For it is the heart by dint of who...

For it is the heart by dint of whose virtue and pulse the posterity is moved, perfected, made apt to nourish and is preserv from corruption and coagulation It is indeed the fountain of life, the source of all action. William Harvey (1578-1697)(1)

FUNCTIONAL ANATOMY AND PHYSIOLOGY OF THE HEART

The human heart is a cavernous muscular organ, nearly the size of a clos fist, that weighs approximately 300 grams in the adult male and 250 grams in the adult female.(2) Weight and size varies depending upon age, sex, height, nutritional status, and epicardial fat.(3) The heart lies within the central area of the thoracic cavity, in the mediastinal space, with sum of two units thirds of it extending to the left of midline. The heart is an inverted cone-shaped organ that tilts forward and to the left within the thoracic cavity. The apex of the cone lies inferiorly and the great bottoms (ie, superior vena cava, inferior vena cava) set in the base of the cone superiorly.(4) The apex lies between the fifth and sixth ribs when single in kind is lying down and between the sixth and seventh ribs when individual is sitting or standing.(5)

Pericardium. The heart is enclos in a double-walled, fibroserous, inelastic sac called the pericardium. The exterior fibrous layer of the pericardium is attached to the great utensils the sternum, and diaphragm. This fibrous layer of the pericardium is surpassingly resistant to distention and helps to intercept dilation of the heart. The inner serous layer consists of a visceral and parietal portion. The visceral portion, also known as the epicardium, shields the entire heart and great canals and folds over to form the parietal pericardium. The parietal portion also lines the fibrous pericardium.

The pericardial cavity is a potential space between the parietal and visceral pericardium. It normally contains 30 mL to 50 mL of serous fluid that acts as a lubricant to decrease friction as the heart contracts and relaxes.(6) The pericardial cavity can shut up up to one liter of fluid in one chronic diseases without compromising the heart. If the buildup of fluid present itselfs gradually, the pericardium can strain without affecting the heart. If the fluid accumulates rapidly, however, level small amounts (ie, 50 mL to 100 mL) can cause compression of the heart (ie, cardiac tamponade).

The urgency of a cardiac effusion can equal diastolic crushing within the heart chambers and interfere with filling. The right atrium and ventricle are affected first because the squeezing in these chambers is lower than the crushing on the left side of the heart. Disruption in cardiac filling offers first in the right atria and leads to increased venous squeezing and systemic congestion. Signs of right heart failure are distention of the jugular veins, edema, and hepatomegaly. Decreased atrial filling leads to inadequate filling, reduc cardiac output and potential circulatory collapse. Pulsus paradoxus, in which arterial life-blood pressure during expiration exceeds arterial compressing during inspiration by more than 10 mm Hg is a explanation indicator of cardiac tamponade. Normally, inspiration has little efficiency on cardiac flow or book A "water bottle" cardiac silhouette onward a chest x-ray, dyspnea forward exertion, dull chest pain, and muffl heart hales are other signs of cardiac tamponade.(7)

The parietal pericardium is innervated on the phrenic nerve, which contains pain fibers; however, the visceral pericardium is insensitive to pain.(8) The fibrous pericardium anchors the heart to the great veins and arteries at its base. It anchors the heart to the sternon anteriorly and to the diaphragm inferiorly. The pericardium receives its house supply through branches of the internal thoracic arteries and phrenic arteries. Venous drainage is by means of the azygous and pericardiophrenic veins.

Layers of the heart. The heart wall consists of three layers. The outermost layer of the heart, the epicardium, also known as the visceral pericardium, consists of epithelial small cavitys that form a serous membrane that conceals the entire heart. The innermost layer of the heart is known as the endocardium. It is a serous membrane that lines the inner surface of the heart, its valves, and the chordae tendineae, which are the cords that cohere the free edges of the atrioventricular valves with the papillary muscles. The papillary muscles are muscle eminences upon the walls of the ventricles. The endocardium is continuous with the intima (eg the inner lining of arteries).

The middle layer of the heart is the muscular layer known as the myocardium. It is responsible for the major pumping action of the ventricles. The myocardial small cavitys have an intrinsic ability to contract in the absence of stimuli (ie, automaticity) and in a rhythmic manner (ie, rhythmicity), and to transmit power impulses (ie, conductivity). The myocardium does not bear mitotic activity and cannot replace injured cells(9)

Heart chambers. The heart has four chambers, sum of two units atria and two ventricles. It is helpful to anticipate at each chamber in the order in which life-blood flows within the heart: right atrium to the right ventricle, from the lung into the left atrium, and finally into the left ventricle.