L11 The Skin Flashcards
What are the 3 different layers of the skin?
Epidermis
Dermis
Hypodermis
Epidermis is the uppermost epithelia layer
What is in the integumentary system?
Skin, hair, nails and cutaneous glands (Relates to skin)
Sebaceous and sweat glands relate to the cutaneous glands
What is the largest organ?
The skin
What does ECM stand for?
Extracellular matrix
Which is bigger in length, the dermis or the epidermis?
The dermis is thicker than the epidermis
What are fibroblasts?
They are responsible for producing the extracellular matrix (ECM)
Fibroblasts are the most common type of cell in connective tissue.
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
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.
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
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
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
What does DEJ stand for?
Dermal - epidermal junction
What is unique about the dermal-epidermal boundary?
It has a wavy boundary of finger- like projections (dermal papillae) with epidermal ridges ( rete ridges)
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
The epidermis is composed of five distinct layers, what are they?
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
Big Sexy Grandma Loves Cookies
B,S,G,L,C
All stratified
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
Why does the epidermis rely on diffusion from the underlying connective tissue?
It lacks blood vessels
Does the epidermis regenerate?
The epidermis (uppermost layer of the skin) undergoes self regeneration, with a complete cycle typically taking 2-4 weeks
What is the stratum Basale?
The outermost layer of your skin (the epidermis)
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
What do melanocytes do?
This produces melanin, the pigment responsible for skin colour. Also protects skin from UV light
In the stratum basale layer
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
Where is the stratum Spinosum located?
Located in the second layer of the epidermis
Between stratum basale and stratum granulosum
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)
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
Keratin filaments flatten cells
Describe the behaviour of the stratum granulosum
- Cells are post- mitotic, meaning they are no longer dividing
- Tight junctions between cells which contributes to the skin’s barrier function
- 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
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
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
S,E,A,C,M
How is the skin a multi-layered defense system?
- Physical barrier
- Biochemical barrier
- 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?
- Midly acidic pH (4-6)
- Sebacaeous gland sebocytes (sebum) contains:
saturated+ unsaturated FA = inhibit bacterial growth
Lysozymes
C6H - inhibit development of antiobiotic resistance
FA = fatty acids
What does LC stand for?
LC - Langerhans Cells
Where within the cell are Langerhan cells present?
Stratum spinosum
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
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?
- Vasodilation/ vasoconstriction
- Sweating
- 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
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?
- Cell shape - keratinocytes flatten as they move towards the skin’s surface
- Cytoplasm - more filled with keratin filaments (provides protection)
- Cell connections - Number of desmosomes, and cell to cell junctions
- Lipid production - produces lamellar granules which forms a water-resistance barrier
