8 and 9: skin hair and nails Flashcards
(20 cards)
What are the functions of skin
- Protection against injury
- Protection against pathogenic organisms
- Waterproofing and fluid conservation
- Thermoregulation
- Protection against radiation, absorption of ultra violet radiation and vitamin D production
- Surface for grip
- Sensory organ
- Cosmetic
Describe the components of the epidermis
“The epidermis consists of keratinocytes arranged in 4 layers (stratum basale, spinosum, granulosum and corneum).
Other cell types in the epidermis include the melanocyte (involved in the production of melanin), Langerhans cell (antigen presenting cell) and Merkel cell (involved in sensation).
Describe the basement membrane zone
“The basement membrane zone is a specialised region where the epidermis is attached to the dermis via hemi-desmosomes, anchoring plaques and a multitude of proteins. The area is clinically important as a genetic abnormality resulting in an abnormality of a protein in this region can give rise to a blistering condition eg epidermolysis bullosa”
Describe the dermis
“The dermis is supportive connective tissue consisting of collagen, elastin and glycosaminoglycans.
The thickness varies between 0.1mm (eyelids) and 3 mm (back).
The dermis contains fibroblasts that synthesize collagen, elastin and glycosaminoglycans. Dermal dendritic cells are found along with other immunocompetent cells.
Describe the subcutaneous layer
“This consists of connective tissue and fat.
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Describe melanocytes
“Melanocytes are dendritic cells located within the basal layer of the epidermis. They produce the pigment melanin in organelles known as melanosomes. These are packaged into granules which move down the dendritic processes and transferred by phagocytosis to adjacent keratinocytes.
The melanin granules form a protective cap around the keratinocyte nuclei and protect the DNA within the nucleus from UV induced damage and lead to skin pigmentation. UV radiation mainly within the 290-320 nm spectrum stimulates the melanocytes to produce more melanin.
Variation in racial pigmentation is not from differences in melanocyte numbers, but from the number and size of melanosomes produced
What are the 3 hair types
“Lanugo are fine and long, formed in the fetus at 20 weeks. Normally shed before birth but may be seen in premature babies. Also occur in anorexia.
Vellus are short, fine, light coloured and cover most of the body.
Terminal are longer, thicker and darker. Found on the scalp, eyebrows, eyelashes, and pubic, axillary and beard areas. They originate as a vellus hair, differentiation is stimulated at puberty by androgens.
What the the functions of hair
“Protection e.g. against UV damage, minor injury and eyelashes protect the eyes.
Sensation, hairs have sensory innervation within the follicles which can amplify sensation.
Thermoregulation
Communication
What are the 3 phases of hair growth
Anagen Growing phase. Lasts 3-7 years for scalp hair, only 4 months for eyebrows. At any one time 80-90% of scalp hair are in anagen.
Catagen Resting phase and lasts 3-4 weeks. Hair protein synthesis stops, the follicle retreats towards the surface. At any one time, 10-20% of scalp hairs are in catagen.
Telogen Shedding phase, distinguished by the presence of hairs with a short club root. Each day 50-100 scalp hairs are shed, with less than 1% of hairs being in telogen at any one time
Describe the structure of nails
“The nail matrix contains dividing cells which mature, keratinize and move forward to form the nail plate.
The nail plate has a thickness of 0.3-0.5mm and grows at a rate of 0.1mm /day for the finger nail. Toenails grow more slowly.
The nail bed which produces a small amount of keratin is adherent to the nail plate. The adjacent dermal capillaries produce a small amount of pink colour of the nail; the white lunula is the visible part of the the matrix.
The hyponychium is the thickened epidermis that underlies the free margin of the nail.
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What is the function of a nail
“It protects the fingertip or toe tip and facilitates grasping and tactile sensitivity in the finger / toe pulp.
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Describe sebaceous glands
“Sebaceous glands are found associated with follicles, especially those of the scalp, face, chest and back. They are formed of epidermis derived cells and produce an oily sebum. The glands are small in children but become large and active at puberty, being sensitive to androgens. Sebum is produced by holocrine secretion in which the cells disintegrate to release their lipid cytoplasm”
What makes up the pilosebaceous unit
Hair follicle, hair shaft, erector pilli muscle, sebaceous gland
What cells are in the hair bulb
“The germinative cells are in the hair bulb, as are melanocytes which synthesize pigment.
What is androgenic alopecia
X
What is hirsutism
X
What is allopecia areata
Where follicles break Anagen hair down, so follicles don’t make hair
What is folliculitis
Inflammation of follicles, acne
What are some causes of clubbing
Pulmonary, cardiac, gastrointestinal
What do beau’s lines indicate
Systemic illness
