SSS Week 1

Functions of the skin

• thermoregulation (evaporation of sweat, in hot or cold weather, cutaneous blood vessels dilate or constrict to give off/conserve heat, arrector pili contraction produces heat (goosebumps))

• protective function and repair

• sensation

• immunological response

• metabolic (vit d synthesis)

• psychological and communication (aesthetic appearance, apocrine gland secretion - odour)

Important notes on epidermis

• stratum corneum - anuclear

• (stratum lucidum)

• stratum granulosum

• stratum spinosum

• stratum basale - melanocytes, keratocytes (where it develops but migrates up) and merkle cells

  +basement membrane zone and then dermis

epidermis is avascular

cells of epidermis

• keratinocytes: develops from basal layer and then migrates upwards to the stratum corneum where it is shed

• langerhan cells - APCs found in epidermis

• melanocytes produce pigment, protect cells of epidermis and dermis from sun damage

• Merkles cells - (sensory mechanoreceptors) transducers associated with fine touch via fine unmyelinated nerve fibres — only present in thick skin

epidermis has an undulating surface with cross-crossing ridges and valleys, with invaginations due to follicles and sweat duct ostia (what we see as fingerprints)

Important notes on dermis (major fibres, major cells)

• fibrous connective tissue in skin

major fibres

• collagen: provide the skin with strength and toughness. Collagen bundles are small in the papillary dermis and form thicker bundles in the reticular dermis (deeper).

• Elastin: provides the properties of elasticity and pliability to the skin.

dermis also contains nerves, blood vessels, lymphatics, epidermal adnexal structures, arrector pili muscle and cells.

major cells

• fibroblasts

• macrophages

• mast cells

• t and b lymphocytes

What are the physiological changes of the skin in aging

• thinning of epidermis

• flattening of dermal-epidermal junction

• hyperpigmentation

• loss of melanocytes

• degradation of collagen and elastin

Hypodermis

Adipocytes organised into lobules (between these lobules are septa) septa contain nerves, larger blood vessels, fibrous tissue and fibroblasts — cna form cellulite

function

• cold insulation

• site of fat and energy storage

• epidermal crosstalk

• immune surveillance

Epidermal appendages - hair types, hair cycle

on all body except glabrous skin (lips, glans penis, labia minora, palms and soles)

• provides protection, sensation and social communication

three types

1. lanugo - fine long hair of fetus that is shed 1 month prior to birth

2. vellus - fine short hair found all over body

3. terminal - thick hair on scalp, beard, axilla and genital area

hirsutism - vellus to terminal

male pattern alopecia - terminal to vellus

hair growth cycle

1. anagen - long growth phase

2. catagen - where active hair growth stops and the follicle begins to regress

3. telogen - ‘resting’ follicle shrinks and atrophies, and new hair follicle begins to grow

4. exogen - hair shed

Epidermal appendages - nails

specialised plates of hard keratin that develop from epidermis overlying small bones at ends of fingers and toes

• stratching

• grooming

• picking up ifne objects

• psycho-sexual communication

• weapon

paronychium - skin around nail

lunula - white area of base of nail

Types of glands - epidermal appendages

1. sebaceous glands

• associated with hair follicles

• secreted onto skin through pilosebaceous canal-discharge into hair follicle ducts

• antibacterial and antifungal action

2. eccrine sweat glands

• all over body

• merocrine

• opening directly into skin

• cholinergic innervation

• watery (hypotonic) secretion

• sweating/thermoregulation

• onset of activity: birth

3. apocrine sweat glands

• axilla, groin, mammary area, umbilicus

• apocrine

• opens into hair follicle (like sebaceous glands)

• adrenergic innervation

• viscous secretion

• body odor

• onset of activity: puberty (androgen dependent)

Macule

flat area of altered colour ≤ 1cm

Patch

flat area of altered colour > 1cm

Papule

elevated, solid, palpable lesion that is ≤ 1cm in diameter.

may be

• acuminate (pointed)

• dome shaped (ronded)

• filiform (thread like)

• flat-topped

• oval or round

• pedunculated

• sessile

• umbilicated

• verrucous

Nodule

elevated, solid, palpable lesion > 1cm

Cyst

papule or nodule that contains fluid or semi-fluid material so is fluctuant

Plaque

circumscribed, palpable lesion > 1cm, most plaques are elevated, with a flat top

Vesicle

raised clear fluid-filled lesion ≤ 0.5cm

Bullae

raised clear fluid-filled lesion > 1cm

Pustule

pus-containing lesion < 0.5cm

Abscess

localised accumulation of pus in dermis or subcutaneous tissue (u can’t rlly see pus that much compared to a pustule)

Wheal

transient-raised lesion due to dermal oedema —> indicates urticaria

Comedone

papule due to blocked sebaceous follicle (occurs in acne) —— open (blackhead) or closed (whitehead)

What is diascopy

test where a clear glass slide is pressed against a skin lesion to assess if it blanches

helps differentiate between telangiectasia and petechiae

Petechiae is caused by blood leaking out from capillaries into surrounding tissue, whereas telangiectasia is the blood is still in the vessel but the capillaries are just dilated which means the blood can be pushed aside in the vessel —> blanching

Auspitz sign

peeling off surface scale to reveal areas of pinpoint bleeding (typical in psoriasis)

Woods light

fluorescence in visible range when applied to certain skin conditions

dermographism

where skin is stroked and a wheal is formed (indicative of tendency to urticaria)

nikolski’s sign

shearing stress of skin causes separation of skin resulting in traumatic bulla

koebner phenomenon

localisation of a non-infective skin disorder to area of trauma eg. psoriasis developing at site of a scar

dariers sign

rubbing of area of mastocytosis causes an intense urticarial reaction

pathergy

penetrating injury to skin causes area of pustulation 72 hours afterwards

bullous diseases types

1. subcorneal —> impetigo (children)

2. intraepidermal —> pemphigus vulgaris (middle aged), herpes zoster (older adults)

3. subepidermal —> bullous pemphigoid (elderly), dermatitis herpetitiformis (adults)

subcorneal - thin roof, not usually intact

intraepidermal - thin roof, rupture easily and leaves oozy denuded surface

subepidermal - thick roof so tending to be tense and intact - may contain blood