"Normal functioning" refers to the way something is expected to work or operate correctly. It means everything is happening as it should, without any issues or problems. Full definition
This is essential for normal functioning of muscles (including the heart) and kidneys, and for the formation and maintenance of healthy bones and teeth. (brittonroadveterinaryclinic.com)
Approximately 70 % of renal function is usually lost before symptoms are noticeable since only 30 % of kidney capacity is needed for normal functioning in cats. (darwinspet.com)
Vitamin B12 helps with normal functioning of the nervous system, including the brain. (mindbodygreen.com)