The heart has two valves between the atria and the ventricles (tricuspid valve on the right and mitral on the left) and between the ventricles and great arteries (pulmonic valve on the right and aortic valve on the left). The pressure on these valves while they are closed during Undertale Skeleton Heart the cardiac cycle is constantly changing and is quite high – the atrio-ventriculat valves have a pressure during systole of around 30 mmHg on the right and 120 mmHg on the left. The pulmonic valve has a pressure against it of about 30 mmHg when it closes, dropping to about 10 mmHg and the aortic valve has a pressure against it close to 120 mmHg when it closes, dropping to 80 mmHg.
The fibrous skeleton consists of 2 ring-shaped fibrous structures, fused together providing a semi-rigid support for the valve leaflets separating atria from ventricles. Undertale Skeleton Heart Without this structure the valve leaflets would stretch at the point they insert into the heart muscle and fail to close properly. The valves would then become “incompetent” and would leak. See below for a more formal description of the “skeleton.”
The fibrous rings surround the atrioventricular and arterial orifices, and are stronger upon the left than on the fight side of the heart. Undertale Skeleton Heart The atrioventricular rings serve for the attachment of the muscular fibers of the atria and ventricles, and for the attachment of the bicuspid and tricuspid valves.
The left atrioventricular ring is closely connected, by its fight margin, with the aortic arterial ring; between these and the fight atrioventricular ring is a triangular mass of fibrous tissue, the trigonum fibrosum, which represents the os cordis seen in the heart of some of the larger animals, as the ox and elephant. Lastly, there is the tendinous band, already referred to, Undertale Skeleton Heart the posterior surface of the conus arteriosus.
The fibrous rings surrounding the arterial orifices serve for the attachment of the great vessels and semilunar valves. Each ring receives, by its ventricular margin, Undertale Skeleton Heart the attachment of some of the muscular fibers of the ventricles; its opposite margin presents three deep semicircular notches, to which the middle coat of the artery is firmly fixed.
The attachment of the artery to its fibrous ring is strengthened by the external coat and serous membrane externally, and by the endocardium internally. From the margins of the semicircular notches the fibrous structure of the ring is continued into the segments of the valves. The middle coat of the artery in this situation is thin, and the vessel is dilated to form the sinuses of the aorta and pulmonary artery. Undertale Skeleton Heart