Skin lecture week 4 Flashcards
True or false: Skin is the largest organ in the body composing 15-20% of body mass. As an organ, it is made up of a combination of tissues (epithelial, nerve, muscle, and CT).
True.
What are the fxns of skin?
- Barrier (to physical, chemical and biologic agents)
- Thermoregulation (homeostasis)
- Conveys somatosensory information from environment to the nervous system
- Immunologic: antigen presentation/processing to effector cells
- Endocrine: secretes hormones, cytokines, and growth factors; converts precursors into Vitamin D
- Excretion: secretion from sweat and sebaceous glands
What are the 3 layers of skin? What is the composition of each layer? What emybryonic tissue layer are they derived from?
epidermis, dermis, and hypodermis. epidermis and dermis are the 2 main layers
epidermis: derived from ectoderm. keratinized stratified squamous epithelium. continuous growth and turnover. is avascular. contains keratinoctyes, melanocytes, and Langerhan’s cells
dermis: derived from mesoderm. dense irregular CT. imparts mechanical support
hypodermis: layer below dermis with variable amounts of adipose tissue separated by CT. insulates and serves as an energy source.
What are somethings found associated with the epidermis (epidermal derivatives, skin appendages)?
hair and hair follicles
sebaceous glands
eccrine and apocrine glands (sweat glands)
mammary glands
nails
note that eccrine glands go all the way to surface of skin while apocrine glands do not. apocrine glands dump their contents into hair follicles
What are the 2 types of skin? How are they classified/what are their differences? Where are the 2 types found in the body?
Thick and thin skin. Thick skin is classified by having a thicker epidermis (thick stratum corneum layer of epidermis). Also, thick skin does not have hair follicles. Thick skin is found on palmar and plantar surfaces while thin skin is everywhere else. Thick skin is adapted for a great amount of abrasion bc is subjected to mechanical stress.
What are the layers of the epidermis? (just list)
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Stratum Corneum
Stratum Lucidum (will not have to ID histologically)
Stratum Granulosum
Stratum Spinosum
Stratum Basale
What is the stratum basale? What is its fxn/contents? What are the fxns of its cell types?
the stratum basale is also known as the germinativum. It is a single layer of mitotically active stem cells resting on a basal lamina that give rise to the main cell type in the epidermis-keratinocytes. The major fxn of keratinoctyes is to form the physical and chemical barrier of skin. They are specialzied for the production of cytokeratin proteins that organize as intermediate filaments (tonofilaments). The stem cells maintain extensive junctional attachments to each other via desmosomes and to underlying CT via hemidesmosomes. Melanocytes are also located in the stratum basale and synthesize melanin pigment from tyrosine. Melnocytes are neural crest cells that migrate to developing epidermis in the embryo. They are clear appearing in histo sections bc they immediately secree melanin for keratinocytes to absorb.
What is the stratum spinosum? What is its fxn/contents?
multiple cell layers thick; spinous processes of keratinocytes attached to each other by multiple desmosomes
What is the stratum granulosum? What is its fxn/contents?
Thin layer (1-3 cells thick) characterized by the appearance of intense basophilic granular staining in keratinocytes due to keratohyalin granules containing the precursor to filaggrin, which later bundles keratin filaments in the stratum corneum
What is the stratum corneum? What is its fxn/contents?
most superficial layer of skin. Thickness varies depending on anatomic location and amount of skin abrasion. Are anucleate cells that lose organelles as they migrate toward the surface. Only contain keratin
Where is the water barrier located in skin and how is it formed?
The water barrier is located at the base of the stratum corneum and is formed by complex arrangement of proteins and lipids secreted by lamellar bodies of the stratum granulosum
What is the life cycle of a keratinocyte? Be sure to discuss difference in pH btwn layers.
Stage 1. basal cells synthesize intermediate filaments (keratin) that bundle together as tonofilaments
Stage 2. keratinocytes in the stratum spinosum layer begin to make lamellar bodies (membrane bound probariier lipds and enzyme containing molecules)
Stage 3. keratinocytes in the granulosum cell layer produce keratohyalin granules and more lamellar bodies which are secreted by exocytosis in the ECM btwn the stratum granulosum and corneum (forming water barrier of epidermis)
Stage 4. stratum corneum cells are keratinized: granule contents released and keratin aggregates into tonofibrils.
Stage 5: pH decreases from deep to superficial layer (pH activates proteases). Controls exfoliation of cells. Proteases cause molecular cascade leading to digestion of desmosomal proteins & detachment of most superficial layer of stratum corneum.
What is the function of melanocytes? Where are they located? What product do they make and what is the fxn of their product? Where are they derived from embryologically?
Melanocytes are derived from neural crest cells that migrate to epidermis. Melanocytes are located in the stratum basale and secrete melanin that is immediately taken up by keratinoctyes via phagocytosis. Melanin abosrbs UV light to protect keratinocyte DNA. Aging is associated with a decrease in melanocytes-increased skin cancer risk
What is skin pigmentation determined by?
Skin pigmentation is primarly dependent on the quanity of melanin in keratinocytes and is regulated by how long melanin granules persis in the keratinocyte before degradation. Lighter skinned people are thought to have melanosomes that are degrated faster than darker skinned people.
What are Langerhan’s cells? Where are they located? What is their fxn? From where are they derived?
Langerhan’s cells are derived from bone marrow and are a part of the mononuclear phagocytic system. They are antigen presenting cells in the epidermis. Upon uptake and processing of an antigen, the migrate and present antigen to T-cell in dermis or migrate to local lymph nodes to present antigens