Category:Myocardial Pathology

The myocardium provides the bulk of the heart tissue, and enables the co-ordinated contraction needed for efficient pumping of blood to the body.

Cardiac muscle is intermediate in appearance between skeletal muscle and visceral muscle with characteristics of both:

• Contracts with the force of skeletal muscle.
• Contracts continually like visceral muscle.

Cardiac muscle cells are long, striated, cylindrical cells with one or sometimes two nuclei. Cells contain a sarcoplasmic reticulum which slowly leak calcium ions into the cytoplasm, allowing automatic contractions without the need for external input. The rate of contractions is modulated by external autonomic and hormonal inputs. The sino-atrial node is the pace-maker of the heart as its rate of automatic firing is the greatest.

Intercellular junctions are known as intercalated discs and provide anchorage. They also allow the rapid progression of contractile stimuli throughout the heart muscle, making a functional syncytium.

The ventricular muscle is much thicker than that of the atria, and the atrial myocardium has a more fibrous component.

Blood supply is from the coronary arteries, sinuses beind the leaflets of the aortic valve allow entry of blood into the coronary system at diastole.

Disease of the myocardium may be incidental at post mortem and cause no clinical signs, or may be clinically evident. Disease must be severe and widespread to lead to observable clinical signs. Myocardial disease most often leads to heart failure.

The heart cannnot regenerate by hyperplasia and so responds with hypertrophic change in order to maintain normal function.