The Skin Flashcards
What is the location of the hypodermis?
- the lowest layer of skin
- sometimes called the subcutaneous layer
How does the thickness of the hypodermis vary between males and females?
Men: thickest on the abdomen and shoulders
Women: thickest on the hips, thighs and buttocks
What is the hypodermis composed of?
- mainly adipose tissue
- loose connective tissue (fibroblasts, macrophages, fibres)
What is the function of the hypodermis?
- provides energy store for heat production
- insulates underlying muscle
- shock absorber
- connects skin to underlying muscle and bone
- makes hormone leptin (controls eating habits)
Where is the dermis located?
Between the hypodermis and the epidermis
- also called the cornium
What are the 3 layers of the dermis called and what are their functions?
- papillary layer (upper layer)
- reticular layer (lower layer) contains many fibres
- dermal papillae ( interdigitiating layer) holds the top layer layer together. Damage can cause the epidermis to fall off
What are the functions of the dermis?
- thermoregulation - contains hairs and sweat glands
- sensory structures for touch
- gives skin structure and shape (by collagen and elastin fibres)
Where is the epidermis located what cells is it composed of?
- outermost layer of skin composed of keratinocytes
What is the structure of the epidermis?
- either 4 or 5 layers of skin depending on body location
- held together by adherens junctions
- no blood vessels
- some nerve terminals
What is the function of the dermis?
- prevents water loss
- prevents entry of bacteria and parasites
- special cells that present pathogens to immune cells
- keratin synthesis
- prevents tissue loss due to abrasion
What are the 5 layers of epidermis called? ( in order)
- Stratum Corneum
- outer layer of dead keratinocytes
- thick on palms and soles of feet
- continuously shed - Stratum Lucidium
- ONLY on palms and soles of feet
- very thin, transparent layer - Stratum Granulosum
- stratified squamous epithelium
- lamellar granules that assemble & secrete keratin
- tonofibrils. Bundles of keratin filaments and keratohyalin made forum lamellar bodies - Stratum spinosium
- cuboidal epithelium arranged in 3 layers held by desmosomes
- produce lamellar bodies
- 1st time Golgi apparatus is seen - Stratum basale
- tall columnar epithelial cells
- constantly renewing keratinocytes by mitosis
- daughter cells differentiate to tonofilaments as they move further from epidermis- dermis junction
- home to melanocytes
What are melanocytes and where are they found?
Melanocytes produce melanin
They’re found in the stratum basale layer of the epidermis
Describe the role of keratin in the epidermis
In epidermis keratinocytes synthesise keratins which are fibrous proteins. They contribute to strength and protection of the epidermis
Describe what happens in psoriasis
Normal transit time of a keratinocytes from basal layer to st. corneum is 28-40 days.
In psoriasis the transit time is reduced to 2-3 days. Produces silvery scales on skin surface.
Psoriasis is a persistent condition
What is hyperkeratosis?
Too much keratin on the surface of the skin.
Can happen anywhere on body but especially hands and feet.
Caused by defective apoptosis mechanism- cells don’t die so desmosomes aren’t broken and cells are not got rid of in the normal way.
How do melanocytes release melanin?
Mature melanocytes transfer melanin to neighbouring keratinocytes by pigment donation where tops of the dendritic processes are phagocytosed by the keratinocyte
What are langerhan cells?
- highly specialised cell found in the epidermis
- present antigens to T cells to mediate immune reactions e.g contact dermatitis
What are Merkel cells?
Mechanoreceptor cells in the epidermis associated with sensory nerve endings to senses touch
Account for 6-10% of cells in the epidermis
Dark skin has more Merkel cells (10%) than light skin (6%). Number lost with ageing
Describe the location, structure and function of non hairy thick skin
Location: plantar surfaces of hands and feet and webs of fingers and toes
Structure: no hair, pilli muscles or sebaceous glands
- thick stratum corneum
- thinner dermis
- increases density of mechanoreceptors
Function: prevents tissue loss from abrasion, increases friction between skin and surfaces to stop slips and increases sensation
Compare thick (non hairy) and thin (hairy) skin
Thick:
- no hair follicles
- no sebaceous glands
- no arrector pili muscles
- pronounced ridges and furrows on surface (fingerprints)
- regular shaped dermal papillae
- stratum lucidum often seen
Thin:
- hair follicles
- sebaceous glands
- arrector pili muscles
- small ridges and furrows
- irregular dermal papillae
- stratum lucidum absent
Identify and describe the 3 types of hair
Lanugo: covers developing foetus, only found in utero and lost in foetal development
Vellus: replaces lanugo. Short, thin, soft and light hair not connected to a sebaceous gland
Terminal: found on the scalp, eyebrows, nasal passage, external genital regions
- long, wide, dark and coarse hair
- produced by the actions of testosterone
What are the 4 functions of hair?
- Thermoregulation
- arrector pili contracts when stimulated by sympathetic fibre from the autonomic NS - Sexual attraction
- apocrine sweat glands secrete pheromones, trapped by hair which accentuates pungency - Sensation
- air movement, physical interactions and vibrations sensed and transmitted to CNS - Protection
- eyelashes and nasal hair protect from dust and pathogens
- eyebrows reduced light and sweat entering the eyes
- axilla(armpit) hair conducts sweat away from the body
Describe the structure and function of arrector pilli muscle
Structure: smooth muscle fibres attached to papillary region of dermis (origin) and then hair bulb (insertion)
Function: sympathetic NS controls fight or flight response. Cold causes involuntary contraction and goosebumps
Also induces sebum release from sebaceous gland when muscle contracts- makes skin more slippery
Identify the different mechanoreceptors in skin and what their function is
End bulbs- thermoreceptor in dermal layer
Free nerve ending- pain receptors (nociceptors) in epithelial layer
Tactile discs- vertical dimpling of skin that attaches basal layer to keratinocytes. Senses touch, pressure and texture
Messiner corpuscle- detects tapping and flicker movements
Pacinian corpuscle- detects vibration
Ruffini’s corpuscle- joint movement and tissue stretch
Root hair plexus- detects vibrations in the hair shaft
Describe the structure of nails
Consists solely of alpha keratin
Has 4 important sections:
- Nail plate
- The nail matrix
- The nail bed
- Surrounding grooves
What are the functions of nails?
- Protect distal phalanges from damage
- enhance precise delicate movement of digits
- enhance fingertip sensitivity (nail itself has no nerve endings)
- can be used as a tool
How does growth rate of nails correlate to length of phalanges?
The longer the phalanx, the faster the rate of nail growth
