The Heart and Circulation

Cardiovascular System Function Functional components of the cardiovascular system: Heart Blood Vessels Blood General functions these provide: Transportation Everything transported by the blood Regulation Of the cardiovascular system Intrinsic v extrinsic Protection Against blood loss Production/Synthesis.

To create the “pump” we have to examine the Functional Anatomy of: Cardiac muscle Chambers Valves Intrinsic Conduction System

Functional Anatomy of the Heart Cardiac Muscle Characteristics Striated Short branched cells Uninucleate Intercalated discs T-tubules larger and over z-discs

Functional Anatomy of the Heart (Continued) Chambers 2 Atria 2 Ventricles 2 systems Pulmonary Systemic

Functional Anatomy of the Heart (Continued) Valves Function is to prevent backflow Atrioventricular Valves Prevent backflow to the atria Prolapse is prevented by the chordae tendinae Tensioned by the papillary muscles Semilunar Valves Prevent backflow into ventricles

Functional Anatomy of the Heart (Continued) Intrinsic Conduction System Consists of “pacemaker” cells and conduction pathways Coordinate the contraction of the atria and ventricles

The heart circulates the blood round the body The heart circulates the blood round the body. The left side of the heart transfers blood from the pulmonary veins to the aorta.

whilst the right side of the heart transfers blood from the great veins, the superior and inferior venae cavae, to the pulmonary artery.

Each side of the heart consists of two chambers, an atrium, previously known as the auricle, and a ventricle.

Valves exist between the atria and the ventricles, and between the ventricles and the aorta and pulmonary artery. The left atrioventricular valve has two cusps and is termed the mitral valve. The right atrioventricular valve known as the tricuspid valve has three cusps; so also have the aortic and pulmonary valves.

These valves enable the alternate contraction and relaxation of the ventricles to pump blood round the body. If a valve becomes faulty, the efficiency of the heart as a pump is greatly impaired.

The Structure of the Heart: The heart lying in the thorax resembles an inverted cone. The superior aspect of the heart, where the vessels enter, is called its base. The extremity of the ventricles is termed the apex.

The two atria and the two ventricles of the heart lie side-by­ side.

When the heart is beating the atria contract simultaneously, then, after a short pause, both the ventricles contract. There is then a longer pause during which time the whole heart is in a state of relaxation.

The inlet and outlet valves of each ventricle lie alongside one another. All the four valves lie in the same plane, in the fibrous septum or ring which separates the atria from the ventricles.

The heart is composed of cardiac muscle, and such muscle has the inherent property of rhythmicity, that is, the muscle fibres contract and relax alternately in a rhythmical manner. This property is developed to the greatest extent in a region known as the sino-atrial node (S.A. node) which is situated in the wall of the right atrium near the entrance of the superior vena cava.

The S.A-node originates each heart beat. It is known as the pacemaker. Cardiac muscle cells, known as fibres, are cylindrical in shape with central nuclei and faint cross-striations. The fibres branch to form a network or sheet of muscle in which it is difficult to see where one cell ends and another begins.

It behaves like a syncytium It behaves like a syncytium. (If it were a true syncytium, there would be no cell boundaries at all.) This syncytial-like arrangement enables a contraction wave to spread rapidly from cell to cell until the whole muscle mass is in a state of contraction.

No nerves are involved in the spread of a contraction wave through cardiac muscle. This may be confirmed by making a series of interdigitating cuts in a piece of atrial muscle. Such cuts would sever any nerves running in the muscle, yet when one part of the muscle is made to contract, the contraction wave spreads through the intact parts of the muscle to reach the whole muscle mass.

Furthermore, in the embryo the heart beats before the nerves have developed. Although the two atria are separate chambers, the muscle fibres are arranged in rings round both atria.