Structure and Function of the skin Flashcards
What is the largest organ of the body?
The skin (duh)
What are the two layers of the skin?
Epidermis
Dermis
What is more superficial, the epidermis or the dermis?
The Epidermis
What is the epidermis made of?
Stratified squamous epithelium
Embryologically, what kind of cells does the epidermis arise from?
Ectoderm cells
How thick is the epidermis?
1.5mm
True or False, 95% of the cells in the epidermis are melanocytes?
FALSE
95% are keratinocytes
What are the four layers of the Epidermis?
Keratin layer
Granular layer
Prickle cell layer
Basal layer
What other cells are found in the epidermis?
Melanocytes
Langerhans cells
Merkel cells
Where is the dermis in relation to the epidermis?
Beneath it
What is the dermis made of?
Connective tissue
What is the dermis formed from (embryologically)?
Mesoderm
How many layers are there to the foetal skin at 4 weeks?
3
Periderm
Basal layer
Dermis
Name 2 Skin appendages:
Hair follicles
Melanocytes
What is the function of the arrector pili?
Controls temperature
What are the lines of skin development known as?
Blaschko’s lines
What three factors control the regulation of epidermal turnover?
Growth factors
Cell death
Hormones
How long does the regeneration of the epidermis take in healthy skin?
28days
How long does the regeneration of the epidermis take in psoriasis patient’s?
5days
How thick is the basal layer?
One cell thick
Are there intermediate filaments in the basal layer?
Yes, lots of keratin
Is the basal layer metabolically active?
Yes
Why are there desmosomes in the prickle cell layer?
Because the cells are constantly vibrating and moving upwards so do not stay together
What happens to the prickle cell layer in psoriasis?
It thickens
How thick is the granular layer?
2-3 cells thick
What to the large keratohyalin granules in the granular cell layer contain?
Filaggrin and Involucrin
Where is the origin of the cornified envelope?
The granular cell layer
What is the keratin layer made up of?
Corneocytes
What are the 4 different types of epidermal cells?
Keratinocytes
Melanocytes
Langerhan’s cells
Merkel cells
Where do melanocytes come from?
Neural crest
Where are melanocytes found?
Basal layer and above
What kind of cell are melanocytes?
Pigment producting dendritic cells
What organelles do melanocytes contain?
Melanosomes
What are melanosomes responsible for?
Converting tyrosine to melanin
Eumelanin (brown or black)
Phaeomelanin (red or yellow)
T/F melanin absorbs light?
True
What stimulates the production of melanin?
UV light
Hormones
Where do langerhan’s cells come from?
Mesenchyme (bone marrow)
Where are langerhan’s cells found?
Prickle cell layer
Dermis
Lymph noders
What type of cell are Langerhan’s cells?
Antigen presenting cells
What type of cells are Merkel cells?
Basal cells
Mechanoreceptors
Where are merkel cells found?
On the end of nerve fibres
DIrect extension of the brain
T/F - Merkel cells can turn cancerous
True
Very rare
Caused by a viral infection
High mortality
What causes vitiligo?
Hypopigmentation of the skin caused by T cells attacking melanocytes
What is Nelson’s syndrome and what causes it?
Bronzing of the skin due to excess ADH production from the pituitary stimulating melanin excess
What is the name for a tumour of the melanocyte cell line?
Malignant melanoma
What always accompanies a hair follicle?
Sebaceous gland
What is the name for the unit formed by a hair follicle and a sebaceous gland?
Pilosebaceous unit
What is contained in the pilosebaceous unit?
Epidermal component Dermal papilla Specialised kertains Sebaceous gland Hair pigmentation via melanocytes
What are the three stages of hair growth?
Anagen
Catagen
Telogen
What is the anagen pahse?
The growing phase
What is the catagen phase?
The involuting phase
What is the telogen phase?
The resting phase
What can induce the telogen phase?
Chemotherapy
Hair loss
What do nails contain?
Specialised keratin
Where do nails orignate from?
Nail matrix
How fast do nails grow?
0.1mm a day
Which nails grow faster (toenails or fingernails)?
Fingernails
Where is the dermal-epidermal junction?
Interface between the epidermis and the dermis
What interactions does the DE junction play a key role in?
Epithelial-mesenchymal interactions
How is the DE junction involved in Basal cells?
Involved in support, anchorage, adhesion growth and differentiation
Is the DE junction permeable?
Semi-permeable
What are the three layers of the DE junction?
Lamina Lucida
Lamina Densa
Sub-lamina densa zone
What can occur when the junction is non-functioning?
Fragile skin
Fluid filled blisters
What is the dermis made up of?
Ground substance Cells Fibres Muscles Blood vessels Lymphatics Nerves
What does ground substance consist of and what does it do?
Glycans, proteins and acids
Gives the dermis structure
What cells are found in the dermis?
Mainly fibroblasts Macrophages Mast cells Lymphocytes Langerhan's cells
What fibres are found in the dermis?
Collagen
Elastin
What is the pathway for the flow of blood?
Arteriole>Precapillary sphincters>Arterial>Venous capillaries>Post capillary venules> collecting venules
What are lymphatics?
Sub-epidermal meshed networks
Smaller non-contractile vessels drain to larger contractile lymphatic trunks
Continously drains plasma proteins, dead cells and excess interstitial fluid
What is neurofibromatosis?
Overgrowth of nerve endings
What is angioma?
Overgrowth of blood vessels
What are the three types of skin glands?
Sebaceous
Apocrine
Eccrine
What do sebaceous glands secrete?
Holocrine into the pilary canal Sebum Wax TG FFA
Where are sebaceous glands found?
Widely distributed
Largest glands in the face and chest
What do sebaceous glands control?
Moisture loss
What do sebaceous glands protect from?
Fungal infection
Where are apocrine glands from?
Underarm
Groin
What are apocrine glands dependent on?
Androgens
What do androgens produce?
Oily fluid and odour
What is the function of apocrine glands?
Unknown
Which glands are the most active?
Eccrine
Where are eccrine glands found?
Everywhere
Specifically palms, soles and axillae
What is the nerve supple to the eccrine glands?
Sympathetic cholinergenic
Mental, thermal and gustatory stimulation
How much fluid can eccrine glands filter?
> 10L a day
How many eccrine glands are present in the body?
2-4 million glands
What is the function of eccrine glands?
Moistens palms and soled to aid grip
What are the main functions of the skin?
Barrier function Metabolism and detoxification Thermoregulation Immune defence Communication Sensory function
What does the skin act as a barrier from?
Friction Mechanical trauma UV radiation Chemicals Bacterias Viruses Fungi
What are the consequences of skin barrier failure?
Fluid loss > Dehydration
Protein loss > Hypoalbuminaemia
Infection
T/F the skin is metabolically active?
True
How does vitamin D metabolism occur?
Cholecalciferol to Vitamin D3 occurs in the dermis
Where does thyroid hormone metabolism occur?
Tryroxine to Triiodothyrnine in the periopheral tissues and thyroid
What is the consequences of metabolism and detoxification?
Disordered thyroxine metabolsim
What does thermoregulation protect against?
Hot and cold
What are does thermoregulation control?
Sweating, shivering and blood supply
What is the consequence of failure of thermoregulation?
Heat loss>Hypothermia
What is immune defence important in?
Protection against infection
Sunlight responses
Allergic reactions to chemicals and drugs
What cells act in the immune defence?
Langerhans and T cells
What is the consequence of failure of immune defence?
Spread of infection
What is the skin involved in communicating?
Visual
Odour
Sociosexual behaviour
What does the sensory function of the skin regulate?
Touch Pressure Vibration Pain Itch Heat and cold
