Structure and function of skin 1-4 Flashcards
What germ layers are the epidermis and dermis formed from?
Epi- ecto
Dermis- meso
What are the four layers of the epidermis?
Keratin layer
Granular cells
Prickle cells
Basal cells
Where do melanocytes develop from?
Neural crest
What does disease which abides Blatschko’s iines indicate?
That it is congenital
What are the possible consequences if control is lost over skin turnover?
Skin cancer
Psoriasis
What is the rate of migration of keratinocytes in psoriasis compared to normally?
around 3-5 days compared to 28 days normally
What is the basal cell layer characterised by?
Single layer of cells, many intermediate filaments
What is the distinguishing feature of the prickle cell layer?
Desmosomes between cells- cells are motile but retain a cohesive structure
Which layer of the epidermis is the origin of the cornified envelope?
Granular layer
Which proteins are contained within keratohyalin granules in the granular layer, and what is their purpose?
Fillagrin and involucrin
Structural
What are corneocytes and where are they found?
Non-nucleated remnants of keratinocytes, within the keratin layer
Truncation mutations in fillagrin and involucrin are associated with which disease?
Eczema
What is the distinguishing feature of the keratin layer?
Waterproof, but can also transpire- helps maintain fluid homeostasis
Which layer of the epidermis is infected by HPV, and how does it cause the characteristic symptoms?
Prickle cell layer- reactive hyperkeratinisation
Which reaction takes place in melanosomes?
Tyrosine is converted to melanin
How does the melanin produced in melanocytes protect adjacent cells from UV damage?
“full” melanosomes are transferred to adjacent keratinocytes via dendrites, where they form a protective shield around the nucleus and absorb UV light
Describe the underlying cause in these diseases associated with melanin production:
a) Vitiligo
b) albinism
c) Nelson’s syndrome
a) autoimmune destruction of melanocytes
b) disruption in biochemical pathway of melanin production
c) excess melanin stimulating hormone from the pituitary
What is the function of Langerhans cells?
Antigen presenting cells of the skin
Which structural element are Langerhans cells distinguished by?
Racket organelles (Birbeck granules)
Where are Merkel cells found and what is their function?
In the basal layer between keratinocytes and nerve fibres- mechanoreceptors for the sensation of light touch
Where does hair pigmentation derive from?
Melanocytes above the dermal papilla
What is the hair shaft lubricated by?
Adjacent sebaceous glands
What are the three phases of hair growth?
Anagen -growing (90% of hairs)
Catagan- involuting (10%)
Telogen- shedding
What is telogen effluvium and when does it typically occur?
Thinning/shedding of hair
Post-partum and in ageing males (male-pattern baldness)
What is alopecia areata?
Autoimmune hair loss
Where does nail growth occur from?
The nail matrix
What are the three layers of the basement membrane?
Lamina lucida
Lamina densa
Sub-lamina dense
How are the basal cells of the epidermis linked to basement membrane?
Hemidesmosomes
How are the cells of the papillary dermis linked to the basement membrane?
Anchoring fibrils
What causes
a) epidermolysis bullosa
b) bullous pemphigoid
a) lack of adhesion at the DEJ causing blistering
b) auto-antibodies to DEJ proteins
What are the main fibres found in the dermis, and which cells produce them?
Collagen and elastin, secreted by fibroblasts
What kinds of cells are found in the dermis?
Fibroblasts Macrophages Langerhans cells Lymphocytes Mast cells
What is ground substance?
Polysaccharides and glycosaminoglycans- an intercellular amorphous gelatinous material that resists compression
What is photoaging?
Characteristic changes to skin caused by chronic UV exposure
What is solar elastosis?
Accumulation of abnormal elastin in the skin of patients with history of chronic UV overexposure
Describe the blood supply to the dermis.
Greater than the metabolic needs of the tissue
Superficial (supplies the dermis) and deep vascular plexuses
What is an angioma?
Localised overgrowth of blood vessels in fixed dilatation. Often seen from birth
Describe the lymphatic drainage of the dermis.
Sub-epidermal networks of small vessels leading to larger contractile lymphatic trunks.
Jobs- drainage of plasma proteins, extravasated cells, excess tissue fluid
What can be the consequence of blockage in the lymphatic vessels of the skin?
Chronic lymphoedema
Which sensory corpuscles are responsible for the sensation of
a) pressure
b) vibration
a) Pacinian
b) ) Meissners
Other than sensory, describe the nerve supply to the skin
Autonomic- parasympathetic and sympathetic motor fibres
What causes neurofibromatosis?
Overgrowth of neural tissue in the skin
Which substance is produced by sebaceous glands?
Sebum- antibacterial
What causes acne? Why is it more prominent in puberty?
Overproduction of sebum, blockage of sebaceous glands, bacterial activity
Sebaceous glands are hormone sensitive
What is the role of apocrine glands and where are the found?
Produce sweat- in the axilla and perineum
Where are eccrine sweat glands found and what is their purpose?
The whole skin- ultrafiltration and cooling by evaporation
What is the innervation of the eccrine sweat glands?
Sympathetic supply- inputs from mental, thermal and gustatory systems
How is the skin involved in:
a) Vitamin D metabolism
b) Thyroid hormone metabolism
c) Drug metabolism
a) 290-320nm UV light converts cholecalciferol to Vit D3
b) conversion of T4-T3
c) Cytochrome enzymes are present in skin
What actions are initated by skin thermoreceptors to regulate temperature?
Sweating
Shivering
Hair erection
Changes in blood flow
For each function of the skin, describe what the consequences of skin failure might be:
a) barrier
b) metabolism
c) thermoregulation
d) communication/social
e) immune defebce
a) Fluid loss and dehydration Protein loss Infection b) disordered thyroxine metabolism c) hypothermia d) stigma/social isolation e) spread of infection
