File:A text-book of physiology - for medical students and physicians (1916) (14747315796).jpg

Identifier: textbookofphysio1916howe (find matches)
Title: A text-book of physiology : for medical students and physicians
Year: 1916 (1910s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Medicine
Publisher: Philadelphia and London : W. B. Saunders Company
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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butedto Thebesius (1708), the flaps of the semilunar valves are thrownback during systole and shut off the coronary circulation, andtherefore the coronary vessels, unlike those of other organs, arefilled during diastole. In modern times this view has been revivedby Brucke, who made it a part of his theory of the self-regulationof the heart beat. According to this view, the coronaries are shutoff from the aorta during systole by the flaps of the semilunar valves,so that the contraction of the ventricle is not opposed by thedistended arteries, while, on the other hand, the reinjection of thesevessels from the aorta during diastole aids in the dilatation of theventricular cavities. Experimental work has shown decisively thatthe part of this theory relating to the closure of the coronary arteriesby the semilunar valves is incorrect.* Records of pressure changesin the coronary arteries during the heart beat made by Martin andSedgwick and by Porter show that they are substantially identical
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Fig. 235.—Simultaneous record of the blood-pressure (A) and the blood-velocity (B)in the coronary arteries (Chauveau and Rebatel): a, Marks the beginning of the systole(there is a rise in pressure and in velocity); b, marks a second rise of pressure (.4) due tothe closure of the coronary capillaries by the contracting ventricle (at this moment in Bthe velocity falls off rapidly); c, curve (B) shows an increase in velocity due to the open-ing of the small coronary vessels at the beginning of diastole. with those in the carotid or aorta, and records of the velocity of theblood-flow made by Rebatel show that at the beginning of systolethe flow in the coronaries suffers a sudden systolic acceleration as inthe case of other arteries. During systole, therefore, the mouths ofthe coronary arteries are in free communication with the aorta.But the coronary system—arteries, capillaries, and veins—is inpart imbedded in the musculature of the ventricles, and we should * See Porter, American

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