The Lumleian lectures on the muscular arterioles : their structure and function in health and in certain morbid states : delivered at the Royal College of Physicians / by George Johnson.

  • Johnson, George, 1818-1896.
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: The Lumleian lectures on the muscular arterioles : their structure and function in health and in certain morbid states : delivered at the Royal College of Physicians / by George Johnson. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    the blood-vessels of the submaxillary gland, and a rapid and profuse secretion of saliva. Many experiments of various kinds have proved that the vessels may be made to contract or to dilate by an influence conveyed through in- cident nerves to the centre, and thence reflected through other fibres to the arterioles. Thus when a sensitive nerve, such as the fifth, or a mixed nerve like the sciatic, has its central end stimulated, a reflex contraction of the arterioles occurs throughout the body, and the blood- pressure rises. On the other hand, Ludwig and Cyon discovered that one branch of the pneumogastric, when its central end is stimu- lated, has a reflex influence on the vaso-motor nerves, which causes a general relaxation of the arterioles and a consequent fall of the blood- pressure. This nerve, therefore, is called the depressor nenie. There is now a very general agreement amongst physiologists with respect to the influence which the heart, the large elastic arteries, and the muscular arterioles respectively exert upon the circulation. The force which propels the blood through the systemic arteries is derived entirely from the contraction of the muscular walls of the left ventricle of the heart. The elastic walls of the large arteries, distended by the injecting force of the ventricle, contract and force the blood onwards during the diastole of the ventricle. This forcible resiliency in the wallb of the arteries is as obviously derived from the muscular con- traction of the heart as the elastic power of an archer's bow has its source in the contracting muscles of the arm which bends the bow. The resiliency of the arterial wall, reacting upon the blood during the diastole of tlie ventricle, gradually converts the interrupted jet of blood from the heart into a continuous current in the minute arteries and ca- pillaries. The muscular arterioles, under the influence of the vaso- motor system of nerves, regulate the blood-supply to the various organs and tissues. The action of the muscular arterioles is, as I have ventured to suggest {Medico-Chirurgical Transactions, vol. 51, p. 60), that of stopcocks. By the contraction of the muscular walls, their canals are narrowed, the blood-stream is in a corresponding degree lessened, and the pressure of blood in the larger arteries is increased. On the con- trary, relaxation of the walls of the arterioles enlarges their canals, permits a fuller stream of blood to pass, and lowers the blood-pressure in the arterial trunks. The minute muscular arteries, therefore, through their stopcock action, exert a regulating but not a propelling influence upon the blood-current. The influence of the heart, the larger elastic arteries, and the mus-