CIRCULATION: BLOOD VESSELS

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.

OTHER DISORDERS OF HRT: WOMEN WITH HIGH BLOOD PRESSURE OR A HISTORY

Such women need more intensive surveillance than usual if they try HRT. In any case, it is a good idea for women on HRT to have their blood pressure checked regularly. If significant changes occur, it is important to have a full medical assessment and prompt treatment to control the problem (with blood pressure medications).

If you have a personal history of blood clots that developed for no apparent reason, or a family history of clotting disorders, you should tread cautiously where HRT is concerned. A thorough investigation of clotting function should be completed before deciding about whether or not to embark on hormone therapy. Genevieve developed a spontaneous clot in one leg during her thirties and, many years later, when she was contemplating HRT, a full investigation of her clotting factors was carried out. These revealed some minor abnormalities. However, Genevieve decided to start on a hormone patch to relieve her wide-ranging and severe menopausal symptoms. She asked her doctor about using aspirin to minimise the risk of further clot development, and was told that this was appropriate in her situation.

If clots are triggered by something definite like pregnancy, childbirth or previous surgery, HRT in patch form may be considered suitable. Some studies suggest that HRT does not significantly increase the risk of clots. But where there is any doubt it is wise to avoid taking the hormones in pill form, giving preference to patches. This is because the liver, which plays a major role in blood pressure control and blood clot formation, may become overactive when called on to handle the larger hormone load that occurs with pill formats (the patch releases hormones more gradually).