Size and Location of the Heart

Heart size varies with body size. However, an average adult's heart is generally about 14 centimeters long and 9 centimeters wide (fig. 15.2).

The heart is bordered laterally by the lungs, posteriorly by the spinal cord, and anteriorly by the sternum (fig. 15.3 and reference plates 50, 56, 71, and 72). Its base, which is attached to several large blood vessels, lies be ing and targeting angiogenesis may help to save starved heart parts. One approach is to package growth factors in time-release capsules that are implanted near small vessels while large ones are being surgically bypassed. In one clinical trial, this technique increased blood flow to the area and halted chest pain. Another strategy is gene therapy, which delivers the genes that encode the growth factors to oxygen-starved areas.

Cancer Treatment: Preventing Angiogenesis

A tumor surrounds itself with blood vessels. Once it reaches the size of a pinhead, a tumor secretes growth factors that stimulate nearby capillaries to sprout new branches that extend toward it. Endothelial cells within the tumor assemble into sheets, roll into tubules, and, eventually, snake out of the tumor as new capillaries. Other cancer cells wrap around the capillaries, spreading out on this scaffolding into nearby tissues. Some cancer cells enter blood vessels and travel to other parts of the body. For a time, maybe even years, these secondary tumors stay small, adhering to the outsides of the blood vessels that delivered them. But when the primary tumor is removed, angiogenesis-inhibiting factors that it released vanish, and, instead, angiogenesis-promoting growth factors wash over the tumors, and they grow. Experiments with mice demonstrated these events.

In the 1970s, researchers began to study the antiangiogenesis factors that keep secondary tumors small, to develop them as cancer treatments. Two candidates that have had spectacular results in mice are angiostatin and endostatin. So far clinical trials in humans have shown endostatin to be safe even at high doses; trials for efficacy have not yet been completed. (Angiostatin is derived from plasminogen and endostatin from collagen.) Unlike other cancer treatments, angiostatin and endostatin can be used over and over without the targeted tissue becoming resistant, as is the case with conventional drugs. By combining different antiangiogenesis factors, it may be possible to make tumors disappear entirely—as happens experimentally in mice.

neath the second rib. Its distal end extends downward and to the left, terminating as a bluntly pointed apex at the level of the fifth intercostal space. For this reason, it is possible to sense the apical heartbeat by feeling or listening to the chest wall between the fifth and sixth ribs, about 7.5 centimeters to the left of the midline.

10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

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