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Physiology > Lecture 10: Functional anatomy of CV system > Flashcards

Lecture 10: Functional anatomy of CV system Flashcards

1
Q

How does the heart maintain homeostasis?

A

Provides potential energy (pressure)

Moves oxygen, nutrients, electrolytes, hormones to meet metabolic requirements

Removes waste (nitrogenous waste and carbon dioxide) that are by-products of oxidation

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2
Q

What is heart failure?

A

When the heart muscle is unable to contract optimally to pump blood (into systemic and/or pulmonary circulation) at a rate sufficient to meet the requirements of metabolizing organs

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3
Q

What is the incidence of heart disease?

A

Very high

Complications after onset of heart failure remains a primary cause of death in Canada and other developed nations

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4
Q

Different terminology for heart failure

A

Acute heart failure = cariogenic shock

Chronic heart failure = heart failure (used to be called congestive heart failure)

High output failure = high CO in heart failure

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5
Q

Symptoms of heart failure

A

Congestion in lungs results in breathlessness (main symptom of left-sided heart failure)

Fatigue, swelling in ankles and legs, enlargements of liver

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6
Q

Components of the CV system

A

1) The heart
2) The blood vessels
3) Blood itself

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7
Q

What is the heart?

A

A pump that serves to pressurize the arterial tree

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8
Q

In what direction does blood move in systemic circulation?

A

From an area of high pressure (left ventricle) to regions of lower pressure (capillary beds).

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9
Q

Where does a major loss of blood pressure occur?

A

Points of restriction within the arterial tree (arterioles)

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10
Q

What is the role of the blood vessels?

A

Serve as the delivery mechanisms for blood as it moves from the heart and for its return to the heart

Arteries: carry blood away from heart

Veins: carry blood to the heart

** naming is independent of the state of blood oxygenation

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11
Q

Two loops of the circulation

A

Blood travels continuously through the closed circulatory system via two separate loops which begin and end at the heart

Pulmonary circulation

Systemic circulation

Heart works as a dual parallel pump

See figure

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12
Q

Where does pulmonary circulation carry blood?

A

Between heart and lungs

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13
Q

Where does systemic circulation carry blood?

A

From the heart to all the peripheral organ systems (brain, liver, skeletal muscles, skin)

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14
Q

Shape and location of heart

A

Fist sized, hollow muscular organ

Located mid-chest between the sternum and the vertebrae

Left ventricle is a thick spiral and RV is an add on

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15
Q

What is the left side myth of the heart

A

Heart’s apex thumps the chest wall to the left of the sternum, so people concluded that the whole heart is located there

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16
Q

Chambers of heart

A

Upper: atria (receive returning blood and transfer to ventricles)

Lower: ventricles (pump blood from the heart)

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17
Q

What separates the two halves of the heart? Role?

A

Ventricular septum

Part of left ventricle

Directly contributes to cardiac pump function,

Prevents mixing of blood from the low oxygenated blood in the right and the highly-oxygenated blood in left side.

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18
Q

Where does systemic return enter the heart?

A

Right atrium via vena cava

Blood the flows into RV, which pumps the blood out via the pulmonary artery to the lungs, where it is oxygenated

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19
Q

Which side of the heart pumps blood into pulmonary circulation?

A

Right side

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20
Q

What happens to blood in the lungs? After the lungs?

A

Blood loses CO2 and gains O2 before returning to the LA via the pulmonary vein

Blood moves from LA to LV to the aorta and thus into the systemic circulation

See figure

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21
Q

Which loop of circulation does the left side of the heart handle?

A

Systemic

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22
Q

What does the aorta do?

A

Carries blood away from the LV.

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23
Q

How is output from the LV distributed?

A

So the each relevant capillary bed receives a fresh supply of blood.

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24
Q

What happens in the capillary beds?

A

02 is extracted from the blood, and its then shunted back to the heart via the veins.

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25
Q

How much blood does each side of the heart pump per unit time relative to each other?

A

Both sides of the heart pump equal volumes of blood per unit time

BUT, the left side does so at high pressure (120 mmHg max systolic pressure), whereas the right side is a low pressure circulation (25 - 30 mm Hg max systolic pressure).

26
Q

When do the RV and LV contract?

A

Together

Otherwise, you would have a waggle in the septum

27
Q

Why does the LV do more work per unit time than the RV?

A

LV is much more massive than RV

LV is able to easily generate more contractile force. It is required to do so, because its pumping an equal volume of blood into a high resistance system.

28
Q

What do cardiac valves allow?

A

Unidirectional movement (forward)

Allows efficient pump action

Behave like one-way doors, open in response to pressure.

Backward pressure forces the valves closed.

29
Q

Role of atrioventricular valves

A

Right and left

allow for the movement of blood from the atria to the ventricles during filling.

Keep blood in the ventricles when they contract.

Rising ventricular pressure (blood trying to move backward) forces them closed.

30
Q

What is the right AV valve called?

A

tricuspid (three cusps)

31
Q

What is the left SV valve called?

A

mitral (two cusps)

32
Q

What is the role of the chordae tendinae?

A

AV valves are anchored by fibrous chordae tendinae, which are attached to pupillary muscle

Tendinae prevent leaflet eversion with high pressure.

33
Q

Where are the semilunar valves? Role?

A

Opening of aorta

Opening of pulmonary artery

Govern blood flow where major arteries leave the ventricles

34
Q

How many cusps do the semilunar valves have?

A

Three

35
Q

Functioning of semilunar valves

A

When ventricular pressure exceeds that in the aorta (systole), they are forced open

Close when blood tries to regurgitate

36
Q

What is the heart wall composed of?

A

Spirally arranged cardiac myocytes (muscle fibres)

Muscle cells are branched and interconnected, have intercalated discs to allow passage of ions

Form an electrical syncytium

37
Q

What are the junctions between myocytes called? Function of these junctions?

A

Intercalated discs

Porous, allow electrical connectivity

Contain gap junctions (low resistance regions, electrical connections) and desmosomes (structural anchoring)

See figure

38
Q

Layers of the heart

A

Endocardium (endothelial tissue)

Myocardium (muscle)

Epicardium (thin external membrane)

39
Q

Electrical connections between atria and ventricles

A

Electrically isolated

Except for specialized connections or ‘wiring’ (internal pathway)

40
Q

What separates the atria and ventricles electrically?

A

non-conductive fibrous skeleton

41
Q

What does the spiral arrangement of myocytes in the heart allow?

A

allow the heart to wring blood from ventricular cavities with each contraction.

42
Q

Difference between cardiac and skeletal muscle contraction

A

Cardiac contraction uses all or none recruitment of muscle cells

43
Q

Number of mitochondria in cardiac myocytes

A

A lot

Heart needs a lot of ATP

Depends on anaerobic metabolism

44
Q

Generation of new heart cells after birth

A

Does not happen (although this concept is now challenged)

Increase in heart size occurs due to increase in cell size

45
Q

What is the pericardial sac?

A

double walled serous membrane that holds the heart in position.

Removed during cardiac transplantation.

46
Q

What is secreted by the pericardial sac? Role?

A

Pericardial fluid

Reduces resistance to movement

47
Q

What does haemorrhage into the pericardial space cause?

A

May compress the heart and lead to dysfunction our to insufficient filling

48
Q

Characteristics of cardiac contractions

A

Must be coordinated for efficient pumping

The heart functions as two separate pumps in series.

Atrial excitation and contraction normally precedes ventricular contraction.

Contraction of each chamber must occur as a unit.

Contraction of the pair of atria and the pair of ventricles must occur simultaneously.

49
Q

What does slow conduction through the AV node allow?

A

Slow conduction through the AV node ensures a delay between contraction of the atria and the ventricles.

Allows the atria to send blood and ventricles to fill properly

50
Q

How is coordination of contraction achieved?

A

Structurally

51
Q

What initiates contraction in the atria?

A

SA node (pacemaker)

52
Q

How does excitation occur throughout the atria?

A

Via cell to cell contact (gap junctions) and the interatrial pathway.

53
Q

How is the AV node excited?

A

through the internodal pathway and by cell to cell contact.

54
Q

Spread of cardiac excitation

A

An action potential initiated at the SA node first spreads throughout both atria.

Its spread is facilitated by the interatrial and internodal pathways.

The AV node is the only point where an action potential can spread from the atria to the ventricles

From the AV node, the action potential spreads rapidly throughout the ventricles, hastened by a specialized ventricular conduction system consisting of the bundle of His and Purkinje fibers.

55
Q

Pacemaker activity

A

The pacemaker of the heart is the structure that is firing the fastest

56
Q

What would happen if the SA node failed?

A

AV node would take over and set the rate

57
Q

What would happen if only the AV node failed?

A

The atria would fire at the SA node rate

The ventricles would fire at the purkinje fibre rate

58
Q

What happens if an ectopic focus takes over as the pacemaker?

A

Ectopic focus goes faster than SA node

Whole heart is driven by rapidly abnormal pacemaker

59
Q

What is Excitation-contraction coupling

A

In cardiac muscles, electrical signal is converted into contractile signal

60
Q

What is the signal for heart contraction?

A

Elevation of cytosolic Ca2+ derived from ECF and sarcoplasmic reticulum

Creates a plateau in the AP graph

61
Q

What does elevated Ca2+ lead to?

A

Cross-bridge cycling between actin and myosin

62
Q

What does relationship between electrical and mechanical events of heart prevent?

A

Tetanus

Physiology (19 decks)

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