1. Pharmacology of drugs acting on cardio vascular system
a. Introduction to hemodynamic and electrophysiology of heart.
Human heart – human heart is a mesodermally (originates from mesoderm) derived organ, it is situated in the thorax and its dimension is about 12 cm x 9 cm.
The wall of the heart consists of three layers, the external layer is also known as covering layers, the intermediate cardiac tissue or myocardium (made of cardiac muscular tissue) and the internal layer or endocardium which is direct contact with the blood.
Hemodynamic or Haemodynamic - Hemodynamic is all about the dynamic behaviour of blood, in general term is referred to the movement or flow of blood. This term refers to the measurement of heart rate (HR), pressure and resistance are major determinants of the amount of circulatory blood flow. Measurement of certain hemodynamic parameters, such blood pressure (BP), can be determined.
Electrophysiology: The contraction and relaxation of the cardiac muscle follows a specific pattern between the atria and the ventricles. This rhythmic contraction and relaxation are preceded by electrical activity called the action potential that is represented in the depolarization and repolarization of the cardiac muscle, respectively
Phase 0 - rapid depolarisation occurs in an adjacent cell and the threshold potential is met. Fast voltage-gated sodium channels (INa) open and sodium ions enter the cell rapidly.
Phase 1 - the first stage of repolarisation. Potassium ions leave the cell via transient K+ channels.
Phase 2 - plateau phase. Inward movement of calcium ions via voltage-gated L-type channels prolongs repolarisation.
Phase 3 - completion of repolarisation (second phase of repolarization). Outward movement of potassium ions returns the membrane to its resting potential.
Phase 4 – it is known as pacemaker potential; the membrane of contractile cells remains essentially at rest at about -90 mV until excited.
1. Rhythmicity - means the ability of the heart to beat continuously without external stimulation.
2. Excitability - The heart muscle responds to stimuli which may be mechanical, electrical or chemical
3. Conductivity - The ability to conduct impulse from one cell to another
4. Contractility – It is the ability of myocardium to contract and pump blood out of the heart.