Heart and cardiac muscles of animals

Heart and cardiac muscles of animals

Heart

Heart is situated in the middle mediastinal space. It has two anterior chambers, the atria and two posterior chambers, the ventricles. The heart is separated into left and right sides by a septum. The atria and ventricles communicate with each other through the atrio-ventricular orifices, which are guarded by the AV valves, the bicuspid or mitral valve and tricuspid valve on the left and right sides, respectively.

Chorda tendinae are the elastic structures attached to the valves with the internal muscular projections of the heart known as the papillae and prevent the evertion of the valves during ventricular contraction.

AV valves prevent the back flow of blood into the atria during ventricular contraction (systole). Of the four chambers, the left ventricular wall is much thicker to provide effective force during its contraction to pump its contents throughout the body.

The venous system provides blood to right atrium of the heart and the blood is pumped from the right ventricle to the lung; hence, it is referred to as venous or pulmonary side.

The left atrium of the heart receives the oxygenated blood from the lungs and the left ventricle pumps it to the peripheral systemic organ which is known as systemic or arterial side. Blood vessels between aorta and vena cava supplying blood to all organs except to the lungs are called systemic circulation.

The blood vessels of lungs constitute pulmonary circulation. Pulmonary circulation and heart are collectively termed as central circulation.In the orifices of the aorta and the pulmonary artery the Semilunar valves are present which prevent the back flow of blood from aorta and pulmonary artery into the ventricles during ventricular relaxation (diastole).

The major function of the cardio vascular system is to transport oxygen, nutrients, water electrolytes and hormones to the tissues and remove the metabolic wastes such as CO₂, urea, creatinine etc from tissues to the lung and excretory organ like kidney.

Cardiac muscles

Heart is composed of three major types of cardiac muscle namely- Atrial, Ventricular and Special excitatory and conductive muscle fibres.

The atrial and ventricular muscle fibres contract similarly to skeletal muscle fibres except the duration of contraction is longer. The excitatory and conductive muscle fibres contract only feebly but exhibit rhythmicity and varying rates of conduction providing an excitatory system that controls rhythmical beating of the heart.

Cardiac muscle fibres are arranged in a lattice network, fibres divide, recombine and spread again. The cardiac muscle fibres contain intercalated discs that contain many gap junctions through which action potential can spread from one to other cardiac muscle cell very easily.

When one of the cardiac muscle cells is excited, and the action potential spreads to all of them, hence the cardiac muscle obey all or none law.

The heart is composed of two separate functional syncytia, the atrial and the ventricular walls. They are separated from each other by fibrous tissue surrounding the valves between atria and ventricles, but are connected to each other by specialised conduction system fibres. This type of two functional syncytia allows the atria to contract a short time before ventricular contraction which is important for effectiveness for pumping of the heart.

Normal heart rate in animals