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Equine Cardiovascular System - Horse Anatomy (view source)
Revision as of 21:55, 18 November 2012
, 21:55, 18 November 2012no edit summary
Grooves on the surface represent the divisions of the internal structure of the heart. The right surface of the heart is marked by the '''subsinusoidal groove''', which extends from the coronary groove to the apex of the heart. The '''paraconal groove''' runs over the left surface of the heart from the coronary groove to the distal end of the cranial margin. The '''coronary groove''' contains the coronary blood vessels and marks the separation of the atria and ventricles.
Grooves on the surface represent the divisions of the internal structure of the heart. The right surface of the heart is marked by the '''subsinusoidal groove''', which extends from the coronary groove to the apex of the heart. The '''paraconal groove''' runs over the left surface of the heart from the coronary groove to the distal end of the cranial margin. The '''coronary groove''' contains the coronary blood vessels and marks the separation of the atria and ventricles.
===Heart Wall===
The wall of the heart consists of three layers: the epicardium (external layer), the myocardium (middle layer) and the endocardium (inner layer). The epicardium is the thin, transparent outer layer of the wall and is composed of delicate connective tissue. The myocardium, comprised of cardiac muscle tissue, makes up the majority of the cardiac wall and is responsible for its pumping action. The thickness of the myocardium mirrors the load to which each specific region of the heart is subjected. The endocardium is a thin layer of endothelium overlying a thin layer of connective tissue. It provides a smooth lining for the chambers of the heart and covers the valves. The endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart.
===Chambers of the Heart===
The heart contains four chambers. The two upper chambers are the atria and the two lower chambers are the ventricles. On the cranial surface of each atrium is a pouch-like appendage called an auricle which is thought to increase the capacity of the atrium slightly.
The thickness of the myocardium of the four chambers varies according to function. The atria are thin-walled because they deliver blood into the adjacent ventricles and the ventricles are equipped with thick muscular walls because they pump blood over greater distances. Even though the right and left ventricles act as two separate pumps that simultaneously eject equal volumes of blood, the right side has a much smaller workload. This is because the right ventricle only pumps blood into the lungs, which are close by and present little resistance to blood flow. On the other hand, the left ventricle pumps blood to the rest of the body, where the resistance to blood flow is considerably higher. Consequently, the left ventricle works harder than the right ventricle to maintain the same blood flow rate. This difference in workload affects the anatomy of the ventricular walls; the muscular wall of the left ventricle being significantly thicker than that of the right.
====Right Atrium====
The right atrium forms the dorsocranial section of the base of the heart and receives blood from the cranial vena cava, caudal vena cava and coronary sinus. The interatrial septum is a thin partition dividing the right and left atria and possesses a characteristic oval depression called the '''fossa ovalis''' which is a remnant of the foetal '''foramen ovalis'''. The right atrium also houses the sinoatrial node. Blood flows from the right atrium to the right ventricle through the '''tricuspid valve''' (also know as the right atrioventricular valve).
====Right Ventricle====
The right ventricle forms most of the anterior surface of the heart and is crescent-shaped in cross-section. The cusps of the tricuspid valve are connected to tendon-like cords, the chordae tendinae, which, in turn, are connected to cone-shaped papillary muscles within the ventricular wall. The right ventricle is separated from the left by a partition called the '''interventricular septum'''. The '''trabecula septomarginalis''' is a muscular band that traverses the lumen of the right ventricle. Deoxygenated blood passes from the right ventricle through the '''pulmonary semi-lunar valve''' to the pulmonary trunk, which conveys the blood to the lungs.
====Left Atrium====
The left atrium forms the dorsocaudal section of the base of the heart and is similar to the right atrium in structure and shape. It receives oxygenated blood from the lungs via the pulmonary veins. Blood passes from the left atrium to the left ventricle through the bicuspid or left atrioventricular valve; known as the '''mitral valve''''.
====Left Ventricle====
The left ventricle forms the apex of the heart and is conical in shape. Blood passes from the left ventricle to the ascending aorta through the '''aortic semi-lunar valve'''. From here some of the blood flows into the coronary arteries, which branch from the ascending aorta and carry blood to the heart wall. The remainder of the blood travels throughout the body.
==Pericardium==
==Pericardium==