Epidermis Structure and Function

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Questions and Answers

What is the primary role of hemidesmosomes in keratinocytes?

Facilitating nutrient absorption

Enhancing cell-to-cell communication

Anchoring cells to the basal lamina (correct)

Regulating cell signaling pathways

Which layer of the epidermis is primarily responsible for forming epidermal ridges?

Stratum spinosum

Stratum granulosum

Stratum germinativum/basale (correct)

Stratum lucidum

Why is the shape of dermal papillae considered beneficial to the epidermal-dermal junction?

It enhances the exchange of oxygen and carbon dioxide

It provides insulation to the epidermis

It allows for more keratinocyte production

It increases the surface area for attachment (correct)

What is the primary function of keratin in the epidermis?

To stiffen and protect epidermal tissue Signup and view all the answers

Which of the following best describes the difference between thick and thin skin?

Thick skin is characterized by having an additional layer called the stratum lucidum Signup and view all the answers

What is the primary function of melanin in the skin?

To protect against UV radiation Signup and view all the answers

What determines the breakdown of melanosomes in light-skinned individuals?

Fusion with lysosomes in the lower skin layers Signup and view all the answers

How does carotene contribute to skin color?

It is an orange/yellow pigment converted to vitamin A Signup and view all the answers

In which skin layer does melanin primarily provide UV protection?

Stratum germinativum Signup and view all the answers

What is the consequence of UV exposure on skin regarding skin cancer risk?

Damage to DNA in the stratum germinativum Signup and view all the answers

What is the primary consequence of melanocyte loss in vitiligo?

White patches on the skin Signup and view all the answers

Which layer of the dermis is primarily composed of dense irregular connective tissue?

Reticular layer Signup and view all the answers

What effect does an increase in blood flow have on skin color?

It produces a flushed, bright red appearance Signup and view all the answers

What is the role of calcitriol in the body?

To facilitate calcium absorption in the intestines Signup and view all the answers

What is the composition of the dermal papillae in the papillary layer?

Aerolar tissue Signup and view all the answers

What physical condition can result from a deficiency in vitamin D3 during childhood?

Rickets Signup and view all the answers

How are lines of cleavage in the dermis primarily oriented?

In parallel bundles to resist skin forces Signup and view all the answers

What happens to capillaries in the skin during cold temperatures?

They constrict, decreasing blood flow Signup and view all the answers

Which type of fibers in the reticular layer provide strength and resistance to stretching?

Collagen fibers Signup and view all the answers

A lack of sun exposure can lead to which deficiency-related condition in children?

Rickets Signup and view all the answers

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).
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.
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.