Anatomicalchanges
In most mammals, growth virtually stops soon after puberty and body weight remains relatively constant for the rest of the life span. Each animal has its preferred body size at any age and will attempt to attain this size if proper food is available.
The common observations with regard to aging are1. Decline in muscular performance:
As the animal grows and increases the size and strength of the muscles, the size of the individual fibers increases but not their numbers. In senescence, the number of fibers decreases, the muscle mass tends to decrease with age, but the amount of decrease is quite variable.
2. Loss in central nervous system:
It has been estimated that the average man loses about 10,000 brain cells per day out of about 10 billion.
3. Accumulation of Collagen:
Once the collagen Once collagen is deposited, it is very insoluble and tends to remain in the tissues for years. Many of the connective tissue cells die and are replaced by collagen fibers. These fibers tend to shrink and join in the course of time, forming a dense network. This accounts for the wrinkled appearance of the skin of old persons. In addition, the dense network tends to impede normal function. Most of the other organs of the body tend to decrease in size as the individual ages. The liver and kidneys decrease by about 20% in man between 25 and 70 years of age, and the spleen by as much as 40%. Another tendency in both animals and humans is to accumulate fat as they grow older. This obesity varies greatly among different animals and even among individuals of the same species (Figure 25.2).
25.4