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INTEGUMENTARY SYSTEM:THE EPIDERMIS AND ITS LAYERS
INTEGUMENTARY SYSTEM
Includes your entire outer layer of skin (16% of your total body weight), accessory organs like hair, nails, and glands.
Consists of two major parts: (1) Cutaneous membrane (2) Accessory structures
CUTANEOUS MEMBRANE (SKIN)
Made up of two layers: (1) Epidermis (superficial epithelium), and
Dermis (underlying connective tissue) (2) Accessory structures – Including hair,
nail , exocrine glands. Located mostly in the dermis and protrude into the epidermal layer
(3) Subcutaneous layer deep to the dermis is known as the hypodermis; often not considered part of the integumentary system, but because its fibers extend into the dermis, we will include it here
STRUCTURE OF THE SKIN
FUNCTION OF THE SKIN
(1) Protection of underlying tissues and organs against shocks, abrasion, and chemicals
(2) Excretion of salts, water, and organic wastes (3) Maintenance of normal body temperature via
insulation or evaporative cooling (sweating) (4) Synthesis of vitamin D3 (5) Storage of nutrients – including lipids/adipose (6) Detection of touch, pressure pain, and
temperature stimuli and relaying information to the control center (brain)
EPIDERMIS Recall epidermis composed of
stratified squamous cells for the purpose of protection
Most abundant epithelial cells are called keratinocytes
EPIDERMIS
Keratinocytes make up five layers of thick skin, and four layers in thin skin
Thick skin is found in the palms of your hands and soles of your feet
Thin skin is found everywhere else in your body
Thick and thin refer to the thickness of the epidermal layer
EPIDERMAL LAYERS OF THICK SKIN
Top layer of skin
Bottom layer of skin
STRATUM GERMINATIVUM/STRATUM BASALE
Stratum germinativum, also known as stratum basale, is the bottom most layer of skin
Epidermal ridges are found here, and they extend into the dermis.
Projections called dermal papillae creates an interlocking arrangement that increases the strength of the bond between the dermal and epidermal layers
STRATUM GERMINATIVUM/STRATUM BASALE
The contours of the skin surface follow the ridge patterns
Ridges on the palms and soles of feet increase the skin’s surface area and friction, helping to maintain grip
Ridge shapes are genetically determined, unique to you, and do not change throughout your life
Ridge prints located on your fingers are called fingerprints
STRATUM GERMINATIVUM/STRATUM BASALE
Basal cells dominate this layer. Basal cells are stem cells whose divisions replace skin cells lost to shedding at the skin’s surface
Merkel cells are also found in this layer. Merkel cells are sensitive to touch.
STRATUM GERMINATIVUM/STRATUM BASALE
Basal Cell
Melanocytes are pigment cells that give skin its color; they are also found in this layer
STRATUM GERMINATIVUM/STRATUM BASALE
STRATUM SPINOSUM Means “spiny layer” Contains Langerhans
cells, which are part of the immune system
Langerhans cells are responsible for stimulating a defense against:
(1) microorganisms that penetrate the epidermis
(2) superficial cancer cells
STRATUM GRANULOSUM
Known as the “grainy layer”
By the time the cells reach this layer, they have stopped dividing and now begin to make lots of the protein keratin
Keratin makes up our hair and nails
STRATUM LUCIDUM Present only in thick skin “Clear layer” filled with keratin
STRATUM CORNEUM Top layer of epidermis;
consists of 15-30 layers of cells
Keratinization or cornification, is the formation of protective, superficial layers of cells made of keratin
Dead layers of cells so tightly connected that when they slough off they separate as sheets of cells
EPITHELIAL CELL LIFE CYCLE
Takes 15-30 days for epithelial cells to move from stratum basale/germinativum to the stratum corneum
They stay in the stratum corneum for about two weeks before being washed/shed
STRATUM CORNEUM
A dry layer, so few microorganisms can survive here
Layer is water resistant, but not waterproof. Water from inside the body slowly penetrates to the surface where it is evaporated. We lose ~500mL (1 pint) of water/day
This process is called insensible perspiration If this layer is damaged or lost (as in burns),
the rate of water loss dramatically increases and you are at risk of dehydration
OSMOTIC PRESSURE Recall from biology that
freshwater will move into cells, causing them to SWELL
This is why when you take a bath your hands swell and look like raisins
Likewise, water will leave cells if placed in highly concentrated solutions, like oceanwater
Although the process occurs slowly, it will accelerate the dehydration process in shipwreck survivors
After 51 hoursof exposure to seawater andwearing gloves