The skin is important+complicated

What I learned in physical therapy school is: skin is important and complicated.

I am currently taking a wound and burn care class for PT school, and we went over skin anatomy.  The skin is part of the integumentary system which is the largest body system. The skin is made up of all these tiny little cells in all their tiny little layers. It’s amazing to me how everything works together so perfectly. So here’s some nerdy anatomy for ya.

There are two layers of skin: epidermis and dermis

  • Epidermis.
    • the top layer we can see and touch
    • there isn’t any blood flow “avascular”
    • has five layers (from bottom to top)
    • top layers are old and dying while bottom layers are new
      • Stratum Basale “the base”
        • single row with diving cells called keratinocytes
          • keratinocytes produce keratin, a protein
      • Stratum Spinosum
        • multiple rows of keratinocytes
      • Stratum Granulosum
        • 3-5 rows of flatter keratinocytes cells
      • Stratum Lucidum
        • few layers of flat, dead keratinocytes
      • Stratum Corneum
        • dead keratinocytes
          • physical barrier from the outside keeping out infection and water.
          • cells are constantly being removed and replaced by new dead keratinocytes taking 14-21 days to get a whole new skin!
          • a callus forms as a build up of these cells
    • cell types of the epidermis
      • melanocytes in the stratum basale produce melanin
        • melanin gives skin color and helps protect against the sun
      • merkel cells are mechanoreceptors that attach to keratinocytes
        • mechanoreceptors are little cells that respond to touch
      • langerhans’ cells help against infections
    • structures inside the epidermis
      • hair helps regulate body temperature
        •  hair sits inside a hair follicle containing a sebaceous gland secreting an oil called sebum
      • sudoriferous glands make sweat that travels up to the skin
        • sweat is evaporated off of us to keep us cool
      • nails are made of hard keratin from the stratum basale and protect the ends of our fingers.
  • Dermis
    • has a blood supply “vascular”
    • contains the lymphatic system which makes sure substances get from tissues to the blood
    • brings nutrition to the skin
    • helps with injury repair
    • protection from infection
    • regulating temperature
    • provides sensation
    • has only two layers
      • papillary dermis has ridges and valleys called dermal papillae that connect to the rete pegs of the basement membrane
        • basement membrane is in between the epidermis and the dermis holding them together
          • FUN FACT! A blister happens at the basement membrane. the rete pegs and the dermal papillae separate from each other.
      • reticular dermis is thick and gives support to the skin
    • call types
      • fibroblasts make collagen and elastin
        • collagen makes things strong
        • elastin makes things flexible
      • macrophages and white blood cells fight infection and eat harmful substances
      • mast cells make chemicals to promote inflammation
        • cause vasodilation (increases the size of the blood vessels)
        • calls for other cells to come to that area
          • fights infection or repairs injuries
      • sensory receptors that send touch, pressure, vibration, and temperature information to the brainshowing-the-layer-of-epidermis-and-dermis


Underneath the epidermis and dermis is subcutaneous tissue that is basically fat (adipose tissue) and connective tissue (fascia). The adipose tissue keeps us warm, energized, and a built-in cushion. The fascia helps separate muscles, tendons, and bones. There are also lymphatic vessels.

Underneath the subcutaneous tissue are the muscles, tendons, ligaments, joint capsules, bones, nerves, and blood supply. We call these “named structures” because, well, they have names like biceps brachii muscle and sciatic nerve.

Why is all this important to a physical therapist?

For wound care! If someone has a deep wound with muscle showing, we know they have a full thickness wound. If someone has a second degree burn or blister, we know they have a partial thickness wound. If they have a sun burn, it’s a superficial wound. Each type of wound calls for different types of care, has different risks for infection, ranging chances of scarring. Who knew it was that important and complicated?







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