Cells in the body are in need of continuous nourishment, oxygenation and excretion of waste, otherwise they die. The only way these exchanges are made is via the tissue fluid (blood) that passes through it. This is where the cardiovascular system comes into the picture.

The cardiovascular system is composed of blood, the blood vessels and the heart. This system is vital to life because it is responsible for carrying oxygen and nutrients to every cell via blood.  In simple words, its major function is transportation. Oxygen, cell wastes, nutrients, hormones and other substances vital to life are transported using the blood.

Physiology of the Heart

The heart normally functions as a highly effective pump. Blood moves around the body due to the force provided by the heart (heartbeat). With every heartbeat, nutrients and oxygen are deployed to cells. A normal young adult’s heart beats approximately 60 to 80 times per minute, ejects roughly 70 ml of blood per beat and has a total of 5 liters per minute of blood circulated.

Intrinsic Conduction System of the Heart

Cardiac muscles have an inherent rhythmic action, meaning to say they can contract spontaneously and independently if maintained under proper conditions. However, the rhythmicity of the heart muscles occurs differently in each area of the heart. Atria and ventricle must contract sequentially to provide the most effective flow. The order of contraction takes place due to specialized cells of the conduction system that generate and conduct electrical impulses to myocardia cells, otherwise the heart would pump inefficiently and without coordination.

Intrinsic Conduction system, otherwise known as the nodal system, is responsible for setting the basic heart rhythm. It is built in the heart tissue which is a cross between the nervous and muscular tissue. It’s presence in the heart is important as it causes the heart to depolarize in only one direction – from atria to the ventricles.

The parts of the intrinsic conduction system are:

  1. Sinoatrial (SA) node – this crescent-shaped node of tissue is located at the junction of the superior vena cava and the right atrium. SA node is the start of the conduction system. It functions as a pacemaker for the entire myocardium and initiates roughly 60 to 100 beats per minute in a resting normal heart, although it might change depending on the body’s condition and needs.
  2. Ventricular (AV) node – this node is located at the right atrial wall near the tricuspid valve. It is conducted along the myocardial cells when initiated by the SA node. Quite similar to SA node, its intrinsic rate is approximately 40 to 60 beats per minute. One important role of AV node is how it coordinates the incoming electrical impulses to the ventricles through the atrioventricular (AV) bundle or the bundle of his. The bundle of his divides into the left and the right bundle branches, which terminates in the fibers called Purkinje fibers.

Heart rate is determined by the myocardial cells with the fastest intrinsic rate which is the SA node. Consequently, SA node is called the pacemaker. From the SA Node, the impulse travels to atria, to the AV node, then the atria contract. The impulse is delayed to give time for the atria to finish contracting then it travels to the bundle of his, to the Purkinje fibers, then the ventricles contracts starting at the apex of the heart.

Physiology of the Blood Vessels

To determine a person’s circulation efficiency, arterial pulse and blood pressure should be measured. A pulse is a pressure wave produced by the alternating expansion and recoil of arteries with each beat of the left ventricle. Blood pressure on the other hand is the pressure the blood exerts against the inner walls of the blood vessels. This force is responsible for the circulation of blood in the body.

To measure the blood pressure in the body it is important to get acquainted to two terms: systolic and diastolic pressure. The presence of these two pressures is brought about by the contraction-relaxation cycle of the heart. Systolic is the pressure the arteries make at the peak of a ventricular contraction whereas diastolic is the pressure produced when the ventricles are relaxing. Blood pressure is measured in millimeters of mercury (mmHg). The systolic pressure is written at the upper portion while diastolic at the bottom. So if the BP is 110/80 mmHg, 110 is the systolic and 80 is the diastolic.

The cardiovascular system can be compared to a car’s engine. Without it, nutrients, oxygen and hormones cannot flow to the rest of the body.