L22. Skin Flashcards
Name characteristics of the skin
- largest organ in the body
- waterproof and protective
- regulates body temperature
- sensory receptors for pain, pressure and touch
What are the 2 layers of the skin
- epidermis
2. dermis
Describe the epidermis
- stratified squamous keratinized epithelium
- contains specialized cell types
- Merkel cell
- Langerhan cells
- melanocytes - gives rise to specialized skin appendages
- sebacous and sweat glands
- hair follicles
Where is the epidermis derived from ( which germ layer)
ectoderm
Which germ layer is the dermis derived from
mesoderm
Describe the dermis
- underlying layer of dense irregular connective tissue
- blood vessels
- sensory nerves
- temperature, pain, touch ( Meisner’s corpuscles)
- deep pressure sensors ( Pacinian corpuscles)
What are Pacininan Corpuscles , and where are they found
deep, reticular layer of the dermis
What are the Meisner corpuscles, where are they located
pain, temperature and touch receptors, located at dermal ridges which are the papillae
What is the hypodermis
loose Connective tissue and adipose tissue
What is the function of the hypodermis
connects skin to underlying tissue and organs
Identify all structures on page 3 of L21. ( draw the stratum corneum , stratum spinosum and stratum basale)
pg 3 L 21
Identify all features of the epidermis
pg 4 L 21
What are the 5 layers of the epidermis ( name from outer to inner)
- stratum coneum
- stratum lucidum
- stratum granulosum
- stratum spinosum
- stratum basale
Describe the stratum basale
- stem cells that are undifferentiated
- high mitotic activity
- cell-cell adhesions with desomosomes
- cubodial to low columnar epithelial cells/keratinocytes
- hemidesmosomes at cell-basement membrane interface of the stem cell phenotype
- as the basal keratinocytes move up the stratum layer they begin to differentiate
- contains melanocytes and merkel cells
Why are hemisdesmosomes important in the stratum basale
- needed for attachment of epidermis to dermis layer
2. maintain stem cell phenotype
What is the function of melanocytes? Describe the melanocytes
- produce skin pigments
- are neural crest derived
- migrate into epidermis where they reside in the basale
What are the functions of the Merkel cell? Describe their function
mechno/touch receptors, are neural-crest derived. migrate into the epidermis and reside in the stratum basale
Describe the stratum spinosum
- are differentiated epithelial keratinocytes
- cells begin to produce large numbers of tonofilaments
- desmosomes are prominent in the cell-cell interaction points at the end of the small keratinocyte cell-processes
What are tonofilaments
keratin intermediate fibers
What are lagerhan cells
- antigen producing cells
- migrate into the epidermis , reside in the stratum spinosum layer
- hematopoietic stem cell derived
Describe the stratum granulosum
- cells begin to fully differentiate and become squamous
- lipid rich vesicles/granules are made and secreted between s. granulosum and s. lucidum
- produce proteinacious ‘keratohyaline’ that forms cytoplasmic ‘granules’ (not membrane-bound/vesicular) cross links the tonofilament
Describe the stratum lucidum
- last layer of living cells
- above the water proof layer this cells fully differentiate to produce ‘eleidin’ a protein that aligns cross-linked keratin tonofilaments in // arrays
- cells above water proof layer begin to die and lose their nuclei
Describe the stratum corneum
- enucleate flat cells that are already dead
- filled with protective cross-linked and bundled keratinized filaments =squames
- desmosomes deteriorate ; squames are slough-off/released =desquamated
What ar squames?
protective cross linked and bundled keratinized filaments
Where is the S. Cornuem and S. Lucidum most prominent ?
In soles of feet and palms ( no hair follicles)
Describe the hair follicle
- invagination of the epidermis that pushes down into the dermis
- follicle terminates at the hair root which is indented by the dermal papilla which supplies blood vessels and nerves to the area of the hair root.
- the outer external root sheath of the hair follicle consists of a modified stratum basale and stratum spinosum
- inner internal root sheath of hair follicle consists of differentiating stratum grnulosum-like cells ( they are orderly arranged , move inwards and die to produce the hair shaft )
Describe the sebacous gland
- forms as an outpouching of the hair follicle epidermis above the hair bulb.
- secretory portion is alveolar
- secretes sebum ( pale staining on HE)
- mode of secretion is by necrosis ( death of cell to release all contents)
- ducts may branch slightly and empty into the hair canal
How does acne form?
obstruction of sebacous glands’ ducts leads to bacteria infection -> acne
Where is the hair canal?
small space between the fully formed hair shaft and follicular epithelium
What are arrector pilli
smooth muscle fibers that anchor to the dermal connective tissue that surrounds the hair follicle
- under autonomic control
- generate raised hair
Draw the structure of the hair ( pg14 L 22)
pg 14 L22
Describe the eccrine sweat glands
- simple coiled tubular glands that form as invaginations of the epidermis
- widely distributed in the skin; secrete sweat with a slight mucous content by regular polarized , exocytosis based secretion
- secretory portion of tubules, have contractile cells which are ectodermally derived
- contractile cells help to expel secretory products into ducts efficiently
Where are myoepithelial cells found
present in mammary gland
