Lecture 19 - Skin Flashcards
3 defining structure of the skin
- Epidermis
- Dermis
- Hypodermis
Hypodermis
How is distinguished between males and females?
Men- thickest in the abdomen and shoulders
Women - thickest in the hips, thighs and buttocks
-thick on the palm of the hands on both sexes
Location of the Hypodermis
- lowest layer of the skin
- also known as the sub-cutaneous layer
Structure of the Hypodermis
- contains adipose tissue
- nerves/blood vessels/lymphatic
- loose connective tissue ; fibroblasts/macrophages/fibres/mastcells
Function of the Hypodermis
- provides energy store : generates heat
- insulator for underlying muscle heat generation
- shock absorber: cushions impacts/protection for underlying structures
- connects skin to underlying muscle and bones
- makes hormones ,e.g:leptin to control eating habits
- causes skin wrinkling and hypothermia in old age when thinned during ageing
Location of the Dermis
-Between epidermis and Hypodermis
Structure of the Dermis
3 layers
- papillary : upper
- reticular: lower
- dermal papillae:interdigitating
Function of the Dermis
- contains hairs and sweat glands; thermoregulation
- contains sensory structures ;special senses - touch
- gives structure to skin and so body shape
- thinning of this layer during ageing is also responsible for skin wrinkling
Location of the Epidermis
Outermost layer of the skin
Made up of epithelial cells (keratinocytes )
Keratinised stratified squamous epithelium
Structure of the epidermis
- 4 layers of cells (thin skin)
- 5 layers (thick skin)
- held together laterally by adherens junctions
- some terminal nerve endings
- NO blood vessels ( Avascular )
-
Function of the Epidermis
- Prevents water loss
- Prevents entry of bacteria and parasites
- Special cells that present pathogens to immune cells
- Synthesis of Keratin
- Prevent underlying tissue loss due to abrasion
The Epidermis is made up of four layers / 5 layers in palms and soles of feet
What are the layers?
- Stratum Corneum ( horny cell layer)
- Stratum Lucidum (transparent layer):only on palms and soles of feet
- Stratum granulosum (granular layer )
- Stratum Spinosum (Spinous /prickle cell layer)
- Stratum basale (basal cell layer)
Epidermis layers
Features of the Stratum Corneum ( horny cell layer )
- outermost layer,made of squames (dead keratinocytes )
- thick on palms and soles of feet ; prone to injury
- continuously shed
Epidermis layers
Features of Stratum granulosum ( granular layer )
- Stratified squamous epithelium
- Lamellar granules
- Tonofibrils made by lamellar bodies
What are lamellar granules ?
Filament associated proteins that assemble keratin fibrils and secret it
What are tonofibrils?
Bundles of keratin filaments and keratohyalin granules
Epidermis layer
Features of Stratum Spinosum ( spinous/prickle cell layer )
- Cubiodal epithelium arranged in 3 layers ( held together by desmosomes )
- Producers of lamellar bodies ( keratin factories )
- first time Golgi appears
Epidermis layer
Features of Stratum Basale ( basal cell layer )
- innermost of the cell layers of the epidermis
- Tall columnar epithelial cells
- constantly renew keratinocytes by cell division
- As daughter cells differentiate , they move away from the epidermis dermis junction (loose their ability to differentiate )
- produces keratin filaments (tonofilaments)
- home to the melanocytes (produces melanin )
Role of Keratinocytes
Synthesise keratins (fibrous proteins) that contribute to the strength of the epidermis
Apart form contributing to the strength of the epidermis , what other roles is keratin used for ?
- Hair
- Nail
- Animal horns
What is the normal transit time of a keratinocyte from basal layer to stratum Corneum ?
28-40 days
Cells found in the Epidermis
- Melanocytes (stratum Basale)
- Langerhans cells
- Merkel cells
- Keratinocytes
Features of Melanocytes
- produces melanin
- number not increased in black /dark skin individuals
- difficult to see histologically without special stain ( immunohistochemistry with S100 antibody )
Features of Langerhans cells
- difficult to see histologically without stains
- macrophages ; highly specialised capacity to present antigens to T lymphocytes to mediate immune reactions
Features of Merkel cells
- difficult to see histologically without special stains
- mechanoreceptor cells associated with sensory nerve ending ;pressure touch
6% in white individuals
10% in black individuals
State the two types of skin
Hairy skin - thin skin
Non hairy skin - thick skin
Location of non hairy (thick) skin
- Palmar surface of hand
- Plantar surface of foot
- Area between fingers and toes
Structure of Non hairy (thick) skin
- No hair, arrest or pills muscle, no sebaceous glands
- Thicker stratum Corneum
- Thinner dermis
- Increased density of mechanoreceptors
Function of Non hairy (thick) skin
- Prevents tissue loss due to abrasion
- Increased friction between skin and surfaces
- Increased sensation
Features of thick (non hairy ) skin
- No hair follicles
- No sebaceous glands
- No arrector pili muscles
- Pronounced ridges and furrows on surface
- Regular shaped dermal papillae : interdigitation
- Stratum lucidum often seen
Features of thin (hairy skin)
- Presence of hair follicles
- Presence of sebaceous glands
- Presence of arrector pili muscles
- Smaller ridges and furrows
- Irregular dermal papillae
- Stratum lucidum absent
What are skin appendages ?
Skin appendages are skin associated structures that serve a particular function
Name 5 skin appendages
- Hair
- Arrector pili
- Sebaceous glands
- Sweat glands
- Nails
Skin appendages -Hair
Sate the three types of hair
Lanugo - covers developing foetus
Vellus - replaces lanugo after 2-3 days
Terminal - head ( scalp and eyebrows, nasal passage) armpit and external genital region
Skin appendages - Hair
Features of Lanugo
- sometimes seen at birth
- covers developing foetus
- very soft fine hair
Skin appendages - Hair
Features of Vellus
- replaces lanugo
- short
- thin
- light coloured
- soft
- not connected to sebaceous gland
Skin appendages - Hair
Features of Terminal
- found on the head, armpit and external genital region
- long, wide, dark coloured and coarse
- produced by actions of testosterone
Function of Hair on the skin
- Thermoregulation
- Sexual attraction (apocrine sweat glands)
- Sensation (sensory nerve endings)
- Protection (eyelashes , nasal hair, eyebrows , axillae hair)
Skin appendages- Arrector pili muscle
Features of this
- Consist of smooth muscle fibres attached to the papillary region of dermis and hair bulb
- controls thermoregulation function of hair
- may also induce sebum release from sebaceous gland
Skin appendages-mechanoreceptors
State the mechanoreceptors found in the skin
End bulbs
Free nerve endings
Tactile discs
Meissner Corpuscle
Pacinian corpuscle
Ruffini’s corpuscle
Root hair plexus
Skin appendages - mechanoreceptors
Role of end bulbs
Thermo receptors
Register temperature
Skin appendages - mechanoreceptors
Role of free nerve endings
They have nociceptors
Register pain
Skin appendages - mechanoreceptors
Role of tactile discs
Vertical dimpling of skin
Attaches to the basal layer keratinocytes
Senses touch, pressure and texture
Merkel in non hairy skin
Meissner in hairy skin
Skin appendages - mechanoreceptors
Role of Meissner corpuscle
Detects tapping and flicker movements
Skin appendages - mechanoreceptors
Role of pacinian corpuscle
Senses vibrations
Skin appendages - mechanoreceptors
Role of Ruffini’s corpuscle
Senses joint movements and tissue stretch
Skin appendages - mechanoreceptors
Role of root hair plexus
Senses vibrations in the hair shaft
Skin appendages - sebaceous gland
Features of this
Produces an oily substance called sebum by Holocrine secretion
Found near the top and inside hair follicles or with sweat pores
Found on thick (eyelids ,nose) and thin skin (face, scalp)
Not found is the palms of hands and soles of feet
Skin appendages - sweat glands
Features of this
- simple coiled tubular gland
- found deep to sebaceous gland and a little to one side
- eccrine sweat glands and apocrine sweat glands
Skin appendages - Nails
Location of Nails
Distal surface of fingers and Toes ( Phalanges)
Skin appendages - Nails
Structure of nails
Consists solely of alpha keratin
- nail plate
- nail matrix
- nail bed
Skin appendages - Nails
Function on nails
- protection of distal phalanx and surrounding soft tissue from injuries
- enhances precise delicate movements
- enhances sensitivity of finger tips (nails bed itself has no nerve endings )
- as a tool e.g, extended precision grip
Function of the skin
- Protection and repair (kartinocytees, melanocytes, Langerhans cells, fibroblasts )
- temperature regulation and excretion of waste products (sweat gland-apocrine)
- lubrication (sebaceous glands)
- storage ( white adipose cells provide lipids for energy )
- vitamin d synthesis
- absorption ( small amounts of water and oxygen)
- aesthetics (as a mode of communication or attraction)
- sensation (mechanoreceptors)
