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The heart of man is of the ‘Myogenic type’.

Normal activities of the heart are intrinsically regulated, i.e. auto regulated by the nodal tissues. Due to this, the heart is called myogenic.

 The SA Node is responsible for initiating and maintaining the rhythmic contractile activity or beating of the heart. Due to this, the SA Node is called the pacemaker.

The closure of AV – valves.

In human heart, Sino atrial node initiates the conduction of heart beat. The excitory wave of SA node is called cardiac impulse and it determines the rate of heart beat and sets the pace of the activities of the heart. Hence Sino atrial node is termed as pacemaker of the heart.

Human heart is myogenic because the heart beat originates in the heart itself.

The heart beat initiated by Sino atrial node is picked up by the Atrio – ventricular node and the action potential is conducted to the ventricular side. From the AV node the heart beat is transmitted to the AV bundle (Bundle of His) which transmits it through the entire ventricular musculature.

 AV Node and AV Bundles are responsible for conduction of heart beat to different parts of the heart after initiation in the SA node.

 Lub and Dub Sounds: Two prominent sounds are produced during each cardiac cycle. These sounds can be easily heard through a stethoscope. The first sound is called lub and is associated with the closure of the tricuspid and bicuspid valves. The second sound is called dub and is associated with the closure of the semi-lunar valves. These sounds are important for clinical diagnosis. 

During each cardiac cycle two prominent sounds lub and dub are heard. The first heart sound (lub) is associated with the closure of the tricuspid and bicuspid valves which extends for 0.16 – 0.9 sec. The second heart sound (dub) is associated with the closure of the semilunar valves and extends for 0.10 sec.

The sequential events that occur from the beginning of one heart beat to the beginning of the next heart beat which is cyclically repeated is called the cardiac cycle. The volume of blood pumped by the ventricle per minute is called the cardiac output. It ranges about 5000 ml (5 L) in a healthy individual.

Cardiac Cycle: The sequential contraction and dilatation of different chambers of heart in a cyclical manner is called cardiac cycle.

Cardiac Output: The volume of blood pumped by the heart in one minute is called the cardiac output. The average cardiac output is 5000 ml or 5 litre per minute.

About 0.8 seconds.

Cardiac output is the volume of blood ejected out from the ventricles over one minute.

Cardiac output is the product of stroke volume and heart rate/minute. Equation for cardiac out put is,

CO = SV x HR i.e = 70 x 72 = 5040 ml.

CO is cardiac output, SV = Stroke Volume HR = heart rate (Number of heart beats/minute).

Normal activities of the heart are regulated intrinsically by specialised muscles, and hence the heart is called myogenic. A special neural centre in the medulla oblongata can moderate the cardiac function through Autonomic Nervous System. (ANS).

Neural signals through the sympathetic nerves can increase the rate of heart beat, the strength of ventricular contraction and thereby the cardiac output. Para sympathetic neural signals decrease the rate of heart beat, speed of conduction of action potential and thereby the cardiac output. Adrenal medullary harmones can also increase the cardiac out-put.

Fibrinogen, globulins and albumins are the major plasma proteins. Fibrinogen are needed for clotting or coagulation of blood. Globulins primarily are involved in defense mechanisms of the body. Albumins help in osmotic balance.