1.  Ch 4: Skin and Body Membranes
Integumentary System
-Skin Layers & Functions

2. Skin Structure
Figure 4.3

3. Skin Structure Epidermis – outer layer Stratified squamous epithelium
Often keratinized (hardened by keratin)
5 layers within the epidermis
Dermis - inner layer
Dense connective tissue
Found underneath the epidermis
Figure 4.3

4. Epidermis Skin Layers From outermost to inner most layer:
Stratum Corneum
Stratum Lucidum
Stratum Granulosum
Stratum Spinosum
Stratum Basale (Germinativum)

5. Stratum Stratum is Latin and means “layer”
Did you notice that weird word in front of all the layers?
Stratum
Stratum is Latin and means “layer”
The rest of the name depends on the function or appearance of the layer.

6. Skin Structure
Figure 4.3

7. Layer of Epidermis 1. Stratum Basale “base layer”
Also called Stratum Germinativum
Deepest layer
Intertwines with underlying dermis
The strength of the bond is responsible for fingerprints
Cells in this layer are undergoing mitosis
Why would this be necessary?

8. Layer of Epidermis “Spiny Layer”
2. Stratum Spinosum
“Spiny Layer”
Cells look like pin cushions because cytoplasm shrank due to chemical exposure
8-10 layers of keratinocytes
Some cells stop dividing. Some cells keep dividing, making skin thicker

9. Layer of Epidermis Stratum Granulosum “Grainy Layer”
Most cells have stopped dividing
Cells start making large amounts of keratin
Keratin: a tough fibrous protein
Basic structural component of hair and nails
As keratin fibers develop, cells grow thinner and flatter
Cell’s membranes become thicker and less permeable
The cell dehydrates, organelles disintegrate, and the cell dies.

10. Layer of Epidermis cont’d
4. Stratum lucidum (Lucid
“Clear Layer” = clear)
Occurs only in thick skin
Palms of hands and Soles of feet
Cells are flattened, densely packed, and filled with keratin

11. Layer of Epidermis cont’d
5. Stratum Corneum
Cornification - the formation of protective, superficial layers of cells filled with keratin.
Process occurs on all exposed layers of skin
Outermost layer of the epidermis
Shingle-like dead cells
Sheets of tightly connected keratinocytes flake off slowly and are replaced by new cells
Once cells reach this layer, it takes around two weeks until they are shed

12. Skin Structure
Figure 4.3