Week 5 - Cardiac structure and Function Flashcards

1
Q

Brief outline of the journey of blood in the heart.

A

Right atrium receives blood from super and inferior vena cava.
Travels to right ventricles via tricuspid valve.
Goes into pulmonary circulation via the pulmonary artery and returns to the left atrium via the pulmonary vein.
Then into left ventricle through the mitral valve and ejected through aorta into systemic circulation.

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2
Q

What are the 3 structures of the heart wall?

A

1) Epicardium
2) Myocardium
3) Endocardium

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3
Q

Describe the characteristics and function of the 3 structures that make up the heart wall.

A

Epicardium
- Characteristics: serous membrane including blood capillaries, lymph capillaries and nerve fibers
- Function: serves as a lubricative outer cover.

Myocardium:
- Characteristics: cardiac muscle tissue separated by connective tissues and includes blood capillaries, lymph capillaries and nerve fibers
- Function: provides muscular contractions that eject blood from the heart chambers.

Endocardium
- Characteristics: endothelial tissue and a thick subendothelial layer of elastic and collagenous fibers
- Function: serves as protective inner lining of the chambers and valves.

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4
Q

The heart receives blood supply (oxygen and nutrients) via what arteries?

A

coronary arteries - it has a high demand for oxygen and nutrients

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5
Q

Myocardial infarction (MI) and influence of exercise.

A

Blockage in coronary blood flow which results in cell damage.

Exercise training protects against heart damage during an MI.

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6
Q

Structural differences between heart muscle and skeletal muscle.
1) Nuclei
2) Neural control
3) Calcium store
4) Shape of muscle fibers
5) Regeneration potential
6) Energy production

A

1) Nuclei: heart muscle has single, whereas skeletal has multiple
2) Neural control: heart is involuntary and skeletal voluntary
3) Calcium store: heart sources are SR and extracellular calcium, skeletal is SR
4) Shape of muscle fibers: heart has shorter muscle fibers and have branching, skeletal is elongated - no branching.
5) Regeneration potential: heart has none (no satellite cells) whereas skeletal has some possibilities via satellite cells.
6) Energy production: heart is aerobic (primary) whereas skeletal muscle is aerobic and anaerobic

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7
Q

The contraction of the heart depends on the electrical stimulation of…
a) Epicardium
b) Myocardium
c) Endocardium

A

Myocardium

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8
Q

Cardiac automaticity

A

when the heart can generate its own action potentials

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9
Q

What are the two types of cells in the heart?

A

Nodal cells (e.g. SA node, AV node - makes up 1%) and muscular cells (actin, myosin)

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10
Q

What is the intrinsic regulation of the heart controlled by?

A

SA node - pacemaker and initiates depolarization by generating AP.

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11
Q

Atrioventricular node (AV node)

A

Passes depolarization to ventricles and has a brief delay to allow for ventricular filling.

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12
Q

What are the two mechanistic reasons for AV node having a brief delay for ventricular filling?

A

1) There are less gap junctions at the AV node so conduction moves slower through.
2) Diameter of the cells are smaller in the AV node so slows conduction.

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13
Q

Bundles branches / Bundle of His

A

branch that connects the atria to left and right ventricle - travels down the septum

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14
Q

Purkinje fibers

A

spread wave of depolarization throughout the ventricles

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15
Q

Describe the 4 steps of the conduction system of the heart.

A

1) Action potentials originate in the sinoatrial (SA) node and travel across the wall of the atrium from the SA node to the atrioventricular (AV) node.

2) There is a slight pause in the AV node to allow for ventricular filling. APs then pass through the AV node and along the AV bundle, which extends from the AV node, through the fibrous skeleton, into the interventricular septum.

3) The Atrioventricular (AV) bundle divides into right and left bundle branches, and APs descend to the apex of each ventricle along the bundle branches.

4) APs are carried by the Purkinje fibers from the bundle branches to the ventricular walls.

Bundle branches become depolarized, the ventricles contract, the ventricular pressure increases, and blood exits the ventricles.

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16
Q

In electrocardiograms (ECG), what do the following represent:
a) P wave
b) QRS complex
c) T wave

A

a) atrial depolarization
b) ventricular depolarization and atrial repolarization
c) ventricular repolarization

17
Q

What is the rate of the intrinsic pacemaker?

A

100bpm

18
Q

Describe the cardiac cycle.

A

1) Atrial diastole: fill with blood from vena cava/pulmonary vein.
2) Ventricular diastole: AV valves (tricuspid and mitral valves) opens and fills with blood.
3) Atrial systole: atria contracts squeezing any leftover blood into ventricles (P wave).
4) Ventricular diastole: AV valve shuts. As the ventricles contract, ventricular pressure increases causing the aortic valve (semilunar valve) to open and blood to be ejected out the aorta into the systemic circulation.
5) Isovolumetric relaxation of the ventricles (all valves closed).

19
Q

What is the relationship between intraventricular pressure and ECG?

A

Intraventricular pressure rises as ventricles contract - Q to R

Intraventricular pressure falls as ventricles relax - R to S

20
Q

What does S-T segment depression on ECG during exercise suggest?

A

myocardial ischemia - lack of oxygen supplying cardiac muscle which means calcium ions aren’t taken up into SR.

21
Q

What is the graded exercise test?

A

the diagnostic use of ECG during exercise to measure cardiac function and changes in bp (e.g. coronary artery disease)

22
Q

What is a potential cause of myocardial ischemia?

A

atherosclerosis - fatty plaque that narrows coronary arteries which reduces blood flow and oxygen to myocardium

23
Q

How is regular exercise cardioprotective?

A
  • Reduces incidence of heart attacks.
  • Improves survival from a heart attack.
24
Q

How does exercise reduce the amount of myocardial damage from heart attack?

A
  • Improves heart’s antioxidant capacity.
  • Improved function of ATP-sensitive potassium channels.
25
Q

Identify the 2 nervous systems that extrinsically regulate HR and explain how they increase/decrease HR?

A

Autonomic NS:

1) PNS via vagus nerve which slows HR by inhibiting SA and AV node (via acetylcholine which binds to muscarinic 2 receptor. This activates G-inhibiting protein which gets potassium to exit the cell and this reduces AP and HR.)

2) SNS via cardiac accelerator nerves which increases HR by stimulating SA and AV node (via norepinephrine which binds to beta-1 adrenergic receptor which causes more calcium to come into the cell which increase the AP and subsequent HR. Also increases force of contraction).

Although the heart can generate AP by itself, when it needs to slow down or increase HR a bit more, the SNS and PNS influence its regulation.

26
Q

How does heart rate increase as exercise intensity increases?

A

Initially there is parasympathetic withdrawal that increases HR. Then we get sympathetic outflow for the further increase in HR.

27
Q

What are two key characteristics of the cardiac muscle (myocardium)?

A
  1. Highly oxidative
  2. Very dense network of capillaries
28
Q

At rest, what % does the heart receive of 5L-min of cardiac output?

A

5% = 0.25L-min

29
Q

In exercise, what % does the heart take of 25L-min of cardiac output?

A

5% = 1.25L-min

30
Q

In the heart, what is the % of oxygen extraction at rest and during exercise?

A

At rest = 65-75%
Exercise = +90%

31
Q

Although oxygen extraction increases during exercise, what is increased oxygen delivery to the heart mainly reliant upon?

A

an increase in coronary blood flow - important in delivery of oxygen and nutrients to the heart muscle

32
Q

What is oxygen consumption by the heart principally required for?

A

Contraction
- requirements for maintaining basal metabolism comprises of only 10-20% of total oxygen consumption.

33
Q

Explain the metabolic factors that control coronary circulation/blood flow.

A

The main metabolic vasodilator of coronary blood vessels is adenosine (from ATP breakdown), there is also some b-adrenergic vasodilation via ANS.

34
Q

What % of coronary flow takes place during diastole? Why?

A

80% - because of vessel compression (contraction) during systole which reduces blood flow

35
Q

During heavy exercise, what % of coronary flow occurs during systole? Why?

A

40-50% - this is because we have less time in diastole (filling) due to a greater HR

36
Q

Which circulation requires a greater mean pressure to deliver blood and return it to the heart? Why?

A

Systemic circulation - it has a greater resistance to flow therefore to achieve the same blood flow through the body tissues as through the lungs (pulmonary circulation), it requires a mean pressure that is 4x greater.

37
Q

During exercise, what happens to the time spent in diastole and systole?

A

Its decreases, with the greatest decrease occurring in diastole

38
Q

Stroke volume continues to increase during incremental exercise up to what % of V02max?

A

40% of V02max