Questions and Answers
What is the main factor that causes increased melanin production in the skin?
From which layer does the dermis develop?
What role do the developing afferent nerve fibers play in the skin?
What is the origin of most mesenchyme that differentiates into connective tissue of the dermis?
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How do dermal ridges interact with epidermal ridges during development?
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What is the earliest stage of the epidermis derived from?
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What substance is formed by exfoliated peridermal cells?
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What role does vernix caseosa play during the fetal period?
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At what point does the replacement of peridermal cells significantly decline?
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What does the stratum germinativum primarily produce?
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What happens to the periderm by the 21st week of development?
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What type of epithelium primarily composes the peridermal layer?
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Which layer of the epidermis is directly responsible for forming the intermediate layer by 11 weeks?
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At what point in the embryonic development do epidermal ridges begin to appear?
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Which type of skin lacks hair follicles and sebaceous glands?
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What is the main determining factor for the patterns of epidermal ridges?
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What do melanoblasts differentiate into during skin development?
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Which embryonic structure contributes to the formation of melanocytes?
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By how many days after migration do melanocytes start appearing in developing skin?
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What is produced by the epidermal ridges on the palms and soles?
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What does the transformation of surface ectoderm into multilayered epidermis involve?
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What is the primary secretion produced by sebaceous glands?
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Where do eccrine sweat glands primarily develop from?
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What role do myoepithelial cells play in eccrine sweat glands?
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Where do apocrine sweat glands typically open?
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Which statement about sebaceous glands located in the glans penis and labia minora is correct?
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At what stage do eccrine sweat glands begin to function?
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What forms the initial structure of sebaceous glands?
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Which of the following is a characteristic of apocrine sweat glands?
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At what week do mammary buds begin to develop?
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What are mammary crests?
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Which type of skin disorder results from excessive keratinization?
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Which cells produce enamel in teeth development?
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What causes generalized albinism?
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What characteristic is most commonly associated with hypertrichosis?
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At approximately how many weeks do fingernails develop relative to toenails?
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What is the common outcome when small areas of skin fail to form?
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Study Notes
Epidermis Development
- Primordium of the epidermis arises from surface ectodermal cells.
- Proliferation leads to a peridermal layer (squamous epithelium) and a basal (germinative) layer.
- Periderm undergoes keratinization and is continuously replaced by basal layer cells.
- Exfoliated peridermal cells contribute to vernix caseosa, a protective substance covering fetal skin.
- Vernix contains sebum from sebaceous glands and safeguards skin from amniotic fluid exposure during fetal development.
Basal Layer Functions
- The basal layer transforms into the stratum germinativum, responsible for new cell production.
- By 11 weeks, the intermediate layer forms from stratum germinativum cells.
- Peridermal cell replacement continues until the 21st week; thereafter, the stratum corneum emerges.
- Stratum germinativum proliferation creates epidermal ridges, established by 10 weeks and permanent by 17 weeks.
- Dermal ridges intertwine with epidermal ridges, influencing fingerprint patterns based on genetic factors.
Skin Classification
- Skin is classified as thick or thin based on epidermis thickness.
- Thick skin (e.g., palms, soles) lacks hair follicles and sebaceous glands but has sweat glands.
- Thin skin covers most of the body and contains hair follicles, sebaceous glands, and sweat glands.
Melanocyte Development
- Neural crest cells migrate to differentiate into melanoblasts in the dermis, later becoming melanocytes.
- Melanocytes appear at 40-50 days of development, primarily in the basal epidermis.
- Melanin production begins before birth; darker-skinned fetuses show prenatal pigment formation.
- Skin color variations result from the relative melanin content in melanocytes, increasing with UV exposure.
Dermis Formation
- The dermis develops from mesenchyme, which originates from the mesoderm beneath the ectoderm.
- Differentiation into connective tissue fibers, such as collagen and elastin, begins by 11 weeks.
- Dermal and epidermal ridges interdigitate, aiding in the establishment of the dermal structure.
- Capillary loops formed in dermal ridges nourish the epidermis; sensory nerve endings contribute to skin innervation patterns.
Skin Glands
- Sebaceous glands develop from epithelial buds associated with hair follicles, producing sebum.
- Sebum contributes to vernix caseosa when mixed with desquamated cells.
- Sweat glands are classified into three categories: eccrine, apocrine, and mammary.
Eccrine Sweat Glands
- Develop as epidermal downgrowths into mesenchyme, forming secretory parts around 20 weeks.
- Ducts develop lumens as central cells die off, leading to the formation of myoepithelial and secretory cells.
- Eccrine glands become functional shortly after birth.
Apocrine Sweat Glands
- Develop from stratum germinativum downgrowths into hair follicles, secreting at puberty.
- Ducts open into hair follicles rather than directly onto the skin.
Mammary Glands
- Develop as solid downgrowths from the epidermis during the 6th week, originating from the mammary crest.
Appendages Development
- Fingernails and toenails appear as thickened epidermis fields at digit tips, with fingernails developing before toenails.
- Nails migrate to the dorsal surface, surrounded by lateral and proximal epidermal folds.
- Teeth form from ectoderm, mesoderm, and neural crest cells, with enamel produced by ameloblasts.
Congenital Anomalies
- Ichthyosis: Characterized by excessive keratinization and fish-skin-like scaling.
- Albinism: Autosomal recessive trait leading to lack of pigment in skin, hair, and retina due to deficient tyrosinase.
- Hypertrichosis: Excessive hairiness due to supernumerary hair follicles.
- Absence of Skin: Rare condition where small skin areas fail to form, potentially appearing ulcerative.
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Description
This quiz covers the development of the integumentary system focusing on the epidermis and its layers. It explores the role of surface ectodermal cells in forming the epidermal layers. Perfect for students of ANA 204.
