L11 The Skin Flashcards by Brandon Sham

What are the 3 different layers of the skin?

Epidermis
Dermis
Hypodermis

Epidermis is the uppermost epithelia layer

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What is in the integumentary system?

Skin, hair, nails and cutaneous glands (Relates to skin)

Sebaceous and sweat glands relate to the cutaneous glands

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What is the largest organ?

The skin

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What does ECM stand for?

Extracellular matrix

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Which is bigger in length, the dermis or the epidermis?

The dermis is thicker than the epidermis

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What are fibroblasts?

They are responsible for producing the extracellular matrix (ECM)

Fibroblasts are the most common type of cell in connective tissue.

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The dermis is seperated into two zones, what are they?

Papillary dermis - The upper layer, which contains loose connective tissue (areolar)
Reticular dermis - The lower layer, thick dense irregular connective tissue

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What is the areolar tissue?

Characterised by loose arrangment of fibers and cells (fibroblasts, macrophages, and mast cells)

Found in the papillary layer of the dermis.

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How does the dermis play a crucial role in thermoregulation?

It has a dense network of blood vessels which may undergo vasodilation/vasoconstriction and lymphatic vessels

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What are arteriovenous anastomoses (AVAs)?

They are a direct connection between small arteries and small veins, bypassing the capillary bed

They play a signficant role in regulating blood flow and temperature control

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What is one reason why the dermis is essential for sensory perception?

The dermis has numerous nerve endings

This allows it to perceive a wide range of sensations, including touch, pressure, temperature and pain

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What does DEJ stand for?

Dermal - epidermal junction

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What is unique about the dermal-epidermal boundary?

It has a wavy boundary of finger- like projections (dermal papillae) with epidermal ridges ( rete ridges)

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Why is the dermal papillae important in highly sensitive areas?

Dermal papillae contain a high concentration of sensory nerve fibres that reach close to the surface

Allows for rapid detection and transmission of sensory signals to the brain, enabling quick responses to stimuli

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The epidermis is composed of five distinct layers, what are they?

Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum

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B,S,G,L,C

All stratified

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Epidermis has a thick skin and a thin skin. Where are they generally located?

Thick skin - Found on the palms (fingertips) and feet
Thin skin - rest of body

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Why does the epidermis rely on diffusion from the underlying connective tissue?

It lacks blood vessels

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Does the epidermis regenerate?

The epidermis (uppermost layer of the skin) undergoes self regeneration, with a complete cycle typically taking 2-4 weeks

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What is the stratum Basale?

The outermost layer of your skin (the epidermis)

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What are the key functions of the stratum basale?

Contains Keratinocytes (most prevalent) which are mitotically active
Melanocytes gives skin colour
Tactile/ Merkel cells - connected to sensory nerves

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What do melanocytes do?

This produces melanin, the pigment responsible for skin colour. Also protects skin from UV light

In the stratum basale layer

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What are Merkel cells?

They are responsible for transmitting touch information to the brain. They are connected to the sensory nerves

Located in the stratum basale layer

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Where is the stratum Spinosum located?

Located in the second layer of the epidermis

Between stratum basale and stratum granulosum

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What is the structure of the stratum Spinosum?

Composed of several layers of keratinocytes
Usually the thickest layer of the epidermis

Usually thickest (except in thick skin, where the stratum corneum is thicker)

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What do keratinocytes produce?

It produces keratin filaments which causes cells to flatten (more so in the upper layers)

What cell connections are present within the stratum spinosum?

- Keratinocytes strongly linked by desmosomes - Tight junction ensure water retention of skin - Dendritic cells (Langerhans cells) are present

Are keratin filaments present in the Stratum Spinosum?

Yes. It contains several layers of keratinocytes which produces keratin filaments

Describe the structure of the stratum granulosum

- Composed of 3-5 layers of flat keratinocytes - Cells are flattened and have a dark appearance due to the present of dark-staining granules ## Footnote Keratin filaments flatten cells

Describe the behaviour of the stratum granulosum

1. Cells are post- mitotic, meaning they are no longer dividing 2. Tight junctions between cells which contributes to the skin's barrier function 3. Cells undergo apoptosis

What does the stratum granulosum produce?

- Produces granules: Bind to cytoskeleton - Produce glycolipid- filled vesicles (lamellar bodies/granules) - acts as a waterproof barrier between Stratum Spinosum

What is the significance of lamellar bodies in the stratum Granulosum?

Lamellar bodies/ granules creates a waterproof barrer between that layer and the Stratum Spinosum

Descibe the structure of the Stratum Corneum

Composed of 15-30 layers of flattened corneocytes/ squames Divided into two sublayers: Stratum disjunctum and Stratum compactum ## Footnote Stratum disjunction - beneath apical acid mantle and lipid barrier Stratum compactum - cohesive

What are corneocytes (squames)?

They are enucleated terminally differentiated, dead keratinocytes

What is a cornified envelope?

It's a tough, insoluble structure that surrounds each corneocyte ## Footnote Cornified envelope - mortar Corneocyte - bricks

What are the main components of the cornified envelope?

Keratins Cross-linked proteins Lipid envelope

What is the main function of the stratum corneum?

Prevents water loss Resistance to abrasion Resistant to penetration

What are nails composed of?

Nails are composed of dead scaly cells densely packed with 'hard' keratin fibres

How do nails regrow?

New cells are added by mitosis in the nail matrix

What can the appearance of nails indicate?

Appearance can indicate underlying health issues, e.g: Iron deficiency - flat/concave Long term hypoxemia

What are the 5 gland types within the skin?

Sebaceous glands Eccrine sweat glands Apocrine sweat glands Ceruminous glands Mammary glands ## Footnote S,E,A,C,M

How is the skin a multi-layered defense system?

1. Physical barrier 2. Biochemical barrier 3. Immunological barrier

What is the approximate number of different species that make up the human skin microbiome?

Over 1000 species

How does the skin act as a physical barrier?

Cross- linked keratin layer - provides impenetrable barrier

How does the skin act as a biochemical barrier?

1. Midly acidic pH (4-6) 2. Sebacaeous gland sebocytes (sebum) contains: saturated+ unsaturated FA = inhibit bacterial growth Lysozymes C6H - inhibit development of antiobiotic resistance ## Footnote FA = fatty acids

What does LC stand for?

LC - Langerhans Cells

Where within the cell are Langerhan cells present?

Stratum spinosum ## Footnote Dendritic cell

What are dermal cells?

They are cells that make up the dermis, the middle layer of the skin

Does the dermis have more different types of cells compared to the epidermis?

Yes. Dermis layer has a larger variety

What is vitamin D?

It is a fat-soluble hormone that maintains calcium homeostasis

What is UVB?

Ultraviolet B radiation

What causes photochemical reactions?

UVB radiation does ## Footnote Photochemical reaction is essential for vitamin D synthesis. Without UVB radiation, our bodies would not be able to produce this vital vitamin

What are the key mechanisms in skin's thermoregulation?

1. Vasodilation/ vasoconstriction 2. Sweating 3. Insulation - pilerection

Where are central thermoreceptors located?

Located in the preoptic anterior hypothalamus

How does countercurrent heat exchange work?

Minimises heat loss in extremities (dermis) by transferring heat from arterial blood to venous blood

What does overperfused mean?

Means that a particular tissue or organ is receiving more blood flow than it typically needs

What is AVA?

Arteriovenous anastomoses ## Footnote They regulate body temperature

Why does the apical skin have a rich sympathetic innervation?

It's due to the high density of arteriovenous anastomoses (AVA) in apical skin

What is the dermis predominantly made up of?

Connective tissue Richly innervated and vascular

What is the skin made up of?

A superficial epidermal layer with an underlying dermal layer

What are the keratinocyte changes as they push upwards from the basement membrane?

1. Cell shape - keratinocytes flatten as they move towards the skin's surface 2. Cytoplasm - more filled with keratin filaments (provides protection) 3. Cell connections - Number of desmosomes, and cell to cell junctions 4. Lipid production - produces lamellar granules which forms a water-resistance barrier