Your Stomach Lining Is: 5 days old
Also known as the mucosa, your stomach lining plays a key role in helping you digest food. Special cells produce the acid and enzymes responsible for your stomach’s low pH, which promotes the chemical breakdown of, say, your lunch. In a work of genius, the same cells also secrete protective mucus that safeguard the stomach lining from the wear and tear of all that acid. All that and less than a week on the job!
Your Taste Buds Are: 10 days old
Small, but hard-working, your body’s 10,000-odd taste buds contain microscopic hairs called microvilli that convey facts about food to your brain—that Ben & Jerry’s scoop of Chunky Monkey is sweet, that hot pretzel is salty. Your taste buds are replaced often, but this process slows down (and some taste buds stop being replaced) with age. So older adults may only have 5,000 taste buds, according to KidsHealth.org, which is why certain foods don’t taste as flavorful to seniors.
Your Skin Is: 2 weeks old
The outermost layer of your skin is called the stratum corneum. It mainly serves as a protective barrier between the rest of the more sensitive layers of your skin and the environment around them, letting only tiny particles pass through. According to Discovery Health, this layer contains minor skin imperfections such as fine lines and blemishes. (And you thought it took years to develop wrinkles!)
Your Eyelashes Are: 2 months old
They may be pretty, but eyelashes serve an important body function, which is why many animals besides humans have them too. They shield your eyes from danger by blocking particles like dust and dirt, and prevent your eyes from drying out. Top lids contain about 150 to 200 hairs and bottom lids have around 75 to 100. Although women have been faking the length and lushness of eyelashes for decades with mascara and lash extensions, the Guinness World Record for eyelash length actually belongs to a man: Stuart Muller recorded 2.75 inch-long lashes in December 2007.
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Your Red Blood Cells Are: 4 months old
A single drop of blood contains millions of these powerhouse cells, which deliver oxygen to and remove waste from other cells, according to the Franklin Institute. It’s an important, life-sustaining function. Iron in your diet facilitates this process, which is why getting enough of the mineral is crucial for optimal health. (It’s most common in red meat, fish, poultry, eggs, and beans.)
Your Liver Cells Are: About a year old (300-500 days)
The ultimate cleansing organ, your liver is responsible for filtering blood from the digestive tract before it circulates to the rest of the body, metabolizes drugs, and detoxifies chemicals, according to WebMD. It’s a big job for the large, meaty-looking organ, weighing in at about three pounds and located on the right side of your stomach—no wonder it needs to regenerate cells about every year or so.
Your Bones Are: 10 years old
Your bones may feel strong and sturdy, but the cells that comprise them are constantly dying and being reborn, producing an entirely new skeleton every decade, according to WebMD. Bone density is strongest in your early 20s and then gradually weakens. Osteoporosis, a serious condition of low bone mass, occurs when bone loss occurs more often than bone rebirth.
Your Rib Muscle Cells Are: About 15 years old (15.1)
Your ribcage protects vital internal organs like the heart and lungs. Its 12 pairs of bones, in turn, are supported by ligaments and muscles. Those muscles between the ribs are called intercostal muscles, which allow your ribcage to expand in and out when you breathe—a constant workout.
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Your Cerebellum Is: 3 years younger than you are
This is part of the brain—located in the lower back, near the stem—that controls motor skills and balance. Although it only accounts for 10 percent of total brain volume, the cerebellum contains more than 50 percent of its total neurons (or brain cells), according to the University of Texas Health Science Center at Houston. The cerebellum is one of the first areas to develop in babies but ages slowly; it's primarily involved in maintaining balance and posture, coordinating voluntary movements, learning new motor skills (like hitting a baseball, or for babies, any movement), and certain other cognitive functions, such as language.