Il sistema cardiovascolare
Il sistema cardiovascolare è costituito da tre elementi:
(1) il sangue - un fluido che circola per il corpo e che porta sostanze alle cellule e ne allontana altre;
(2) i vasi sanguigni - condotti attraverso which the blood circulates;
(3) the heart - a muscular pump that distributes blood flow in the vessels.
The cardiovascular system can deliver substances throughout the body more quickly than you can do the spread, since the molecules in the blood move in the liquid assets such as particles of water in a river. In the bloodstream the molecules move faster because they do not proceed at random, forward-backward or zig-zag as in the spread, but precise and orderly.
Blood flow is so crucial for our existence that if blood flow is stopped at some point, we would lose consciousness within a few seconds and spirit after a few minutes. Of course the heart has to perform its function continuously and correctly, every minute and every day of our lives.
Heart
The heart is contained in the center of the rib cage, located in front and slightly to the left. Its shape roughly resembles that of a cone, whose base is facing up (right), while the tip is pointing down toward the left.
The myocardium, the heart muscle that allows the heart to contract, sucking blood from the periphery e pompandolo nuovamente in circolo.
Internamente, il cuore è rivestito da una membrana sierosa, detta endocardio. Esternamente, invece, il cuore è contenuto in un sacco membranoso detto pericardio, che costituisce lo spazio entro il quale il cuore è libero di contrarsi, senza dover per forza dare luogo ad attriti con le strutture circostanti. Le cellule del pericardio secernono un liquido che ha il compito di lubrificare le superfici per evitare tali attriti.
La cavità del cuore è divisa in quattro aree: due aree atriali (atrio destro e atrio sinistro) e due aree ventricolari (ventricolo destro e ventricolo sinistro).
Le due cavità di destra (atrio e ventricolo) are communicating with one another through the right atrioventricular orifice, which is periodically closed by the tricuspid valve. The two cavities are in communication through the left atrioventricular orifice left by the cyclically closed bicuspid valve or mitral valve.
The right cavities are completely separated from the cavity of the left, this separation is performed by two weeks: the septal (which separates the two atria) and the interventricular septum (which separates the two ventricles).
The operation of the tricuspid valve (three flaps connective) and the mitral valve (formed by two edges connective) allow blood to flow along one direction, starting from the atria, right up to the ventricles, and not vice versa.
The right ventricle originates from the pulmonary artery, and is separated from this through the pulmonary valve (consisting of three flaps of connective). The left ventricle is separated from the aorta through the aortic valve, which has a morphology quite comparable to the pulmonary valve.
These two valves allow blood to flow from the ventricle to blood vessel (pulmonary artery and aorta), and that this can change direction.
The right atrium receives blood from the periphery through two veins : the superior vena cava and inferior vena cava. This blood, known as venous, and low in oxygen reaches the heart muscle because of reoxygenation. In contrast, the left atrium receives arterial blood (oxygen rich) from the four pulmonary veins, so that the blood can be passed around and carry out its mission: reoxygenate and give nutrients to various tissues.
The heart, like skeletal muscle, it contracts in response to an electrical stimulus: for skeletal muscle this stimulus comes from the brain through various nerves to the heart, however, the pulse shape so self in una struttura chiamata nodo seno-atriale, da dove l'impulso elettrico raggiunge il nodo atrio-ventricolare.
Dal nodo atrio-ventricolare origina il fascio di His, che conduce l'impulso verso il basso; il fascio di His si divide in due branche, quella di destra e quella di sinistra, che discendono rispettivamente sul versante destro e sinistro del setto interventricolare. Questi fasci vanno progressivamente ramificandosi, raggiungendo, con le loro ramificazioni, tutto il miocardio ventricolare, dove l'impulso elettrico produce la contrazione del muscolo cardiaco.
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