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Cardiology BMSc > Inherent properties of the heart (Dr Murdoch) > Flashcards

Inherent properties of the heart (Dr Murdoch) Flashcards

1
Q

772,632,000 is the answer but what is the question?

A

It is approximately the number of heartbeats a 21 year old has had throughout their lifetime

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2
Q

What are the 4 main properties of the heart

A

1) Rhythmicity2) Excitability 3) Conductivity4) Contractility

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3
Q

What is the trabeculae of the heart?

A

The trabeculae carneae (columnae carneae, or meaty ridges), are rounded or irregular muscular columns which project from the inner surface of the right and left ventricle of the heart.

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4
Q

What are the three layers of the heart

A

Epicardium (visceral layer of the serous pericardiu)-(outer), myocardium (middle) and endocardium (inner)

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5
Q

Describe the epicardium and its role

A

The outer protective layer of the heart. Its role is to prevent cardiac distension to allow extensive movement and to lubricate

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6
Q

Describe the myocardium and its role

A

The myocardium is the middle layer of the heart and its role is to allow synchronized contraction and relaxation of the heart

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7
Q

Describe the endocardium and its role

A

This is the inner layer of the heart and acts to line the heart, reduce friction of blood flow in the chambers and a conduction system.

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8
Q

Describe the main differences between skeletal and cardiac muscle

A

Skeletal: Not branches, arranged in bundles, slow rhythmic, heavily striated and fatigues quickly.

Cardiac: Branched, interlocking, intercalated disks, single nucleus, lightly striated and short

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9
Q

Which has more mitochondria (skeletal or cardiac muscle) and why

A

Cardiac has more and this is because cardiac muscle must produced a lot of energy as it cannot fatigue. This is why skeletal muscle can fatigue and it builds up an oxygen debt (anaerobic metabolism and lactic acid accumulation)

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10
Q

Describe the connective tissue layers of the heart

A

Subendothelial layers are thin collagen fibres

Subcardiac layers are thick collagen fibres

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11
Q

What are intercalated discs in cardiac muscle?

A

A staircase shaped formation that acts to support the cardiac muscle

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12
Q

Fat accumulation in the heart occurs in which layer

A

The epicardium (outer)

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13
Q

List the 6 inherent properties of cardiac muscle

A

Structure, ion transport and resting membrane potential, contraction, length-tension relationship, force-frequency relationship and cardiac cycle

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14
Q

List all the parts of the sarcomere

A

T-tubule, Z-disk, I band (thin filaments), A band (thick filaments) and M-line.

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15
Q

How often does the sarcomere repeat itself

A

Every 2 micrometres

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16
Q

What is the dyad

A

The association between the sarcoplasmic reticulum and the t-tubules which is essential in the regulation of excitation-contraction coupling

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17
Q

Where are T-tubules alwaus found in the sacromere

A

Z disks

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18
Q

What is the site at which the thin filaments are anchored in the sarcomere

A

The z disk

19
Q

What shape does the cross section of the sacromere show

A

A regular lattice pattern

20
Q

Why is cardiac muscle so branched (each myocyte is connected to three or four)

A

To create a meshwork that will withstand high pressure and allow electrical contact and depolarization to flow over the heart rapidly.

21
Q

What are the three main stuctures in the intercalated disk and what do they do

A

Desmosomes: Cell anchors
Adherens junction (AJ: Provides strenght
Gap junction: Couples cells electrically and metabolically

22
Q

Describe the three main types of ion transporters in cardiac muscle

A

1) Ion pumps (Na/K pump) are membrane proteins that are driven by metabolic energy (ATP) usually against their conc. gradient
2) Ion exchangers/symports (Ca/Na exchanger) are membrane proteins that allow ions to be driven by prevailing gradients (they go down a concentration gradient)
3) Ion channels (Ca channel) allow ions to move down their concentration gradient

23
Q

The myocyte membrane is freely permeable to which ion

A

Potassium

24
Q

The resting membrane potential is determined by high level of what ion permeability of the resting cell membrane

A

Potassium

25
Q

What equation can calculate the equilibrium potential

A

The Nernst equation

26
Q

What brings about repolarization

A

Repolarization is brought about by a delayed increase in K permeability and potassium ions leaving the cell

27
Q

What is the nernst equation

A

E(cell)=E^0 - (RT/nF) x In(Q)

or at 25 degress C:

E=E^0 - (0.0592/n) x log (Q)

E=cell potential
E^0=Standard cell potential
R=Real gas constant
T=Temp in kelvin
n=no. of electrons transferred
F=Faraday constant
Q=Reaction quotient
28
Q

What is the calcium transient

A

This is the rise in intacellular calcium

29
Q

Explain how the action potential is sent to the intracellular calcium stores in the sacroplasmic reticulum to initiate calcium release

A

1) T tubules are extensions of the cell membrane that run through cardiac muscle cells
2) T tubules contain clusters of L-type calcium channels that are voltage activated
3) Very close to the opening of these calcium channels inside the cell lies the membrane of the sacroplasmic reticulum
4) The sacroplasmic reticulum also has calcium channels and these are called calcium release channels
5) A wave of action potentials causes increase of intracellular calcium and this is sensed by the calcium release channels and the number of calcium ions in the sarcoplasm increases
6) The rest of the SR is covered with SR calcium ATPase whose job is to pump calcium back into the SR from the cytoplasm

30
Q

What are L-type calcium channels on the T-tubule also known as

A

DHP receptors

31
Q

What are the calcium release channels also known as

A

Ryanodine channels as ryanodine binds to it

32
Q

What are calcium ATPases on the sarcoreticulum known as

A

SERCA

33
Q

What are SERCAs surrounded by

A

Accessory proteins known as phosphlamban (PLB)

34
Q

Out of actin and myosin which is the thick and which is the thin filament

A

Actin is thin

Myosin is thick

35
Q

List the important accessory proteins of the myofilament

A

Tropomyosin, troponin I, troponin C and troponin T

36
Q

What molecule is responsible for un-attaching the myosin head

A

ATP

37
Q

Describe rigor mortis

A

When dead no ATP so the myosin and actin form ‘rigot bonds’

38
Q

What binds to troponin C to move it out of the way to allow the myosin head to bind to the actin filament

A

Calcium

39
Q

Describe the frank-starling law of the heart

A

The law states that the stroke volume of the heart increases in response to an increase in the volume of blood in the ventricles, before contraction (the end diastolic volume), when all other factors remain constant

40
Q

What is the optimal length of sarcomere

A

2.05-2.25 micrometres as an overlap can reduce force of contraction

41
Q

Describe lenght dependence of calcium sensitivity and maximally activated force

A

The effect of calcium sensitivity is mediated by an increase of troponin C for calcium and the increase in maximally activated force is mediated by the effects on myofilamen overlap

42
Q

Describe the force-frequency relationship

A

The more heart beats the more calcium is stored inside the cell and the stronger the force. In heart failure this is a negative relationship

43
Q

Why is the relationship between force and frequency negative in heart failure

A

A down-regulation of SERCA, an upregulation of Na/Ca exchange and an elevation of intracellular Na. These result in more Ca extrusion between beats and less Ca cycling through the SR

Cardiology BMSc (4 decks)

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