The heart is one of the most important organs of the human body. It is a hollow organ and is composed almost entirely of muscles. The weight of a normal heart is about 250-350 grams, yet has enough power to beat over 70 times per minute, thus pumping blood throughout the body.
Presents: From the outside:
A peak (apex).
From the inside:
The lower face or diaphragmatic lies beneath, consisting of right and left ventricles, separated from the posterior interventricular groove.
The front face or sternocostal is on the front of the heart behind the breastbone and ribs being formed mostly from the right ventricle.
The left face or pulmonary consists mainly of the left ventricle.
The heart base is posterior and consists mainly of the left atrium.
The right edge is formed by the right atrium and is directly related to the pleura and with the medial face to the right lung.
Anterior and posterior edges are not well highlighted.
Peak heart (apex) is the tip of the left ventricle and is usually found behind the fifth left intercostal space, about 10 cm from the midline. In this point, heart pulsations can be felt.
The structure of the atria: is slightly different from that of the ventricles. The atria located above the ventricles which are separated by the atrioventricular valves. All venous blood from the body is brought into the right atrium from the superior vena cava and inferior vena cava. Coronary sinus, which collects venous blood vessel from the heart tissues, and it drains into the right atrium. The interior has a posterior, smooth wall, and some previous rough wall. The anterior wall consists of muscle pectin, which gives the appearance of a comb inner surface.
Pectin muscles are extending is into a small hole from the right atrium called the auricle, because has the form of the ear. This conical cavity is wrapped around the main artery of the heart, aorta, and acts to increase the capacity of the right atrium.
The right ventricle is located anterior, forming a large part of the front face of the heart. Receives blood from the right atrium, is impeded by the tricuspid valve backflow. The blood is then pumped due to ventricular myocardium contraction, through the pulmonary vein into the pulmonary trunk and from there into the lungs. The right ventricle forms, in cross-section, a crescent because it is distorted by the left ventricle, which is more muscular.
The left ventricle is located posterior-inferior, occupying most of the lower face. Receives blood from the left atrium through the left atrioventricular orifice, where is located the bicuspid valve. Strong contractions of the left ventricle pump the blood through the aortic valve into the aorta. The muscle walls of the left ventricle are twice as thick as those of the right ventricle and in the cross-section form a kind of circle.
Heart valves: the heart is a strong muscular pump, through which blood flows in one direction only. Reflux is impeded by four valves, which have a vital role in maintaining circulation. On the right side of the heart, the tricuspid valve between the atrium and ventricle and the pulmonary valve is located at the junction ventricle with the pulmonary trunk. On the left side of the heart, the mitral valve separates the left atrium from the ventricle, while the aortic valve is located between the left ventricle and aorta.
Mitral or tricuspid valve and the atrioventricular valves are made of tough conjunctive tissue covered by endocardium, a thin layer of cells that lines the heart. The upper surface of the valves is smooth, while the lower surface contains chordae tendon insertions.
Tricuspid valve presents three cusps or wings.
Bicuspid or mitral valve has 2 cusps. The name of ”mitral” comes from its supposed resemblance to a bishop’s miter.
When the heart is in systole, the ventricles contract, and the aortic and pulmonary valves open, allowing the blood to be pumped out of the heart.
During diastole, the ventricles of the heart muscle relax. Tricuspid valve and the mitral valve opens, allowing blood to pass from atrium and to fill the ventricles.
Semilunar valves or pulmonary and aortic valves monitor the way out of the blood from the heart, preventing reflux of blood into the ventricles when they relax after contraction. Each of these valves has three cusps of the crescent-shaped, having a core of connective tissue covered by endothelium lining. This ensures a smooth lining for blood circulation.
Aortic valve: located between the left ventricle and aorta. It is stronger and more robust than the pulmonary valve because you have to face greater pressure of systemic circulation. Above each valve cusps are found aortic sinuses formatted by the dilated aortic walls. In two of these sinuses the coronary arteries originate from right and left, which carries blood to the myocardium and heart shells.
Pulmonary valve: separates the ventricle from the pulmonary trunk, large artery that carries blood from the heart to the lungs. Immediately above each valve cusps, the pulmonary trunk expands slightly and forms pulmonary sinuses, blood-filled spaces that prevent cusps from sticking to the arterial wall behind them, when they open.
Cardiac wall structure: cardiac wall is made from the outside in: epicardium, myocardium and endocardium.
Epicardium represents foil visceral serous pericardium and aims at preventing the occurrence of friction during rhythmic contractions of the heart. Between epicardium and endocardium is found myocardium with fibrous skeleton of the heart conduction system.
The myocardium shows a contractile myocardium and the conduction system. Myocardium Contractile is the myocardial muscle fibers and ventricular fibrillation, the atrial are located deep and superficial, and the spiral are ventricular and in the interventricular deeper layers.
The heart innervation: The heart represents sympathetic and parasympathetic innervation.
Parasympathetic Innervation is supported with cervical and thoracic cardiac branches of the two nerves vague. The superior cervical cardiac nerves emerge from the vagus nerve, above the inferior ganglion of the vagus and the inferior cardiac nerves emerging from the recurrent laryngeal nerve. Parasympathetic innervation is cardio-moderate action: decreases heart rate and cause coronary artery vasoconstriction.
Sympathetic Innervation is achieved through superior cervical cardiac nerve, middle and lower thoracic cardiac nerves with 3-4. Superior cervical cardiac nerve originates in the superior cervical sympathetic ganglion. Middle cervical cardiac nerve has its origins in the middle cervical ganglion and the inferior cervical cardiac nerve originates in the stellate ganglion. Sympathetic innervation action is to increase the heart rate and dilates coronary.
Excito-conduction system of the heart
When the body is at rest, the heart beats at a rate of about 70-80 beats per minute. In its muscular walls, a proper management provides the rhythm and watches the muscle to contract constantly.
Excito-conduction system consists of myocardial cells with specific properties such as automaticity and impulse management. Myocardial cells which present automatism myocardial cells are called P type or pacemaker. Automatism represents the property to get heart esteem. Removed from the body, the heart continues to beat. In the absence of extrinsic influences the nerve, autonomic and humoral heart rhythmic activity continues for hours or days, if irrigated with a special nutrient liquid. Automaticity is generated in certain centers, which have in their composition cells which initiate and conduct the impulses. Normally, there are three centers in the heart of cardiac automatism:
Sinoatrial node (Keith-Flack node): represents a group of cells in the wall of the right atrium. Each cell contraction of the sinoatrial node generates an electrical impulse, which is transmitted to other muscle cells in the right atrium and the left and then to the atrioventricular node. In the sinoatrial node, the frequency of discharge is faster, of 70-80 beats per minute and therefore, cardiac activity is led by this center, the heart beating normally in sinus rhythm.
Atrioventricular node (Aschoff-Tawara node, atrioventricular junction): is a group of nodal tissue; oval-shaped and is located in the right atrium floor. Atrioventricular node cells will initiate their own contraction and will transmit pulses with a lower cadence if not stimulated by the SA node. Impulses from the AV node are transmitted to the ventricles, the impulse conduction system. At this level, the frequency of discharge potential is 40 per minute. Therefore, the center cannot occur normally, although he constantly runs in parallel with the SA node. If the sinus is removed from office center, the heart is taken over command of the AV node, which prints the heart nodal rhythm or junctional.
His bundle and Purkinje network: here, the discharge frequency is 25 pulses per minute. This center can control the heart only if atrioventricular disruption, printing idiopathic ventricular heart rhythm.
Functional rhythm of the command center can be changed under the influence of some external factors. Heat or stimulation of the sympathetic nervous system accelerates the heart rate, tachycardia, while cooling the sinus node or the parasympathetic nervous system stimulation, bradycardia have the opposite effect.
Excitability: are the properties of cardiac muscle cell to respond to a stimulus by action potential propagation. Some manifestations of excitability (the excitability threshold law, all or nothing”) are common to other excitable cells. The heart shows the particularity of being excitable only in the relaxation phase (diastole) and contraction of inexcitability phase (systole). This is the law of periodic inexcitability heart. During systole, the heart is in absolute refractory period: no matter how strong it would be stimulating, it has no effect. This feature of myocardial excitability presents great importance for preserving rhythmic pump function. High frequency stimuli cannot tetanize by summing heart contractions. Refractory status explanation lies in the particular form of the heart of the potential action of myocardial fibers.
Conductivity: represents the property the myocardium to spread excitement to all its fibers. Conduction velocity differs: it is 10 times through the His bundle and Purkinje fibers than in myocardial contractile atrial and ventricular.
Contractility: represents the property of developing myocardial tension between the fibers ends. Thus, in cavities heart generates pressure and shortening due to myocardial fibers, blood expulsion occurs. Genesis tension and shortening velocity are fundamental manifestations of contractility. The force of contraction is proportional to the thickness of heart wall: lower in atria and stronger in the ventricles, bigger in the left ventricle that in the right ventricle.