What Causes Fiyblood

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Shier-Butler-Lewis: I VI. The Human Life Cycle I 22. Reproductive Systems I I © The McGraw-Hill

Human Anatomy and Companies, 2001

Physiology, Ninth Edition minimize the side effects of chemotherapy with additional drugs, and by using a regimen of lower but more frequent doses.

Drugs called selective estrogen receptor modulators (SERMs) are used for women whose cancer cells have receptors for estrogen. These drugs include tamoxifen, which has been used for more than 20 years, and a newer drug called raloxifene. SERMs block the receptors, so that estrogen cannot bind and trigger division of cancer cells. In contrast to standard chemotherapies, which are given for weeks or months, SERMs are taken for many years. Ongoing clinical trials are investigating whether tamoxifen can prevent cancer in certain women who are at very high risk for inherited forms of the illness.

Another new breast cancer drug, Herceptin, can help women whose cancer cells bear many receptors that bind a particular growth factor. Herceptin is a type of immune system biochemical called a monoclonal antibody. It prevents the growth factor from stimulating cell division.

prevention strategies

Healthcare agencies advise women to have baseline mammograms by the age of forty, and yearly mammo-grams after that. Although a mam-mogram can detect a tumor up to two years before it can be felt, it can also miss some tumors. Breast self exam is also important in early detection.

Genetic tests are becoming available that can identify women who have inherited certain variants of genes — such as BRCA1, BRCA2, p53, and her-2/neu—that place them at very high risk for developing breast cancer. Women at high risk can be tested more frequently, and some have even had their breasts removed because they have inherited a gene variant that, in their families, predicts a very high risk of developing breast cancer. In one family, a genetic test told one woman whose two sisters and mother had inherited breast cancer that she had escaped their fate, and she canceled the surgery. Yet her young cousin, who thought she was free of the gene because it was inherited through her father, found by ge netic testing that she would likely develop breast cancer. A subsequent mammogram revealed that the disease had already begun.

Only five to ten percent of all breast cancers are inherited directly. This means that a person inherits one mutation that is present in all cells (a germinal mutation), and then the cancer starts when a second mutation occurs in a cell of the affected tissue (somatic mutation). Most cancers are caused by two mutations in a cell of the affected tissue. Much current research seeks to identify the environmental triggers that cause these somatic mutations. ■

Figure 22E

Mammogram of a breast with a tumor (arrow).

Figure 22E

Mammogram of a breast with a tumor (arrow).

Hormonal Control of the Mammary Glands

Before Pregnancy (Beginning of Puberty)

Following Childbirth

Before Pregnancy (Beginning of Puberty)

Following Childbirth

Ovarian hormones secreted during menstrual cycles stimulate alveolar glands and ducts of mammary glands to develop.

1. Placental hormonal concentrations decline, so the action of prolactin is no longer inhibited.

2. The breasts begin producing milk.

3. Mechanical stimulation of the breasts releases oxytocin from the posterior pituitary gland.

4. Oxytocin stimulates ejection of milk from ducts.

5. As long as milk is removed, more prolactin is released; if milk is not removed, milk production ceases.

During Pregnancy

1. Estrogens cause the ductile system to grow and branch.

2. Progesterone stimulates development of alveolar glands.

3. Placental lactogen promotes development of the breasts.

4. Prolactin is secreted throughout pregnancy, but placental progesterone inhibits milk production.

Essentials of Human Physiology

Essentials of Human Physiology

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