Inherent properties of the heart (Dr Murdoch) Flashcards
772,632,000 is the answer but what is the question?
It is approximately the number of heartbeats a 21 year old has had throughout their lifetime
What are the 4 main properties of the heart
1) Rhythmicity2) Excitability 3) Conductivity4) Contractility
What is the trabeculae of the heart?
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.
What are the three layers of the heart
Epicardium (visceral layer of the serous pericardiu)-(outer), myocardium (middle) and endocardium (inner)
Describe the epicardium and its role
The outer protective layer of the heart. Its role is to prevent cardiac distension to allow extensive movement and to lubricate
Describe the myocardium and its role
The myocardium is the middle layer of the heart and its role is to allow synchronized contraction and relaxation of the heart
Describe the endocardium and its role
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.
Describe the main differences between skeletal and cardiac muscle
Skeletal: Not branches, arranged in bundles, slow rhythmic, heavily striated and fatigues quickly.
Cardiac: Branched, interlocking, intercalated disks, single nucleus, lightly striated and short
Which has more mitochondria (skeletal or cardiac muscle) and why
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)
Describe the connective tissue layers of the heart
Subendothelial layers are thin collagen fibres
Subcardiac layers are thick collagen fibres
What are intercalated discs in cardiac muscle?
A staircase shaped formation that acts to support the cardiac muscle
Fat accumulation in the heart occurs in which layer
The epicardium (outer)
List the 6 inherent properties of cardiac muscle
Structure, ion transport and resting membrane potential, contraction, length-tension relationship, force-frequency relationship and cardiac cycle
List all the parts of the sarcomere
T-tubule, Z-disk, I band (thin filaments), A band (thick filaments) and M-line.
How often does the sarcomere repeat itself
Every 2 micrometres
What is the dyad
The association between the sarcoplasmic reticulum and the t-tubules which is essential in the regulation of excitation-contraction coupling
Where are T-tubules alwaus found in the sacromere
Z disks
What is the site at which the thin filaments are anchored in the sarcomere
The z disk
What shape does the cross section of the sacromere show
A regular lattice pattern
Why is cardiac muscle so branched (each myocyte is connected to three or four)
To create a meshwork that will withstand high pressure and allow electrical contact and depolarization to flow over the heart rapidly.
What are the three main stuctures in the intercalated disk and what do they do
Desmosomes: Cell anchors
Adherens junction (AJ: Provides strenght
Gap junction: Couples cells electrically and metabolically
Describe the three main types of ion transporters in cardiac muscle
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
The myocyte membrane is freely permeable to which ion
Potassium
The resting membrane potential is determined by high level of what ion permeability of the resting cell membrane
Potassium
What equation can calculate the equilibrium potential
The Nernst equation
What brings about repolarization
Repolarization is brought about by a delayed increase in K permeability and potassium ions leaving the cell
What is the nernst equation
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
What is the calcium transient
This is the rise in intacellular calcium
Explain how the action potential is sent to the intracellular calcium stores in the sacroplasmic reticulum to initiate calcium release
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
What are L-type calcium channels on the T-tubule also known as
DHP receptors
What are the calcium release channels also known as
Ryanodine channels as ryanodine binds to it
What are calcium ATPases on the sarcoreticulum known as
SERCA
What are SERCAs surrounded by
Accessory proteins known as phosphlamban (PLB)
Out of actin and myosin which is the thick and which is the thin filament
Actin is thin
Myosin is thick
List the important accessory proteins of the myofilament
Tropomyosin, troponin I, troponin C and troponin T
What molecule is responsible for un-attaching the myosin head
ATP
Describe rigor mortis
When dead no ATP so the myosin and actin form ‘rigot bonds’
What binds to troponin C to move it out of the way to allow the myosin head to bind to the actin filament
Calcium
Describe the frank-starling law of the heart
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
What is the optimal length of sarcomere
2.05-2.25 micrometres as an overlap can reduce force of contraction
Describe lenght dependence of calcium sensitivity and maximally activated force
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
Describe the force-frequency relationship
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
Why is the relationship between force and frequency negative in heart failure
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
