Cardiology Physiology
Cardiology Dx
Conduction
Cardiac Muscle
Cardiac cycle
Cardiac output
Conduction
Cardiac Muscle
- Striated
- Short, fat and branched (v skeletal which are long, cylindrical)
- 1 or max 2 central nuclei (v skeletal multinucleate)
- intercellular space filled with loose connective tissue matrix (endomysium) containing capillaries
- plasma membrane of adjacent cells interlock (v skeletal which are independent) therefore propagation of contraction, (i.e. whole heart contracts as one v one motor unit contracting as one in skeletal)
- 25% mitochondria by volume (v 2% in skeletal muscle) = highly resistant to fatigue
- Some (1%) of cardiac muscle cells are self excitable (skeletal must be stimulate by a nerve)
- Sequence
- Na influx from extracellular fluid, opens Ca channels
- Ca influx (20% from extracell, then 80% from sarcoplasmic reticulum
- Tropinin binding, cross bridge activation, myofilament sliding
Cardiac cycle
Cardiac output
- stroke volume (EDV-ESV) x HR
- Preload = degree of muscle stretch. increasing EDV (i.e. stretch) increases contractility by increase the number of cross bridges available (cardiac muscle at rest is at less than optimal length)
- Afterload = arterial backpressure i.e. pressure needed to be reached to open VA valves