How does the epidermis grow, shed or rebuild?

Answer 1

The epidermis makes new cells in the base layer which push up, flattening cells above them, which eventually flake off in desquamation, to be replace by the newer cells below.

The base layer, the furthest from the surface, is where the epidermis forms columnar cells, which are young, healthy cells derived from dividing keratinocyte stem cells.

More cells push upward, pushing all the cells up and squashing the immature cells into flatter, more cuboid shapes.

More living keratinocytes are created in the process, pushing the ones above them up and eventually squashing them until they are nearly the consistency of flakes, at which point they die and eventually flake off.

Desquamation, derived from the Latin desquamare, which means scraping off fish scales, is the process of losing the outermost layer of skin cells. It counteracts the formation of new skin cells in the basal (base) layer.

From the young keratinocyte to the dead corneocyte on the top layer of skin, the entire process takes about 14 days.

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Answer 2

The epidermis, the outermost layer of the skin, constantly renews itself through a process called keratinization. This process involves the following steps:

  1. Basal layer (Stratum basale): New skin cells, known as keratinocytes, are generated in the basal layer of the epidermis. These cells are alive and actively dividing.

  2. Upward movement: Over time, these new cells gradually move up through the layers of the epidermis towards the surface. As they migrate, they undergo a process of differentiation, changing in shape and composition.

  3. Keratinization: During their journey to the surface, the keratinocytes start to produce keratin, a type of protein that is a key component of hair, nails, and the outer layer of skin. This process makes the cells flatter and more rigid. The cells also lose their nuclei and other organelles, essentially dying and transforming into a tough, protective layer.

  4. Stratum corneum (outermost layer): By the time the cells reach the stratum corneum, they are fully keratinized, forming a barrier that protects the underlying tissues from infection, dehydration, and physical damage.

  5. Shedding (Desquamation): Eventually, these dead skin cells on the surface are shed from the body through a process known as desquamation. This shedding process is natural and continuous, allowing for the replacement of old cells with new ones from the basal layer.

The entire process from cell birth to shedding takes about 28-30 days in a healthy adult, though this can vary with age and other factors.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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