Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee.

  • Gamgee Arthur, 1841-1909.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    The action of the heart as a pump commences with the systole of the ventricles, which changes the negative pressiu-e of the con- tents into a positive pressure, and causes the auriculo-ventricular valves to close. The closure of the valves is furthered by the simultaneous contraction of the musculi papillares, whilst the contraction of the ventricles forces their whole contents, with- great energy, into the arteries (aorta and pulmonary artery). As soon as the systole ceases, the high pressure of the blood in the large arteries closes the semilunar valves, so that a reflux of blood into the relaxed ventricle is impossible. After a short pause, during which, as was previously mentioned, the ventricles receive blood from the previously filled auricles, the action recommences with the auricular systole. The auriculo-ventricular valves, viz., the tricuspid on the right and the mitral on the left side of the heart, consist respectively of three and two segments, which are connected by a broad basis to the walls of the auriculo-ventricular openings, whilst their free margins are connected to the musculi papillares by means of the chordce tencUnece. When not in action these valves hang slackly in the ventricles. As soon as the pressure within the ventricle surpasses that in the auricle, the back current drives them up, causes them to unfold, and as they are prevented by the chordce tendinece from passing into the auricle, their inner borders are pressed together, so that a complete closure is effected. The semilunar valves are formed by three pocket-like membranes situ- ated at the commencement of the aorta and pulmonary artery. These pouches oppose no obstacle to the passage of blood into the arteries, but so soon as the pressure in the latter becomes greater than that in the ventricles, they fall together, and by their edges press against one another. Their edges then form a three-pointed star. In this position the semilunar valves form a strong barrier between the ventricle and artery. The position of the semilimar valves during systole, and their relation to the coronary arteries, which take their origin in the sinuses of Valsalva, at the commencement of the aorta, are subjects of dispute. Some (Scaramuzzi, The- besius, Briicke ^) suppose that during sj^stole the valves lie close to the arterial wall, in such a manner as to close the openings of the coronary arteries, so that the latter are only supplied vnth blood during diastole. The result of this would be a more easy entrance of blood into the substance of the heart during its relaxation, and a distension of the ventricle in diastole, due to a tm-gescence of its walls, whereby an active asjnration of the blood streaming out of the auricle would be effected ('Selbststeuerung des Herzens' of Briicke). _ Others (Hamberger, Hyrtl,^ Riidinger,^ Oehl, Oeradini*) raise the following objections to this view. (1.) The valves are not pressed against the wall during systole, but are stretched across and away from the sinuses. (2.) When the coronary arteries are cut across, blood flows from them, specially during systole, and from their central ends. (3.) Blood meets with less resistance in flow- ing through the capillaries of muscles during contraction than relaxation (com- pare Chapter VIII.) (4.) The capacity of the cavities of the heart is not only not increased by injection of the coronary arteries, but diminished. According to the most recent researches (Oeradini), the diastolic closure of the semilunar valves is not brought about by a regurgitation of blood, but by the elastic re- bound of the aortic walls at the time when the systolic stream through the axis of the aorta is interrupted; for, during the passage of blood through the aorta., 1 Briicke, Verschluss der Kraiizsch'aqadern dtirch d. Anrtenklaj)pen. VVien, 1855, 2 Hyrt], Ueher d. Selhsisteuerung d. ticrztns. Wien, 18,55. 9 Rudinger, Beitrmje ziir Median, d. Aortenklappen. Erlangcn, 1857. * Ceradini, Der Mechanismus der halbtnondformigen Herzklappen. Leipzig, 1872 G 2