Questions and Answers
What types of cells compose the epidermis?
What are stem cells?
Undifferentiated cells that give rise to keratinocytes.
What is the role of keratinocytes?
They synthesize keratin.
Melanocytes are found in the stratum corneum.
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What do melanocytes synthesize?
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What are tactile cells?
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Where are dendritic cells located?
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What is the dermis primarily composed of?
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What layers exist in the dermis?
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What are striae?
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What are the three layers of hair?
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What is the medulla in hair?
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What does the cortex of hair consist of?
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What is the cuticle of hair?
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What are the two principal layers of a hair follicle?
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Study Notes
Epidermis Cells
- Composed of five cell types: Stem cells, Keratinocytes, Melanocytes, Tactile cells, and Dendritic cells.
Stem Cells
- Undifferentiated cells that divide to create keratinocytes.
- Located in the deepest epidermal layer, the stratum basale.
Keratinocytes
- The most abundant cells in the epidermis, primarily responsible for keratin synthesis.
- Nearly all visible epidermal cells in histological specimens are keratinocytes.
Melanocytes
- Found in the stratum basale, alongside stem cells and keratinocytes.
- Synthesize melanin, a pigment that provides skin color and protects against UV radiation.
- Melanin granules accumulate on the "sunny side" of keratinocyte nuclei, shielding DNA from UV potential mutations.
Tactile Cells
- Few in number, these cells serve as touch receptors.
- Located in the basal layer of the epidermis and linked to dermal nerve fibers, forming tactile discs.
Dendritic Cells
- Immune cells located in the stratum spinosum and stratum granulosum.
- Originate from bone marrow, migrating to the epidermis and other epithelia to monitor for toxins and pathogens.
- Help alert the immune system upon detection of invaders.
Dermis
- Positioned beneath the epidermis, with thickness ranging from 0.2 mm to 4 mm.
- Composed mainly of collagen, along with elastic and reticular fibers, fibroblasts, and blood vessels.
- Contains nerve endings, cutaneous glands, and embeds hair follicles and nail roots.
- The boundary between dermis and epidermis features dermal papillae (upward extensions) and epidermal ridges (downward extensions) for interlocking stability.
- Divided into two layers: papillary (loose areolar tissue, rich in blood vessels) and reticular (dense irregular connective tissue).
Hair Structure
- Composed of three layers in cross-section: Medulla, Cortex, and Cuticle.
Medulla
- The innermost layer of hair, characterized by loosely arranged cells and air spaces.
- Prominent in thick hairs, such as eyebrows, but narrower or absent in thinner hair types.
Cortex
- The main bulk of a hair, consisting of elongated keratinized cells.
- Appears cuboidal to flattened in cross-sections.
Cuticle
- Composed of multiple thin, scaly cells that overlap, resembling roof shingles with edges pointing upward.
Hair Follicle
- A diagonal tube extending into the dermis and sometimes hypodermis.
- Composed of two primary layers: an epithelial root sheath (an extension of the epidermis) and a connective root sheath.
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Description
Explore the key types of cells found in the epidermis, including stem cells, keratinocytes, melanocytes, tactile cells, and dendritic cells. Understand their functions, locations, and roles in skin health and protection. This quiz will test your knowledge on the structure and significance of these essential skin components.
