THE HEART
Anatomy
The heart is the central organ which pumps blood continuously through the blood vessels. It is located between the lungs, ribs and sits cranially to the diaphragm. The heart is conical in shape and is placed asymmetrically within the thorax such that 60 % sits to the left of the median plane. The base is dorsal; the apex is ventral and placed close to the sternum opposite the 6 th costal cartilage. The long axis of the heart slopes caudoventrally, caudal to the triceps. It consists of 4 chambers; right & left atria and right & left ventricles. The 2 atria are separated by an internal septum (interatrial septum) as are the 2 ventricles (interventricular septum. The right side of the heart receives deoxygenated blood, while the left side receives oxygenated blood. The size of the heart varies among the species and in horses the mass of the heart may be estimated to be 1% of the total body weight.
Structure of the Heart Wall
The heart is almost completely invested by the pericardium or pericardial sac. The pericardium is essentially a double layered closed serous sac that is invaginated by the heart. Superficial Fibrous Pericardium : tough, dense irregular CT rests on the diaphragm Deep Serous Pericardium : deeper layer, thinner and more delicate forming a double layer around the heart. Outer Parietal Layer : fused to the fibrous pericardium
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