The pieces and parts that make up your body update at different paces. In a race, your stomach lining wins, being replaced every two to nine days; while the lens of your eye and most of your brain are the same as when you were born. 

2-9 days: Stomach lining – your gut epithelium regenerates relatively quickly because of its exposure to stomach acid and bile.

7 days: Taste buds – the taste buds have about 10 to 50 sensory cells each that are renewed every week.

2-3 weeks: Lungs

2-4 weeks: Outer layer of skin (epidermis)

4 months: Red blood cells – 100 million cells are born every minute, while 100 million others are destroyed.

6 months: Nails

2-7 years: Hair – 100 hairs fall out every day and are generally replaced.

10 years: Skeleton

15 years: Muscle

25 years: Fat cells – they may seem to multiply, but they actually expand and contract.

Life: The lens of your eye, most of your brain and about half of your heart, stay with you from birth to death.