Studies on Human Capillaries

Abstract

Until the later years of the nineteenth century the current view of the capillary circulation was that the capillaries were passive and that the rate of blood flow through them was determined by the state of the arteriole supplying them. Since then many researches have been carried out which show changes in the capillaries which the observers were unable to explain on the basis of arteriolar changes. The discovery by Rouget (1) of cells on the walls of the capillaries which he believed to be of a contractile nature lent strong support to the view that there is independent contractility of the capillaries. Of late years most observers agree that the capillaries both in man and in animals have the power of independent contractility. Whether they can do this normally without the application of a stimulus to them is disputed and there is also considerable doubt as to the mechanism which is involved in this action.The literature on the subject of capillary physiology has been so admirably reviewed by Krogh (2) that only some important points in the literature of more recent date will be referred to. There seems to be no doubt that the capillaries in both man and in animals can be made to contract by the application of suitable mechanical or chemical stimuli. It has also been definitely shown in animals that electrical stimulation of nerves can cause changes in the caliber of the capillary loops independent of the changes which take place in the arterioles. The work of Krogh (2) on the muscle capillaries has demonstrated that the number of capillaries in which blood is flowing is constantly changing and that the vascular supply is adjusted to the needs of the 351

Are the precapillary sphincters and metarterioles universal components of the microcirculation? An historical review

“…However, the vascular components with contractile activity in the rabbit ear were different from metarterioles, since the metarterioles as proposed by Chambers and Zweifach [17] represented thoroughfare channels connecting arterioles and venules. Chambers and Zweifach [17] claimed that the contractile mechanism observed at the arteriolar source of the capillaries in three previous studies, including Richards and Schmidt’s [28] research on the glomerular capillaries of the frog, Crawford’s [29] research on the epidermal papillae at the base of the human finger, and Fulton and Lutz’s [30] study on frog retrolingual membrane, was so variable and ambiguous that the specific vasoconstriction at the origin of the capillaries could not be determined and that the last one described the precapillary contractility.…”

The Nailbed Capillaries in Disseminated Sclerosis

“…The rate of flow probably depends to some extent on the degree of this shunt so that no comparisons can be made on the number of capillaries or the rate of flow seen at any one time. Crawford and Rosenberger (1926) studied the nailbed capillaries of eight normal individuals by means of cinematography over a period of days. Changes took place from moment to moment and from day to day.…”