Cardiovascular mechanics 1 Flashcards
(28 cards)
What events lead up to a contractile event in the heart
- Electrical event
- Calcium influx
- calcium release
- contractile event
Where must calcium enter from
Outside of the cell
What are T-tubules
Invaginations of cardiac cells spaced at each Z line that carry surface depolarisation deep into cells
What is one of the most important organelles for cardiac excitation-contraction
Sarcoplasmic reticulum for calcium storage
Describe the excitation process in the heart
- Depolarisation causes the L-type Ca2+ to open to allow Ca2+ to enter the cell down its concentration gradient
- Calcium binds to the ryanodine receptor to cause a conformational change (some is used in contraction)
- Calcium stored inside the sarcoplasmic reticulum can move into the sarcoplasm
- Contraction
How are calcium levels reduced after excitation
Calcium ATPase pumps calcium against its concentration gradient from cytoplasm to the SR. Additionally use of the sodium calcium exchanger (no ATP needed)
Describe the length-tension relationship in the heart
As the length of cardiac muscle increases the active force production increases, as well as base line passive force
What differentiates cardiac from skeletal muscle
Cardiac muscle is more resistant to stretch/less compliant due to its ECM and cytoskeleton. Only the ascending limb is important for cardiac muscle
Why can you not overstretch cardiac muscle
Containment in the pericardial sac
Where does isotonic contraction occur in the heart
increasing the pressure in the ventricles
Where does isometric contraction occur in the heart
ejecting the blood from the ventricles
Define preload
The weight that stretches muscle before it is stimulated to contract
Define afterload
The weight not apparent to muscle in the resting state, only encountered when muscle has started to contract
Describe preload in the heart
The amount of blood returning in diastole, stretching the resting ventricular walls. Determines the preload on the ventricles before ejection
How can one measure preload in the heart
End-diastolic volume
End-diastolic pressure
Right atrial pressure
Describe after load in the heart
the load against the left ventricle ejects blood after opening of the aortic valve
How does after load relate to hypertension
Afterload is greater and requires the ventricle to work harder in order to expel blood
How does after load affect velocity
Increasing afterload decreases the amount of isotonic shortening and decreases the velocity of shortening
What is Starlings law of the heart
Increased diastolic fibre length increases ventricular contraction
What are the causal factors of starlings law
Changes in the number of myofilament cross bridges that interact or changes in the calcium sensitivity of the myofilaments
Define stroke work
work done by the heart to eject blood under pressure into the aorta and pulmonary artery
How is stroke work calculated
stroke volume x pressure
Which factors affect stroke work
stroke volume - preload and after load
pressure - cardiac structure
How is tension affected by an increase in radius (pressure of cylinder is the same)
tension of the walls increases with increasing radius
