The fine subdivisions of blood vessels result in every minute portion of the body getting supplied, as you may readily realize when you consider how even a pin prick produces bleeding. A little way back the resemblance of the blood system to the branching tree was suggested. It has often been so depicted. But if a branch is broken, the leaves at its tip wither.
Such a calamitous result is uncommon in the body, for the blood system really is like the network of highways in the country. If the main route is blocked, it is bothersome, but traffic can be rerouted. The side routes for the blood are referred to as collateral circulation.
John Hunter, the famous eighteenth-century English surgeon, did a great deal to study and described these side circulations.His most famous experiment consisted in tying the vessels which carry blood to a deer’s antler. One would naturally suppose that this constriction would interfere with the growth of the antler, but Hunter found that other large vessels appeared, or at least enlarged so that they became noticeable, and the antler continued to grow.
We used to think that there were a number of places in the body that were supplied by what we called end arteries; that there was only one route for the blood to traverse, and if this was blocked then no blood reached the part. The more the matter has been investigated, the more we find that this is not so. The coronary arteries in the heart were among the last to be proved to have this side circulation. Recent investigations have shown that coronary arteries can be blocked off and in many instances the blood does get to the tissues by side routes.
There is a theory that in the early stages of life all these vessels are equally important, but then some one vessel takes over most of the load and the others do not develop. When your pulse is counted, the throb comes through the radial artery in the wrist for that is carrying lots of blood to your very important hand. Most of you could find no evidence of blood getting through by any other channel. Yet the’ radial artery can be cut and tied off, and other vessels will take over the work with very little difficulty.The veins which bring the blood back have even more side routes to help out.
The circulation of blood in the brain has to be carefully adjusted. Too little or too much makes a great difference here. The jugular veins, one on each side of the neck, are tremendous big pipes; but when we dissect the side of the neck, as we frequently do for cancer, we think little of removing the jugular. That big flow of blood goes off by other channels and the brain minds it not at all. The patient may be up and around the next day. Nature is a good traffic engineer. She can adjust to peak loads and times of light traffic more successfully than is done on our streets.
John Hunter, the famous eighteenth-century English surgeon, did a great deal to study and described these side circulations.His most famous experiment consisted in tying the vessels which carry blood to a deer’s antler. One would naturally suppose that this constriction would interfere with the growth of the antler, but Hunter found that other large vessels appeared, or at least enlarged so that they became noticeable, and the antler continued to grow.
We used to think that there were a number of places in the body that were supplied by what we called end arteries; that there was only one route for the blood to traverse, and if this was blocked then no blood reached the part. The more the matter has been investigated, the more we find that this is not so. The coronary arteries in the heart were among the last to be proved to have this side circulation. Recent investigations have shown that coronary arteries can be blocked off and in many instances the blood does get to the tissues by side routes.
There is a theory that in the early stages of life all these vessels are equally important, but then some one vessel takes over most of the load and the others do not develop. When your pulse is counted, the throb comes through the radial artery in the wrist for that is carrying lots of blood to your very important hand. Most of you could find no evidence of blood getting through by any other channel. Yet the’ radial artery can be cut and tied off, and other vessels will take over the work with very little difficulty.The veins which bring the blood back have even more side routes to help out.
The circulation of blood in the brain has to be carefully adjusted. Too little or too much makes a great difference here. The jugular veins, one on each side of the neck, are tremendous big pipes; but when we dissect the side of the neck, as we frequently do for cancer, we think little of removing the jugular. That big flow of blood goes off by other channels and the brain minds it not at all. The patient may be up and around the next day. Nature is a good traffic engineer. She can adjust to peak loads and times of light traffic more successfully than is done on our streets.
No comments:
Post a Comment