Physiology and biochemistry in modern medicine . Fig. 77.—Tracing to show the effect of gravity on the arterial blood pressure. At A, theanimal was placed in the vertical position; at B, the abdomen was compressed; at C, a crucialincision was made in the abdomen; at D, the pleural cavity was opened; at F, the animal wasreturned to the horizontal position. (From Leonard Hill.) the second factor by cutting the great splanchnic nerves, or the spinalcord. After such an operation, even while in the horizontal position, aswe have seen, the blood pressure falls to a considerable extent. If theanimal
Physiology and biochemistry in modern medicine . Fig. 77.—Tracing to show the effect of gravity on the arterial blood pressure. At A, theanimal was placed in the vertical position; at B, the abdomen was compressed; at C, a crucialincision was made in the abdomen; at D, the pleural cavity was opened; at F, the animal wasreturned to the horizontal position. (From Leonard Hill.) the second factor by cutting the great splanchnic nerves, or the spinalcord. After such an operation, even while in the horizontal position, aswe have seen, the blood pressure falls to a considerable extent. If theanimal is now placed in the vertical tail-down position, however, it falls 246 THE CIRCULATION OF THE BLOOD to the zero line and the animal soon dies (Fig. 78). The influence of thethird factor is not so great as of the other two, but can be shown by theincreased respiratory activity which is likely to develop in the vertical. Fig. 78.—The effect of gravity on the aortic pressure after division of the spinal cord in theupper dorsal region. By placing the animal in the vertical feet-down posture, the pressure fellalmost to zero, but on returning it to the horizontal posture, the circulation was restored. (FromLeonard Hill.) tail-down position, the anemic condition of the respiratory center beingno doubt the cause of the increased respiration. CHAPTER XXVIII PECULIARITIES OF BLOOD SUPPLY IN CERTAIN VISCERA Up to the present we have been considering the circulation of the bloodfrom a general point of view. There are certain organs and tissues, how-ever, in which the general mechanism is altered in order to meet pecu-liar requirements of blood supply. Thus, it is evident that the brain,incased as it is in the rigid cranium, will be unable to contract andexpand as a result of vasoconstriction or vasodilation. On the otherhand, we know that the blood supply to this organ does vary con-siderably from time to tim
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