Skin structure and function Flashcards
What are the 3 main functions of the skin?
Protection
Physiological regulation
Sensation
List ways in which skin has a protective function
Epidermis acts as a physical barrier to prevent Protection from:
Injury
infection (immune cells present which achieve phagocytosis)
UV rays
Pressure
Weak chemicals and gases
Trauma (hypodermic acts as shock absorber)
Regeneration of epidermis provides immune defence as bacteria is constantly shed
How does the skin regulate hydration?
Stratum corneum has lipids such as glycolipids and keratin which make the skin waterproof.
This means that water is unable to leave so prevents dehydration and cannot enter so prevents absorption.
How doe she skin achieve thermoregulation?
When the body is too hot, eccrine glands secrete sweat to cool the body down.
Vasodilation of veins also occurs to maximise heat loss.
When the body is too cold:
Arrector pilli muscle contract to raise the arm hairs which traps a layer of warm air.
how does the skin provide sensation?
Merkel cells are present in epidermis which provide feeling and sensation.
Free nerve endings also act as receptors in detection mechanical stimuli (tough, pressure, pain)
What are the 3 layers of the skin?
Epidermis, dermis, hypodermis
What is the histology of the skin?
Keratinised, stratified, squamous epithelium
What are the layers of the epidermis from Botton to top?
Stratum Basale Stratum Spinosum Stratum Granulosum Stratum Lucidum Stratum Corneum
Describe stratum basale?
A single layer of cuboidal stem cells and melanocytes.
Stem cells are mitotically active and Synthesise keratinocytes.
Attached to the basement membrane via hemidesmosome
Describe stratum spinosum
Cells are irregular in shape
Cells are pale, biosynthetically active (contains golgi) as they are producing keratin.
Thick bundles of intermediate filaments (keratin in the skin) are present which are bound together tightly by desmosomes.
Describe the stratum granulosum
Contain lamellar and keratohyalin granules which are needed to cross link keratin.
Cells lose their organelles, became brittle and flattened,
Describe the stratum lucidum?
Found in thick skin (e.g. soles of the feet and palms of hand)
Several layers of flattened dead cells
describe the stratum corneum?
25-30 layers of flattened, dead keratinocytes. Cells are very thin and flat, with no nucleus or organelles. They only contain cross linked keratin.
Contains lipids (glycolipids and keratin) which make it waterproof.
Describe the basement membrane?
It is a sheet-like layer of ECM proteins (collagen + glycoproteins)
NOT MADE OF CELLS
List the different skin cells
keratinocytes Langerhans cells Merkel cells Melanocytes Stem cells
Where are keratinocytes found and what is their function?
They are found in keratinised squamous epithelium.(all throughout epidermis in this case)
Function: Protection and barrier, hydrates skin and synthesis of Vitamin D
Where are Merkel cells found and what is their function?
Throughout epidermis
Function: Provide sensation/feeling, they attach to free nerve endings coming up from the dermis
Where are Langerhans cells found and what is their function?
In epidermis (MOSTLY stratum spinosum) and papillary layer fo dermis
It is a dendritic cell involved in antigen presentation and phagocytosis.
Where are melanocytes found and what is their function?
In stratum basale
They produce melanin which provides UV protection.
Where are stem cells found and what is their function?
In stratum basale
they produce keratinocytes to allow self renewal of the epidermal layers.
What molecules are found in keratohyalin granules and what are there functions?
Profilaggrin: converted to filaggrin which aggregates keratin filaments into tight bundles
Involucrin: Formation of a cell envelope around cells in stratum corneum
Loricrin: cross links to involucrin
what molecules are found in lamellar granules? What is their collective function?
Polysaccharides
Glycoproteins
Lipids
They extrude into the intercellular space. form the cement that holds the stratum corneum together.
What is the dermis and what is it made up of?
It is connective tissue
Made up of type 1 collagen, ground substance and elastin.
What are the two layers of the dermis? Which one is upper?
Papillary (upper)
Reticular
Describe the papillary layer of the dermis?
Layer of thin, loose, connective tissue. Less elastin, fibres form a loose mesh.
it is abundant with blood vessels and closely linked to basal layer through projections of dermal papillae. Contains free nerve endings and langerhans cells.
Describe the reticular layer of the dermis?
Thick, dense connective tissue, rich in elastin, as fibres form a strong mesh. Also well vascularised and contains free nerve endings.
What are the cell of the dermis?
Fibroblasts
Dermal dendritic cells
Lymphocytes
Mast cells
What is the function of fibroblasts?
Synthesis of all molecules (elastin, ECM, collagen)
Synthesises growth factors
What do lymphocytes do?
Immune surveillance
What is the role of dermal dendritic cells?
Antigen presentation
Phagocytosis
What is the role of mast cells?
Produces inflammatory mediators (e.g. histamine, heparin) and chemotactic factors for eosinophils and neutrophils.
Describe the role of free nerve endings in the skin
Free nerve endings are found in the papillary layer of the dermis and they form attachments with Merkel cells in the epidermis and act as mechanoreceptors.
What do Meissner’s corpuscles do?
They are rapidly acting mechanoreceptors which are responsible for sensitivity to touch
What do Pacinian corpuscles do?
They are mechanoreceptors responsible for sensitivity to pressure and vibration. (in pictures, usually deeper in dermis than Meissner’s)
What are the functions of the dermo-epidermal junction?
Connects epidermis to dermis
Acts as a barrier for nutrients/oxygen passing between epidermis and dermis
Serves as a base for re-epithelialisation in wound healing.
Aligns cells
Involved in signalling
What are the functions fo the subcutis?
Shock absorbs
Provides insulation
Energy source
What are some skin-related appendages?
Glands
Nails
Hair
Name 3 glands
Sebaceous
Apocrine
Eccrine
what are sebaceous glands formed from and what’s their function?
They are formed from hair follicles, present in most of the skin apart from hands and feet.
They secrete sebum - which is a mixture of lipids - and provides lubrication to the hair shaft and waterproofing mechanism of skin.
What is the role of eccrine glands and where are they mostly found and not found?
They are sweat glands which secrete sweat everywhere except the lips, external auditory canal and genitalia.
Most abundant in the axillae (armpits) and soles of feet and palms of hands.
what are apocrine glands and where are they found?
they are scent glands (function not understood)
Found in axillae and genitals
what is a hair follicle?
A tubular invagination of the epidermis (anchors hair to skin)
How are Hairs formed?
As cells from the hair bulb proliferate and move upwards, the cells become keratinised to produce hair. Dermal papillae provide blood supply.
what is hair colour determined by?
Melanin synthesis
What is the nail plate?
modified form of stratum corneum.
It provides a laminated, keratinised structure overlying the nail bed and nail matrix.
what is the nail matrix?
area of specialised epithelium that produces the nail plate.
What external factor may influence the skin?
UV radiation
What can chronic exposure of UV radiation lead to?
Wrinkles and premature ageing Haemorrhage of blood vessels Abnormal pigmentation Loss of skin elasticity Damage of cells, DNA, proteins
What does UV light initiate the synthesis of ?
Vitamin D
What are melanocytes
Dendritic cells which produce melanin against UV radiation. Their role is to protect cells from DNA damage which could potentially be mutagenic.
Describe how cells receive melanin
Melanocytes package melanin into melanosomes and these packages get sent to cytoplasmic extensions. Keratinocytes receive the melanosomes to protect their nuclei from UV. The melanosomes surround the nuclei.
