Diseases of the veins are different from those of the arteries because of the structural differences. Blockages can occur in the veins, but these are usually caused by blood clots (thrombi) and not by atherosclerosis.  When a thrombus forms in a vein, blood is prevented from traveling back toward the heart. The collection of blood results in increased pressure and often leads to swelling and tenderness. For example, a blood clot in the deep vein of the calf will cause the calf and foot to become swollen and tender. This condition is referred to as deep venous thrombosis.seepage of fluid into the surrounding tissues (edema) can be uncomfortable. Clotting of blood in the veins tends to occur whenever the blood flow in the vein is slow or becomes stagnant. Typically this occurs in the legs when you are still, as in a long ride in a car c plane, when you are constantly in bed because of illness or surgery, or after an injury to the leg.The main risk of blood clots forming and causing deep venous thrombosis is that the blood clot can enlarge and extend up the vein. If a piece breaks off, it can travel upstream and lodge in the heart or lungs. Just as in the arterial circulation, this disorder is called thromboembolism. A thrombus that dislodges from a vein in the leg will travel through larger and larger veins until it reaches the right side of the heart. From there it will enter the pulmonary artery and lodge in a branch, at which point it blocks blood flow to part of the lung. A clot in the lung circulation is a pulmonary embolus.Treatment with anticoagulants (“blood thinners”) in the early stages of deep venous thrombosis can prevent enlargement of the clot and lessen the likelihood of pulmonary embolism.*205\252\8*

Hormones also contribute to regulation of the amount of blood that your heart pumps. Norepinephrine is one of several hormones that affect blood pressure by varying the quantity of blood your heart pumps. Because your heart is composed mostly of muscle that is affected by hormones, hormones can cause it to contract more vigorously with each beat. More vigorous contractions mean that more blood is pumped with each beat.Hormones also can change the total quantity of your blood. When the quantity increases, your heart pumps more blood and your blood pressure increases. Your kidney makes a hormone called renin, which increases blood volume because it causes your body to retain salt, which in turn causes retention of water. Some of this extra water joins your bloodstream and adds to the volume of blood in your body. Renin also causes formation of another hormone, angiotensin, which acts to constrict or squeeze the muscle cells of the arterioles.Your arterioles and heart are also regulated by your nervous system, specifically your autonomic nervous system, over which you have no conscious control. In the presence of any type of stress, including excitement or exercise, your body increases the quantity of blood that is pumped by your heart, and blood pressure goes up. Your autonomic nervous system also is responsible for releasing the hormone norepinephrine, which causes veins to contract and blood to return to your heart more rapidly. This also increases the amount of blood pumped by your heart.
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Over the years there has been growing evidence that tamoxifen induces tumor growth in the lining of the uterus (or endometrium). In a recent study many of the women who developed irregular vaginal bleeding due to tamoxifen therapy were found also to have small noncancerous growths or polyps of the uterine lining. A number of them went on to develop tumors of the endometrium.Although many physicians consider the incidence of tamoxifen-induced uterine tumors to be small, there is still a significant risk. In one clinical study evaluating 46 nonhysterectomized postmenopausal women receiving tamoxifen for 6 to 36 months, 13 patients developed noncancerous growths or polyps, 8 had thickening of the uterine lining, and 2 developed cancer of the endometrium.The incidence of uterine tumors appears to increase with higher doses of tamoxifen. With the usual dose of 10 mg twice daily, an incidence of 0.17 percent was reported, while patients receiving 20 mg of tamoxifen twice daily had an incidence nearly ten times higher (1.2 percent).Although surgical hysterectomy can be performed once a tumor develops in the uterus, new evidence suggests that the types of tumors that develop while a woman is taking tamoxifen are extremely aggressive. Women who develop uterine cancers induced by tamoxifen therapy may be more likely to die from uterine cancer than those who spontaneously develop this form of cancer.*35\320\2*