Lecture 3- Histology of the Skin Flashcards
Skin Functions
- Protection against physical/chemical/biological attacks
- Water barrier
- Thermoregulation (conservation/dissipation of heat)
- Defense barrier to microbes
- Excretion of salt
- Vitamin D synthesis
- Sensory organ
General Organization of Skin: the 3 layers
3 layers firmly attached to each other
- Epidermis: outermost, from ectoderm
- Dermis: deeper, from mesoderm
- Hypodermis/Subcutaneous layer
General Organization of Skin
Surface of palms/soles have narrow epidermal ridges separated by furrows
- each epidermal ridge corresponds to dermal papilla, are permanent/unique, create finger prints
- Dermal-epidermal junction has primary epidermal ridge, interlocks w primary dermal ridge, subdivides it into 2 secondary dermal ridges
- Some dermal papillae project upward and interlock w downward projections from epidermis (Hairless, thick skin)
- Thin skin has less and smaller dermal papillae
Stratum Basale
- aka stratum germinativum
- deepest layer, single layer of cuboidal to low columnar cells on basement membrane
- Have nucleus and keep dividing to replace superficial cells
Stratum Spinosum
- 2nd deepest, made of many layers of polyhedral cells that have desmosomal bridges w other cells
- contain Langherhans (combat foreign organisms) cells and processes Melanocytes (pigment producing)
Stratum Malpighi
-Name for layers 1 and 2, responsible for cell renewal
Stratum Granulosum
- Flat cells that contain Keratohyaline granules
* absent in thin skin`
Stratum Lucidum
- Thin, transparent layer whose cells have eleidin (a transformation product of keratohyalin
- Cells lack nuclei bc are filled w keratin
- absent in thin skin
Stratum Corneum
-Made of squames that are densely packed w keratin
Keratinocytes
- Most predominant cell type
- All 5 layers
- produce keratin (IF protein)
Melanocytes
- Melanin production
- Deplete w age, skin gets lighter, more prone to skin cancer
- neural crest
Langerhans Cells
-Antigen trapping cells, interact w T cells
Merkel Cells
- tactile sensations
- neural crest
Keratin
-IF protein in all epithelium
-a helical, rod shaped
K5 and K14 in basal keratinocytes
K1 and K10 in stratum spinosum
Dermis
- CT deep to epidermis w vessels, hair follicles, sweat glands and sensory receptors
1. Papillary layer: superfical layer of irregular CT - Dermal ridges -Dermal papillae, capillary loops, Meissners corpuscles -Free nerve endings
2. Reticular layer: deeper layer of denser irregular CT - Thicker layer -Pacinian corpuscles -Ruffinis corpuscles
Blood Supply to Skin
- Role in nutrient supply and thermoregulation
1. Cutaneous Plexus: arteries and veins found at dermo-hypodermal junction
2. Sub-papillary plexus: located in papillary layer of dermis, capillary loops extend into papila and result in convective heat loss/epidermis nutrient supply
3. AV shunts: between 1 and 2. Supplied by sympathetic nerves, restrict flow through superficial plexus to reduce heat loss in extreme cod
Epidermis vs Dermis
Epidermis: -highly cellular -little ECM -avascular
Dermis: -predominantly ECM
-low proportion of cells
-highly vascularized
Sensory Receptors
Meissner Corpuscles: Dermal papila, tactile receptor
Merkel Cell: Basal layer of epidermis, tactile receptor
Free nerve endings: no myelin or schwann cells, pain and temp
Ruffini end organs: in skin and joint capsule, stretching
Pacinian corpuscle: hypodermis and deep fascia,, pressure
Peritrichial nerve ending: base of hair follicle, hair movement
Hair
- Composed of shaft of cornified cells and a root contained w in hair follicle
- associated w sebaceous gland, called pilosebaceous unit
- Arrector pili muscle attaches to hair follicle
Hair growth
Anagen: Growth period, 80% of hair in anagen phase
Catagen: brief period of follicle regression or involution, 3 weeks
Telogen: inactive phase, 14%
Sweat Glands
- Simple, coiled, tubular glands
- produce sweat delivered to surface via long ducts
- secretory portions surrounded by myoepithelial cells
Sebaceous Gland
- Branched, acinar, holocrine glands
- produce oily secretion (sebum)
- secretion delivered into lumen of hair follicle
Epidermolyis Bullosa Simplex
- Mutated K5 & K14 (affacts basal keratinocytes)
- weak keratin filaments
- blisters in area of trauma
- mild
Epidermolytic Hyperkeratosis
- Mutated K10
- keratinocytes in spinosum/granulosum lyse in response to trauma
- thick,scaly skin, blisters
Psoriasis
- Increase in proliferating cells
- decreased mitotic cycle time (7days instead of 20-30)
- causes epidermal thickness = thick scaly skin
Ichthyoses
-hereditary
-thickening of corneum
Due to: 1. increased cohesiveness of corneum
2. defective keratinization from keratin gene mutations 3. increased mitotic activity in basal keratinocytes
Malignant Melanoma
-Skin cancer that stems from melanocytes (in basal layer of epidermis)
Mole: benign cluster of melanocytes, can become malignant and are then melanoma
-most virulent skin cancer
Squamous Cell Carcinoma
- Dermal invasion by abnormal cells of epidermis
- pleomorphism (different cells at different stages) of tumor cells
- kerartinization w/in cells = pink cytoplasm
Bullous Pemphigoid
- Blister formation
- auto-immune response against proteins associated w desmosomes/ hemi-desmosomes
Junctional Epidermolysis Bullosa
- Blisters at epidermal basal lamina
- mild to severe, fatal by 2
- due to gene mutations for structural proteins
Acne Vulgaris
- inflammatory disorder of pilosebaceous unit
- excessive keratinization w/in the unit causes excessive sebum production = blockage of ducts in follicle
- anaerobic bacteria grow in accumulated sebum = localized inflammation/neutrophil infiltration
