Cardiovascular Mechanics Flashcards
What happens during contraction in a single ventricular cell
Electrical event, ca influx and ca release, contractile event
What is the structure of a single ventricular cell structure
T tubule openings up to 200nm in diameter
T tubule lies alongside each Z line
Carries surface depolarisation deep into cell
Ventricular cells 100micrometers long and 15 micrometres wide
What happens during the excitation-contraction coupling in the heart
- Myocyte depolarises
- Action potential travels down t-tubles
- Activates L-type Ca channels to open
- Calcium flows in and binds to SR Ca release channels (ryanodine receptor)
- Ca enters cytoplasm from sarcoplasmic reticulum
- Ca binds to troponin C
- Myosin head binds to actin
- Muscle fibres shorten
- Na/Ca exchanger removes Ca by usign the energy of the gradient of L type Ca channel
How to add calcium to SR
Sympathetic stimulations
Increase phosphorylation of protein which increases Ca influx
What type of relationship is cyotplasmic Ca contration and force
Sigmoidal
What is the passive force in cardiac muscle
Liek elastic band recoiling
What is active force in cardiac muscle
Caused by crossbridge formation from the calcium release from SR
How does cardiac muscle differ from skeletal muscle
Cardiac muscle is more resistant and less compliant
Due to properties of the extracellular matrix and cytoskeleton
Is the total force regardless of muscle length improatn
Only ascending limb of the relation is important
Why does skeletal muscle produce less passive force
It is strechier
What is isometric cardiac contraction
Muscle fibres do not change length but pressure inceases in both ventricles
What is isotonic cardiac contraction
Shorterning of fibres and blood is ejected from ventricles
What is preload
Weight that stretches muscle before it is stimulated to contract
What is afterload
Weight not apparent to muscle in resting state; only encountered when muscle has started to contract
Diagram of preload and afterload
What is an example fo afterload
Backload of the aorta
What is an example of preload
Ventricular filling
What are measures of preload
End-diastolic volume
End diastolic pressure
Right atrial pressure
What happens during invivo preload of the heart
Stretches the resting ventricular walls
Filling determines the preload
Preload is dependent on venous return
What happens during invov cardiac afterload
Load against which the left ventricle ejects blood after opening of the aortic valve
What is a measure of afterload
Diastolic blood pressure
What is the Frank starling relationship
Increased diastolic fibre length increases ventricular contraction
Cardiac output exactly balances the augmented venous return
As the filling of the heart increases, the force of contraction also increases
Why does the frank starling relationship happen
There are changes in the number of myofilament cross bridges that interact: more myofilament interact as stretching, more indigitation of thick and thin filaments and increase chance of crossbirdge formation
Change in Ca sensitivty: At longer sarcomere lengths, the affinity of TnC for Ca is increased due to conformational change in protein. Furthermore, with decreasing myofilament lattice spacing, probability of forming strong binding cross bridges increases
What is stroke work
Work done by heart to eject blood under pressure into aorta and pulmonary artery
What is the formula for stroke work
Stroke work = volume of blood ejected multiplied by the pressure as which the blood is ejected
What is the Law of LaPlace
When the pressure within a cylinder is held constant, the tension on its walls increases with increasing radius
T=P X R
T= (PXR)/h
Why is the radius of LV less than RV
LV generates higher pressures
Picture of failing heart
