2 - Cardiovascular mechanics 1 Flashcards
What is a cardiac myocyte?
The muscle cells that make up the cardiac muscle. They contract and relax.
What shape are cardiac myocytes? How big are they?
Rod shaped. 100um long, 15um wide. Striated structure
What 2 events lead to myocyte contraction?
- Electrical event (action potential)
- Calcium influx (rise then fall)
- Contraction
What are T-tubules? (transverse tubules)
Finger-like invaginations on the myocyte cell surface.
Where are T-tubles found?
In line with every Z-line of each myofibril.
Approx. 2um apart
What is the function of T-tubules?
To carry surface depolarisation deep into the cell.
Where is the main store for calcium in the cell and where is this found?
The sarcoplasmic reticulum. Lace-like structure.
It is at the bottom of the T-tubules. Overlies the myofibrils.
Draw a cardiac myocyte.
Picture. Rod shaped, t-tubules, sarcoplasmic reticulum, mitochondria, myofibrils.
Where are cell proteins found, in realtion to T-tubules?
On their inner surface. Next to cell proteins on the sarcoplasmic reticulum.
Exitation-contration coupling in the heart - Outline the process of calcium induced calcium release.
- Depolarisation causes L-type calcium channels to open.
- Calcium from outside the cell enters cell down conc. gradient.
- Some will activate myofilaments. MOST will bind to SR calcium release channel. (ryanodnine receptor).
- Conformational change - SR calcium release channel opens.
- Calcium stored in the SR leaves via SR calcium release channel into the cytoplasm.
Called calcium induced calcium release.
Calcium goes on to stimulate contration.
How does calcium released from the SR get back inside?
Calcium ATPase pumps calcium back up into SR.
What is the sodium-calcium exchanger?
Pump that removes excess calcium from the cell by transporting sodium INTO the cell down conc. gradient.
Used when cell is relaxing.
At what calcium concentration is forge generated at its maximum?
When cytoplasmic calcium conc. is at it’s highest.
What is the length-tension relation in cardiac muscle? (during isometric contraction) Draw the graph.
The more you stretch the tissue, the higher the baseline force (passive) produced and more (active) force is produced.
(up to a point)
What is isometric contraction?
When muscle fibres do NOT change in length, but pressure increases. E.g. pushing something with a straight arm, when ventricles fill with blood.
What is isotonic contraction?
Shortening of the muscle fibres. E.g. lifting a barbell, when blood is ejected from the ventricles.
Can skeletal muscle produce more or less force than cardiac muscle? why?
Less.
Cardiac muscle is more resistant to stretch and less compliant than skeletal muscle.
This is due to properties in the extracellular matrix and cytoskeleton.
Does cardiac muscle work on the ascending or descending limb of the force-muscle length graph?
Only on the ascending limb (when force is increasing as length increases)
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 AFTER muscle has started to contract.
What happens when you increase afterload? How does preload affect this?
Increased afterload = the less the muscle will shorten.
If preload is increased, with the same afterload more shortening can occur so more force produced.
What is preload in the heart? What is it dependent on?
When blood fills the heart during diastole, it stretches the resting ventricular walls. This is the preload. It its dependent on venous return to the heart.
What are the measures of preload in the heart?
End diastolic volume
End diastolic pressure
Right atrial pressure
What is afterload in the heart?
The load AGAINST the left ventricle when its pushing blood through the valve out of the aorta.
