Lecture 4: The skin Flashcards
Who described the skin as a protective covering 150 years ago?
Virchow
What is skin the largest of?
Largest organ in weight and surface area
What is the weight of the skin?
3-5kg in adult
What is the surface area of the skin?
1.5-2 meters squared in adults
Where is skin the thickest and where is it the thinnest?
Thickest: soles of feet
Thinnest: eyelids
What is skin rich in?
Antigen presenting cells (langerhans cells) for immune response uppon breach
What does skin facilitate the synthesis of?
Vitamin D3
What receptors does the skin contain?
Touch, pressure, pain and temperature
How does the skin provide protection from UV?
Pigmentation from melanin
How does the skin help thermoregulate?
Via blood circulation in extremities and sweat
What are the three main layers of the skin?
The epidermis, dermis and subcutis
What is the epidermis?
Continuously proliferating stratified squamous epithelium which provides a non-living layer of keratin
What is the dermis?
Consists of fibrous and fibroadipose tissue which supports the epidermis physically and metabolically
What does the subcutis consist of?
Adipose tissue and supporting fiborous bands
What are some of the specialised appendages found in the skin?
Nails, hair follicles, sebaceous glands, eccrine glands and apocrine glands
How is the epidermis adapted to withstand constant abrasion and deiccation?
Tough non-living surface layer composed of keratin wrapped in plasma membrane
The epidermis is _____, nourished by diffusion from the ____
Avascular
Dermis
What type of cell makes up 95% of the epidermis?
Keratinocytes
Other than keratinocytes, what 4 other cell types make up the epidermis?
Melanocytes
Langerhans cells
Merkel cells
Inflammatory cells
What is the area of tissue that joins the epidermis and the dermal layers called?
The dermoepidermal junction
What is the structure of the dermoepidermal junction?
Highly corrugated and has many downward, ridge like extensions of the epidermis called epidermal or rete ridges
Epidermal, or rete, ridges, project between alternating, upward projections of the dermis known as what?
Dermal papillae
What are the dermal papillae and rete ridges responsible for?
Exchange of nutrients
What would happen without rete ridges?
Skin would suffer premature ageing and damage
How many distinct layers are there to the epidermis?
4 or 5
What is the deepest layer of the epidermis called?
Basal layer/stratum basale
What is the structure of the basal layer?
Closely backed basophilic cuboidal to columnar epithelial cells (keratinocytes) resting on basemement membrane
What layer of the epidermis rests of the basal layer?
The prickle cell layer/ stratum spinosum
How thick is the prickle cell layer?
Several cells thick
What is the structure of the prickle cell layer?
Polyhedral cells become progressively flatter towards the surface
What is the second to the top layer of the epidermis?
Granular layer/ Stratum Granulosum
What is the structure of the granular layer?
3-5 layers of flattened cells, contains numerous basophilic granules (keratohyalin)
What is the keratin layer also called?
Stratum Corneum
What is the structure of the stratum corenum?
Dead, anucleate cells, keratin replaces cytoplasm
What is the stratum basale and spinosum sometimes collectively called?
Malpighian layer
What is the 5th layer of the epidermis?
Stratum lucidum
Where is the stratum lucidum found in the body?
Absent in thin skin, present in thick skin
What is the structure of the stratum lucidum?
A few layers of tightly packed squamous cells that lack organelles and nuclei
What colour is the stratum lucidum
Translucent
Where in the layers of the epidermis is the stratum lucidum found?
Transition from stratum granulosum to the corneum
What are mealanocytes?
Melanin pigment-producing cells that determine colour of skin and hair
How are melanocytes linked?
Via dendritic processes (not desmosomes)
What part of the cell produces melanin?
Membrane bound organelles known as melanosomes
What form of melanin produces brown to black pigments?
Eumelanin
What form of melanin produces yellow to red pigments?
Pheomelanin
What do melanoma’s develop from?
Melanocytes in the skin and some in mucous membranes, uvea of the eye and meninges
Malnocytes proliferate to form what?
Nevi
What occurs subsequent to nevi formation?
Dyplasia, hyperplasia, invasion and metastasis
What two things are used to detect melanoma cells?
Melan-A and human melanoma black (HMB)
Where are Langerhans cells derived from and where are they found?
Monocyte-derived dendritic cells that reside in the epidermis
What are Langerhans cells?
Phagocytic and antigen-processing and presenting cells
What do Langerhans cells do once they have captured invading surface antigens?
Migrate to regional lymph nodes, induce immune response via antigen presentation to CD4+ and CD8+ T lymphocytes
Where in the epidermis are Langerhans cells common?
Stratum spinosum and stratum granulosum
What are merkel cells?
Intra-epidermal touch receptors
What do Merkel cells contain in their cytoplasm?
Membrane bound vesicles
What type of junction do merkel cells make with sensory nerves in the upper demis?
Synaptic junctions
What are apocrine glands?
Limited distribution, possible function in producing odour
What are eccrine glands?
Sweat glands- essential for thermoregulation
What are sebaceous glands associated with?
Hair follicles
What do sebaceous glands do?
Secrete sebum which may provide waterproofing
Where is hair produced?
Follicles
What shape are hair shafts and what are they composed of?
Cylindrical shafts composed of keratin
What is the structure of a hair shaft?
Surface cuticle composed of a single layer of flattened keratin scales
Other than sebaceous glands, hair is produces in association with what?
A smooth muscle bundle called arrector pilli
What is the function of hair and fur in mammals?
Thermoregulation
Hair growth is _____
cylindrical
What are the three phases of hair growth?
Anagen, catagen, telogen
What is anagen?
Long phase of active growth of hair
What is catagen?
Short phage of involution
What is telogen?
Short inactive involuted phase
Where are sebaceous glands located?
Between hair follicles and its arrector pilli muscle
What is sebum?
Lipid-rich decomposed cells
Sebaceous glands empty their secretions via a ducts in the upper part of the hair follicle. This is known as?
Holocrine secretion
Each sebaceous gland contains what layers?
A peripheral layer of cuboidal cells with spherical nuceli resting on a thin basement membrane
The peripheral layers of cuboidal cells in the sebaceous gland give rise to what?
Larger, sebum-producing cells
What is the structure of the sebum-producing cells?
Polyhedral with large amounts of lipid in the cytoplasm
What happens to sebum producing cells nuclei?
They become pyknotic
What gradually happens to sebum producing cells?
They gradually disintegrate into the secretory product
What type of muscle to sebaceous glands have?
Smooth muscle (arrector pili)
What does contraction of arrector pili in sebaceous glands do?
Compresses the gland to expel sebum
What shape are eccrine (sweat) glands?
Simple, coiled tubular gland
What to portions to eccrine (sweat) glands consist of?
Secretory and excretory duct portions
The secretory part of the gland deep in the dermis consist of what?
Two types of cuboidal to pyramidal secretory cells: clear cells and dark cells
What do clear cells in eccrine gland secrete?
Water and electrolytes
What do dark cells in eccrine glands secrete?
Macromolecules
What cells border secretory cells in the ecrrine gland?
Myoepithelial cells (smaller, intensely eoisinophilic)
What do myoepithelial cells do?
Mainly contractile and help expel sweat into the lumen
What two layers make up the excretory duct of the eccrine gland?
Dark staining cuboidal epithelial cells
What does the excretory duct of the eccrine gland lack?
Myoepithelial cells
Where in the body are apocrine glands found?
Mainly in the axilla and groin
Where is the secretory compartment of the aporcine gland located?
In deep reticular dermis or subcutis
How is the secretion of the apocrine gland carried to the upper part of the hair folicle?
A duct system
What shape is the secretory gland of the apocrine gland?
A coiled tubular type with a widely dilated lumen
What shape are the apocrine glands secretory cells?
Low cuboidal, eosinophilic cytoplasm
What is between the secretory cells and the basement membrane of the apocrine gland?
A discontinous layer of myoepthilial cells
What is the dermis composed of?
Bundles of collagen fibres and strands of elastic fibres embedded in acellular ground substance
What do fibroblasts in the dermis do?
Synthesise collagen, elastic fibres and the matrix
What are the two layers of the dermis?
Superficial papillary dermis
Deeper reticular dermis
What is the papillary dermis?
Loose, contains fine interlacing collagen (red) and elastic fibres (black)
What else does the papillary dermis contain?
Arterioles, capillary loops and venules as well as lymphatics
What is the reticular dermis?
Generally a thicker layer, interface may be poorly defined
