E3: Skin Flashcards
Describe the basic functions of the skin
Skin Functions
1. Protection
- Physical barrier against thermal & mechanical insults (i.e. friction) & against most potential pathogens.
- MO’s that penetrate the skin alert resident lymphocytes & APC’s, triggering an immune response
- Dark pigment melanin in the Epidermis protects cell nuclei from UV-radiation
- Permeability barrier against excessive loss/uptake of water
- Selective permeability allows for some lipophilic drug administration
2. Sensory
- Sensory receptors allow for constant monitoring of the external environment
3. Thermoregulation:
- Insulating components (fatty layer & hair)
- Mechanisms for accelerating heat loss (sweat production & a dense superficial microvasculature
4. Metabolism
- Cells of the skin synthesize Vitamin D3 through the local action of UV light on the vitamins precursor
- Excess electrolytes can be removed in sweat
- Subcutaneous layers can store energy in the form of fat
5. Sexual Signaling*
- Skin features (i.e. pigmentation & hair) are visual indicators of health
Describe the Major layers of the Epidermis (Deep to Superficial)
Layers: Deep to Superficial
- Stratum Basale
- Stratum Spinosum
- Stratum Granulosum
- Stratum Lucidum* (not covered; only in Thick skin)
- Stratum Corneum
What are the components present in the Epidermis
Cells:
Keratinocytes:
- Highly proliferative cells which synthesize Keratins
- Progressively move towards surface as new cells proliferate and “push” older cells up
- Continuously accumulate Keratin granules
- Eventually, they lose their nucleus and retain only Keratin granules
- Exfoliated at the top
Melanocytes:
- Synthesize Melanin
Sensory receptors:
Merkel cells:
- Mechanoreceptors;
- Sense; Fine touch
Free nerve endings:
- Senses; Pain, temperature, touch
- Extends into the Epidermis
Describe the basic movement & action of cells in the epidermal layers
Where does mitotic activity end?
Where does Keratinization begin?
Mitotic activity ends at S. Granulosum
Keratinization begins at S. Spinosum
Describe the Stratum Basale
Stratum Basale:
- Single layer of basophilic cuboidal or columnar cells
- Anchored to the BM @ the Dermal-Epidermal junction via Hemi-Desmosomes
Cell types:
- Primarily Keratinocytes
- Stem cells
- Melanocytes
- Merkel cells (sensory)
Explain Melanocytes & Melanin function
Melanin Synthesis:
In Melanocytes:
- Synthesis occurs in vesicles (Melanosomes)
- Melanosomes are transported to the tips of the Melanocytes
- Tips are phagocytosed by Keratinocytes
In Kerertinocytes:
- Melanosomes surround the nucleus; providing a protective barrier for the nucleus against UV radiation
Describe the Stratum Spinosum
Stratum Spinosum:
- Typically the thickest layer
- Polyhedral cells w/ central nuclei
- Cytoplasm actively synthesizing Keratins
- Connected by desmosomes which gives rise to the “Spines” when shrinkage occurs
Cells;
- Primarily Keratinocytes
-
Langerhan’s cells
- Immune Cell: Permanent Resident APC
- Neutrophils (as needed)
- Only enters when infection is present
ID this tissue
What are the cells present actively synthesizing?
What forms the connections between them and what are they referred to?
Epidermis: Stratum Spinosum
Polyhedral cells actively synthesizing Keratins
- Connected by desmosomes which gives rise to the “Spines” when shrinkage occurs
Explain Vitamin D
Vitamin D:
Function:
- Major role in calcium homeostasis;
- Increases intestinal absorption of calcium
Synthesis:
- Keratinocytes in the Stratum Basale & Granulosum synthesize the Vitamin D pro-hormone in response to UVB
- The prohormone is then activated in the liver/kidney
Sources:
- Major: Skin
- Other:
- Dietary: vitamin D3 (cholecalciferol) & vitamin D2 (ergocalciferol) found in fatty fish, egg yolks and from supplements
Describe the Stratum Granulosum & Corneum
Stratum granulosum:
- Consists of 3-5 layers of flattened cells
- Undergoing Keratinization
- Last layer of nucleated cells
- Abundant keratin granules -> Color
Stratum corneum:
- Consists of 15-20 layers of Squames (Squamous, Keratinized cells w/o nuclei)
- Bags of keratin w/o nuclei
Skin turnover (desquamation)
Slows down with age:
- Babies: 2 weeks
- Adults: 1 month
- Over 50 : > 2 months
What is the primary difference between thick and thin skin?
S. Spinosum is larger/thicker in thick skin
*S. Lucidum Present
Explain Nail formation
Nail Formation:
- Similar process of keratinization
Cuticle:
- Extension of the epidermis
Nail plate:
- Formed from the nail matrix
- Contributes keratinized cells to the nail
- Bound to a bed of epidermis
- Lunula is opaque because it is immature
Describe the components of the Dermis & major structures
(2) Major subsections:
-
Papillary dermis
- Supports the epidermis
- Dermal papillae intertwine with rete ridges (pegs))
-
Reticular dermis
- Loose CT
Consists of:
- Nerves:
- Meissner Corpuscles
- Pacinian Corpuscles
- Hair follicles
- Sweat glands
What is the structure ID’ed here?
Where is it located?
What is it’s function?
Meissner’s corpuscles
- Located in Dermal papillae
- Senses: light touch
What structure is pictured here?
Where is it located?
What is it’s function?
Pacinian corpuscles:
- Located in the Deep dermis
- Senses Pressure
- Looks like an onion in cross section
What are the components of the Pilosebaceous unit?
Where are they located & where are they not?
Pilosebaceous unit:
- Widespread over the body
- Except Glabrous skin (hairless skin)
Includes;
1. Hair bulb/follicle and shaft
- Keratinized structures formed by Epidermal invaginations
- Base: Hair bulb
- Indentation: Hair Papilla
- Blood vessels to nourish Hair
2. Arrector pili muscle
3. Sebaceous gland
Describe the sebaceous glands & their function
Where do they secrete their product?
Sebaceous Glands:
Function:
- Secrete sebum directly into shaft
- Sebum (high lipid content)
- Holocrine secretion
Appearance:
- Foamy cytoplasm (like brown fat)
What are the (2) types of Sweat glands?
How are the Acini & Ducts distinguished?
Eccrine:
- Function: skin cooling
- Location: Widely distributed
- Develop from the Epidermis
- Simple coiled gland
Apocrine:
- Develop at puberty
- Axilla and perineum
- Open into hair follicles
- Larger lumens than eccrine glands
- Stress responsive (adrenaline)
- Odorless until bacterial processing
- Contains pheromones
Histology:
Secretory acini (pale)
- Modify interstitial fluid to make sweat
Ducts (darker)
- Stratified cuboidal -2 layers
- Stain darker than surrounding acini
- Absorb Na+ and Cl- ions from sweat to maintain electrolyte balance
- Defective in CF: Salty sweat
ID the tissue in this image
The hypodermis (Subcutaneous) layer
How does skin change with age?
Age-related: dermal & epidermal atrophy
- You lose thickness of the skin when you age, making it easier to damage at a later age
UV-Elastosis: abnormal deposition of elastin-blue/grey aggregates
Describe the process of wound healing.
Where can Infections occur?
Skin Damage:
Repair Steps;
1. Re-epithelialization:
- Stem cells
2. Granulation tissue: (immature CT)
- Dermal fibroblasts become myofibroblasts after injury
- Contractile - reduces the size of the wound
Infections occur EVERYWHEREEE
What are the characteristics of Psoriasis?
Epidermis (whole):
- Acanthosis: diffuse epidermal hyperplasia (thickening of skin)
- Implies increased thickness of S. Basale & S. Spinosum
Stratum Corneum:
- Perakeratosis; Nuclei retained
- Large amount of Neutrophils
Stratum Granulosom:
- Larger/paler than normal
Dermis:
- Neutrophilic absesses
- Enlarged capillaries
- Prominent Dermal Papillae w/ thinned overlying suprapapillary plates
Describe the characteristics of Melanoma
Melanoma:
- Cancer of melanocytes within the Stratum Basale
Late-stage Melanomas:
- Homogenous appearance of Epidermis & Dermis;
- No distinct layers
**Serum; oozes out due to lack of dessecation control
- Crust formation
Describe the characteristics of Ringworm
Ringworm: Tinea Corporis
- Caused by a fungus that infects the SC
- Fungus forms filaments that are divided into “cells” by cross-walls (septae)
Manifestations:
- Inflammatory response in SC
- Neutrophils*?
- Fungal filaments in s.Corneum (PASD)
- Appear Black in GMS stain
Describe the characteristics of Bullous Pemphigoid
Bullous Pemphigoid:
- Autoimmune condition
- Eosinophilic attack of hemidesmosomes @ Dermal-Epidermal Junction (DEJ)
- Results in dissociation of Epidermis from Dermis
- Immunoflourescent Anti-IgG Ab:
- Concentrated @ DEJ
•Indicates IgG is targeting Hemidesmosomes
