Integumentary 1 Flashcards
What are the two layers of the integumentary system?
-epidermis and dermis
Epidermis-epithelium + cells
- keratinized stratified squamous epithelium
- derived from ectoderm
Dermis- dense connective tissue
-derived from mesoderm
What is the hypodermis?
Found deep to (beneath). The dermis
-often referred to as the subcutaneous fascia in gross anatomy
What is contained in the hypodermis?
Contains variable amounts of adipose tissue (panniculus adiposus) arranged in lobules and separated by connective tissue septa
Can find hair follicles, glands and mechanireceptors in this layer
In what countries are the hypodermis thick?
Cold countries
What. Are the associated appendages of the hypodermis?
- hair follicles
- sweat glands
- sebaceous glands
- nails
- mammary glands
What are the functions of skin?
Barrier
- immunological role- presents antigens to the lymphatic tissue
- homeostasis-regulation of body temperature and water loss
- Sensory information- samples the external environment and relays this information to the nervous system
- Endocrine functions- secretes hormones, cytokines and growth factors, converts vitamin D into its hormonally active from D3
Excretion- secretes sweat and other products from the body
What is the largest population of cells in the integumentary system?
Keratinocytes
What are the pigments producing cells in the integumentary system?
Pigment producing cells of the epidermis
-makes up about 5% of the cell population
What is the merchankreceptor in the epidermis?
Merkel cells
Merchanoreceptors
- associated with sense nerve endings
- constitutes 6%-10% of cells in the epidermis
What are langerhans cells?
Antigen presenting cells (APC’s)
-plays a role in the immunological function of skin
-accounts fir 2%-5% of cells
What are keratinocytes?
- Constitutes most of the cell types (85%) of the epidermis
- Differentiates. From basal layer, and continues throughout all layers of the epidermis
What are the functions of keratinocytes?
- produces keratin (cytokeratin) - mainly the keratinocytes of stratum basale
- produce keratohylain granules- cells in spinosum & granulosum
- contributes to the formation of the epidermal water barrier
Where are melanocytes located?
Melanocyte to keratinocytes ratio 1:4 to 1:10
-varies according to the region of the body
Where are melanocytes located?
Located in the basal layer (stratum basale)
What are the origins and formations of melanocytes?
Originates from neural crest
- Appear clear with elongated nuclei
- Multiple cytoplasmic processes that extend between keratinocytes
- 1 melanocytes can communicate with up to 40 keratinocytes
- No desmosome connections but are attached to the basal lamina via hemidesmosomes like structures
- lacks keratin filaments
- Cytoplasm contains oval dark staining premelanosomes (responsible for the synthesis of melanin)
What are the functions of melanocytes?
- Produce melanin that is transferred to surrounding keratinocytes (cytocrine secretion)
- UV protection
- Skin color-amount and ratio of melanin types present
- Lighter skinned individuals have increased melanin degradation
-Oxidation of tyrosine to 3,4 dihydroxyphenylalanine (DOPA) and subsequent transformation of DOPA into melanin
How are mature melanosomes formed?
Premelanosomes formed by Golgi-transformed into early melanosomes
Contain tyrosinase molecules and small amounts of melanin
Conversion. Into melanin gradually occurs until the. Mature melanosome is forned
What are the factors associated with skin pigmentation?
-UV Radiation- melanin production is influenced by the surrounding keratinocytes in response to UV radiation
- Melanin distribution- dispersed differently in light vs dark skinned persons
- Light skinned persons- concentrated in stratum basale
- Dark skinned persons- dispersed throughout stratum basale and spinosum
Type of melanin-each type of melanin has a different function and is driven by different genetic factors
- The pigment produced by melanocytes consist of two different forms+eumelanin and pheomelanin
- The ratio between the two determines skin and hair color
Describe eumelanin
Protection against UVR damage
- scatter and absorb UV rays and eliminate UV generated free radicals
- Degrades faster in lighter skinned individuals
Describe pheomelanin
-Allows a greater amount of light to pass through thereby increasing vitamin D production at altitudes where light intensity is low
Found more commonly in atypical nevi and melanomas
Increased oxidative damage
Describe langerhans origins
Originate from common lymphoid progenitor (CLP)
-Present in all epidermal layers but most easily recognized in stratum spinosum
What is the function of langerhans?
Immunological role
- Encounters, processes and expresses antigens (Antigen presenting cell(APC))
- Migrates to the lymph node to present the antigen to T-lymphocytes
- Express both MHC-1 and MHC-2 and receptors for IgG
- Involved in delayed type hypersensitivity reactions
What do Langerhans look like under light microscopes?
Nucleus stain well with hematoxylin (blue)
Cytoplasm is clear
Describe the TEM structure
Nuclear membrane- indented structure making the nuclear profile uneven (“N” On right TEM image)
Possesses tennis racquet shaped granules (Birbeck granules)-
- small linear (rod-like) structure with a bublbous expansion (vesicle) at one end
- regular cross striations
- function unclear but may be part of the endosome system
Describe the structure of Merkel cells
- least numerous cell structure after langerhans cell
- most abundant in skin where sensory perception is acute (fingertips )
- closely associated with the expanded terminal bulb of afferent myelinated nerve fibers- Merkel’s corpuscle
What is the function of Merkel cell?
Detect touch sensations
Have desmosomes and contain keratin filaments
Nucleus is lobed
Cytoplasm contains neurosecretory granules
Possess antigenic markers of both epidermal and neural type
What is the distinction between thick and thin filaments?
This is made on the thickness of the epidermis
Summarize thick skin
- found only in the palms and soles
- usually hairless and much thicker epidermis
- carries a stratum lucidum
Summarize thin skin
- Found everywhere else
- thinner epidermis than thick skin
- Hair follicles are widespread except for a few locations
Summarize the epidermis
Stratified squamous keratinized epithelium
5 layers
-stratum basale-can differentiate
- stratum spinosum- maturing and slowly dying cells
- stratum granulosum- cells that are about to die
- stratum lucidum- thick skin only
- stratum corneum- dead keratinized cells
Describe stratum basale
Single layer of cuboidal to low columnar cells
- mitotically active
- keratinocytes stem cells (stratum germinativum )
- Merkel cells
- melanocytes
- noticeable basophilia on H&E staining
Describe stratum basale staining
Small cells with scant basophilic staining cytoplasm
- nuclei closely spaced
- contains many melanin granules
- synthesize keratin filaments
Where are stratum basale connected to and located?
Rests on the basal lamina
Attached by hemidesmosomes
Extensive other anchoring cell junctions
Desmosomes
Clinical correlations: bullous pemphigod
Describe stratum spinosum
Several cell layers thick
Keratinocytes are larger than those in the stratum basale
Make cytokeratin/keratin filaments
Exhibit numerous cytoplasmic processes or spines
- Prickle cell layer
- Processes of neighboring cells are connected to each other via desmosomes
- Appears as a slight thickening and is known as node Bizzozero
How do stratum spinosum cells change?
Gradually change their appearance as they move closer to the surface
-Increase in size and become flattened in a plane parallel to the surface
What are the noticeable cells of the stratum spinosum?
-most noticeable in the most superficial layer of cells- nuclei become elongated instead of ovoid
- Keratinocytes in uppermost part of this layer
- begin to produce keratohyalin granules
- lamellar bodies
- Langerhans cells
- Also found predominantly in this layer, but are able to move freely throughout epidermis
Clinical correlation: pemphigus vulgaris
Describe stratum granuosum
Most superficial of the no keratinized cells
Averages 1-3 cell layers thick
Contains conspicuous granules which give them a granulated appearance
- keratohyalin granules
- Irregular shaped, variably sized, stains intensely basophilic
- Cystine and histidine rich proteins= precursors for fillagrin
- Responsible for aggregating the keratin filaments within the cornfied cells
What are the keratinocytes of the stratum granulosum?
Keratinization (soft keratin)
-loss of organelles, thickened cell membrane, decreased pH
Lamellar bodies
-epidermal water barrier