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30.1A: Development of the Integumentary System

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  • The integumentary system develops from all embryonic layers (ectoderm, mesoderm, and neural crest cells).

    Learning Objectives

    • Outline the developmental process of the integumentary system

    Key Points

    • Ectoderm forms at 4 weeks.
    • Between 4 and 12 weeks, the stratified epithelium forms and mesoderm forms the blood vessels and connective tissue.
    • At 16 weeks, the basement membrane folds and melanoblasts start producing melanin.
    • At 20 weeks, hair begins to grow from sebaceous glands and sweat glands form.

    Key Terms

    • sebaceous gland: A gland of the skin that secretes an oily substance, sebum, usually into a hair follicle near the surface of the skin.
    • neural crest cells: A transient, multipotent, migratory cell population that gives rise to a diverse cell lineage including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons, and glia.
    • fetal skin: This forms from three layers: ectoderm, mesoderm, and neural crest cells.

    The integumentary system is the largest organ system in the human body, responsible for protection from physical and environmental factors. The integumentary system is both a barrier and a sensory organ, and includes the skin (the largest bodily organ), as well as appendages, sweat and sebaceous glands, hair, nails and arrectores pillorum (tiny muscles at the root of each hair that cause goose bumps).

    Fetal Skin Formation

    This diagram of the integumentary system indicates the hair shaft, sweat pore, dermal papilla, sensory nerve ending for touch, epidermis, dermis, subcutis (hypodermic), vein, artery, sweat gland, pacinian corpuscle, blood and lymph vessels, nerve fiber, papilla of hair, hair follicle, sebaceous gland, arrector pili muscle, stratum basale, stratum spinosum, stratum germinativum, pigment layer, and stratum corneum.

    Human Skin: This image details the parts of the integumentary system.

    Fetal skin forms from three layers: ectoderm, mesoderm, and neural crest cells. Figure 1 shows a diagram of the skin structure.

    At 4 weeks gestation, simple ectoderm epithelium forms. Between 4 and 12 weeks, the basal cells divide repeatedly to form the stratified epithelium while the mesoderm forms the blood vessels and connective tissues. Epidermal ridges (e.g. fingerprints) begin to develop around 10 weeks gestation and are completed by 17 weeks gestation. Sensory nerves also develop.

    At 16 weeks gestation, the basement membrane folds. Melanoblasts that form melanocytes migrate with neural crests cells to the epithelium and begin producing melanin prior to birth. The connective tissue differentiates into the various layers of the dermis. Ectoderm thickens into fingernails and toenails. Other regions of the ectoderm form into epithelial columns called cords which become hair follicles and sebaceous and sweat glands.

    At 20 weeks gestation, hair begins to grow from sebaceous glands, while sweat glands are formed from coiled cords. Other cords begin to form mammary glands.

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