Session 11 - Dermatology: Skin Structure and Function Flashcards
What are the 3 main layers of skin and how are these layers subdivided?
Epidermis: 1) Stratum Corneum 2a) Stratum Lucidum (only in palms and soles of feet) 2b) Stratum Granulosum 3) Stratum Spinosum 4) Stratum Basale Dermis: 1) Papillary 2) Reticular Hypodermis (sometimes not considered part of the skin)
Describe the structure and function of the hypodermis
Structure:
- Mainly contains adipose tissue (loose connective tissue)
- Contains some neurovascular bundles/lymphatics
Function:
- provides an energy store
- Insulator for underlying muscle heat generation
- Connects skin to underlying muscle and bones
- Makes hormones e.g. leptin which controls eating habits
Why does skin become wrinkly during aging and what effects can this have?
- Thinning of hypodermis is responsible for skin wrinkling and as such hypothermia (both insulation and heat generation) in old age
- Also to a lesser extent thinning of the dermis less collagen and elastin
Describe the structure and function of the dermis
Structure:
- Two layers:
- Papillary - upper
- Reticular - lower (dense irregular connective tissue)
Functions:
- It contains hair and sweat glands - thermoregulation
- Contains sensory structures - touch
- Gives structure to skinDescribe the structure and function of the epidermis
Structure:
- 4 layers in (thin skin) / 5 layers in (thick skin)
- Held together laterally by adherens and vertically by desmosomes
- Some terminal nerve endings
- Avascular (no blood vessels)
Functions:
- prevents water loss, bacteria and parasitic entry, Langerhans cells (special immune presenting cells), allows gas exchange (obviously not enough to support life)
What are the 4/5 layers of the epidermis and outline their functions
1) Stratum Corneum: outermost layer of squamous (dead keratinocytes), Thick on palms and soles of feet (places prone to injury), continuously shed
2) Stratum Lucidum: (only found on the palms and soles of the feet)
3) Stratum Granulosum (Granular layer): cuboidal epithelium arranged in 3 layers, producers of lamellar bodies (keratohyalin factories)
4) Stratum Basale: Tall columnar epithelial cells, constantly renew keratinocytes by cell division, hoem to melanocytes - produce melanin
Outline the keratin synthesis pathway
1) Basal cell produces tonofilaments (which are intermediate keratin filaments)
2) These then differentiate to spinous cells which contain lamellar bodies (keratin forming factories)
3) Further differentiation to granulocytes and keratohyalin granules are produced the cell undergoes apoptosis
4) Tonofibrils and filaggrin proteins contribute to the water barrier
What are melanocytes?
They are cells found in the Stratum Basale of the epidermis which produces melanin. They transfer mature melanosomes (pigment) to neighbouring keratinocytes. They can be found at intervals of 1 in 8 on the basal layer.
- Dark skin doesn’t have more melanocytes than white only the cells produce more melanin
Name the main cells found in the epidermis
Melanocytes - produce melanin
Keratinocytes - synthesise keratins
Langerhans cells - specialised antigen presenting cell
Merkel cells - Mechanoreceptor cells with an associated sensory nerve ending ~ 6-10% of cells in epidermis
What are the 4 types of skin and how can they be generalised further?
- Hairy skin
- Non-hairy skin
- Thin skin (usually hairy)
- Thick skin (usually non-hairy)
Exceptions are the lips, back of the ear, some areas of external genitalia
What are the main differences between thick (non-hairy) and thin (hairy) skins?
Key:
- Thick / Thin
- No hair follicles / presence of hair follicles
- No sebaceous glands / presence of sebaceous glands
- No arrector pili muscle / Arrector pili muscles
- Pronounced ridges and furrows on surface / smaller ridges and furrows
- Regular shaped dermal papillae / Irregular dermal papillae
- Stratum lucidum often seen (the thin clear layer)/ Stratum lucidum absent
Name 5 skin associated structure (skin appendages)
- Hairs - Thermoregulation
- Arrector Pili
- Subcutaneous Glands
- Sweat Glands
- Nails
Name 3 types of hair and the functions of hair
Types:
- Lanugo - covers developing foetus
- Vellus - replaces lanugo, short, thin, light and soft, NOT connected to sebaceous gland
- Terminal - head, axillae, external genital region (long wide, dark coloured and coarse, produces by testosterone)
Functions:
- Thermoregulation
- Sexual attraction - Adipose sweat gland secretes pheromones that attract opposite sex
- sensation - Nerve endings associated within hair bulb
- Protection - eye lashes, nasal hair
Name of mechanoreceptors and what they are able to sense.
- End Bulbs - thermoreceptor
- Free nerve endings have nociceptors - register pain
- Tactile discs - vertical dimpling of skin - senses tough and texture
- Meisner corpuscle - tapping and flicker movements
detected - Pacinian corpuscles - vibrations and pressure
- Ruffini corpuscles - joint movements and tissue strtch
- Root hair plexus - vibrations in the hair shaft
What is the function of nails?
- Protect the distal phalanx
- Enhances precise delicate movements of the distal digit
- Enhances sensitivity
- As a tool
