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60 Cards in this Set

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Size of skin:
Largest organ in the body.

15-20% of body weight

1,5- 2 square meters
Skin consists of:
Epidermis (from ectoderm)
Dermis (connective tissue layer from mesoderm)
Hypodermis (subcutaneous):
Loose connective tissue layer beneath the skin, mainly consists of adipocytes.
Functions of the skin:
Protection
Sensory
Thermoregulation
Metabolic
Sexual signaling
Protective function of skin:
Physical barrier (friction, pathogens, water loss etc.)
Sensory function of skin:
Sensory and mechanoreceptors
Thermoregulation by skin:
Insulting (fat, hair)
Sweating+ superficial vasculature
Metabolic function of skin:
Produce vit. D needed in calcium metabolism and proper bone formation.

Removal of excess electrolytes
Sexual signaling of skin:
Visual indicator of health--> attraction

Sex pheromones produced by apocrine sweat glands
Dermatoglyphs:
Finger and footprints
Main cells of epidermis:
Keratinocytes (stratified squamous keratinized epithelium)

Melanocytes (pigment producing)

Langerhan`s cells (antigen presenting)

Merkl`s cells (tactile epithelial cells)
Thick skin:
On palms and feet

Thicker epidermal layer (up to 400 micrometers in contrast to up to 150 micrometers in thin skin)
Epidermis consists of 4 layers (5 in thick skin):
1. Stratum basale
2. Stratum spinosum
3. Stratum granulosum
4. (Stratum lucidum- thick skin)
5. Stratum corneum
Stratum basale:
Columnar- cuboidal cells
Basophilic (intense mitotic activity)
Bound to basal lamina by hemidesmosomes
Bound to Stratum spinosum by desmosomes
Stem cells for keratinocytes
Renewed every 15-30 days
Keratin intermediate filaments
Stratum spinosum:
Polyhedral or flattened cells
Central nuclei
Actively synthesizing keratin filaments
Keratin filament bundles called "tonofibrils"
Thicker in thick skin
Skin cancers are most common in which layers of the skin:
Basal layer--> basal cell carcinoma

Spinous layer---> squamous cell carcinoma
Stratum granulosum:
3-5 layers of flattened polygonal cells undergoing terminal differentiation
Cytoplasm filled with basophilic keratohyaline granules (linked to cytoplasmic structures, important in keratinization)
Lamellar granules with lipids (protect against water loss)
Stratum lucidum (only in thick skin):
Translucent layer of flattened cells
Cytoplasm of dens packed keratin filaments (eosinophilic)
No nuclei or organelles
Desmosomes still present
Stratum corneum:
15-20 layers of flattened nonnucleated keratinized cells
Cytoplasm filled with filamentous keratins
After keratinization the cells contain only proteins with thick plasma membrane
What is responsible for skin color?
Melanin
Carotene
Vascularization
Melanocyte:
Neural crest origin
Located in stratum basale
Round cell bodies, hemidesmosomes with basal lamina
NO desmosome with keratinocytes
Many mitochondrias, well developed golgi, short cisternae RER
Ratio melanocyte/ keratinocyte in stratum basale:
1 melanocyte/ 5-6 keratinocytes
Malignant melanoma:
Rapidly dividing melanocyte penetrate basal lamina and enter dermis and invades blood and lymph vessels---> metastasis
Synthesis of melanin:
Tyrosinase are transmembrane proteins synthesized in RER and located in vesicles in Golgi. Tyrosinase converts tyrosine--> DOPA--> polymerization---> melanin (which accumulates in vesicles called melanosomes)
Function of melanin:
Function as a supranuclear cap of keratinocytes which absorbs and scatter sunlight to protect nuclear DNA from UV radiation
Mechanism of tanning:
UV radiation causes keratinocytes to secrete paracrine factors that stimulate melanocyte activity---> increased rate of melanin synthesis and transfer to keratinocyte+ UV darkens preexisting melanin.
Transport of melanosomes to keratinocytes:
Via kinesin along microtubules to actin- rich tips of melanocyte`s dendrites. Keratinocytes of basal and spinous layer phagocytose these tips and the granules fuse with lysosomes. Then keratinocytes microtubules with dynein transport them to the nucleus of keratinocytes.
Stratum corneum cells:
Mostly fully differentiated and lost nuclei and cytoplasm.
Consist of flattened, keratinized structures called squames bound by hydrophobic, lipid- rich intercellular cement and at the surface they are worn away (thick skin) or flake (thin skin).
Albinism:
Melanocytes lack tyrosinase activity or lack the possibility to take up tyrosine.
Dendritic (Langerhans) cells:
Usually in spinous layer
Derived from bone marrow
APC- presents antigens to T- lymphocytes (adaptive immunity)
2-8 % of cells in the epidermal layer
Tactile (Merkel) cells:
Mechanoreceptors (similar to pale staining keratinozytes)
Located in basal epidermal layer
Derived from neural crest
Merkel cell carcinoma is 40 times less common then melanoma but twice the mortality
Dermis:
Connective tissue that supports epidermis
Binds to hypodermis
Papilla that reinforce the dermal- epidermal junction in areas of great friction
Determine embryological development of epidermis
Basal membrane between dermis and epidermis.
Nutrient diffuse from dermis to avascular epidermis
Papillary layer of dermis:
Loose connective tissue
Fibroblasts
Mast cells
Macrophages
Anchoring fibrils of type VII collagen insert into basal lamina (binds dermis to epidermis)
Reticular layer of dermis:
Thicker
Irregular dense connective tissue (type I collagen)
More fibers and fewer cells then papillary layer
Elastic fibers
Derivatives (hair and glands)
Rich supply (NO parasympathetic)
Subcutaneous tissue:
Loose connective tissue that binds skin loosely to adjacent organs allowing the skin to slide over them.
Fat
Two major plexuses supply skin:
1. Deep at the interface between hypodermis and dermis

2. Superficially between the papillary layer and reticular layers of dermis.
Arteriovenous anastomoses and its relation to thermoregulation:
Located between the two plexuses, and decrease blood flow in the papillary layer to minimize heat loss in cold, and increase blood flow to stimulate blood flow.
Lymphatics in skin:
Lymphatic vessels begin as closed sacs in the derma papillae and converge to form two plexuses located within the blood vessels
Uncapsulated sensory receptors:
Tactile discs (epidermal tactile cells, responsible for light touch)

Free nerve endings in papillary dermis and epidermis (temp, pain, itching)

Root hair plexuses (web around bases of hair follicles, detect movement of hair)
Encapsulated sensory receptors of skin:
Tactile corpsules (Meissner corpsules)- perpendicular to epidermis in dermal papilla (light touch)

Lammelated (Pacinian) corpsules- deep in reticular dermis or hypodermis, lamellae of Schwann- type cells and collagen (sustained touch)

Krause corpsules- dermis (pressure and low frequency vibrations)

Ruffini corpsules- dermis (continuous pressure and tissue distortion)
Distribution of hairs in face VS. rest of the body:
Face: 600 hairs/ square meter

Rest of the body: 60 hairs/ square meter
Hair growth:
Discontinuous :
Growth periods: anagen
Follicle regression period: Catagen
Period of inactivity: telogen
Hair bulb: terminal dilatation of hair follicle in growth period (a dermal papilla insert and has high blood supply)
Epithelial cells/ keratinocytes of hair bulb are similar to:
Those in the basal spinous layers of epidermis
Hair cuticle:
Thin layer of heavily keratinized cells covering the cortex
What separates hair follicles from dermis?
An acellular hyaline layer, the thickened basement membrane called the glassy membrane
Arrector pili muscle:
Muscle running from dermal papillary layer to connective tissue sheath of hair follicle. Contraction causes erection of hair---> trapping of warm air near the skin
Cells of hair proliferates, take up melanin granules and undergoes keratinization from:
The matrix
Differens in keratin and keratinization between hair and epidermis:
Harder and more compact keratin in hair then in stratum corneum and keratinization in hair is intermitted not continuous.
What causes white color of lunula?
From the nail matrix and immature nail plate below it.
Hyponychium:
Where the free end of nail plate is bound to epidermis.
Classical example of holocrine secretion, in which the whole cell dies and contributes to the secretion:
Sebum secretion from sebaceous glands
Location of sebaceous glands:
Dermis of whole skin except thick skin of palms and soles
Sebaceous glands:
Branched acinar glands with several acini converging at a short duct which usually empties into the upper portion of a hair follicle
At some places sebaceous glands open directly to the skin surface:
Hairless regions:
- genital glands
- eyelids
- nipples
Sebocytes:
Lipid producing
Small fat droplets in cytoplasm
Is terminally differentiated
Differentiate from a basal layer of flattened undifferentiated layer of epithelial cells on the basal lamina in the acinus
Loose nuclei
Sebum:
wax esters
squalene
cholesterol
TAG

Hydrolyzed by bacterial enzymes after secretion (smell from sweat). Secretion stimulated by androgens
Function of sebum:
Maintaining stratum corneum and hair
Weak antibacterial and anti fungal functions
Acne:
A chronic inflammation and obstruction of sebaceous glands during and after puberty, caused by disturbances in normal secretion and flow of sebum (which should be continuous)
Eccrine sweat glands:
Most numerous on soles of feet
Coiled secretory portions and ducts with thin lumen
Pale pyramidal or columnar clear cells produce sweat by transporting interstitial fluid directly from capillary in dermis to the duct
Have abundant mito and microvilli
Lumen is lined by dark pyramidal cells which do not touch basal lamina (mucoid cells)
Myoepithelial cells on basal lamina
Ducts have Na+/K+ ATPase to resorb Na+ to avoid excess Na+ loss
Cholinergic innervation
Apocrine sweat glands:
Axilla and perineal region
Development (but not function) depends on sex hormones
Have much larger lumen then eccrine
Secretory portion: simple cuboidal eosinophilic cells (apical secretory granules)
Have MEOCRINE, NOT apocrine secretion
Open into hair follicles
Innervated by adrenergic nerve endings