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Questions and Answers
What is the primary role of hemidesmosomes in keratinocytes?
Which layer of the epidermis is primarily responsible for forming epidermal ridges?
Why is the shape of dermal papillae considered beneficial to the epidermal-dermal junction?
What is the primary function of keratin in the epidermis?
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Which of the following best describes the difference between thick and thin skin?
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What is the primary function of melanin in the skin?
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What determines the breakdown of melanosomes in light-skinned individuals?
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How does carotene contribute to skin color?
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In which skin layer does melanin primarily provide UV protection?
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What is the consequence of UV exposure on skin regarding skin cancer risk?
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What is the primary consequence of melanocyte loss in vitiligo?
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Which layer of the dermis is primarily composed of dense irregular connective tissue?
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What effect does an increase in blood flow have on skin color?
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What is the role of calcitriol in the body?
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What is the composition of the dermal papillae in the papillary layer?
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What physical condition can result from a deficiency in vitamin D3 during childhood?
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How are lines of cleavage in the dermis primarily oriented?
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What happens to capillaries in the skin during cold temperatures?
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Which type of fibers in the reticular layer provide strength and resistance to stretching?
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A lack of sun exposure can lead to which deficiency-related condition in children?
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Study Notes
Epidermis
- Keratinocytes are the main cells that form the strata of the epidermis.
- Hemidesmosomes connect keratinocytes to the basal lamina.
- Newly formed keratinocytes are pushed towards the surface and eventually shed.
- Epidermal ridges interlock with dermal papillae, increasing surface area for stronger attachment.
Layers of the Epidermis
- Thin skin has four layers of keratinocytes and covers most of the body.
- Thick skin has five layers of keratinocytes and covers palms and soles.
- Stratum corneum: The outermost layer, consisting of 15-30 layers of dead, keratinized cells tightly connected by desmosomes. It's water resistant and responsible for insensible water loss (500 ml/day).
- Stratum lucidum: Clear layer found only in thick skin, densely packed with keratin and devoid of organelles (dead cells).
- Stratum granulosum: Grainy layer where cells start to die and produce keratin and lipid-rich granules, contributing to water resistance.
- Stratum spinosum: Spiny layer with cells connected by desmosomes.
- Stratum germinativum (basale): Basal layer containing stem cells that continuously divide and produce new keratinocytes. It's anchored to the basal lamina by hemidesmosomes and forms epidermal ridges that interlock with dermal papillae.
Skin Color
- Melanin: Yellow to brown pigment produced by melanocytes in the stratum germinativum. It protects against UV radiation and gives skin its color. Melanosomes, vesicles containing melanin, are transferred to keratinocytes.
- Carotene: Orange-yellow pigment found in orange vegetables and stored in adipocytes. Humans cannot produce carotene.
- Hemoglobin: Red pigment carrying oxygen in the blood.
- Light skin: Melanins are broken down by fusion with lysosomes in the stratum germinativum and spinosum.
- Dark skin: Melanins are broken down in the stratum granulosum, making them more visible closer to the surface.
- Freckles and moles: Areas with more active melanocytes.
- Vitiligo: Loss of melanocytes causing white patches on the skin.
Vitamin D3 Production
- Stratum spinosum and germinativum produce Vitamin D3 (cholecalciferol) in response to sunlight.
- Vitamin D3 is converted by the liver and kidneys into calcitriol, a hormone that helps the intestines absorb calcium.
- Rickets, a disease caused by Vitamin D3 deficiency, leads to weak and flexible bones.
Dermis
- Two layers: Papillary and reticular layers.
- Papillary layer: Composed of areolar tissue, containing capillaries, lymphatics and sensory neurons. It's thrown into folds on the surface forming dermal papillae.
- Reticular layer: Composed of dense irregular connective tissue with interwoven collagen and elastic fibers. It also contains hair follicles, sweat glands, lymphatic vessels, and nerve fibers.
- Lines of cleavage: Collagen and elastin in the dermis are arranged in parallel bundles, determining the direction of skin elasticity.
- Skin turgor: The water content of the skin, contributing to its elasticity.
Hair
- Insulates and protects the scalp.
- Protects nostrils and ear canals from debris.
- Detects movement through hair plexus sensory nerves.
- Arrector pili muscle stands up hair, causing goosebumps.
- Hormones influence hair growth and development, especially in the armpits and pubic region.
Hair Growth Cycle
- Anagen Phase: Active phase where hair grows continuously, lasting 2-5 years.
- Catagen Phase: Regression phase where follicle begins to shrink.
- Telogen Phase: Resting phase where hair loses its attachment and becomes a club hair.
- Exogen Phase: Shedding phase where club hair is shed and new hair growth begins.
Sebaceous Glands
- Secrete oil through holocrine secretion.
-
Types:
- Simple branched alveolar glands: Share a duct with hair follicles and are squeezed by the arrector pili muscle.
- Sebaceous follicles: Not attached to hair.
- Sebum: Secretion composed of lipids, electrolytes, proteins, and cholesterol. It inhibits bacterial growth due to acidity, lubricates and protects keratinized cells.
- Vernix caseosa: Full-term newborns produce copious sebum in the last few weeks of gestation.
- Acne: Inflammation caused by sebum build-up and bacterial infection.
Sweat Glands (Sudoriferous Glands)
-
Merocrine (Eccrine) Sweat Glands:
- Structure: Coiled tubular ducts.
- Secretion: Watery sweat using exocytosis.
- Function: Regulate body temperature, excrete water and electrolytes, flush chemicals, contain dermicidin (antibiotic protein).
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Apocrine Sweat Glands:
- Structure: Coiled tubular structures that open into hair follicles.
- Secretion: Sticky, cloudy, odorous secretion influenced by hormones.
- Function: Nutrient for bacteria which intensifies odor.
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Ceruminous Glands:
- Location: External ear.
- Secretion: Cerumen (ear wax).
- Function: Trap foreign particles, protecting the eardrum.
Notes
- Apocrine sweat glands use merocrine secretion, not apocrine secretion.
- Apocrine secretion involves the release of a portion of the cell's cytoplasm along with the secreted product.
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Description
This quiz explores the structure of the epidermis, focusing on the types of cells and their functions within the skin layers. It covers topics such as keratinocytes, the significance of the stratum corneum, and the differences between thin and thick skin. Test your understanding of skin anatomy and its protective roles.
