Skin Flashcards
To learn the anatomy of the skin
Why is the skin recognised as an organ?
It is a combination of the 4 primary body tissues; connective, epithelium, muscle and nerve and it has it’s own blood supply. It is the largest organ in the body.
Epidermis
The top layer of skin which prevents water loss by evaporation and forms a boundary between the internal and external compartments. It has stratified squamous keratinising epithelium and is of ectodermal origin. It consists of 5 layers.
Epidermis; stratum basale
It’s use is in continuous cell proliferation. It is made up of tall columnar cells interspersed with melanocytes and merkel cells. It has one cell row. It has an irregular interface with the dermis, bound by hemidesmosomes and adhering cells.
Epidermis; stratum spinosum
A preparative layer for keratinisation. It is a spinous layer (seen post-mortem) which is 5-10 cells thick.
Epidermis; stratum granulosum
Keratin proteins and lipids create protective cells. Granules of keratohyalin define the layer. It has a lost nuclei which appears like flattened dark clumps of cytoplasmic material.
Epidermis; stratum lucidem
It reduces friction and is only present in thick skin. It converts keratohyalin to keratin. It is a clear, smooth, amorphous, homogeneous layer to which disulphide linkages give strength.
Epidermis; stratum corneum
Used for water absorption and forms a protective barrier. It contains corneocytes (horny, flattened, dead cells) bound by desmosomes with a 15-30 day turnover.
Epidermis cell types
Keratinocytes; most common and contain keratin and sulphur. They are hard and resistant to abrasion. They extrude lipids for water proofing and are constantly dividing and regenerating to protect from trauma and damage.
Melanocytes; make melatonin for pigment formation.
Langerhans cells; immune surveillance.
Merkel cells; touch receptors
Dermis
The middle layer of skin containing connective tissue, blood capillaries, oils and sweat glands, nerve endings and hair follicles. It is split into 2 layers. The papillary layer on top which is loose connective tissue and is cellular. It has an irregular interface with the epidermis (“papillae”). It protects against pathogens, contains blood vessels for thermoregulation and nutrition and has nerve endings.
The bottom reticular layer is dense irregular connective tissue. It contains collagen in 3 planes and elastin fibres.
Hypodermis
AKA subcutaneous/fatty layer or superficial fascia. It is made up of adipose amd connective tissues, contains larger blood vessels and nerves. It anchors skin to underlying structures and is not technically a part of the skin.
What is keratinisation?
An organic process by which keratin is deposited in cells and the cells become horny (dead skin, hair, nails). Important for the regeneration of skin. Over keratinisation can lead to psoriasis/eczema.
Hair
It was once thermoregulatory, it is still responsive to cold but is not effective. It’s main use is in vanity but does still have a practical use in skin repair. Derived from the epithelial layer, present in thin skinned areas.
Hair follicles
Originate in the epidermis in utero where there is a downgrowth of cells allowing hair growth. Arrector pili muscles are attached to the follicle root and base epidermis. When the muscle contracts the hair straightens. Sebaceous glands are between the follicle amd muscle and secrete sebum.
Nails
The nail plate is made from hard keratin which grows out from a nail bed (specialised form of skin epithelium). It is part of the stratum corneum.
Apocrine glands
Protein rich secretions. Found in armpits, genitals and anal regions
