A&P Honors: Ch. 5.2 — Epidermis

What are the four district cell types the epidermis consists of?

Keratinocytes, melanocytes, dendritic cells, and tactile epithelial cells.

What are keratinocytes?

Cells with the role of producing keratin.

What do keratinocytes do?

Produce keratin.

Where are keratinocytes located?

The stratum basale.

Why are the desmosomes and tight junctions connecting the keratinocytes so important?

Desmosomes give strength against friction and stretching.

Tight junctions hinder movement of water between cells.

What is the structure of melanocytes?

Spider-shaped epithelial cells.

What do melanocytes do?

Synthesize melanin.

Where are melanocytes located?

The stratum basale.

Where is melanin made? After, where is it transferred to?

Made in membrane-bound granules called melanosomes, then transferred to nearby keratinocytes.

What are dendritic cells? What’s another name for them?

Star-shaped cells that arise from bone marrow and migrate to the epidermis. They are also called Langerhans cells.

What do dendritic cells do?

They ingest foreign substances and are key activators of our immune system.

What are traction epithelial cells?

Spiky hemisphere shaped cells that function as a sensory for touch.

In thick skin, how many layers does the epidermis consist of?

Five

What does thick skin cover? Give examples.

Areas subject to abrasion, like palms, fingertips, and soles of the feet.

What are the five layers that the epidermis consists of?

Stratum basale, spinosum, granulosum, lucidum, and corneum.

In thin skin, which epidermis layer appears to be absent?

The stratum lucidum.

If you include the dermis, where is the thickest skin?

On the upper back.

What is the stratum basale?

The deepest epidermal layer, also called the stratum germinativum.

What is the stratum basal attached to? What does it resemble?

Attached to the underlying dermis along a wavy borderline that resembles corrugated cardboard.

What’re the major functions of the stratum basale?

Cellular regeneration (mitosis), pigment production, sensory perception, and anchoring the epidermis.

Where is the stratum basale located?

Attached to the underlying dermis along a wavy borderline that resembles corrugated cardboard.

What percent of the cells in the stratum basale are melanocytes?

10-25%

What the stratum spinosum?

Layer that is several cell layers thick and gets its name from the many spine like extensions of its keratinocytes.

Do the spines in stratum spinosum exist in living cells?

No

What do the cells of the stratum spinosum contain?

Thick bundles of intermediate filaments.

What do the intermediate filaments of the stratum spinosum resist and what are they anchored to?

Resist tension in the cell and are anchored to the desmosomes.

What do the intermediate filaments of the stratum spinosum consist of?

Pre-keratin.

What is pre-keratin?

Tension-resisitng protein.

What cells are the most abundant in the stratum spinosum?

Dendritic cells.

What is the stratum granulosum?

Thin layer that consists of one to five cell layers in which keratinocyte appearance changes drastically.

What process begins in the stratum granulosum?

Keratinization.

What are the two types of granules accumulated in stratum granulosum?

Keratohyaline and lamellar.

What do keratohyaline granules do?

Help to form keratin in the upper layers.

What do lamellar granules contain?

Contain a water-resistant glycolipid that is secreted into the extracellular space.

Along with tight junctions, what does the glycolipid in stratum granulosum do?

Slows water loss across epidermis.

Why are the outermost layers of skin strong and water-tight?

Because proteins within the keratinocytes and lipids deposited outside them make these cells tough and water resistant.

What does the epidermis rely on for its nutrients?

Capillaries in the underlying CT.

What causes stratum granulosum to die?

Being too far from the dermal capillaries to receive nutrients and survive, as well as glycolipids cutting them off from nutrients.

What is stratum lucidum?

A layer found only in thick skin that is a thin translucent band just above the stratum granulosum.

What does the stratum lucidum consist of?

A few rows of flat, dead keratinocytes.

What is the stratum corneum?

The outermost epidermal layer that is 20 to 30 cell layers thick and accounts for up to 3-quarters of the epidermal thickness.