None — The Grizzly Bear
The grizzly bear, scientifically known as Ursus arctos horribilis, is a subspecies of the brown bear family. Its brown fur is often coated at the tips with a white coloring. The grizzly also has a black nose, small, round ears and a hump on the back. Fully grown, a grizzly can weigh nearly 700 pounds.
Grizzlies once inhabited a large area of the Great Plains and Rocky Mountains, but they have been hunted almost to extinction. Today, the National Wildlife Foundation estimates only about 1,500 grizzly bears are left in the continental U.S., mostly in Montana, Idaho, Wyoming and Washington.
Grizzly Bear Hibernation Hibernation, or "winter sleep," is a phenomenon unique to several species of mammals, such as the bear, rodents, bats, shrews and some primates. Researchers are unsure of the exact reason why animals hibernate. However, some experts theorize it's necessary for the animal to survive during times when food supplies are low.
The grizzly prepares for hibernation beginning in late summer, eating massive amounts of food to be stored as body fat. In some cases, the bear may double its body mass. Lynne Nelson, D.V.M., Veterinary Cardiologist at Washington State University in Pullman, WA, says it's actually a misperception that bears sleep all winter. In fact, they may walk around or play. Pregnant female bears give birth during hibernation, feed their babies and get up to keep an eye on the wandering cubs.
Studying Hibernating Bear Hearts
Grizzlies and other bears undergo an amazing transformation during hibernation. No matter whether they sleep or are somewhat awake and moving around, they don't eat or drink for the entire time. They live off their fat stores and replenish them when they come out of hibernation in the spring.
To enable the bear to last through the long period of fasting, the heart undergoes some unique changes. Heart rate drops dramatically, from a normal average of 15 beats per minute to 4-5 beats a minute. This helps the body conserve energy. The blood thickens and the heart muscle stiffens. In addition, the atria (two top chambers) appear to shut down during hibernation, causing only the ventricles (lower chambers) to contract.
Nelson says, in a human, these kinds of heart changes would soon lead to death. On the other hand, the ability to safely slow down a human heart beat may aid an ailing or weak heart. Thus, the scientists are studying the hearts of the grizzly bears to look for clues about how the bear's body controls heart rate and contraction of the upper and lower chambers of the heart. These finding may one day lead to the development of medications or treatments for human hearts.
AUDIENCE INQUIRY
If you would like to learn more about grizzly bears, go to:
National Geographic Society, animals.nationalgeographic.com
National Wildlife Federation, nwf.org
For general information about heart disease in humans:
American Heart Association, heart.org
National Heart, Lung and Blood Institute, nhlbi.nih.gov