Skin, Hair and Nails Flashcards
Why learn about the skin?
20% of GP consultation, overlaps with many specialities. Largest organ, clinical skills needed for diagnosis-and 2000 disease can affect it
What are the functions of the skin?
protection against injury, against pathogens, radiation waterproofing and keeping fluid in, thermoregulation, surface for grip, sensory, cosmetic
What are the 3 layers of the skin? Describe the cells and structure of the epidermis
Explain melanocytes in details
3 layers-epidermis, dermis and subdermis
Epidermis is a thin layer made of keratinocytes (top is dead). 4 layers-stratum basale, spinosum, granulosum, lucidum, corneum (dead keratino, corneocytes joined by lipids and filagrin) (top)-certain legs get sun burnt. Around the basale cells, melanocytes sit and produce melanin to protect from sun-and generally langherhans cells and merkel cells (sensory) sit around the granulosum or basale mebrane-the names are also the stages keratinocytes evolve into (from basal grow to keratinocyte in corneum)
Melanocytes-dentritic cells that sit within the basal membrane. melanin is produced in granules and secreted via dendtritic processes to neighbouring keratinocytes. The melanin goes around the nucleus and protects the DNA from damage-UV light activates melanocytes. Different skin colors depend on activity of melanocyte, not their number
What is the Basal membrane zone of the skin?
Its a specialised region also called the dermo-epidermal junction-rich in hemi-desmosomes, anchoring plaques and proteins-important because many genetic mutations can cause abnormalities (like epidermolysis bullosa)
Describe the cells and structure of the dermis and subcutaneous layer
Dermis is a connective tissue-vary in thickness between 0.1mm (eyelids) and 3mm (back)-usually fibrinogens to produce collagen, elastin and GAGs. ALso has dentritic cells and other immunocompetent cells. Hair follicules will sit there, but traverse all the layers
Subcutaneous layers-connective tissue and fat
What is the function of hair and where does it grow?
Can be found on the whole skin except palm of hand and feet, penis and vagina-densest on the face
Protect vs UV damage, small injury and debris, sensation, thermoregulation (minimal in human), cosmetic
What are the 3 types of hair? Describe the structure of terminal hair
Languno-baby hair, formed in foetus at 20 weeks-normally shed before birth but can be seen in premature or anorexia
Vellus-short and fine hair, not colored-covers most of the body
Terminal-longer and thicker hair, orginiate from vellus hair but androgens at puberty make it change. Found on face (hair, beard, eyelashes, etc), pubic hair, etc
Outer cuticle, then cortex and inner medula of keratin (type I and II) filaments-that form tetramers and join into protfilaments, then filaments, then hair
What is a pilo subcutaneous unit? Describe structure and function.
It describes the basis of a hair follicule and shaft. A hair follicule is the envagination of the epidermis in which you find a hair. The shaft is formed of an outer cuticle, that encloses keratinocytes. Lower down after the shaft-continues into hair bulb/root. top is infundibulum, middle is isthums (where sebaceous gland are and muscle), then suprabulbar and bulb
Bulb contain germinative hairs (that produce the hair) and melanocytes for the pigments. also has an arector pili muscle (SMC) which is vestigial in humans-but does move in cod, scare etc
Sebaceous glands dont sit in the bulb but connect to the gland-formed of epithelium derived cells-and produce cebum, which is oil that covers the hair-small in children but grow in teenagers and become androgen sensitive
The epidermis contributes the shaft, matrix cells and sebaceous gland, while the dermis (other germ layer) makes papilla (bulb), blood vessels and nerves
Describe hair growth, its synchronocity and the effects of testosterone
4 main phases-anagen is the main growin time-bulb is rapidally dividing and gain 1cm every 28days- can last 2-6 years (depending of which hair (head or beard, or etc)
Catagen is the transition period after anagen-forms a club hair at the bulb, cutting off the bloody supply-makes a finalised hair-about 3 weeks
Telogen is the resting phase/end phase, where the club hair is done and the hair is finished-then it can be shed-can be induced by stress (telogen effluvium)
Then the bulb alone (left behind when making club hear) can start remaking a hair, and the cycles continues
Synchronicity of hairs are random-all are on their own clock but it can happen that they sync (at birth)
Androgen-makes vellus hairs become terminal (thicker, longer, colored), but can also cause transition back-and cause balding in men-androgenic alopecia
Folluculitis (or inflamation of hair follicules)-acne as sebum clogs the shaft and damages cells
What is the function of nails?
Remanant of old claws-can be used for protection (weapon), or chemical and physical barrier. used also for manual dexterity and cosmetics
Describe the structure of nails and nail follicules?
hairs are mostly made of hair keratin, longitunidal ridging and slight curvature. keratin fibers are produced in proximal nail fold by the nail germinal matrix, just above the distal phalanx-lunula is visible part of that. hair plates slides above the nail bed-hyponichium (nail plate). keratin is produced, matures and harnedes
adjacent dermal capilaries can produce pigment-when damaged/cancer-change color (same for germinal matrix)
Describe hair and nail pathologies
Classic nail pathologies are clubbing-the nail bends down instead of up-caused by numerous systemic diseases. Other issues can be lines (past break?), spoon shaped nails, pitting, onycholysis (psoriasis), which are all systemic consequences. pigmentation can be due to melanoma-not to be confused by melanochia striata (larger stipes)
Hair pathologies-louse like pubic louse-specific for terminal hair, demodex mite that lives inside the follicules and come out at night
Telogen efflevium, Hirutism (genetic variances, drugs), androgenic alopecia (baldness), Alopecia areata-immune attack of follicules-baldness as well, folluculitis (acne)
