Studied by 4 peopleWhat is the largest, single organ of the body
Skin
How much of total body weight does skin account for?
15-20%
What else is the skin known as?
integument, or cutaneous layer
Epidermis
An epithelial layer of ectodermal origin
Dermis
layer of mesodermal CT
Dermal papillae
projections at the irregular junction between the dermis and epidermis
What do dermal papillae interdigitate with?
invaginating epidermal ridges to strengthen adhesion of two layers
Epidermal derivatives
hairs, nails, sebaceous and sweat glands
Subcutaneous tissue AKA hypodermis
LCT layer containing pads of adipocytes, lies beneath the dermis
What is the function of the hypodermis
binds the skin loosely to the underlying tissues
What are the strata of Epidermis?
Layers of the skin
Where do ducts from a sweat gland enter the epidermis?
From a dermal papilla, and coils to a surface pore through all the strata
__ has coarse bundles of collagen
Dermis
What are important nonkeratinocyte cells in the epidermis?
melanocytes, langerhans cells, tactile Merkel cell
What do nonkeratinocyte cells mean?
Not skin cells
How is the dermis of THIN skin different?
more cellular, well vascularized, has elastin, less coars bundles of collagen
Epidermis of thin skin usually has how many layers?
4 layers
What are the 4 layers found in thin skin epidermis?
S. Basale, S. Spinosum, S. Granulosum, S. Corneum
Stratum Basale
one-cell thick containing most MIOTIC cells
Stratum Spinosum
synthesis of much keratin and other proteins take place
Stratum Corneum
consists of dead squames composed of mostly keratin
Epidermal S. Spinosum of thick skin have keratinocytes with what?
numerous short cytoplasmic projections
What type of junctions are present between keratinocytes in the epidermis?
Desmosomes
What are intermediate filaments?
cytoskeleton structures
Keratohyaline Granules
large, amorphous masses of protein
How do granules in the S. Granulosum stain?
Basophilic
Keratin filaments are cross-link with what protein?
Filaggrin
What is Filaggrin?
filament associated protein
What happens when tight bundles fill the cytoplasm in the S. Granulosum?
flattening of cells
What small organs can be found in the S. Granulosum?
lamellar granules
What so lamellar organs undergo?
exocytosis
What do lamellar granules secrete?
lipid-rich layer
What is important about the lipid-layer around our skin cells
makes the epidermis impermeable to water
The lipid envelope and the keratin-filled cells determine what?
Physical properties of the epidermis
S. Lucidum
dense, thin layer of differentiated cells from the S. granulosum
What do S. Corneum lose?
nuclei and cytoplasm (meaning that the cells are dead)
Do squames like water?
NO, they are hydrophobic
What are squames bound by?
hydrophobic, lipid-rich intercellular cement
What makes up the S. Corneum?
flattened, keratinized structures called squames
What happens to thick skin at the surface?
they are worn away
What happens to thin skin at the surface?
they flake off
Where are melanocytes found?
are present in the epidermal basal layer
What are the function of melanocytes?
synthesize melanin granules
Where do the melanin granules usually travel?
into neighboring keratinocytes of the basal and spinous layers
How do melanocytes stain?
pale-staining on the BM, with lower melanin content than the keratinocytes
How do melanocytes transfer melanin to nearby keratinocytes?
through their irregular, cytoplasmic processes
What important cell organelle do melanocytes have?
Golgi complexes
What do the golgi complexes do in melanocytes?
they make the vesicles in which the melanin is synthezied
What do vesicles become as they fill with melanin?
Melanin granules
Where do melanin granules accumulate before transfer?
tips of dendritic cytoplasmic extensions
What are Langerhans cells?
dendritic, APCs of the epidermis
What are the functions of Langerhan cells?
comprise an important defense against pathogens and environmental insults
Where do Langerhan cells develop?
bone marrow (after they migrate into blood then into skin)
Where can Langerhans cells be found?
in hair follicles and throughout epidermis
What color do follicles and keratin of epidermis stain?
green
_____ of Langerhans cells detects invading microorganisms
network
How do Langerhans carry out their immune response?
they activate lymphoctyes to mount a collective immune response
Merkel cell
have high tactile sensitivity and function as mechanoerceptors
Where are merkel cells found?
basal epidermal layer
What is the general structure of Merkel cells?
mass of dense-core cytoplasmic granules near the basolateral cell membrane
What are cytoplasmic granules in Merkel cells connected with?
nerve endings
What are the cytoplasmic granules in Merkel cells similar to?
granules of neuroendocrine cells
Elastic fibers decrease in diameter as they approach what?
the epidermis (then insert into the BM)
How do elastic fibers of the epidermis stain?
darkly, distributed aomng the eosinophilic collagen bundles
Skin contains servel types of ____ receptors
sensory
What type of nerve endings are foundin the epidermis?
free
What are the purpose of epidermal free nerve endings?
detect pain and temperature
Root hair plexus
present around the bases of hair follicles in the dermis, detect light touch or movement of hair
Tactile receptors
Meissner corpuscles, Lamellated (pacinian corpsuscles), Krause end bulbs, Ruffini corpuscle
Purpose of Meissner corpuscle
light touch
Purpose of Lamellated (pacinian) corpuscles
detecting pressure and high-frequency vibration
Purpose of Karise end bulbs
for low frequency vibrations/movements
Purpose of Ruffini corpuscles
detecting tissue distortion
Where do hair follicles derived from? Where do they extend into?
epidermis, deep into dermis
Major parts of hair and its follicle
vascularized, nutritive hair dermal papilla, arrector pili
What does the arrector pili muscle do?
pulls the hair erect
Parts of hair structure
Matrix, Medulla, cortex (in root), epithelial and connective tissue sheaths
what is the outermost layer of the hair
thin cuticle
What is the hair cuticle made up of
shingle-like cells
How do Sebocytes undergo terminal differentiation?
filling with small lipid droplets, and then disintergrating near the ducts opening at the hair shaft
Small progenitor cells
more specific than stem cells, they differentiate into a cell having specific function
Where do small progenitor cells proliferate?
Just inside the capsule
Lumen size of eccrine sweat glands?
small lumens
What appearance do eccrine sweat glands have?
irregular, stratified cuboidal appearance
What do apocrine sweat glands produce?
protein-rich secretion with pheremonal properties
Lumen size of apocrine sweat glands
larger than eccrine glands
Where do aprocrine sweat glands open into?
Hair follicles
Major stages of cutaneous wound healing
cut blood vessels bleed into wound, 2. blood clot forms, leukocytes clean wound, 3. blood vessels regrow and granulation tissue forms, 4. epithelium regenerates and CT fibrosis occurs
Fibrosis
phenomena where parenchymal tissue is replaced by CT, involves extensive tissue remodeling
Psoriasis
T cells attack healthy skin cells by mistake, as if to heal a wound or to fight an infection
What are mostly prescribed for psoriasis, and what do they do?
topical corticosteroids, they reduce inflammation and relieve itching
Immune system
provides defense or immunity against infecions agents ranging from viruses to multicellular parasites
What does our immune system consist of?
large, diverse population of leukocytes
Where are leukocytes located?
every tissue of the body and lymphoid organs
Primary lymphoid organs
thymus, bone marrow
Secondary lymphoid organs
adenoids, tonsils, lymph nodes, spleen, peyer's patches, appendix
What happens in the primary lymphoid organs?
Lymphocytes are formed initially
What happens in the secondary lymphoid organs?
lymphocyte activiation and proliferation
MALT cells are?
immune cells located in digestive, repisratory and urogenital mucosae
Lymphoid nodules
small and spherical, contain proliferating B lymphocytes in the secondary structures of MALT
Note
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