04 Skin Flashcards
Describe the functions of the skin
Protection from external damage
- UV light, chemical, thermal, and mechanical injury and resistance to shear stress - thick skin
Barrier
- waterproof and barrier to bacteria (sebum)
Sensation
- touch, pressure, pain, and temperature
Metabolic
- synthesises metabolic Vit D3, subcutaneous fat is a major energy store
Thermoregulation
- insulation, heat loss by sweat, evaporation, and vasodilation
Excretion
- sweat
Immune response
- inflammation, antigen presentation on cell
Name the layers of the skin
- Epidermis (epithelium)
- Dermis (connective tissue)
- Hypodermis/subcutis (fascia)
Briefly describe the structure of the skin
Layers
Epidermis
- stratified squamous epithelium (Keratinised)
- Keratinocytes (to make keratin)
- layer of dead cells (with no nucleus)
Dermis
- dense irregular connective tissue
- fibroblasts, collagen I, elastin, blood, nerves, and receptors
- Divided into the papillary and reticular dermis
Hypodermis
- adipose tissue and main blood supply
Name the layers in the epidermis
bottom to top
- Stratum Basale
- Stratum spinosum
- Stratum granulosum
- Stratum Lucidum (in thick skin only)
- Stratum corneum
Describe the layers in the epidermis
Stratum basale (germinativum) - mainly contains stem cells, which divide into Keratinocytes
Stratum spinosum
- cells have connections (spinous processes)
- Connections have cell junctions (desmosomes), that allow for communication
- Cells are also connected to the Stratum Basale
Stratum Granulosum
- granular layer - high amount of granules are seen
Stratum Lucidum
- in thick skin only (soles and palm) (clear)
- subdivision of stratum corneum
Stratum Corneum
- in thick and thin skin
- Uppermost layer - has mainly keratinised cells
Describe how and why cell turnover is important in the epidermis
As cells move up, they die (programmed cell death)
- They lose organelles and get filled with Keratin (protein)
Those keratinised cells then exfoliate, and new cells then produce them
Describe how cell turnover happens in the epidermis
- Mitosis/cell division in the basal layer
- Differentiation + apoptosis as cells move up
- Exfoliation of keratinised cells
Describe the barriers that are involved in the skin (in the epidermis) - that aid function
Tight junctions
- prevent paracellular diffusion
Desmosomes and Hemidesmosomes
- prevent mechanical and sheer forces
Keratin
- microorganism protection
Phospholipid
- waterproofing
Describe the dermis layer of the skin
- Connective tissue
- middle layer
- Contains hair and gland structures
Divided into Papillary and Reticular dermis
In erectile organs (aveolar, nipples)
- below reticular leayer, there is smooth muscle, resulting in puckering of the skin
Describe the Papillary layer of Dermis
Papillary layer - superficial layer
- type I and III collagen
- elastic fibres (fibres are very irregular)
Describe the Reticular layer of the Dermis
Reticular Layer - Deep layer
- mainly type I collagen
- elastic fibres (not regular, BUT run parallel to each other, forming Langer Lines)
Langer Lines
- if wound happens parellel to Langer lines, wound healing is quicker, and a lot less scarring (you are not cutting across the fibres)
What is the Dermal Papillar?
Dermal Papillar
- protrusions of the dermis into the epidermis
What are epidermal ridges/Rete Ridges?
Epidermal Ridges/Rete Ridges
- They are protrusion of the epidermis into the dermis
What is the purpose of the dermal papillar and epidermal/rete ridges?
To increase SA
Describe the Hypodermis layer of the skin
Mainly adipose tissue
- provides insulation and a form of energy store
Also contains erector pili muscles
- pulls hair follicles to stand up (goosebumps)
What are the different skin cell types?
- Keratinocytes (95%)
- Melanocytes
- Langerhans Cells
- Merkel cells
Describe Keratinocyte cells
They are:
- Stratified Squamous Keratinising epithelial cells
Keratinising: produce keratin-filled cells, loss of organelles and nucleus
They produce Keratin (hard - hair and nails, soft keratin)
Describe the process of Keratnisation in the epidermis of the skin
(with how Keratin is made)
Keratin protein needs to be bundled together
- so they first form filaments (keratin filaments)
- which then further bundle together - Tonofibrils
[for the Keratin to form Tonofibrils, Keratohyalin granules needed]
Once the cells from the basal layer reach the stratum spinosum
- granules (Keratohyalin) begins to form in cells
Once they reach stratum granulosum
- high concentrations of Keratokyalin granules are present
When cells go from granulosum to corneum
- Cells have been completely Keratised
Describe Melanocyte cells
Melanocytes make melanin
- they are neural crest-derived cells in Stratum Basale
- pigment synthesising cells responsible for skin and hair colour
- ratio of Melanocytes:Keratinocytes is the same for all people, but the amount of melanin secreted varies
Melanosomes in the cytoplasm contain Melanin and are passed to Keratinocytes
- leading to scattering of UV light - protecting for DNA
- there is a higher concentration of Melanin above the nucleus, for the protection of the DNA
Describe Langerhans cells
All layers and upper dermis-prominent in spinosum
- they are bone marrow-derived
They are dendritic, antigen-presenting cells
- that migrate to regional lymph nodes
- and communicate with the immune system (activate T cells)
Invasion of Pathogen into the epidermis
- it must be phagocytosed
- and present antigen on MHC Class II on the cell surface (dendritic cells)
Describe Merkel Cells
They are clear cells in the Stratum Basale
- plentiful in touch areas
- they act as Mechoreceptors (pressure)
- connected to keratinocytes and afferent nerves
- Neuroendocrine function
Merkel cells connect to free nerve endings
- acting as a Mechanoreceptor
Describe the vascular supply to the skin
Maintains skin nutrition
- whilst being able to alter flow to facilitate heat loss/conservation of heat
Name some skin specialisations
Down-growth from the epidermis
- Hair follicles
- Sweat glands
- Sebaceous glands
Describe Hair follicles as a skin specialisation
Hair follicles
- they produce hair shafts (keratin) for thermoregulation and display
- Erector pili muscle - can pull on hair to make it sit/stand (hence, trap air for insulation, vice versa for goosebumps)
Describe sweat glands as a skin specialisation
2 types:
Eccrine
- dermal-subcut junction of all skin, produce sweat
- The Ducts open directly onto the skin surface (thermoregulation)
Apocrine
- localised (axilla/groin) scent production
- open into hair follicles above the sebaceous gland
- functional at puberty
Describe sebaceous glands as a skin specialisation
The majority are associated with hair follicles
- they secrete lipid mixture - sebum
- into the hair follicle (for Waterproofing)
Located in the dermis and subcutis
Describe the sensory (afferent) innervation of the skin
Pacinian corpuscle (modified Schwann cells) > in subcutis, deep pressure + vibration
Meissner’s Corpuscle
- in the papillary dermis, rapidly adapting mechanoreceptors - light touch/pressure sensation
Ruffini Corpuscle
- mechanoreceptors, stretching of the skin
Free nerve endings
- (pain, itch, temperature)
- in the papillary dermis
- when associated with Merkel cells, they are slowly adapting mechanoreceptors
Describe the efferent (motor) nerve endings of the skin
- Vessel diameter and blood flow
- Information to sweat glands and erector pili muscles
