Skin: Structure and Function Flashcards
What is integument?
A collective word to describe the Skin, Hair and Nails
List some functions of the skin.
Barrier - Protects against dehydration, infection, injury/abrasion, solar radiation
Thermoregulation - helps in regulation of body temperature
Sensation - skin also functions as a sensory organ
Repair - skin is capable of repair
Vitamin D production - skin is a site of vitamin D production
List the three layers of the skin.
Epidermis - outermost epithelial layer
Dermis - middle layer that is made up of lots of connective tissue, particularly collagen
Hypodermis - inner fatty layer.
What are some functions of the epidermis?
- Most superficial layer of the skin (outermost)
- Gives skin its colour
- Protection from pathogens and environment
- Vitamin D production
- Made up of multiple layers of upwards differentiating keratinocytes
What are the 4 main layers of the epidermis?
Basal Layer (Stratum basale) - Contains stem cells, and attached to dermis. Stem cells constantly proliferate. Dynamic since there is constant motion of the keratinocytes up through the epidermis.
Spiny Layer (Stratum spinosum) - Keratinocytes have many desmosomes, (junctions) between the cells. These spiny structures have strong bonds holding the epidermis together.
Granular layer (Stratum granulosum) - 1-4 layers of cells containing granules of keratohyalin (precursor of keratin). Also contain lamellar bodies containing lipids. Cells start to lose their nuclei because they are differentiating into the cornified layer.
Cornified layer (Stratum corneum) - outer protective layer of the epidermis. Cell are keratinised so the skin is tough and resistant to injury. Flattened cells and have lost their nuclei. Nonpolar lipids (waterproof) between the cells - formed from lamellar bodies. Layer constantly shed and replaced.
List some epidermal cell types
- Keratinocytes (most prominent epidermis cell)
- Melanocytes (responsible for skin pigment)
- Langerhans cells (responsible for immune function/defense)
- Merkel cells (sensation e.g. touch)
Describe melanocytes.
- Melanocytes synthesise melanosomes (granules which pigment skin) and transfers them to basal keratinocytes through long dendrites.
- Melanocytes then arrange melanin pigment in a cap-like conformation distal to the nucleus (sunny side). This protects the nucleus from radiation damage
from UV rays. - Present especially in basal layer
- Hard to tell the difference between melanocytes and Merkel cells using H&E alone because they both have pale cytoplasm so can use DOPA stain for melanin.
Describe Langerhans cells.
Immune system defence - seeks and deals with invading microbes
Antigen-presenting cells - behave like macrophages
They are dendritic cells, forming a network
Hard to see with H&E so seen with immunoperoxidase staining.
Describe Vitamin D production.
- Vitamin D3 (inactive precursor), made in the epidermis.
- Synthesised mostly in basal cells, and also somewhat in the stratum spinosum.
- Requires UV light
- Requires more UV light in dark skin to make the same amount of Vitamin D in individuals with lighter skin (due to the melanin barrier).
- Converted to active form in liver and kidney: 1,25 dihydroxyvitamin D3
Describe the dermis.
- The skin layer that lies below the epidermis
- It is made up of two layers
- It is responsible for the tensile strength and elasticity of the skin
- The dermis houses blood vessels, skin glands and sensory receptors
- Fibroblasts are the principal cell of the dermis
- Made up of layers of connective tissue characterized by interconnected mesh of elastin and collagen fibres produced by dermal fibroblasts.
- Dense (full of collagen fibres), irregular (fibres run in all directions) connective tissue
What are the 2 layers of the dermis?
Thin papillary layer - consists of finger-like protrusions (which go into the epidermal region) called papilla.
Deeper reticular layer - interconnected mesh of fibres.
What are some functions of the dermis?
- Collagen provides tensile strength so protects against abrasion and impact e.g. hits to the skin.
- Also contains elastin, a protein complex that provides elasticity.
- Dermis also carries blood and nerve supply for epidermis. Rich in blood vessels, sensory receptors and skin glands.
Describe the dermal-epidermal border.
- Often wavy, to resist shear forces (rubbing sideways)
- Dermal papillae - Finger-like protrusions of dermal connective tissue into the epidermal layer.
- Rete ridges - Extensions of epidermis into the dermal layer
- The wavy appearance more apparent in thick skin of hands and feet = fingerprints
Explain how you would stain to see the fibrous dermis network.
Verhoeff - van Gieson (VVG) stain
- To visualise elastin fibres the first stain with the Verhoeff stains elastin in black
- Then counter stained with the van Gieson which stains collagen in red.
UV light causes damage/loss of elastic fibres, resulting in loss of some of its elasticity and wrinkles.
Describe the hypodermis.
- Skin layer below the dermis
- Helps insulate deeper tissue - due to fatty cells
- Anchors skin to muscle with connective tissue
- Hypodermis also referred to as Fascia (fatty) or subcutis (Cutis = epidermis + dermis)
- Made up of well-vascularized, loose, areolar connective tissue and adipose tissue for fat storage, insulation and cushioning for the integument.
- Composed of fat, glands, hair follicles, nerves, blood vessels.
- Often the thickest layer of skin. Thickness varies with age, body site, nutrition etc.
