Skin Biology Quiz

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Questions and Answers

What percentage of body mass does the skin typically account for?

10% (correct)

15%

20%

Which function is NOT associated with the skin?

Protection against viruses

Sensation of touch

Regulation of body temperature

Nutrient absorption (correct)

What is the primary function of adipocytes in the subcutaneous tissue?

Production of sweat

Energy reserve and shock absorption (correct)

Protection against bacteria

Temperature regulation through hair growth

Which layer of skin primarily provides structure, strength, and flexibility?

Dermis Signup and view all the answers

What changes occur to the adipocytes in the face and hands as a person ages?

Decline in amount Signup and view all the answers

What is the primary role of the stratum corneum in skin health?

Maintaining functional integrity Signup and view all the answers

Which component is most associated with the defensive barrier function of the skin?

Epidermal lipids Signup and view all the answers

What does the extraction of natural moisturizing factor from the stratum corneum indicate about skin?

It increases skin molecular mobility Signup and view all the answers

What type of skin condition can moisturizers help address according to recent studies?

Various kinds of dermatitis Signup and view all the answers

Which study provides insights into collagen turnover and its effect on skin?

Effect of collagen turnover on advanced glycation end products Signup and view all the answers

What type of connective tissue forms the papillary dermis?

Loose areolar connective tissue Signup and view all the answers

Which component primarily provides strength and support in the extracellular matrix of the dermis?

Collagen Signup and view all the answers

What percentage of the dermis is primarily composed of collagen?

80% Signup and view all the answers

Which structure is NOT typically found in the reticular dermis?

Dermal papillae Signup and view all the answers

Which group of glycosaminoglycans (GAGs) includes hyaluronic acid?

Hyaluronic acid Signup and view all the answers

What is the primary type of collagen predominant in the dermis?

Type 1 collagen Signup and view all the answers

What role does elastin play in the dermis?

Allows flexibility and stretching Signup and view all the answers

How many layers does the epidermis typically have?

4 - 5 layers Signup and view all the answers

What is the primary structural component of the stratum corneum?

Corneocytes Signup and view all the answers

What is the primary function of melanocytes in the skin?

Produce pigment and protect from sun's radiation Signup and view all the answers

Which lipid component constitutes the largest percentage by mass in the stratum corneum?

Ceramides Signup and view all the answers

Which of the following molecules is NOT part of the natural moisturizing factor (NMF)?

Cholesterol Signup and view all the answers

Which of the following substances contributes to the acid mantle of the skin?

Lactic acid Signup and view all the answers

What happens to cells as they move from the stratum basale to the stratum corneum?

They undergo keratinization and eventually die Signup and view all the answers

What role does filaggrin play in the epidermis?

Binds to keratins to aid cell flattening Signup and view all the answers

Which component is NOT a constituent of sebum?

Amino acids Signup and view all the answers

Which layer of the epidermis is primarily characterized by dead, flattened cells?

Stratum corneum Signup and view all the answers

What is the significance of keratohyaline granules in the granular layer?

They facilitate the bundling of keratin in terminal differentiation Signup and view all the answers

How much lipid must the skin generate daily to replace that lost through desquamation?

100-150 mg Signup and view all the answers

What is the primary mode through which sebaceous glands secrete sebum?

Holocrine secretion Signup and view all the answers

What regulates the thickness of the stratum corneum?

The balance between proliferation and desquamation Signup and view all the answers

What is the main role of Natural Moisturizing Factors (NMFs) in the skin?

Bind water Signup and view all the answers

Which of the following is a major source of the natural moisturizing factor (NMF) in the stratum corneum?

Granular layer of the epidermis Signup and view all the answers

In which layer do lamellar bodies begin to form?

Stratum granulosum Signup and view all the answers

What factor does NOT influence the hydration of the stratum corneum?

Sebum production Signup and view all the answers

What is the primary composition of the hydrolipid film on the skin surface?

Water and lipids Signup and view all the answers

Which statement about the lipid bilayers in the stratum corneum is true?

Ceramides are the most important component for maintaining their structure. Signup and view all the answers

What is the primary role of Langerhans cells in the epidermis?

Participate in immune response Signup and view all the answers

Which function is NOT associated with sebum?

Oxygen production Signup and view all the answers

How often does the turnover of the stratum corneum typically occur?

Every 14-28 days Signup and view all the answers

The hydration levels of the stratum corneum are essential for which of the following processes?

Enzymatic activity Signup and view all the answers

Which of the following statements about skin hydration is true?

Hydration influences barrier functions and mechanical properties of the skin. Signup and view all the answers

Study Notes

Skin Biology Refresher

The skin is the largest organ of the human body, covering approximately 1.7-2.0 m² and accounting for about 10% of body mass.
It's smooth, punctuated by hair and sweat pores.
It's flexible but robust.
The skin provides a barrier function, protecting against radiation, viruses, bacteria, and other foreign substances.
It's waterproof, preventing dehydration.
Touch is one of the five senses.
The skin plays a key role in regulating body temperature (traps/releases heat).

Skin Layers

Epidermis: The outermost layer.
Dermis: A layer under the epidermis, containing the papillary and reticular layers.
Subcutaneous Tissue (Hypodermis): The deepest layer, which helps separate dermis from underlying body constituents. It's mostly made of adipocytes (fat cells) in lobules separated by connective tissue. The number and size of these adipocytes can vary across the body and depend on nutritional state. Also acts as insulation, energy reserve, and padding.

Dermal Structure

The dermis is about 1-4mm thick and has papillary and reticular regions.
Main cell type within the dermis is fibroblasts, which provide structure, strength, and flexibility.
The dermis has a rich blood and lymphatic supply.
Contains sensory nerve endings and appendages like hair follicles and glands.

Papillary Dermis

A thin layer directly contacting the epidermis.
Composed of loose areolar connective tissue.
Upper layer has projections called dermal papillae, which are part of the dermal-epidermal junction.
Contains less collagen and more ECM (extracellular matrix) compared to reticular dermis.
Fibers are randomly arranged mainly perpendicular to skin surface.
Supports/contains blood and lymphatic vessels, involved in nutrition, temperature regulation, and waste removal.

Reticular Dermis

Forms the bulk (about 80%) of the dermis.
Dense connective tissue with thick collagen and elastic fibers running parallel to skin surface.
Contains blood and lymphatic vessels, nerves, and appendages.

Elastin

Provides flexibility to the skin.
Makes up approximately 2-4% of dermis (dry weight).
Has a similar half-life to human lifespan.
Difficult to regenerate or replace.

Collagens

Provide strength and support to the extracellular matrix (ECM).
80% of dermis is collagen (dry weight) and consists of related proteins (at least 29 types).
Type 1 collagen is the predominant type within the dermis.
Can aggregate into filaments, fibrils, and meshes.

Extracellular Matrix (ECM)

Primarily consists of fibrillar proteins surrounded by glycosaminoglycans (GAGs).
GAGs are large polysaccharides that retain water in the dermis.
GAGs and proteins form proteoglycans.
Four groups of GAGs include hyaluronic acid, chondroitin sulphate, dermatan sulphate, heparan sulphate, and keratan sulphate.

Epidermis

Epithelial tissue, between 80-200 μm thick.
Multiple layers (4-5): stratum corneum, (stratum lucidum), stratum granulosum, stratum spinosum, and stratum basale (descending).
Contains keratinocytes (main cells), along with melanocytes, Langerhans cells, and Merkel cells.
Keratinocytes are responsible for producing a strong barrier.

Stratum Corneum

Consists of 15-20 layers of flattened, non-nucleated, and keratinized cells called corneocytes.
Continuously shed (desquamated).
Proteases hydrolyse desmosomes to regulate stratum corneum thickness.
Constantly regenerated.
Turnover time depends on age (14-28 days).
Rate-limiting barrier allowing entry of only small and moderately lipophilic molecules.

Stratum Corneum Lipids

Account for roughly 20% of stratum corneum volume.
Form lamellar sheets in intercellular spaces.
Major components include ceramides (50%), cholesterol (25%) and free fatty acids (10-20%).
Skin generates roughly 100-150 mg of lipids daily to replace those lost through desquamation.

Ceramides

A crucial component of stratum corneum lipids for maintaining lamellar structure.
Various subclasses ('free' ceramides) with differences in head group hydroxylation exist in the epidermis.

Lipid Lamellar Bilayers

Stratum corneum is organised into lipid lamellar bilayers.

Skin Surface: Hydrolipid Film/Acid Mantle

An emulsion of water and lipids covering the epidermis.
Contains lactic acid and free fatty acids (from sweat and sebum).
Contains amino acids and natural moisturizing factors (NMFs), by products of keratinisation.

Sebum

Lipid secretion from sebaceous glands, composed of glycerides, free fatty acids, wax esters, squalene, cholesterol esters, and cholesterol.
Holocrine secretion (mature sebocytes disintegrating).
Activity is hormonally regulated.

Skin Functions

Protection: from physical, chemical, and microbial assaults.
Lubrication: Maintaining skin softness and flexibility.
Waterproofing: Preventing excessive water loss.
Photoprotection: Providing some degree of protection against UV radiation.
Antimicrobial activity: Inhibiting the growth of microbes.
Delivering and containing fat-soluble antioxidants to the skin surface and showing pro- and anti-inflammatory action (in relation to lipids).
The understanding of these functions is not yet complete in some respects.

Hydration of the Skin

Water content ranges from 10-30%.
Essential for enzymatic activity for processes such as desquamation and skin regeneration.
Water originates in deeper layers and moves upward hydrating cells in stratum corneum, eventually evaporating. Factors affecting hydration of stratum corneum include pH gradients, gradients of calcium, magnesium, etc from basement membrane to surface, adequate hydration of corneocytes, rate of water transport from dermis to stratum corneum, rate of surface water loss, binding ability, and adequate maturation time of stratum corneum.

Natural Moisturizing Factor (NMF)

A complex mixture of low molecular weight compounds.
Includes amino acids (AA), pyrrolidone carboxylic acid (PCA), urocanic acid (UCA), lactic acid, sugars, urea, glycerol, and various ions.
Derived from the hydrolysis of filaggrin in corneocytes but also from sweat, sebaceous glands, and triglyeride turnover.

Filaggrin

Derived from profilaggrin.
Major component of keratohyalin granules.
Monomers bind to keratin 1 and 10 forming tight bundles.
Allows the collapse and flattening of cells into squames.

Key Terms

Corneocytes: Dead, keratinized cells in the stratum corneum.
ECM: Extracellular matrix.
GAGs: Glycosaminoglycans
NMF: Natural moisturizing factor
SG: Sebaceous gland

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Description

Test your knowledge on the functions, structures, and health of the skin. This quiz covers various aspects of skin biology, including the role of adipocytes, skin layers, and the impact of aging. Perfect for students studying human anatomy or dermatology.