Skin (Structure & Function) Flashcards
What are the 3 main layers of the skin?
Epidermis-squamous keratinised epithelium
Dermis-irregular dense connective tissue
Hypodermis -adipose tissue
How does thickness of the Hypodermis vary?
Thickness varies in different regions of body and can vary between people
In men-its thickest in abdomen and shoulders
In women-its thickest in hips, thighs and buttocks (milk storage areas)
In both sexes it is thick on the palms of hands and soles of feet to act as a shock absorber
What is the location and structure of the Hypodermis?
Location=lowest layer of skin (also known as sub-cutaneous)
Structure=mainly adipose tissue (some neuromuscular bundles + lymphatics), some loose connective tissue (fibroblasts/macrophages/collagen fibres/mast cells)
What is the function of the Hypodermis?
Provides energy store-to generate heat
Insulator for underlying muscle heat generation
Shock absorber-impact cushion + protect structures)
Connects skin to underlying muscle and bone
Makes hormones (Leptin made when cells expand to control eating)
What is the location and structure of the dermis?
Location=between epidermis and hypodermis
Structure=3 layers Papillary (upper), Reticular (lower) and Dermal Papilae (interdigitating). Variable thickness (0.6mm on eyelid, 3mm on hands/feet’s). Made of Dense Irregular connective Tissue
What is the function of the Dermis?
Contains hairs + sweat glands for thermoregulation
Contains sensory structures-touch
Gives structure to skin and so body shape
What is the location and structure of the Epidermis?
Location=outermost layer of skin, made of keratinocytes
Structure=Thin skin has 4 layers, thick skin has 5 layers. Held together by lateral adhesion junctions, has some terminal nerve endings but no blood vessels. Respires by diffusion.
What are the 4/5 layers of the epidermis?
1) Stratum Corneum (squamous/dead keratinocytes, continuously sheds)
2) Stratum Lucidum (transparent keratin, 1 cell thick, palms and soles ONLY-THICK SKIN)
3) Stratum Granulosum (stratified squamous epithelium, lamellar granules secrete keratin, Tonofibrils (bundle of keratin) made by lamellar bodies)
4) Stratum Spinosm (cuboidal epithelium in 3 layers, held by desmosomes, produce lamellar bodies (keratin factory’s), first time Golgi Apparatus appears)
5) Stratum Basale (tall columner epithelial cells, constantly renew keranicytes by division, as cells differentiate they move away from epidermis-dermis junction, make keratin filaments, home to melanocytes)
Describe the keratin synthesis pathway.
Rises from tonofilaments to the spinous cell which have the keratin forming factory in them. Then rise to Tonofibrils and this is where apoptosis is fist seen. The apoptosis cells are held together by desmosomes, the desmosomes are broken by enzymes to release the top squamous cells and prevent excessive build-up
What are the main constitutes of hair, nails and animal horns?
Keratin
What cells synthesise keratin?
Keratinocytes synth the keratin that contribute to epidermis strength.
What is psoriais?.
The transit time of keratinocytes from the basal layer to Stratum corneum is reduced from 28-40 days to only 2-3. The skin appears as silvery scales. The immune cells are exposed, and mast cells degenerate causing redness and itching
What is Hyperkeratosis?
Too much keratin is put on the surface of the skin (esp hands/feet). It causes drying out and cracking allowing pathogens to enter.
What pigment-giving cell an be found in the epidermis and how does it move?
Mature melanasomes contain melanin (the pigment of skin. These can be transferred to neighbouring keratinocytes by pigment donation. This involves phagocytosis of the tips of the dendritic processes of the cell.
Give an example of an immune cell can be found in the epidermis
Langerhan’s cells can be found in the epidermis. They act as macrophages to any foreign bodies. They present antigens to T-lymphocytes to mediate an immune response (ie allergic contact dermatitis)
What are Merkel Cells?
Can be found in epidermis.
Mechanoreceptor cells associated with sensory nerve endings. Make up 6-10% of cells in epidermis, the darker the skin the more merkel cells are present.
Why are black people better suited for sunny climates?
They have more marked constitutional pigmentation, more melanin in their skin. Reduced chances of getting skin cancer, however is still possible.
What are the 2 types of skin and what are the exceptions to this?
Hairy-Thin skin
Non-hairy thick skin
The exceptions are the back of the ear, the lips and some areas of external genitalia
What is the location and structure of Non-hairy thick skin?
Location=Plamar surface of hand, plantar surface of foot, area between fingers and toes
Structure=same as rest of body except: No hair, arrector pili muscles, no sebaceous glands. Thicker stratus corneum, thinner dermis, increased density of mechanoreceptors.
What is the function of non-hairy thick tissue?
Prevent tissue loss due to abrasion, increased friction between skin and surface (palm vs back of hand), increased sensation
Compare the histology of thin (hairy) and thick (non-hairy) skin.
Thick-no hair follicles, Thin-hair follicles
Thick-no sebaceous glands, Thin-sebaceous glands
Thick-no arrector pilli muscle, Thin-arrector pilli muscles
Thick-pronounced ridges + furrows, Thin-small ridges+furrows
Thick-regular dermal papillae, Thin-irregular dermal papillae
Thick-Stratum lucidium seen, Thin-stratum lucidum absent
List some skin appendages.
Hairs Arrector pilli Sebaceous glands Sweat glands Nails
What are the 3 types of hair and when/where are they present?
Lanugo-covers developing foetus (then falls out, occasionally seen at birth)
Vellus-replaces lanugo (short,thin,light colour, soft, not connected to sebaceous gland) back of hand etc.
Terminal-head (scalp, eyebrows, nasal passage), axillae, external genitals, long, wide, dark coloured coarse, produced by actions of testosterone.
What is the thermoregulation function of hair?
Hair lays flat when normal or elevated
Hair stands erect when cold (arrector pilli muscle contract, stimulated by sympathetic fibres from autonomic nervous system)
Also acts as partial UV barrier (scalp)
Describe the sexual attraction function of Hair.
Hair style can be alluring
Apocrine sweat glands secrete oils (pheromones) that attract opposite sex, the hairs trap these oils to accentuate pungency
Describe the sensation function of hair.
Hairs have sensory nerve endings within the bulb
(Air movement, physical interaction, vibrations transmitted to the bulb sensed and transmitted to CNS, provides sensory awareness)
Describe the protective function of hair.
Eyelashes and nasal hair prevent dust and pathogens entering body.
Eyebrows reduce amount of light + sweat from entering eyes
Axilla hair acts as a conduit to conduct sweat away from body
What is the arrector pili muscle?
Consists of smooth muscle fibres attached to papillary region of the dermis (origin) and hair bulb (insertion)
Fight or flight response or cold causes involuntary contraction-‘goose bumps”
May also induce sebum release from sebaceous gland-as bulb moves it compresses sebum gland, oil slides up hair, fight/flight “slipper” harder to catch.
What mechanoreceptors are present in the skinlayers and what do they detect?
End bulb=thermoreceptor
Free nerve endings=nociceptor (pain)
Tactile disks=vertical dimpling of skin-attach to basal layer keratinocyte-sense touch, pressure and texture. In non hairy skin=merkel disc, in hairy skin= Meissner disk
Meissner corpuscle-tapping+flickering movements
Pacinian corpuscle-vibrations
Ruffini’s corpuscle-joint movement and tissue stretch
Root hair plexus-vibration in hair shaft
What is the location and structure of nails?
Location=distal surface of phalanges (finger+toes)
Structure=solely alpha keratin. Has nail plate, nail matrix and nail bed below it, grooves surround it.
What is the function of nails?
Protection of distal Phalenx and surrounding soft tissue from injury.
Enhances precise delicate moment of distal digit through counter pressure on pulp of finger
Enhances sensitivity of finger tip (nail has n nerve endings)
Useable as a tool “extended precision grip” scraping action etc
What are all the overall functions of the skin?
Protection + repair Thermoregulation + waste excretion Lubrication Storage Vitamin D synthesis Absorption Aesthetics Sensation
