Skin Structure and Function Flashcards by Aaron Duff

What is the dermo-epidermal junction?

Interface between epidermis and dermis

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What is the key role in epithelial mesenchymal interactions of dermo-epidermal junction?

Support, anchorage, adhesion, growth, differentiation of epidermal cells.

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What type of membrane is the dermo-epidermal junction?

Semi-permeable membrane acting as barrier/filter

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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

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What are acquired diseases of the DEJ?

Auto-antibodies to proteins in DEJ e.g. pemphigus, pemphigoid, dermatitis herpetiformis

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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

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Describe the blood vessels to the skin.

Supply greater than metabolic need. Supported walls, horizontal plexus.

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Describe the blood flow to the skin.

Flow:
Arteriole > precapillary sphincters >
arterial capillaries > venous capillaries >
post-capillary venules > collecting venules

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What are examples of localised overgrowths of blood vessels in skin?

Capillary or cavernous haemangiomas

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What drainage to lymphatic vessels in the skin provide?

Continual drainage of plasma proteins, extravasated cells and excess interstitial fluid

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What special nerve receptors are there in the skin?

Pacinian (pressure) and Meissners (vibration) corpuscles

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What are the 3 types of skin glands?

Eccrine, sebaceous and apocrine gland

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Where are sebaceous glands found?

Widely distributed: largest glands present on face and chest

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What causes acne?

A mixture of increased sebum, blocked ducts and bacterial activity

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Where are apocrine glands found?

Axillae and perineum

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What do aporcrine glands produce?

Oily fluid- odour after bacterial composition

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Where are eccrine sweat glands found?

Whole skin surface- palms, soles and axillae in particular

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Describe the nervous supply to eccrine sweat glands

Sympathetic cholinergic nerve supply- mental, thermal and gustatory stimulation

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What are the functions of eccrine glands?

Ultrafiltration, cooling by evaporation, moisten palms/soles to aid grip

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What is the epidermis made of?

Stratified cellular epithelium

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What is the dermis made of?

Connective tissue

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Where does the epidermis come from>

Ectoderm cells form single layer periderm. Gradual increase in cell layers. Periderm cells cast off

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Where does the dermis come from?

Formed from mesoderm below ectoderm

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What are melanocytes?

Pigment producing dendritic cells from neural crest

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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)