Structure And Function Of The Skin Flashcards
Name and describe the layers of the skin
Epidermis- thin outermost layer
Dermis- forms connective tissue beneath the epidermis
Hypodermis/subcutis- fat beneath dermis, pigment producing cells from neural crest
What is the appendage?
Nails, hair, glands, mucosa
Embryology- what does the epidermis rise from?
The ectoderm (outermost cell layer in embryo)
Embryology- what does the dermis develop from?
Mesoderm- middle layer of embryo
Embryology- what does the subcutis rise from?
Mesoderm
Embryology- what does the appendages rise from?
Ectoderm
What are the key stages of foetal skin development?
Week 4
Week 16
Week 26
What happens at week 4 of foetal skin development?
Formation of:
Periderm
Basal layer
Dermis (corium)
Melanocytes begins to migrate from neural crest to basal layer
What happens at week 16 of foetal skin development?
-
Keratin Layer (KL)
- Granular Layer (GL)
- Prickle Cell Layer (PL)
- Basal Layer (BL)
- Dermis (D)
What happens at week 26 of foetal skin development?
Epidermis fully formed with all layers, melanocytes are now in basal layer
Sebaceous glands developed
Arector pili muscles (those that cause hair to stand up) are present
What are Blaschko’s lines?
Developmental growth pattern of the skin
Thought to be along lines of cell migration during foetal development
Some skin conditions can develop along †hem
What are the 4 layers of the epidermis?
Keratin
Granular
Prickle cell
Basal
What type of tissue is epidermis made of?
How thick is it?
What cell type is it mostly made up of?
What other cells are present?
Stratified squamous epithelium
1.5mm thick
95% made of keratinocytes
Also contains:
Melanocytes, Langerhans cells, merkel cells
How is epidermal turnover regulated, and how is it lost?
Balance of cells in and out- via growth factors, cell death, and hormones
Loss of control with skin cancer and psoriasis
What is the process of differentiation?
When keratinocytes migrate from the basement membrane to the top- for continuous regeneration
keratin layer-
Latin name
Composition
Function
Stratum corneum
Made of corneocytes- dead keratinocytes that are still rich in keratin- provides structural strength). Source of house dust
Lipid matrix- surrounds corneocytes, crucial for skins waterproof barrier. Rich in filaggrin which contribute to strength and hydration
granular layer
Latin name
Contains..?
What happens to a cell at this stage
Stratum granulosum
Contains:
keratohyalin granules
filaggrin
involcurin proteins
Odland/lamellar bodies
^all contribute to strength and protective barrier
Cells lose nuclei at this stage
prickle cell layer
Latin name
Contains…?
Stratum spinosum
Contains many desmosomes for mechanical strength
and large polyhedral cells which synthesise keratin
basal layer
Latin name
Cell appearance
Contains..?
Significance to cancer
Stratum bassale
One cell thick, small cuboidal cells with many intermediate filaments (keratin)
Basal cell carcinoma is the most common skin cancer as this layer is very metabolically active (continuously produces more cells and melanin)
Melanin-
What are they produced by and where?
Where are they found
Types
Process of formation
Role
Produced by melanosomes in melanocytes (they migrate from neural crest up in first 3 months of foetal development)
Found in basal layer and above
2 types:
Eumelanin- brown/black in colour
Phaeomelanin- red/yellow in colour
Tyrosinase converts tyrosine to dopaquinone
Dopaquinone forms either type of melanin
Roles:
Photoprotection
Pigmentation
Antioxidant activity
langerhans cells-
What are they?
Where do they originate from?
Where are they found?
What do they do?
Type of dendritic cell that is an APC
Mesenchymal origin- bone marrow
Found mostly in prickle cell layer, but also dermis and lymph nodes
They pick up antigens in skin and circulate to lymph nodes, presenting them to T cells (initiating adaptive immune response)
merkel cells
Where are they found?
What do they do?
Possible complication
Found in basal layer between keratinocytes and nerve fibres
Essential for light and touch sensation
Rare but Merkel cell cancer is possible- very high mortality
How does white skin differ from darker skin?
Darker skin has more eumelanin, and keratin layer has more layers
In white skin melanosomes confined to basal layer but in darker skin they exist throughout
What is a key feature of mucosal membranes?
Give examples
Highly specialised for function-
Masticatory mucosa keratinised to deal with friction/pressure
Tongue mucosa specialised to deal with taste
Ocular mucosa- lacrimal and sebaceous glands, eye lashes
What is in between the epidermis and dermis?
What is its role?
The dermo-epidermal junction
Support and anchorage of epidermis
Semi permeable membrane acting as a barrier and a filter
What is the dermis made of?
Collagen (1 and 111) and elastin arranged in ground substance of hyaluronic acid and chondritin sulphate
What is the main cell present in the dermis?
Fibroblast- collagen producing
What other cells does the Dermis contain?
Macrophages
Mast cells
Lymphocytes
Langerhans cells
What does the dermis contain?
Nerves
Muscles
Vasculature (inc lymphatics)
What are the 2 layers of the dermis and how do they differ?
Papillary- thin, just below epidermis
Reticular- thick, bundles of type 1 collagen
Reticular contains appendage structures like sweat glands and pilosebaceous units
Special feature of dermis circulation
Supply to skin exceeds metabolic need-
Arteriovenous anastomoses allow for superficial capillary bypass when cold to prevent heat loss
Role of lymphatic system in skin
Sub epidermal network
Small non contractile vessels feed into large contractile trunks
Drains plasma proteins, extravasated cells and excess interstitial fluid
Innervation of the skin
Autonomic-
Vessels nerves and glands
Somatic- sensory free nerve endings
Pressure detected by Pacinian corpuscle
Vibration detected by Meissners corpuscle
Role of immune cells in the skin
mast cells- release histamine to cause itch
macrophages- phagocytic and APC- release cytokines
What are the 3 types of skin gland?
Sebaceous
Eccrine
Apocrine
What type of gland is a sebaceous gland?
Exocrine- secrets its products
Holocrine- product released by cell breakdown
What are sebaceous glands commonly associated with?
Hair follicles
Acne
Where are sebaceous glands found?
Mostly face and chest
What are sebaceous glands sensitive to?
Hormones
Dormant pre puberty
What do sebaceous glands produce?
What does the product do?
Produces sebum
Controls moisture loss and protects from fungal infection
Where are eccrine sweat glands found?
Entire skin surface
Highest concentration on palms, soles, forehead, and axillae
What do eccrine glands do?
Secrete sweat for thermoregulation (cooling), and moistening palms for grip
Under sympathetic cholinergic supply
NaCl and HCO3 is reabsorbed
Where are apocrine glands found?
Associated with pilosebaceous units, concentrated in places where there is more hair eg groin, axilla, etc
What do apocrine glands secrete?
An oily fluid, thicker than sweat and secreted in instances like arousal or stress
Can lead to odour after bacterial composition
What makes up a pilosebaceous unit?
Hair follicle- bulb, isthmus, infundibulum
Hair shaft
Arrector pili muscle
Sebaceous gland
Structure of Asian hair
Straight and round
Fast growth rate
Strong and durable
Structure of Caucasian hair
Straight or curly
High density
High moisture content
High strength
Structure of African hair
Curly
Low density
Slow growth rate
Fragile
What are the 4 phases of hair growth?
Anagen- active growing (3-7 years)
Catagen- transitional (stopping growing)(3-4 weeks)
Telogen- growth fully stopped (3-4 months)
Exogen- shedding (every day)
What hormones influence hair growth?
Thyroxine, androgens
What are nails made of ?
Specialised keratins
What is the nail growth rate?
0.1mm per day
What do nails do?
Provide protection
Improve sensory feedback
What is meant by 2 way barrier?
Prevents external harm (internal protection)
Prevents internal loss (outward regulation)
How does the skin act as a barrier?
Physical protection- friction, mechanical trauma, UV
Chemical protection- irritants, allergens, toxins
Pathogenic protection- bacteria, viruses, fungi
What is the role of vitamin D
Increase flow of calcium into blood (promotes absorption from food and reabsorption in kidneys)
Vitamin D metabolism explained
UV-B (from sun) penetrates epidermis, and coverts 7-dehydrocholesterol to vitamin D3
Significance of the skin to thyroid hormone metabolism
Only 20% of T4 is converted to T3 in the thyroid gland-
The rest occurs in peripheral tissues including the skin
What is the skins role in thermoregulation?
Sweating to cool down
Blood flows through anastamoses to keep heat away from surface, to prevent heat loss
Pilorection- hairs stand up to trap air layer
Skins role in immune defense
Langerhans and T cells
Protects against infection, sunlight responses, and allergic reactions
Skins role in communication
Visual
Odour
Sociosexual behaviour
Skins role in sensory function
Touch, pressure, vibration
Pain and itch
Hot and cold
Requirements for skin function
Intact barrier
Functioning immune system
Functioning Vasculature
Means of regulation temperature
Normal sensory nerve function
