[{"Title":"Aging cells","UniqueID":"v837983","Index":1.0,"Summary":"

As cells age, they function less well. Eventually, old cells must die, which is a normal part of the body’s functioning.

","HeadType":"H_Head","SchemeItemProp":"","Children":[]},{"Title":"Aging organs","UniqueID":"v838003","Index":2.0,"Summary":"

How well organs function depends on how well the cells within them function. Older cells function less well. Also, in some organs, cells die and are not replaced, so the number of cells decreases. The number of cells in the testes, ovaries, liver, and kidneys decreases markedly as the body ages. When the number of cells becomes too low, an organ cannot function normally. Thus, most organs function less well as people age. However, not all organs lose a large number of cells. The brain is one example. Healthy older adults do not lose many brain cells. Substantial losses occur mainly in people who have had a stroke or who have a disorder that causes the progressive loss of nerve cells (neurodegenerative disorders), such as Alzheimer disease or Parkinson disease .

","HeadType":"H_Head","SchemeItemProp":"","Children":[]},{"Title":"Bones and Joints","UniqueID":"v8967819","Index":3.0,"Summary":"

(See also Effects of Aging on the Musculoskeletal System .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Muscles and Body Fat","UniqueID":"v8967834","Index":4.0,"Summary":"

The amount of muscle tissue (muscle mass) and muscle strength tend to decrease beginning around age 30 and continuing throughout life. Some of the decrease is caused by physical inactivity and decreasing levels of growth hormone and testosterone, which stimulate muscle development. Also, muscles cannot contract as quickly because more fast-contracting (fast-twitch) muscle fibers are lost than slow-contracting (slow-twitch) muscle fibers. However, aging's effects reduce muscle mass and strength by no more than about 10 to 15% during an adult's lifetime. In the absence of disease, most of the loss beyond that 10 to 15% is preventable with regular exercise. More severe muscle loss (called sarcopenia, which literally means loss of flesh) results from disease or extreme inactivity, not from aging alone.

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Eyes","UniqueID":"v8967857","Index":5.0,"Summary":"

(See also Effects of Aging on the Eyes .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Ears","UniqueID":"v8967919","Index":6.0,"Summary":"

(See also Effects of Aging on the Ears, Nose, and Throat .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Mouth and Nose","UniqueID":"v8967945","Index":7.0,"Summary":"

(See also Effects of Aging on the Mouth and Teeth and Effects of Aging on the Ears, Nose, and Throat .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Skin","UniqueID":"v8967959","Index":8.0,"Summary":"

(See also Effects of Aging on the Skin .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Brain and Nervous System","UniqueID":"v8967970","Index":9.0,"Summary":"

(See also Effects of Aging on the Nervous System .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Heart and Blood Vessels","UniqueID":"v8967998","Index":10.0,"Summary":"

(See also Effects of Aging on the Heart and Blood Vessels .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Lungs and the Muscles of Breathing","UniqueID":"v8968006","Index":11.0,"Summary":"

(See also Effects of Aging on the Respiratory System .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Digestive System","UniqueID":"v8968012","Index":12.0,"Summary":"

(See also Effects of Aging on the Digestive System .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Kidneys and Urinary Tract","UniqueID":"v8968021","Index":13.0,"Summary":"

(See also Effects of Aging on the Urinary Tract .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Reproductive Organs","UniqueID":"v8968043","Index":14.0,"Summary":"

(See also Effects of Aging on the Female Reproductive System .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[{"Title":"Women","UniqueID":"v8968047","Index":1.0,"Summary":"

(See also Effects of Aging on the Female Reproductive System .)

","HeadType":"H_Head","SchemeItemProp":"","Children":[]},{"Title":"Men","UniqueID":"v8968063","Index":2.0,"Summary":"

(See also Effects of Aging on the Female Reproductive System .)

","HeadType":"H_Head","SchemeItemProp":"","Children":[]}]},{"Title":"Endocrine System","UniqueID":"v8968069","Index":15.0,"Summary":"

(See also Effects of Aging on the Endocrine System .)

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Blood Production","UniqueID":"v8968088","Index":16.0,"Summary":"

The amount of active bone marrow, where blood cells are produced, decreases. Therefore, fewer blood cells are produced. Nonetheless, the bone marrow can usually produce enough blood cells throughout life. Problems may occur when the need for blood cells is greatly increased—for example, when anemia or an infection develops or bleeding occurs. In such cases, bone marrow is less able to increase its production of blood cells in response to the body’s needs.

","HeadType":"F_Head","SchemeItemProp":"","Children":[]},{"Title":"Immune System","UniqueID":"v8968093","Index":17.0,"Summary":"

The cells of the immune system act more slowly. These cells identify and destroy foreign substances such as bacteria, other infecting microbes, and probably cancer cells. This immune slowdown may partly explain several findings associated with aging:

","HeadType":"F_Head","SchemeItemProp":"","Children":[]}]