Valves Of The Heart:
There are four valves in human heart. Two valves are in between atria and the ventricles called atrioventricular valves. Other two are the semilunar valves, placed at the opening of blood vessels arising from ventricles, namely systemic aorta and pulmonary artery. Valves of the heart permit the flow of blood through heart in only one direction.
Atrioventricular Valves:
Left atrioventricular valve is otherwise known as mitral valve or bicuspid valve. It is formed by two valvular cusps or flaps. Right atrioventricular valve is known as tricuspid valve and it is formed by three cusps.
Brim of the atrioventricular valves is attached to atrioventricular ring, which is the fibrous connection between the atria and ventricles. Cusps of the valves are attached to papillary muscles by means of chordae tendineae. Papillary muscles arise from inner surface of the ventricles. Papillary muscles play an important role in closure of the cusps and in preventing the back flow of blood from ventricle to atria during ventricular contraction. Atrioventricular valves open only towards ventricles and prevent the backflow of blood into atria.
Semilunar Valves:
Semilunar valves are present at the openings of systemic aorta and pulmonary artery and are known as aortic valve and pulmonary valve respectively Because of the half moon shape, these two valves are called Semilunar valves. Semilunar valves are made up of three flaps. Semilunar valves open only towards the aorta and pulmonary artery and prevent the backflow of blood into the ventricles.
Actions Of The Heart:
Actions of the heart are classified into four types.
- Chronotropic Action
- Inotropic Action
- Dromotropic Action
- Bathmotropic Action
1- Chronotropic Action:
Chronotropic action is the frequency of heartbeat or heart rate. It is of two types:
- Tachycardia or increase in heart rate.
- Bradycardia or decrease in heart rate.
2- Inotropic Action:
Force of contraction of heart is called inotropic action It is of two types.
- Positive Inotropic Action or increase in the force of contraction.
- Negative Inotropic Action or decrease in the force of contraction.
3- Dromotropic Action:
Dromotropic action is the conduction of impulse through heart. It is of two types.
- Positive Dromotropic Action or increase in the velocity of conduction.
- Negative Dromotropic Action or decrease in the velocity of conduction.
4- Bathmotropic Action:
Bathmotropic action is the excitability of cardiac muscle. It is also of two types:
- Positive Bathmotropic Action or increase in the excitability of cardiac muscles.
- Negative Bathmotropic Action or decrease in the excitability of cardiac muscle.
Regulation of Actions of Heart:
All the actions of heart are continuously regulated. It is essential for the heart to cope up with the needs of the body. All the actions are altered by stimulation of nerves supplying the heart or some hormones or hormonal substances secreted in the body.