Lecture 21 - Skin Structure & Function Flashcards
What are the 3 primary layers of the skin from bottom to top?
- Hypodermis
- Dermis
- Epidermis
Where is the location of the hypodermis?
What does it contain?
What are its functions?
Where does thickness of this layer differ?
- Hypodermis is the lowest layer of skin (AKA: sub-cutaneous layer)
- Mostly adipose tissue as well as loose connective tissue
- Provides energy store, insulator (for underlying muscle), shock absorber, connects skin to underlying muscles/bone and makes hormones (e.g.: leptin).
- In men thickest in abdomen and shoulders, in women thickest in hips, thighs, buttocks.
- Thinning of this layer responsible for skin wrinkling and hypothermia in old age.
Where is the location of the dermis?
What does it contain?
What are its functions?
What is thinning of this layer responsible for?
- In-between the hypo and epidermis
- A lower reticular layer and an upper papillary layer with interdigitating dermal papillae of various thickness.
- Thermoregulation (contains hairs/sweat glands), special senses (contains sensory structures), gives structure to skin.
- Skin wrinkling in old age due to loss of collagen & elastin (thinning).
Where is the location of the epidermis?
What is its structure & held together by?
What are its functions?
- Outermost layer of skin made from keratinised stratified squamous epithelium.
- 4 layers (thin skin) or 5 layers (thick skin), held together laterally by adherens junctions, vertically by desmosomes. Has NO blood vessels.
- Prevent water loss, entry of bacteria, contains langerhans cells, synthesis of keratin and prevents underlying tissue loss.
What are the 5 layers in the epidermis and what are their features?
1) Stratum corneum (corny layer) - made of dead keratinocytes, thick on palms and soles of feet and shed.
2) Stratum lucidum (transparent layer) - only on palms and soles of feet (thick skin)
3) Stratum granulosum (granular layer) - stratified squamous epithelium where keratin is synthesised & secreted.
4) Stratum spinosum (spinous layer) - cuboidal epithelium in 3 layers held together by desmosomes
5) Stratum basale (basal layer) - columnar epithelial cells, constantly renew keratinocytes and home to melanocytes.
What is keratin synthesised by?
What is keratin the main constituents for?
What is the transit time of the cell that makes it from the basal layer to the corny layer?
What are 2 diseases associated with keratin?
- Keratinocytes - In stratum basale (basal layer)
- Hair, nails and animal horns
- 28-40 days
- Psoriasis (transit time reduced to 2-3 days) to corny layer produced in abundance leading to silvery scales
- Hyperkeratosis - too much keratin on surface of skin (particularly on hands and feet) - can lead to keratin horns.
What are 3 other cell types found in the epidermis?
What are their roles?
1) Melanocytes - produce melanin which protect against UV rays. Melanin = dark skin, NOT increased in dark individuals.
2) Langerhans - present antigens to T-lymphocytes and mediate immune reactions.
3) Merkels - Contain mechanoreceptors associated with sensory nerve endings.
What are the 2 main types of skin?
1) Thick (mostly non-hairy)
2) Thin (mostly hairy)
NB: exceptions to this rule include lips, back of the ear, some areas of external genitalia.
Describe the location, structure and function of thick (non-hairy) skin.
- Palmar surface of hand/plantar surface of foot & webs of fingers and toes.
- Same as rest of the body, except no arrector pili muscles, hairs or sebaceous glands. Thicker corny layer and thinner dermis.
- Prevents tissue loss by abrasion, increased sensation (due to mechanoreceptor population).
What are the main differences between thick (non-hairy) and thin (hairy) skin?
- No arrector pili, hairs or sebaceous glands in thick, all 3 present in thin.
- Bigger ridges and furrows on surface of thick
- Starum lucidum often seen in thick, but absent in thin
What are the 3 main skin-associated structures? (appendages)
Hair, arrector pili muscles, nails
- also sebaceous and sweat glands but we’re looking at these 3 above.
What are the 3 main types of hair and their features?
1) Lanugo -covers developing fetus
2) Vellus - replaces lanugo, short, thin, light coloured, not connected to sebaceous gland
3) Terminal - adult hair, long, wide, dark, produced by actions of testosterone.
What are the 4 main functions of hair?
1) Thermoregulation - hairs erect when cold, arrector pili muscles contract by sympathetic stimulation.
2) Sexual attraction - apocrine glands secrete pheromones which attract opposite sex.
3) Sensation - hairs have sensory nerve endings in bulb which provides sensory awareness
4) Protection - e.g.: eyelashes and nasal hair from pathogens, eyebrows from swear etc.
What do arrector pili muscles consist of?
When are they used?
- Smooth muscle fibres attached to papillary region of dermis and hair bulb
- During ‘fight or flight’ response, or contraction when cold (goose bumps!)
Describe the location, structure and function of nails.
- Distal surface of phalanges
- Consist almost entirely of alpha-keratin
- Protect distal phalanx from injury, enhances precise delicate movements, enhances sensitivity of finger tip, and enables the “extended precision grip”.
