Skin Structure and Function Flashcards
What is the dermo-epidermal junction?
Interface between epidermis and dermis
What is the key role in epithelial mesenchymal interactions of dermo-epidermal junction?
Support, anchorage, adhesion, growth, differentiation of epidermal cells.
What type of membrane is the dermo-epidermal junction?
Semi-permeable membrane acting as barrier/filter
What are inherited diseases of the DEJ?
Skin fragility conditions due to a mutation in one of the proteins in the DEJ e.g. Epidermolysis bullosa:simplex or dystrophic
What are acquired diseases of the DEJ?
Auto-antibodies to proteins in DEJ e.g. pemphigus, pemphigoid, dermatitis herpetiformis
What are the components of the dermis?
Cells(mainly fibroblasts, also macs, mast cells, lymphocytes, Langerhans), fibres(collagen, elastin), ground substance (mucopolysaccharides, glycosaminoglycans), blood vessels, lymphatics, nerves
Describe the blood vessels to the skin.
Supply greater than metabolic need. Supported walls, horizontal plexus.
Describe the blood flow to the skin.
Flow:
Arteriole > precapillary sphincters >
arterial capillaries > venous capillaries >
post-capillary venules > collecting venules
What are examples of localised overgrowths of blood vessels in skin?
Capillary or cavernous haemangiomas
What drainage to lymphatic vessels in the skin provide?
Continual drainage of plasma proteins, extravasated cells and excess interstitial fluid
What special nerve receptors are there in the skin?
Pacinian (pressure) and Meissners (vibration) corpuscles
What are the 3 types of skin glands?
Eccrine, sebaceous and apocrine gland
Where are sebaceous glands found?
Widely distributed: largest glands present on face and chest
What causes acne?
A mixture of increased sebum, blocked ducts and bacterial activity
Where are apocrine glands found?
Axillae and perineum
What do aporcrine glands produce?
Oily fluid- odour after bacterial composition
Where are eccrine sweat glands found?
Whole skin surface- palms, soles and axillae in particular
Describe the nervous supply to eccrine sweat glands
Sympathetic cholinergic nerve supply- mental, thermal and gustatory stimulation
What are the functions of eccrine glands?
Ultrafiltration, cooling by evaporation, moisten palms/soles to aid grip
What is the epidermis made of?
Stratified cellular epithelium
What is the dermis made of?
Connective tissue
Where does the epidermis come from>
Ectoderm cells form single layer periderm. Gradual increase in cell layers. Periderm cells cast off
Where does the dermis come from?
Formed from mesoderm below ectoderm
What are melanocytes?
Pigment producing dendritic cells from neural crest
What are the 4 layers of the epidermis?
Keratin, granular, prickle cell, basal cell layer
What are Blaschko’s lines?
Developmental growth pattern of skin-not following vessels, nerves or lymphatics
What type of cell make up 95% of the epidermis?
Keratinocytes
What occurs in differentiation of the epidermis?
Keratinocytes migrate from basement membrane. Continuous regeneration of epidermis. 28 days from bottom to top
Describe the basal layer
Usually 1 cell thick, small cuboidal. Lots of intermediate filaments, highly metabolically active
Describe the prickle cell layer
Larger polyhedral cells. Lots of desmosomes. Intermediate filaments connect to desmosomes
Describe the granular layer
2-3 layers flatter cells. Large keratohyalin granules- contain structural filaggrin & involucrin proteins, also Odland (lamellar) bodies. High lipid content. Cornified envelope origin, cell nuclei lost
Describe the keratin layer
Made of corneocytes (overlapping non-nucleated cell remnants). Insoluble cornified envelope, 80% keratin & filaggrin. Lamellar granules release lipid, tight waterproof barrier
Describe oral mucosa
Masticatory- keratinized to deal with friction/pressure. Lining- non keratinized. Specialised mucosa- tongue papillae:taste
Describe what can be found in ocular mucosa
Lacrimal glands, eye lashes, sebaceous glands
What cells apart from keratinocytes make up the epidermis?
Melanocytes (basal/suprabasal), Langerhans (suprabasal), Merkel (basal)
During what time do melanocytes migrate from epidermis to neural crest?
First 3 months of foetal development
What do melanocytes contain?
Organelles: melanosomes
What conversion occurs in melanocytes?
Tyrosine to melanin pigment: eumelanin (brown/black), Phaeomelanin (red, yellow)
What happens when melanosomes become full (melanin granules)?
Transferred to adjacent keratinocyte via dendrites
What is a malignant melanoma?
A tumour of the melanocyte cell line
Describe Langerhans cells
Mesenchymal origin-bone marrow. Prickle cell level, also found in dermis/lymph nodes. Antigen presenting cells: pick up antigen in skin and circulate to lymph nodes via lymphatic system
Describe Merkel cells
Basal, between keratinocytes and nerve fibres, mechanoreceptors
Describe Merkel cell cancer
Rare, caused by viral infection. High mortality
Describe hair follicle ‘Pilosebaceous unit’
Epidermal plus dermal papilla. Specialised keratins, adjacent sebaceous gland. Pigmentation via melanocytes above papilla
Name the 3 phases of hair follicle growth
Anagen (growing), Catagen (involuting), Telogen (resting)
Name some types of hair follicles
Lanugo (in utero), vellus (short hair all over body), terminal (long dark hair produced during puberty)
Describe the anagen phase
3-7 years, 90% of hairs
Describe the catagen phase
3-4 weeks, 10% hairs
Describe the telogen phase
Shedding, each day 50-100
Describe nails
Specialised keratins, nail matrix/root similar to hair bulb. Growth rate 0.1mm/d, fingers >toes, summer >winter.
Describe sebaceous glands pre puberty
Quiescent
What do sebaceous glands produce?
Sebum: squalene, wax esters, triglycerides and free fatty acids
What are the functions of sebaceous glands?
Control moisture loss, protection from bacterial and fungal infection
Are apocrine sweat glands androgen dependent or independent?
Dependent
What type of gland are your apocrine sweat glands?
Scent glands
What are the functions of the skin?
Barrier, metabolism & detoxification, thermoregulation, immune defence, communication, sensory
What is toxic epidermal necrolysis an example of?
Acute skin failure
What Vit D metabolisation occurs in the skin?
Vitamin D: Cholecalciferol > Vitamin D3
In what form is Vitamin D3 stored in the liver and kidney?
Hydroxycholecalciferol in liver, converted to 1,25-dihydroxycholecaliferol in kidney
What thyroid hormone metabolism occurs in the skin?
Thyroxine (T4) > Triiodothyronine (T3) (20% in thyroid gland, 80% in peripheral tissues including skin)
