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Cardiorepiratory Y1 > Heart as a pump > Flashcards

Heart as a pump Flashcards

1
Q

The heart works as a pump to eject blood out into the aorta/pulmonary arteries.
The heart consists of 2 pumps: left and right side pumps functioning together. Which side of the heart does the oxygen rich blood go to?

A

oxygen rich blood goes from the lungs to left side of heart which is then pumped to rest of the body

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2
Q

Describe the hearts’ double pump system

A
  • One part pumps oxygen-poor blood to lungs to deposit carbon dioxide, pick up oxygen and go to the other side where it’s going to pump the freshly oxygenated blood to the rest of the body until it arrives back to the first part to deposit the carbon dioxide
  • This double-circuit circulation is the way the heart works in all mammals; prevents deoxygenated + oxygenated blood from mixing
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3
Q

what do we mean when we say ‘cardiac cycle’

A
  • all physiological events associated with a single heartbeat
  • period of time that begins with contraction of the atria and ends with ventricular relaxation
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4
Q

what is each cardiac cycle initiated by?

A

Each cardiac cycle is initiated by spontaneous generation of action potential in SA node

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5
Q

The electrical activity of the heart triggers a _____ ___________which cause the myocardium to contract.

A

The electrical activity of the heart triggers a SPREADING DEPOLARISATION which cause the myocardium to contract.

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6
Q

What does the contraction of cardiac muscle depend on?

A

Contraction of a cardiac muscle is dependent on the number of cross-bridge (between actin+ myosin, binding of myosin to actin causes the actin filaments to slide, shortening the muscle fibre= contraction powered by ATP) cycles that are formed during contraction.

Cardiac muscle contraction occurs as a consequence of calcium entry through L-type calcium channels, which activate ryanodine receptor (RyR) channels in the SR. Alternatively, β-adrenergic receptors on the cell membrane lead to activation of adenylyl cyclase (AC), which stimulates PKA (protein kinase A aka cAMP-dependent protein kinase)

In cardiac muscle, calcium influx through the L-type channels opens RyRs via calcium-induced calcium release (CICR). The RyR is a large tetrameric six-transmembrane-span calcium-release channel. Of the three RyR subtypes, RyR1 is predominantly found in skeletal muscle, and RyR2 is predominantly found in cardiac muscle

N.B. contraction requires a signal from the nervous system (excitation- contraction coupling)

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7
Q

Describe the sequence of events in the cardiac cycle (in general terms)

A

1) electrical activity= spreading depolarisation which causes myocardium to contract
2) mechanical activity= excitation-contraction coupling, myocardium contracts as 2 syncytia first atria followed by the ventricles
3) pressure changes= volume changes + heart sounds (pressure provides force that moves blood

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8
Q

what do we mean by syncytia, when referring to the heart?

A

Syncytia= single cell w multiple nuclei i.e. was formed from many cells
(in heart context) cardiac muscle fibers are syncytia (fusion) of individual cells (cardiomyocytes) joined end-to-end at intercalated discs which not only provide structural stability of fiber, but their content of gap junctions permits the free flow of the action potential down the length of the fiber

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9
Q

describe sarcomere structure

A
  • A sarcomere is the fundamental unit of a muscle’s striated muscle tissue. It is bounded by Z-lines, which are the points that anchor thin filaments. In the center of the sarcomere is the M-line, where thick filaments are anchored.
    • Sarcomeres are made up of long, fibrous proteins as filaments that slide past each other when a muscle contracts or relaxes.
      The main proteins involved are actin (thin filaments), myosin (thick filaments), and regulatory proteins such as troponin and tropomyosin.
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10
Q

describe the function of these 3: actin, myosin, troponin +tropomyosin

A
  • Actin: This is the protein that makes up the thin filaments in muscle fibers. It has binding sites for myosin to attach during muscle contraction.
    • Myosin: The thick filament protein with a head that binds to actin when the muscle is stimulated to contract.
  • Troponin and Tropomyosin: These regulatory proteins are associated with actin filaments. Tropomyosin covers the binding sites on actin molecules, preventing myosin from attaching to actin when the muscle is relaxed. Troponin holds tropomyosin in place and has a binding site for calcium ions.
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11
Q

What is Excitation-Contraction Coupling?

A

in. short its the signal from nervous system for contraction
* process of converting an electrical stimulus to a mechanical response. It is the link (coupling) between the action potential that causes excitation and contraction of the muscle fiber.
* In cardiac muscle cells, an action potential that travels along the sarcolemma and T-tubules, leading to the opening of voltage-gated calcium channels and the influx of calcium ions.
* The increase in intracellular calcium concentration causes the binding of calcium to troponin C, causing a conformational change in the troponin complex.
* This change moves tropomyosin away from myosin-binding sites on actin filaments, allowing myosin heads to bind to actin and initiate cross-bridge cycling.
Cross-bridge cycling, which is powered by the hydrolysis of ATP, leads to the sliding of thin and thick filaments past each other, causing the sarcomere to shorten and generate muscle contraction.

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12
Q

what is systole?

A

systole is contraction.
During systole, the heart contracts and ejects blood

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13
Q

what is diastole

A

heart relaxing (not contracting)
During diastole the heart fills with blood

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14
Q

how long does atrial systole last, compared to ventricular systole?

A

Atrial systole: lasts about 0.1 seconds - both atria contract and force the blood from the atria into ventricles, whereas ventricular systole lasts about 0.3 seconds, both ventricles contract, blood is forced to the lungs via the pulmonary trunk, and the rest of the body via the aorta.

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15
Q

how long does atrial diastole last, compared to ventricular diastole?

A

Atrial diastole lasts about 0.7 seconds - relaxation of the atria, during which the atria fill with blood from the large veins (the vena cavae). Ventricular diastole lasts about 0.5 seconds and begins before atrial systole, allowing the ventricles to fill passively with blood from the atria.

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16
Q

Q: A 51-year-old man has a resting heart rate of 75 beats per minute. What is the duration of the cardiac cycle? And how long are his ventricular (cardiac) systole and diastole?
b) What if his heart rate went up to 100 beats per minute?

A

a)Duration of cardiac cycle (one beat)= 60 sec (a minute)/ heart rate
= 60/75= 0.8 s or 800 ms
-Diastole is around 2/3rd of cardiac cycle - 533ms
-Systole is around 1/3rd of cardiac cycle - 266ms

b)= 60/100= 0.6 s or 600 ms
-Diastole is around 2/3rd of cardiac cycle - 400ms
-Systole is around 1/3rd of cardiac cycle - 200ms

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17
Q

what fraction of cardiac cyle is systole + diastole

A

systole is 1/3rd of cardiac cycle
diastole is 2/3rds of cardiac cycle

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18
Q

what is the duration of the cardiac cycle influenced by?

A

The duration of the cardiac cycle is influenced by SA node firing, which controls the heart rate (how many beats are generated per minute)

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19
Q

What does a Wiggers diagram show?

A

Describes changes in pressure, volume, heart sounds (phonocardiogram) and ECG throughout the cardiac cycle.
SV – Stroke volume
ESV- End systolic volume
EDV-End diastolic volume

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20
Q

What are the phases of the cardiac cycle; start from atrial systole

A

1) atrial systole
2) ventricular isovolumic contraction
3) ventricular ejection
4) ventricular isovolumic relaxation
5) ventricular filling

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21
Q

what is preload?

A
  1. Preload: (aka elasticity/ stretchiness) refers to the degree of tension or load on the ventricular muscle when it begins to contract at the end of diastole.
    The preload can be explained on the basis of change in sarcomere length, which refers to degree of the stretch of the myocardium (amount it expands is the proposed value)
    The index of preload is End diastolic volume (EDV)
    Cross bridge interaction enables a muscle to develop force (isometric contraction) or to shorten (isotonic contraction)
    There is an optimal length between sarcomeres at which the tension in the muscle fiber is greatest, resulting in the greatest force of contraction
    If sarcomeres are closer together or further apart compared to this optimal length, there will be a decrease in contraction tension and strength
    ↑EDV→ ↑ Preload (sarcomere length) →↑ active tension → ↑ contraction
22
Q

What is stroke volume? State equation linking Stroke Volume, End Diastolic Volume, End Systolic Volume

A

Stroke volume (SV): Volume of blood ejected by each ventricular contraction into aorta or pulmonary artery per cardiac cycle/heartbeat
Stroke Volume = End Diastolic Volume - End Systolic Volume

23
Q

What is cardiac output? + state equation between Cardiac Output, Stroke Volume +Heart Rate

A

Cardiac output (CO): Volume of blood pumped out by each ventricle per/minute
CO= Stroke Volume x Heart rate

24
Q

what is ejection fration

A

Ejection fraction (EF): The fraction of EDV that is ejected into the aorta or pulmonary arteries
Ejection Fraction = Stroke volume ÷ End Diastolic Volume x 100

25
Q

What changes preload?

A

Decreased preload:
Decreased venous return
Hypovolemia
Decreased ventricular filling
Impaired atrial contraction
Increased heart rate (decreased ventricular filling time).
AV valve stenosis

Increased preload:
* Increased venous return
Increased blood volume
* Increased ventricular filling
Increased ventricular compliance.
Increased atrial contraction.
Reduced heart rate
(increased ventricular filling time).
AV valve regurgitation

26
Q

How do we calculate the duration of a cardiac cycle (one beat)

A

60 seconds (a min)/ heart rate

e.g. 75bpm heart rate wld mean 60/75= 0.8s/ 800ms
diastole is 2/3rds
systole is 1/3rd

27
Q

Which pump works against a higher pressure?

A

Left ventricle (aorta side)

27
Q

What do we mean by systemic circuit?

A

Systemic Circuit:
Systemic circulation carries oxygenated blood from the left ventricle, through the arteries, to the capillaries in the tissues of the body. From the tissue capillaries, the deoxygenated blood returns through a system of veins to the right atrium of the heart.

27
Q

what part of ECG is represented by atrial depolarisation?

A

P wave

28
Q

what part of ECG is represented by ventricular depolarisation

A

QRS complex

29
Q

what part of ECG is represented by ventricular repolarisation

A

T wave

30
Q

describe the cardiac cycle

A

cardiac cycle comprises a complete relaxation and contraction of both the atria and ventricles, and lasts approximately 0.8 seconds.
Begins with all chambers in diastole, blood flows passively from veins into the atria and past the AV valves into the ventricles. The atria begin to contract (atrial systole), following depolarization of the atria, and pump blood into the ventricles. The ventricles begin to contract (ventricular systole), raising pressure within the ventricles. When ventricular pressure rises above pressure in atria, blood flows toward the atria, producing the first heart sound (S1/lub). As pressure in ventricles rises above two major arteries, blood pushes open the two semilunar valves and moves into the pulmonary trunk and aorta in the ventricular ejection phase. Following ventricular repolarization, ventricles begin to relax (ventricular diastole), and pressure within the ventricles drops. As ventricular pressure drops, there is a tendency for blood to flow back into the atria from the major arteries, producing the dicrotic notch in the ECG and closing the two semilunar valves. The second heart sound (S2/dub) occurs when semilunar valves close. When the pressure falls below that of the atria, blood moves from the atria into the ventricles, opening the atrioventricular valves and marking one complete heart cycle.

31
Q

what is frank starling law

A

The Frank-Starling law states that the force or tension developed in a muscle fiber depends on the extent to which the fiber is stretched
Based on the link between the initial length of myocardial fibers and the force generated by contraction
The left ventricular performance Frank-Starling) curve relates preload (end-diastolic volume or pressure) to cardiac performance (stroke volume or cardiac output)
Shows how changes in ventricular preload lead to changes in stroke volume.

32
Q

What is the S1 heart sound?

A

S1 is the sound created by the closing of the atrioventricular valves during ventricular contraction and is normally described as a “lub,” or first heart sound.

33
Q

increase in intracellular calcium concentration facilitates the binding of calcium to _________

A

increase in intracellular calcium concentration facilitates the binding of calcium to TROPONIN C

34
Q

What is the S2 sound?

A

The second heart sound, S2, is the sound of the closing of the semilunar valves during ventricular diastole and is described as a “dub”

35
Q

What are the function of the valves. What is the largest valve in heart?

A

The valves prevent backflow of blood. Failure of the valves to operate properly produces turbulent blood flow within the heart; the resulting heart murmur can often be heard with a stethoscope.

The largest of the heart’s four valves is the aortic valve. It controls how blood is pumped from the left ventricle into the heart’s main artery: the aorta.

36
Q

What is: End diastolic volume (EDV) (aka preload)

A

END DIASTOLIC VOLUME (PRELOAD)= the amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction

37
Q

What is: End systolic volume (ESV)

A

End systolic volume (ESV)= amount of blood remaining in each ventricle following systole

38
Q

What do we mean when we say ‘heart sounds’

A

Heart sounds= sounds heard via auscultation with a stethoscope of the closing of the atrioventricular valves (“lub”) and semilunar valves (“dub”)

39
Q

Define isovolumic contraction (aka isovolumetric contraction)

A

Isovolumic contraction= (aka isovolumetric contraction) initial phase of ventricular contraction in which tension and pressure in the ventricle increase, but no blood is pumped or ejected from the heart

40
Q

define: isovolumic ventricular relaxation phase

A

Isovolumic ventricular relaxation phase= initial phase of the ventricular diastole when pressure in the ventricles drops below pressure in the two major arteries, the pulmonary trunk, and the aorta, and blood attempts to flow back into the ventricles, producing the dicrotic notch of the ECG and closing the two semilunar valves

41
Q

define heart murmur

A

Murmur= unusual heart sound detected by auscultation; typically related to septal or valve defects

42
Q

Define preload (aka end diastolic volume)

A

Preload= (aka end diastolic volume) amount of blood in the ventricles at the end of atrial systole just prior to ventricular contraction

43
Q

Define the ventricular ejection phase

A

Ventricular ejection phase= second phase of ventricular systole during which blood is pumped from the ventricle

44
Q

define hypovolemia

A

Hypovolemia (aka volume depletion/volume contraction)= is a condition that occurs when your body loses fluid, like blood or water i.e. , it’s a state of abnormally low extracellular fluid in the body

45
Q

How does calcium allow cross-bridge cycling?

A
  • troponin binds intracellular fluid CA2+
    *Tropomyosin moves, exposing myosin- binding sites
    *myosin binds to actin, cross-bridge cycling contracts myofibrils
46
Q

Cardiac muscle contraction requires binding of ____ and _____ filaments and cross bridge cycling to _____ the sarcommere and create muscle _______

A

Cardiac muscle contraction requires binding of THIN and THICK filaments and cross bridge cycling to SHORTEN the sarcommere and create muscle TENSION

47
Q

Excitation Contraction Coupling

A

1) Action potential is generated by pacemaker cells in SAN, AP is transferred from cell to cell via gap junctions
2) As AP travels across sarcolemma it triggers the opening of the L-type Ca2+ channels, this allows calcium to move down it’s electrochemical gradient into the cardiac muscle cell
3) Ca2+ influx opens the RyR receptor on sarcoplasmic reticulum, so large quantities of Ca2+ move into the ICF
4) Calcium induced calcium release creates a calcium ‘spark’ which amplifies the calcium signal
5) Ca2+ binds to troponin; allows cross-bridge cycling= CARDIAC MUSCLE CONTRACTION
We need to make sure CIRCA removes the calcium and puts it back in ECF, NCX (sodium calcium exchanger) it exchanges 3 Na+ ions for 1 Ca2+ ions via the sodium potassium ATPase
6) Troponin releases Ca2+ crossbridge cycling stops; myofibril relaxes= cardiac muscle relaxes

48
Q

Contractility (aka ionotropism) refers to intrinsic ability of cardiac muscle cells to produce force at a given cell length. What factors does contractility depend on?

A

determined by the interaction between intracellular calcium concentration, and the myofilament cross-bridge cycling (I.E. dependent on EXCITATION CONTRACTION COUPLING+ CALCIUM AVAILABILITY)

49
Q

explain what cardiac glycosides do to contractility of heart?

A

cardiac glycodsides (derived from digitalis/foxglove plant) raise ICF calcium conc + increase contractility therefore these are prescribed for heart failure

50
Q

explain what cardiac channel blockers do to contractility of heart?

A

calcium channel blockers block the L type Ca2+ channels and prohibit influx of Ca2+ ions and reduce contractility= treatment for hypertension, angina + some arrhytmias

Cardiorepiratory Y1 (17 decks)

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