Topic 17: The Integumentary System

- skin with sweat and oil glands, hair and nails
- covers the outer surface of the body, as well as inner membranes of eyelids, nostrils and other body openings

Structure and function:

1. Epidermis - outer layer of skin
- formed of stratified (layered) squamous epithelium
- thicker in areas subject to friction (palms, soles)
- 25-30 layers, flattened dead cells that are filled with keratin (makes the epidermis rough, leathery and waterproof)
- cells are produced in the germinative layer, then pushed to the surface and shed.  This process takes about 45 days

Source: http://www.womens-health-advice.com/skin-structure-function.html

- function as a barrier against dehydration and a first line of defense against toxins and microbes

- the epidermis contains melanocytes - cells which produce melanin (brown-black pigment), which protects cells from solar radiation damage.  Melanin production varies with exposure to sunlight and heredity

Source:  http://en.wikipedia.org/wiki/Melanocyte

- no blood vessels are found in the epidermis, all nutrient and gas exchange occurs by diffusion and active transport from capilaries in the dermis.

Source:  http://en.wikipedia.org/wiki/Epidermis_(skin)

2.  Dermis - inner layer of skin
- attached to epidermis by the basement membrane
- formed of connective tissue, which cushions and provides skin with elasticity (lots of elastin fibers)
- thickness varies, 3-4mm on soles and palms, 0.5mm in eyelids
- contains blood capilaries, which supply epidermis and dermis with nutrients and O2 and play a role in thermoregulation
- contains sweat glands (coiled, tubular exocrine glands), which allow skin to excrete H2O, salt and small amounts of organic wastes filtered from capillaries, play a role in thermoregulation.
-contains hair follicles.  The cells at the base of the follicle divide to form long cylindrical hair cells (dead, filled with keratin).  Blood vessels nourish the root (hajhagyma).  Hair colouration is due to melanin. Functions as an insulator (particularly in other mammals).  The arrector pili muscle allows hair to "stand up", trapping air next to the skin, which functions as an additional insulator, or creating the impression that the animal is bigger than it is (defense)
- contains sebaceous (oil) glands, which are found at the sides of hair follicles and produce sebum (faggyú).  Sebum is made of fats, cholesterol, proteins and salts.  It helps prevent drying out and keeps skin soft and pliable.  It also helps inhibit the growth of some bacteria.
- nails grow from epidermal infoldings, similar to hair
- contains nerves and sensory nerve endings for touch, pressure, heat, cold and pain, providing information perception

Source:  http://www.ouhsc.edu/histology/Text%20Sections/Integument.html

3.  Subcutaneous layer or hypodermis
- there is an indistinct transition between the dermis and the hypodermis
- it is loose connective tissue and adipose tissue
- its function is long-term energy storage and insulation

Source:  http://www.tcmimassager.com/CellulessMassager.html

Vital functions of skin
1.  Protection - mechanical (abrasion,injury), physical (water loss, UV radiation), chemical (toxins), microbial (bacteria, viruses)
2.  Sensory - provides a wide range of information about the environment
3.  Thermoregulation - capillaries, sweat