MEC322 Skin Flashcards
What is the integumentary system composed of?
skin, hair, oil and sweat glands, nails and sensory receptors
It is the heaviest single organ in the body. TRUE or FALSE
TRUE
16% of total body weight
1.2-2.3 m^2 surface area
Skin is…….
heterogeneous, anisotropic and non-linear viscoelastic material
Describe how the skin regulates body temperature
The skin contributes to the homeostatic regulation of body temperature by liberating sweat at its surface and by adjusting the flow of blood in the dermis.
Describe how the skin synthesises vitamin D
The skin contributes to the homeostatic regulation of calcium in the body. Vitamin D controls the absorption of dietary calcium in the intestine and the release of calcium from bones and kidney.
Describe how the skin protects the body
Keratin in the skin protects underlying tissues from microbes, abrasion, heat, and chemicals. Lipids released by lamellar granules inhibit evaporation of water from the skin surface.
Describe how the skin senses
Cutaneous sensations. These include tactile sensations (touch, pressure, vibration, and tickling), thermal sensations (warmth and coolness) and pain.
What is the five functions of the skin?
Body temperature regulation. Synthesis of vitamin D. Protection. Cutaneous sensations. Excretion and absorption.
Structurally what are the skins to main parts?
The superficial, thinner portion, which is composed of epithelial tissue, is the epidermis.
The deeper, thicker portion is the dermis, made of dense irregular connective tissue.
What is the epidermis composed of?
keratinized stratified squamous epithelium
What are the principal types of cells in the epidermis?
keratinocytes - 90% of the epidermal cells arranged in four or five layers and produce the protein keratin.
Melanocytes – 8% of the cells and produce the pigment melanin (pigments in skin)
Intraepidermal macrophages (Langerhans cells) participate in immune responses.
Tactile epithelial cells – detect touch sensations.
What are the four strata of epidermis (thin skin)?
Stratum basale – deepest layer
Stratum spinosum – provides strength & flexibility
Stratum granulosum – keratinocytes undergo apoptosis here (genetic programmed cell death)
Stratum corneum – most superficial layer
What is the extra layer of epidermis in the palms and soles?
Stratum lucidum (only found in thick skin and is located between the granulosum and corneum)
What is the dermis?
the deeper part of the skin
What is the dermis mainly composed of?
Connective tissue (matrix) Collagen fibers (type I and type III): are responsible for mechanical properties of skin Elastic fibers: giving elasticity of skin
What does the dermis also include?
Blood vessels: providing oxygen and nutrients
Nervous system: having sensory purpose
Which layers will a third degree burn penetrate?
epidermis, dermis and subcutaneous layer
What do the mechanical properties of skin depend on the nature and organisation of?
- Dermal collagen and elastic fibres network
- Water, proteins and macromolecule embedded in the extracellular matrix
- With small contributions by epidermis and stratum corneum
Describe collagen protein
Constitutes 25–35% of whole-body protein content Collagen molecule (Tropocollagen): triple helix structure with 3 polypeptide strands; length: 300 nm, diameter: 1.5 nm
How many types of collagen are there?
29
What is made up of collagen I?
(90% of all collagen in human body): skin, tendon, vascular, ligature, organs, bone (main component of bone)
What is made up of collagen II?
cartilage (main component of cartilage)
What is made up of collagen III?
reticulate (main component of reticular fibers), commonly found alongside type I.
What is made up of collagen IV?
basis of cell basement membranes
What is made up of collagen V?
cell surfaces, hair and placenta
fibres are made of…
aggregated fibrils which form a network
What is the Young’s modulus along a fibre?
1000MPa
What is the UTS along a fibre?
50 ~ 100 MPa
What is the mechanical response of skin?
Hyperelasticity
Viscoelasticity
Toughness
Anisotropy & Pre-stress
What factor influence the mechanical response of skin?
Growth & Aging
Injury & Healing
How was pre-stress discovered?
1860s langer
punched circular holes in cadavers and they became enlarged and elliptical (inequality of the pre-stress along and across the major axes of the ellipse)
by connecting the long axis of the ellipse he created a pattern of lines which maps the direction of max tension within skin
How does skin act under 30% strain?
Collagen network offers little resistance to deformation and the behaviour is dominated by the elastic fibres. However rotation of collagen fibre bundles involves inter-fibre slippage which leads to significant viscous effects.
How does skin act at 30%-60% strain?
Collagen fibrils begin to offer resistance to deformation. Involves stretching of flexible regions within cross-linked collagen molecules, which contributes to both elastic and viscous effects.
How does skin act over 60% strain?
Involves fibril defibrillation, which occurs as a result of fibril stretching past rupture.
Where is pre-stress highest?
arms, sternum, thigh, patella and tibia
Where is pre-stress lowest?
back
What is the magnitude of pre-stress?
10% of max or 1MPa
Describe how the mechanical behaviour of skin is age dependant, what else does it depend on?
The mechanical behaviour of skin is a function of:
- the degree of crosslinking of collagen fibres
- degradation of the elastic fibre network,
- age dependent changes in molecular components
Skin appears to maintain its thickness and extensibility up to the seventh decade as opposed to the recovery capabilities, which decrease with increased age.
