Introduction to Skin Flashcards
What are the three main layers of skin?
Epidermis, dermis and hypodermis (fat layer)
What is keratin?
Keratin is an intermediate filament that is most abundant in the stratum corneum (top layer), hair and nails.
Where is keratin most abundant in the skin?
Epidermis, stratum corneum (top layer), hair and nails too
What are the two types of keratin?
Soft (alpha) and hard (beta) - determined by the secondary structure and suffice bridges
What are the four main layers of the epidermis?
Stratum corneum, stratum granulosum, stratum spinosum and stratum basale
Describe the stratum corneum layer of the epidermis
Protective layer of the skin with dead cells and intercellular lipids (ceramics) to maintain skin moisture
Describe the stratum granulosum layer of the epidermis
This is 2-3 cells thick and has large granules of keratohyalin
Describe the stratum spinosum layer of the epidermis
3-4 cells thick with many desmosomes to separate the keratinocytes which gives the layer a spiny appearance
Describe the stratum basale layer of the epidermis
Proliferation of epithelial cells occurs here and cells are slightly denser
Describe the composition of the basement membrane of the epidermis of the sin
ECM consists of laminin 332, collagen IV and collagen VII
What is the role of the basement membrane in the epidermis?
To provide cell polarity, regulate basal function and to anchor the epidermis to the dermis
What is the function of the hemidesmosomes in the basement membrane of the epidermis?
Bind the keratin cytoskeleton to the basement membrane
What is the role of the dermis?
Provides strength and elasticity to the skin
What is the most abundant cell in the dermis?
Fibroblasts
What is the function of fibroblasts in the dermis?
Produce elastin, collagen and proteoglycans
What is the neuromuscular supply to the dermis like?
Innervated and vascularised
What are the three layers of the dermis?
Papillary, reticular and adipose
Describe the papillary layer of the dermis
Contains fine, randomly organised type III collagen and elastin, and lies directly below the basement membrane of the epidermis
What type of collagen is present in the dermis?
Type III collagen
Describe the reticular layer of the dermis
The thickest layer densely packed with collagen providing mechanical strength
Which dermal layer is largely responsible for the mechanical strength of the skin, and why?
Reticular layer of the dermis as it is densely packed with collagen
What are adherens junctions?
These are more basal than tight joints and involve a cadherin receptor linked to an actin cytoskeleton
What are desmosomes?
Provide a connection between intermediate filaments of the cell cytoskeletons of adjacent cells; cadherin receptor is linked to the keratin cytoskeleton
What are tight junctions?
These seal adjacent epithelial cells in a narrow band just beneath their apical surface. Claudin and occluding molecules seal the intercellular space
What are gap junctions?
These form intercellular pores made up of connexins
Name four different types of cell-cell adhesions
Adherens, desmosome, tight junctions and gap junctions
Name three types of glands that may be present in the skin
Sebaceous, eccrine sweat gland, apocrine gland
What is a sebaceous gland?
Exocrine gland (secreted into duct) usually found attached to a hair follicle which produces sebum to lubricate skin
What is acne caused by?
Infection of the sebaceous glands
How are sebaceous glands affected by puberty?
The gland is sensitive to androgens, and enlarges at puberty as a result
What is the role of the eccrine gland?
To produce watery sweat for thermoregulation
What is the difference between eccrine and apocrine glands?
They are both sweat glands but apocrine glands are associated with hair follicles whereas eccrine glands are not
Describe the structure of the eccrine sweat gland
Has an excretory duct and a secretory coil
What is the role of the apocrine gland?
To secrete sweat associated with hair follicles, and is found in the armpit and pubic region
Where are apocrine glands usually found?
Axilla and pubic regions
What causes the smell of body odour from sweating?
Sweat secretion itself is odourless, but is broken down by bacteria on the skin leading to the release of volatile fatty acids which produce the odour
What are the two types of hair follicle?
Vellus and terminal
What is a villus hair follicle?
A hair follicle found on body hair
What is a terminal hair follicle?
A hair follicle found on the scalp or with secondary sexual hair
Which cells produce hair?
Keratinocytes in the matrix of the hair follicle
What cells are involved in controlling hair growth?
Dermal papilla fibroblasts
What are the three phases of the hair growth cycle?
Anagen, catagen and telogen
What is the anagen phase of hair growth?
Active phase of hair growth
What is the catagen phase of hair growth?
Regressive phase of hair growth
What is the telogen phase of hair growth?
Resting phase of growth
Where are melanocytes found?
In the epidermis (on basement membrane) and in the hair follicle matrix
What is the function of melanocytes?
Produce melanin and package it into melanosomes (eumelain and pheomelanin) which are injected into keratinocytes to provide skin with protection against UV radiation
Where do melanocytes inject melanin?
Into keratinocytes
What are melanocytes?
A form of dendritic cell in the basement membrane of epidermis and in the hair follicle matrix
What are Langerhan’s cells?
A form of dendritic cell in the basal and spinosum layers of the epidermis
What is the role of Langerhans cells?
Act as antigen presenting cells to T cells and are a first line of defence against infection
What are Merkel cells?
Involved in sensory perception of the skin (basal layer of epidermis)
Where are Merkel cells found?
The basal layer of the epidermis
What are mast cells?
Cells involved in the immune response by secreting histamine
Where are mast cells found?
Dermis of the skin
What is a superficial skin wound?
Damage to epidermis only
What is a partial thickness skin wound?
Damage to epidermis and dermis
What is a full thickness skin wound?
Damage to epidermis, dermis and hypodermis
What are the three stages of wound healing?
Inflammation, proliferation and maturation
How long should it take for a wound to heal?
Less than 6 weeks
Outline the inflammation phase of wound healing
Blood clot is formed to seal wound and immune response is initiated
Outline the proliferation phase of wound healing
Keratinocytes move over the wound to create a barrier, fibroblasts infiltrate wound site to produce ECM to form the new dermis and repair damaged blood vessels
Outline the maturation phase of wound healing
Replace immature tissue with mature tissue
