Structure and function of skin Flashcards
What are the 2 layers of skin?
Epidermis - striatified squamous epithelium
Dermis - connective tissue
What is the embryological origin of the epidermis?
Ectoderm cells form a single layer periderm
What is the embryological origin of the dermis?
Formed from the mesoderm below the endoderm
What is the embryological origin of melanocytes?
Pigment producing cells from the neural crest
What are blaschko’s lines?
Developmental growth pattern of skin that doesn’t follow vessels, nerves or lymphatics
What is an epidermal nevus?
A benign harmatomatous growth following a linear arrangement that follows the lines of Blaschko
What are the appendages of the skin?
Nails
Hair
Glands
Mucosae
How is skin able to move so freely?
The dermis sits on the sub-cutis which is a rolling sheet of fat alowing movement
What is a sebaceous gland?
A small gland in the skin which secretes a lubricating oily matter into the hair follicles to lubricate the skin and hair
What cell type is the epidermis made up of
Keratinocytes
How many layers make up the epidermis?
4 layers
What other cells are situated within the epidermis?
Melanocytes
Langerhans
Merkel
What are the 4 layers of the epiderm?
Basal layer (ectoderm)
Prickle cell layer
Granular layer
Keratin layer
What is an apocrine gland?
Present in armpits, groin and are around nipples
Scent glands that secrete an odor
What regulates epidermal turnover?
Growth factors
Cell death
Hormones
What conditions can arise due to a loss of control in epidermal turnover?
Skin cancer (malignant) Psoriasis (benign)
Why is psoriasis red in appearance?
Blood vessels move closer to the surface of the skin
How many days does it take a keratinocyte to move from the basal cell layer to the keratin layer?
28 days
What are the characteristics of the basal layer?
One cell thick
Small cuboidal
Intermediate filaments (keratin)
Highly metabolically active
What are the characteristics of the prickle cell layer?
Larger polyhedral cells
Lots of desmosomes
Intermediate filaments connect to desmosomes
What are the characteristics of the granular cell layer?
2/3 layers of flat cells Contain large keratohyalin granules Odland bodies High lipid content Origin of cornified envelope
What do the keratohyalin granules contain?
Filaggrin and involucrin
What is a corneocyte?
Lipids and proteins from the burst granular cell
What are the characteristics of the keratin layer?
Made up of corneocytes, keratin and filaggrin
What does filaggrin do?
Attracts and traps water creating not only a tight waterproof barrier but providing moisture to the skin (without you get eczema)
What is the cornified envelope?
Sheath made from protein and lipids
Where are there mucosal membranes?
Eyes, mouth, nose, genito-urinary and GI tracts
What are some specialisations in the oral mucosa?
Keratanised in hard palate to deal with pressure
Tonge papillae
What are some specalisations in the ocular mucosa?
Lacrimal glands
Eye lashes
Sebaceous glands
What is the embryological origin of melanocytes?
Migrate from neural crest to the epidermis in first 3 months of foetal development
What do melanocytes produce?
Pigment producing dendritic cells
What organelles do melanocytes contain?
Melanosomes
What is the function of melanosomes?
Convert tyrosine to melanin pigment
What are the different types of epidermal cells?
Keratinocytes
Melanocytes
Langerhans
Merkel cells
What embryological structure is dermis derived from?
Mesoderm
What embryological structure is epidermis derived from?
Ectoderm
What is the function of melanin?
Absorbs light (natural density filter)
What happens to full melanosomes?
They are transferred to adjacent keratinocytes via dendrites to form a protective cap over the nucleus
What is the pathogenesis of vitiiligo?
The melanocytes are attacked by T cells
What is the pathogenesis of albinism?
Genetic partial loss of pigement production
What is nelson’s syndrome?
Melanin stimulating hormone is produced in excess by the pituitary causing hyperpigmentation
What is a malignant melanoma?
A tumour of the melanocyte cell line
What embryological structure do langerhans cells arise from?
Mesenchymal origin - bone marrow
Where are langerhans cells found in the epidermis?
Prickle cell level in the epidermis
Dermis
Lymph nodes
What is the function of langerhans cells?
Antigen presenting cells
Pick up antigens in skin and circulate to lymph nodes via lymphatic system
Where are merkel cells found?
In the basal layer between keratinocytes and nerve fibers
What is the function of merkel cells?
Mechanoreceptors essential for light touch sensation
Where does the pilosebaceous unit originate from?
Grows out of the basal layer with an adjacent sebaceous gland
How is hair pigmented?
Via melanocytes above the dermal papilla
What are the phases of growth for hair?
Anagen = growing Catagen = involuting Telogen = resting
What are the different types of hair follicles?
Lanugo (in utero)
Vellus
Terminal
What can cause hirsutism?
Polycystic ovaries - too much testosterone
What causes alopecia areata?
Autoimmune hair loss as hair follicle cells are attacked by T lymphocytes
How do nails grow?
Stem cells in basal layer but instead of becoming prickle cells they enter a different differentiation program and start to form flat cells that produce keratin
Where does nail growth start?
Nail matrix
What is the dermo-epidermal junction?
Inferface between epidermis and dermis
What is the function of the dermo-epidermal junction?
Support, anchorag, adhesion, growth and differentiation of basal cells
Semi-permable membrane acts as a barrier and filter
What makes up the dermo-epidermal junction?
Lamina lucida
Lamina densa
Sub-lamina densa zone
What is bullous` pemphigoig?
An autoimmune skin disease, involving the formation of blisters at the space between the epidermis and dermis skin layers. It is a type II hypersensitivity reaction, with the formation of anti-hemidesmosome antibodies
What is epidermolysis bullosa?
A group of genetic conditions that result in easy blistering of the skin and mucous membranes. Blisters occur with minor trauma or friction and are painful
What cells make up the dermis?
Mainly ground substance
Fibroblasts, macrophages, mast cells, langerhans cells, lymphocytes
What do fibroblasts produce?
Collagen and elastin
What is present in ground substance?
Glycosaminoglycans
Why is there a greater blood supply than needed for the skin?
Thermoregulatory processes
How do the blood vessles form in the skin?
Horizontal plexuses
What blood vessels supply the hair follicle?
Deep vascular plexus
What blood vessels supply the epidermis?
Papillary dermis
What is angiomia?
Overgrowth of blood vessles
Benign
What nerves are present in the skin?
Somatic sensory (dermatomes):
Free nerve endings
Autonomic nerve supply - blood vessels, nerves and glands
What are the special receptors present in the skin?
Pacinial corpuscle
Meissners corpuscle
What nerve supply do the sebaceous glands have?
Autonomic supply
What do the pacinal corpsucle detect?
Deep pressure - found deep in the dermis
What do meissner’s corpscule detect?
Touch and vibration
What do pacinial corpuscles look like histologically?
Onion rings
What is a neurofibromatosis?
Overgrowth of nerve endings causing multiple tumours
Linked to underlying CNS tumours
What are the 3 different types of skin glands?
Sebaceous
Apocrine
Eccrine
What do sebaceous glands produce?
Sebum - squalene, wax esters, TG and FFA
What is the function of sebaceous glands?
Control moisture loss
Protect from funal infections
What is the treatment for acne vulgaris?
Topical retinoids
Antibiotics
Roaccutane
What and where are the apocrine sweat glands?
Axillae and perinuem
Androgen dependent
Produce oily fluid that has an odor after bacterial decomposition
What and where are eccrine sweat glands?
Whole skin surface
Cool by evaporation, moisten palms
What is the nerve supply to eccrine glands?
Sympathetic nerve supply
What is the function and consequence of failure of the barrier of skin?
Fluid loss leads to dehydration
Protein loss leads to hypoalbuminaemia
Infection
What is the function and consequence of failure of the thermoregulation of skin?
Heat loss leads to hypothermia
What is the function and consequence of failure of the immune defence of skin?
Spread of infection
What is the function and consequence of failure of the metabolic function of skin?
Disordered thyroxine metabolism
What is the function and consequence of failure of the communication function of skin?
Inability to display healthy skin is a stigma
What is the function and consequence of failure of the sensation of skin?
Pain sensation working lead to pain
What is an example of a barrier failure disease?
Steroid-sulphatasae deficiency X-linked ichythosis
Not normal lipid distribution in keratin layer
Cumulative irritant hand dermatitis
What does the skin aid metabolism of?
Vitamin D
Thyroid hormone
What is a disease example when the skin’s immune defence is inadequate?
Crusted scabies
Tuberculoid leprosy
What is a granuloma?
Specialized macrophages (anitchov cells) around a core of fibrinoid collaged necrosis. Aschoff cells are interspersed between other cells while lymphocytes make up the outer layer
What is eczema herpeticum?
Disseminated herpes simpex virus infection
What is the definition of stigma?
Situation of an individual who is disqualified from full social acceptance
What is a ruffini ending?
Slowly adapting mechanoreceptor responsible for the sensation of the stretch of your skin, sustained pressure on skin and perception of heat
What is a hair follicle?
An invagination of the epidermis
What is contained within the central medulla?
Soft heratin
What is contained within the outer cortex?
Hard keratin
What is the papilla?
Contains multiple vascular channels
What does the matrix region contain?
Keratin producing cells
What is the hypochium?
Secures the free nail edge
What is seen histologically in acute dermatitis?
Intra-epidermal vesicles containing white cells and cell debris
Intracellular oedema called spongiosis
What is seen histologically in psoriasis?
Parakeratosis
Micro-abscesses
Elongated rete pegs
What is seen histologically in normal skin from the sole of the foot?
Thick keratin layer
Prominent granular layer
Irregular DEJ
Eccrine sweat gland duct
What is seen histologically in bullous pemphigoid?
Fluid filled bulla with eosinophils
What it toxic epidermal necrolysis?
Drug induced, keratinocyte death resulting in epidermal detachement at the DEJ
What are the 3 stages to wound healing?
Inflammation
Proliferation and tissue remodelling
Tissue remodelling
What occurs during the inflammation phase of wound healing?
Platelets form the initial clot and release inflammatory mediators
Leucocytes debride the wound bed by phagocytosing bacteria and scavenging cellular debris
Inflammation gradually decreases as keratinocyte proliferation and new tissue formation becomes predominant
What occurs during the proliferation and tissue remoddeling phase of wound healing?
Cells divide to re-epithelialise the wound surface
Granulation tissue formation is stimulated
Fibroblasts lay down matrix and contract the wound (fibroplasia)
Endothelial cells develop into new blood vessels (angiogenesis)
New tissue formed
What occurs during the tissue remoddeling phase of wound healing?
New tissue converted to mature scar tissue
Fibroblasts lay down collagen to improve strength of scar and restore normal dermal matrix
What is primary intention wound healing?
Acute wound closed by approximating wound edges
What is secondary intention wound healing?
An acute wound is left to heal on its own
What should you consider in delayed wound healing?
Infection Poor arterial blood supply Poor nutrition Impaired venous return Repeated traume Systemic disease - diabetes, anaemia
