What is the epidermis
- Epidermis is Avascular (Has no blood vessels)
- Outermost layer of the skin which forms primary Protective layer for the body (waterproof barrier) preventing water loss and maintaining Homeostatic balance
- Made up of three types of cells Keratinocytes, Melaninocytes and Lagerhans
- Produces new skin cells via the Stratum Basale Layer
What are Keratinocytes
- Keratinocytes - Highly specialized cells which produce the protein keratin in order to form a protective barrier and stop foreign substances form entering the body.
- They also play a structural role in the skin forming tight bonds with other cells in order to maintain them in place by way of Dersmosomes
- Produced at the Stratum Basale Layer
Melanocytes
- Melonynocytes produce the protein kown as melanin which is responsible for the skins pigment.
- Melanin protects against UV radiation
What are Lagerhans
- Lagerhan cells are a form of dendretic cells (Antigen presenting cells) which perform phagocytoses (ingest and eliminate foreign substances) protecting against microorganisms and foreign substances.
- They are most common in the Stratum spinosum layer
- After performing phagocytoses the transport portions of the microbe they ingested to the cell membrane presenting it to other immune cells helpin to stimulate immune reactions
What are Merkel cells
- Merkel cells are mechanoreceptors receptor which function as a sensory receptor fo touch
- Found in the stratum basal layer
basement
Detail the Stratum basale layer
- Innermost (deepest) layer of the epidermis
- Also called Stratum Germinativum (as constantly germinating producing new cells)
- Contains Melaninocytes (skin pigment melanin producing) and Merkel Cells (mechanorecptors associated with touch)
- Each time mitosis occurs with a basal cell , one daughter cell is pushed up into the spinosum layer to begin specialization into a mature keratinocyte, with the other cell remaining to continue the germination process
Spiny/prickly layer
Detail The stratum Spinosum layer
- Also reffered to as the Prickly or spiny layer. The Keratinocytes cells here have spiny/prickly intermidiate filamnets which span their cytosol attaching to desmosomesHence the name.
- Contains Largehans cells and
- Responsible for cytokin synthesis (protien that helps regulate immune response
- Thickest layyer of the epidermis
granular layer
Detail the granulosum layer
- Thin layer, Consists of 3-5 cell layers
- Keratinisation process begins here (cells fill with keratin)
- As keratinocytes move through the epidermis they begin to flatten out with nuclei and organelles starting to disintergrate
- Keratinocytes become granular here accumulating kerathylin (help to form keratin) and lamellated granules
- Lamellated granules contain water resistant glycolipid and is a major factor in slowing water loss across the epidermis
detail the stratum lucidium
- Appears translucent through light microscope
- Is made up of dead Keratinocytes (cells above the granulosum layer are to far away from the dermal capilaries and are cut of from vital nutrients by the glycolipids that coat their surface)
- Most commonly found on hairless parts of the body (soles/palms) and can only be seen on thick skin
Detail the corneum layer
- 20-30 layers thick
- Contains flattened dead Keratinocytes known as corneocytes (cornified cells with no nucleus)
- Cornoecytes serve as hard protective layer against trauma and are eventually shed into the enviroment as dandruff or dust
What is the importance of desmosomes connecting keratinocytes together
The skin is the outermost protective layer of the body so undergoes a lot of traumaand abrasion.
Desmosomes which are conecting junctions help hold the cell in the epidermis togther during this time of stress
What is the dermo epidermal junction (basement membrane)
- Narrow multi layered undulating sturcture laying between the epidermis and the dermis providing cohession between the two layers
- Undulates between the epidermis and the dermis and is connected via ridges (rete ridges) Contains Cappillary loops supplying the epidermis with nutrients and oxygen
What are the two layers of the dermis
- Lamina Lucida - Thinner layer directly underneath the epidermis basale layer
- Lamina Densa - Thicker layer in direct contact with the dermis
What is the dermis
- Inner layer of the skin, much thicker than the epidermis
- Primary function is to sustain the epidermis by supplying it with nutrient saturated blood
- Protection - cushioning the deep structres from mechanical injury
- Playing an important role in wound healing
- Maid up of collagen and elastain
What structures does the dermis contain
Blood vessles - supply nutrients and oxygen
Lymph vessles - supply skin with lymph mily like substance containg infection fightng cells
Hair folicles - sheath surroundign hair under the skin
**Sweat glands **- secrete sweat in order to regulate body temprature
Sebacious glands - secrete oil to keep skin supple and smooth
**Mast Cells **- part of the immune system important in inflammatory response
Fibroblasts - Secrete collagen for structural support
What are the two layers of the dermis
Superficial Pappilary Layer and Recticular Layer
Detail the charecteristics of the Papillary layer of the dermis
- Consissts of loosley woven tissue with interlacing collagen and elastic fibres as well as an abundacne of capillaries
- It’s looseness allows phyagcytes to wonder free and patrol for invading bacteria
- Dermal Pappilae (contain cappilary loops) increase the surface area of the dermis and indent the epidermis increasing the exchange of oxygen/nutrients and waste products between the two layers
- Dermal papilae also house other nerve endings and Meissners corpuscules (touch receptors)
Detail the charecterisics of the reticular layer of the dermis
- Course irregularly arranged dense fibrous connective tissue
- The network of Blood vessels that nourish this layer are Cutaneus plexes and lie between this layer and the Hypodermis
What is the Hypodermis Detail its features
- Also known as the subcutis or the subcutaneous layer, the hypodermis lies beneath the dermis
- Consists of mainly fat tissue
- Provides structure and support to the skin as well as insulation from the cold and shock absorption
- Contains blood vessels and nerves
What are sweat glands
- Also known as sudoriferous glands they secrete sweat in order to regulate temprature
- This is done through the contraction of myoepethilial cells that contract when stimulated by nervous system
- This contraction forces sweat though the glands sweat duct to the surface of the skin
What is an Eccrine sweat gland
- True sweat gland found over the entire body
- More abbundant then the Apocrine sweat glands
- Coiled tubular gland with the secretery part laying coiled in the dermis and the duct extending to the open por/channel at the surface of the skin
What is a Apocrine Sweat gland
- Largely found in the armpits and genital areas
- Release there product by Exocytosis
- Larger than eccrine lying deeper in the dermis and even hypodermis
- Their ducts empty into the hair folicles
secretion contains the same components as true sweat + fatty substances and protein
