What is Epidermis
Keratinized stratified squamous epithelium
What are the 5 layers of the epidermis starting with the superficial layer?
Corneum, Lucidium, Granulosum, Spinosum, and Basal
What are the 4 cell types of the Epidermis?
Keratinocytes, Melanocytes, Dendritic cells, and Tactile cells
What is the function of Keratinocytes?
To produce Keratin
What is Keratin?
The fibrous protein that helps give the epidermis it's protective properties
What connects Keratinocytes together?
Where do Keratinocytes arise from?
In the deepest part of the epidermis, the stratum basal
How often do we get a new epidermis?
Every 25-45 days
How do Keratinocytes reproduce and how fast?
By mitosis and continuously
What kind of cells are the majority found in the epidermis?
What are Melanocytes?
Spider shaped epithelial cells that synthesize the pigment melanin
Where are Melanocytes found?
The deepest layer of the epidermis called the stratum basal
What is another name for dendritic cells?
Where do dendritic cells arise from and where do they migrate to?
Bone marrow and migrate to the epidermis
What is the function of Langerhans cells?
Ingest foreign substances and activate our immune system.
What is another name for tactile cells?
Where might you find Merkel cells?
At the epidermal-dermal junction
What is the function of a Merkel cell?
A sensory receptor for touch
What is a Merkel cell shaped like?
Spiky hemisphere with disc like sensory nerve ending
What stratum is missing when skin is thin?
How many stratum does thick skin have?
What kind of cells are located in the Stratum Basal?
A single row of actively mitotic stem cells; keratinocytes
occasional melanocytes and dendritic cells
Stratum Basal is also know as
How do the cells in the Basal
Each time a basal cell divides, one daughter cell is pushed into the cell layer just above to begin it's specialization into a mature keratinocyte . Other basal cells remain to continue to divide mitotically
What % of Stratum Basal cells are Melanocytes?
Describe the Stratum Spinosum
Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin
What cells are found in the Stratum Spinosum?
Keratinocytes, melanin granules, and dendritic cells, which are most abundant
Describe the stratum granulosm
Typically 5 layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules and keratohyaline granules
What do the Keratohyline granules do in the Stratum Granulosm?
They help to form keratin in the upper layers
What are Lamellar granules?
They contain a water resistant glycolipid that is spewed into the extracellular space and is a major factor in slowing water loss across the epidermis
Where are Lamellar granules found?
Which stratum to the keratinocytes "toughen up"?
Above which Stratum are nutrients cut off and the cells die?
Above the Stratum Granulosm
What are tonofilaments?
Large cable like parallel arrays of intermediate filaments
What is the thickest Stratum of the epidermis?
The stratum corneum
Describe the Stratum Corneum
The most superficial layer
20-30 layers of dead cells
Are essentially flat membranous sacs filled with keratin
Glycolipids in extracellular space
What is the function of the Stratum Corneum?
Protection from hostile external environment and from water loss
What are cornified or horny cells?
shinle like cell remnants of the stratum corneum that slough off skin surface. AKA dandruff or dander
How many dead cells does the average person shed each minute?