Kidneys

After the age of 40 there is a decrease in the number of cells within the kidney.  As this is happening there is a thickening of the connective tissue capsule surrounding the organ and a decrease in the thickness of the cortical region.

The loss of kidney cells is explained mostly by a loss of glomeruli. As glomeruli are responsible for filtration, the loss of cells is associated with a loss of kidney functioning.

Bladder and Urethra

The walls of the bladder and urethra are made of smooth muscle.  With age this muscle tissue weakens and is less elastic.  This means that the bladder is less able to expand and contract in older people.  As a result, the bladders of elderly people have a capacity of approximately one-half of young adults and the bladders are unable to fully evacuate during urination.