Hell If I Know

The integumentary system is an organ system consisting of hair, nails, and exocrine glands. The skin is only a few millimeters thick yet is by far the largest organ in the body. The average person's skin weighs 10 pounds and has a surface area of almost 20 square feet. Hair and nails extend from the skin to reinforce the skin and protect it from environmental damage.
One of the main functions of the integumentary system is protection. It protects from mechanical damage- the epidermis contains keratin which toughens cells. It gives protection from infection by microbes, ultraviolet light, and excessive water loss or dehydration. Other functions include excretion, cutaneous sensation, body temperature regulation, it's a blood reservoir, and produce vitamin D.
There's different layers to the skin. The most superficial layer of the skin is the epidermis.
The epidermis is made of several specialized types of cells. Almost 90% of the epidermis is made of cells known as keratinocytes. Keratinocytes develop from stem cells at the base of the epidermis and begin to produce and store the protein keratin. Keratin makes the keratinocytes very tough, scaly and water-resistant. At about 8% of epidermal cells, melanocytes form the second most numerous cell type in the epidermis. Melanocytes produce the pigment melanin to protect the skin from ultraviolet radiation and sunburn. Langerhans cells are the third most common cells in the epidermis and make up just over 1% of all epidermal cells. Langerhans cells’ role is to detect and fight pathogens that attempt to enter the body through the skin. Finally, Merkel cells make up less than 1% of all epidermal cells but have the important function of sensing touch. Merkel cells form a disk along the deepest edge of the epidermis where they connect to nerve endings in the dermis to sense light touch.
The dermis is the deep layer of the skin found under the epidermis.The dermis is mostly made of dense irregular connective tissue...