Inherent properties of the heart (Dr Murdoch)

Question 1

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

Answer 1

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

Question 2

What are the 4 main properties of the heart

Answer 2

1) Rhythmicity2) Excitability 3) Conductivity4) Contractility

Question 3

What is the trabeculae of the heart?

Answer 3

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.

Question 4

What are the three layers of the heart

Answer 4

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

Question 5

Describe the epicardium and its role

Answer 5

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

Question 6

Describe the myocardium and its role

Answer 6

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

Question 7

Describe the endocardium and its role

Answer 7

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.

Question 8

Describe the main differences between skeletal and cardiac muscle

Answer 8

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

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

Question 9

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

Answer 9

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)

Question 10

Describe the connective tissue layers of the heart

Answer 10

Subendothelial layers are thin collagen fibres

Subcardiac layers are thick collagen fibres

Question 11

What are intercalated discs in cardiac muscle?

Answer 11

A staircase shaped formation that acts to support the cardiac muscle

Question 12

Fat accumulation in the heart occurs in which layer

Answer 12

The epicardium (outer)

Question 13

List the 6 inherent properties of cardiac muscle

Answer 13

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

Question 14

List all the parts of the sarcomere

Answer 14

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

Question 15

How often does the sarcomere repeat itself

Answer 15

Every 2 micrometres

Question 16

What is the dyad

Answer 16

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

Question 17

Where are T-tubules alwaus found in the sacromere

Answer 17

Z disks

Question 18

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

Answer 18

The z disk

Question 19

What shape does the cross section of the sacromere show

Answer 19

A regular lattice pattern

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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

Question 22

Describe the three main types of ion transporters in cardiac muscle

Answer 22

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

Question 23

The myocyte membrane is freely permeable to which ion

Answer 23

Potassium

Question 24

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

Answer 24

Potassium

Question 25

What equation can calculate the equilibrium potential

Answer 25

The Nernst equation

Question 26

What brings about repolarization

Answer 26

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

Question 27

What is the nernst equation

Answer 27

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 ```

Question 28

What is the calcium transient

Answer 28

This is the rise in intacellular calcium

Question 29

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

Answer 29

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

Question 30

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

Answer 30

DHP receptors

Question 31

What are the calcium release channels also known as

Answer 31

Ryanodine channels as ryanodine binds to it

Question 32

What are calcium ATPases on the sarcoreticulum known as

Answer 32

SERCA

Question 33

What are SERCAs surrounded by

Answer 33

Accessory proteins known as phosphlamban (PLB)

Question 34

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

Answer 34

Actin is thin | Myosin is thick

Question 35

List the important accessory proteins of the myofilament

Answer 35

Tropomyosin, troponin I, troponin C and troponin T

Question 36

What molecule is responsible for un-attaching the myosin head

Answer 36

ATP

Question 37

Describe rigor mortis

Answer 37

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

Question 38

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

Answer 38

Calcium

Question 39

Describe the frank-starling law of the heart

Answer 39

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

Question 40

What is the optimal length of sarcomere

Answer 40

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

Question 41

Describe lenght dependence of calcium sensitivity and maximally activated force

Answer 41

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

Question 42

Describe the force-frequency relationship

Answer 42

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

Question 43

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

Answer 43

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