This may occur suddenly, as when the resistance is increased in the arterial system by a e on f sudden exertion or strain, and more slowly when the resistance is increased in the pulmonary circulation of the by inflammation of the respiratory passages.
Much light has been thrown upon the variations of arterial and venous blood pressures by Karl Ludwig (1816-1895) and his many followers: by them not only the diseases of the circulatory system itself are elucidated, but also those of other systems - the nervous, for instance - which depend intimately on the mechanical integrity of the circulation of the blood as well as on the chemical integrity of the blood itself.
The heart has a pair of venous ostia, often blending into one, and an anterior arterial aorta.
The arterial system is very completely developed in both Limulus and Scorpio, branching repeatedly until minute arterioles are formed, not to be distinguished from true capillaries; FIG.
And on the influence of these inconspicuous bodies and of the pituitary body in sustaining arterial blood pressures physiologists have thrown some important light.
AC, Arterial canal or foramen.
The connexion is not so intimate in Scorpio, but is nevertheless a very close one, closer than we find in any other Arthropods in which the arterial system is well developed, e.g.
In Scorpio the completion of the horizontal plate by oblique flaps, so as to form an actual diaphragm shutting off the cavity of the prosoma from the rest of the body, possibly gives to the organs contained in the anterior chamber a physiological advantage in respect of the supply of arterial blood and its separation from the venous blood of the mesosoma.
The right and left halves are completely divided by septa, no mixture of the venous and arterial blood being possible, an advance upon reptilian conditions, even the highest.
Nitroglycerin is valuable as a preventive in cases of cardiac pain, such as angina pectoris, and it is also used in other conditions where it is desirable to reduce the arterial tension.