What are the two main layers of the skin and their embryonic origins?

The skin consists of two primary layers: the epidermis, derived from surface ectoderm, and the dermis, derived from mesoderm (including contributions from paraxial, lateral plate, and neural crest cells).

What are the four layers of the epidermis that develop by the third month?

By the end of the third month, the epidermis develops four layers: basal layer (stratum germinativum) with continuously dividing cells, spinous layer with prickle cells, granular layer with keratohyalin granules, and horny layer (stratum corneum) with keratinized dead cells.

What are some common clinical conditions related to the epidermis?

Key clinical conditions include fingerprints formed by epidermal ridges, ichthyosis with excessive keratinization, albinism from defective melanin synthesis, and vitiligo from autoimmune destruction of melanocytes.

How do hair and nails develop embryologically?

Hair develops between 7–12 weeks from epithelial proliferation into the dermis, forming a hair bud and bulb. Nails start at week 10 with a nail field and germinal matrix that produces the nail plate.

What are the two types of sweat glands and their differences?

Sweat glands include eccrine glands, found in most body areas and functioning after birth, and apocrine glands, located in axilla, groin, and nipples, which begin at puberty and produce odorous secretions.

What are some clinical abnormalities related to mammary gland development?

Common abnormalities include amastia and athelia (absence of breast or nipple), polythelia (extra nipples), polymastia (accessory breasts), and inverted nipple from failed evagination.

What is the role of the dermal papillae in skin structure?

Dermal papillae interdigitate with epidermal ridges to support and nourish the epidermis through capillary loops and sensory organs.

Skin Development – Epidermis, Dermis & Appendages

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