurg. As the pressure continue to increase the semilunar valves will open once the pressure exceeds that of the systemic or pulmonary circuit. At the the ejection of the blood will be rapid becuase of the large difference in pressurs, but eventually the pressures will decrease and then equalize at the end of ventricular systole. This will then cause the semilunar valves to close. The process is then repeated.

Question 19

What is cardiac output? Whats the normal value?

Answer 19

The amount of blood ejected by one of the ventricles per minute. 4-6L/min

Question 20

What is stroke volume? What is the normal value?

Answer 20

This is the amount of blood ejected by the heart per beat. 60-130 ml

Question 21

How is CO calculated?

Answer 21

CO= SV x HR

Question 22

How does the parasympathetic nervous system stimulate the SA node?

Answer 22

Vagus nerve (slows the HR)

Question 23

How does the the sympathetic nervous system innervate the SA node? What stimulates them?

Answer 23

beta-1 receptors in the SA node (increases HR)

Stimulated by catecholamines (secreted by the adrenal gland) and thyroid hormone that has catecholamine-like effects.

Question 24

How do baroreceptors affect CO?

Answer 24

In response to HTN, baroreceptors will send impulses to the cerebral medulla which will initiate parasympathetic activity and inhibit sympathetic response. This will lower HR and BP.

and the opposite is true for hypotension

Question 25

What are some ways pre-load is decreased? Increased?

Answer 25

Decreased: reduction of volume entering the ventricles, diuresis, venodilating agents, excessive loss of blood, dehydration. Increased: increasing return of blood to ventricles, controlling blood loss or body fluid loss, replacing fluids (IV fluids or blood transfusion)

Question 26

What is after load? What is the resistance against the left ventricle called? Right ventricle?

Answer 26

Afterload is the resistance of blood ejection from the ventricle, or what the ventricles have to push against. Left: systemic vascular resistance Right: Pulmonary vascular resistance

Question 27

What do preload and afterload dewtermine?

Answer 27

stroke volume

Question 28

What happens to afterload and SV during vasoconstriction?

Answer 28

Afterload increases and SV decreases.

Question 29

What happen to afterload and SV during vasodilation?

Answer 29

Afterload decreases and SV increases

Question 30

How is contractility depressed?

Answer 30

hypoxemia acidosis certain medicaitons

Question 31

How is contractility enhanced?

Answer 31

circulating catecholamines, sympathetic neuronal activity, certain medications

Question 32

In relation contractility, afterload, and preload, how would the heart achieve the highest SV?

Answer 32

Increased preload, increased contractility, and decreased afterload.

Question 33

What is ejection fraction? What is the normal value?

Answer 33

This is the percentage of end-diastolic volume that is ejected with each heartbeat. 55-65%

Question 34

At what ejection fraction should a patient be treated for HF?

Answer 34

less than 40%

Question 35

What are some age-related changes in cardiac function?

Answer 35

The heart will hypertrophy (causes a decrease in chamber size and contractility) The valves stiffen (cause backflow which causes murmurs) The heart cant compensate as well to metabolic needs, and may become fatigued, short of breath, and have palpitations due to stress, exercise, or illness. LOOK AT TABLE 25-1 ON p. 660

Question 36

What are some gender related characteristics of cardiac function?

Answer 36

Womens hearts are smaller and have more narrow coronary vessels, this makes procedures done with atheroscerosis more difficult (caths or angioplasty) Women have increased estrogen which increases HDL, decreases LDL, and dilates blood vessels (enhances blood flow to heart), this decreases their risk of getting CAD until menopause at around 50, then their estrogen slowly decreases until 65 when they are at an equal risk to men. women usually get CAD 10 years later than men

Question 37

Is hormone therapy in postmenopausal women a good idea to deter the development of CAD?

Answer 37

In the past it was thought to have been, but NO NO NO