HISTO P2
- physical barrier against thermal and mechanical insults(friction)
protection
- constantly monitor the surroudings
- mechanoreceptors regulate the body's interaction with physical obejcts
sensory
- constant body temperature is maintained due to the skin's insulating components (fatty layer and hair)
- mechanism for accelearating heat loss (sweat production and dense superficial microvasculature)
thermoregulation
- synthesis of Vit D3 through the local of UV light on vitamin D precursor
- excess electrolytes are removed through sweat
metabolic
- pheromones produced by apocrine sweat glands and other glands
sexual signaling
consist mainly of keratinized stratified squamous epithelium composed of cells (KERATINOCYTES)
epidermis
pigment producing cells
melanocytes
resident macrophages, and antigen-presenting cells
langerhans cells
tactile epithelial cells
merkel cells
- a single layer of basophilic cuboidal or columnar cells located on top of the basement membrane at the dermal-epidermal junction
basal layer/stratum basale
- situated just the basal layer
- thickest layer, specially in the epidermal ridges
- consist of polyhedral cells having central nuclei with nucleoli and cytoplasm actively synthesizing keratins
spinous layer/stratum spinosum
- keratin filaments or "tonofibrils" holds the cells together. They are seen as intercellular bridges
- "spines" or prickles at the cell surfaces
- increased in areas subjected to continuous friction and pressure (foot soles)
spinous layer/stratum spinosum
- three to five layer of flattened cells, undergoing terminal differentiation of keratinization
- cytoplasm is filled with intensely basophilic masses
granular layer/ stratum granulosum
- found only on thick skin (sole of feet, palm of hands)
- composed of thin, translucent layer of flattened eosinophilic keratinocytes held together by desmosomes
- nuclei and organelles are lost
- cytoplasm consist almost exclusively of packed keratin filaments
stratum lucidum
- consists of 15-20 layers of keratinized, squamous cells filled with keratin
stratum corneum
- specialized cells in the epidermis found among the cells of the basal layer and in hair follicles
- neural crest derivatives that migrate into the embryonic epidermis' stratum basale in a 1:6 ratio
- pale-staining round cell bodies attached by hemidesmosomes at the basal lamina, but lacks attachment to the lateral borders
melanocytes
- inside the melanosome
- transported toward the nucleus forming a nuclear cap
- protecting the nucleus from harmful effects og UV radiation
melanin
- Melanocyte + Keratinocyte into which it transfers melanosome
- Number of unites in skin is the same in all individuals
- Rate of production of melanin and rate of accumulation inside the keratinocytes differ between individuals
Epidermal-Melanin Unit
- Antigen-presenting cells, derived from monocytes
- 2-8% of the cells in the epidermis and most are seen in the spinous layer
- Cytoplasmic processes extend in between keratinocytes of all layers
- Bind, process, and present antigens to Tlymphocytes for recognition (adaptive immunity)
Langerhans Cells
- Epithelial tactile
- cells Low threshold mechanoreceptors: gentle touch
- Abundant in highly sensitive areas (fingertips and base of hair follicles)
- Located in the stratum basale Attached to the keratinocytes by desmosomes
Merkel Cells
- Few melanocytes but abundant in Golgi-derived dense-core granules
- Synaptic contacts with nerves located at the basal lamina
Merkel Cells
- Layer of connective tissue that supports the epidermis and binds it to the subcutaneous tissue (hypodermis)
- Has irregular projections (dermal papillae) at the surface that interdigitate with projections of the epidermis (epidermal ridges or pegs) to form the dermal-epidermal junction
- Provide nutrients to the epidermis through its rich vasculature through the basement membrane
DERMIS
- Includes the dermal papillae (dermal projections)
- Loose connective tissue: type I and III collagen fibers, fibroblasts and scattered mast cells + Dendritic cells + Leukocytes
- Anchoring fibrils of type IV collagen (basement membrane) binds the dermis to the epidermis
Papillary Dermis
- Thicker and composed of dense irregular connective tissue with more fibers than cells compared to the papillary dermis
- Network of elastic fibers is also present, providing elasticity to the skin.
- Rich in dermatan sulfate (a proteoglycan of connective tissue)
Reticular Dermis
- Located in between the papillary dermis and the reticular dermis
- Plexus: network of blood vessels and nerves
Subpapillary Plexus
Located in between the reticular dermis and the subcutaneous tissue
Larger Plexus
- Thermoregulatory function
- Located between the 2 plexuses
Arteriovenous anastomoses/shunts
Forms a network in the papillary dermis and around hair follicles
Sensory Afferent Nerve Fibers
Sweat glands and smooth muscle fibers in the skin
Autonomic Efferent Nerve fibers
- Subcutaneous Layer, Superficial Fascia
- Loose adipose connective tissue that binds the skin loosely to the underlying muscle.
- Adipocytes, thin connective tissue fibers
- Its extensive vascular supply promotes rapid uptake of injected drugs (insulin, vaccines).
HYPODERMIS
- The skin functions as an extensive receiver of various stimuli from the environment
- Diverse sensory receptors are present
- Encapsulated Receptors
- Unencapsulated Receptors
SENSORY RECEPTORS
- Elliptical structures located at the papillary dermis arranged perpendicular to the epidermis
- Consist of sensory axons winding among flattened Schwann cells
- Initiate impulses when light touch or low frequency stimuli against skin temporarily deform their shape.
- Numerous in fingertips, palms and soles, decline in aging
MEISSNER CORPUSCLE
- Large oval structures deep in the reticular dermis and hypodermis
- Concentric lamellae of flattened Schwann cells and collagen surrounding a highly branched unmyelinated nerve fibers
- Specialized in sensing coarse touch, pressure (sustained touch), and vibrations
- Also found in the walls of rectum and urinary bladder, where they produce sensation of pressure
PACINIAN CORPUSCLES
- Have collagenous fusiform capsules anchored firmly to the surrounding connective tissue
- Stimulated by stretch (tension) or twisting (torque) in the skin
RUFFINI CORPUSCLES
- Are simple encapsulated, ovoid structures with extremely thin, collagenous capsules penetrated by a sensory fiber
- Found primarily in the skin of penis and clitoris
- Sense low frequency vibrations
KRAUSE END BULBS
- Elongated keratinized structures that form within epidermal invaginations, hair follicles
- Grows discontinuously, with periods of growth followed by periods of rest.
HAIR
– a generally long period of mitotic activity and growth
Anagen
– a brief period of
arrested growth and regression
of hair bulb
Catagen
– a final long period of inactivity, during which hair may be shed
Telogen
– the terminal dilatation of hair follicle
Hair bulb
– portion of hair that is embedded in the dermis
Hair root
– visible extension of hair at the surface of the epidermis
Hair shaft
- Penetrates the base of the hair bulb,
- Contains vasculatures supply nutrients and oxygen for proliferating and differentiating cells.
Dermal hair papilla
central portion of hair composed of large, vacuolated and moderately keratinized cells
Medulla
Surrounds the medulla Composed of heavily keratinized, densely packed cells
Cortex
Most peripheral cells of the hair root Composed of heavily keratinized squamous cells covering the cortex
Cuticle
- Internal root sheath
- External root sheath
Epithelial tissue root sheath
- Surrounds the hair follicle
- Separates the hair follicle from the dermis
Connective Tissue Root Sheath
– an cellular hyaline layer composed of thickened basement membrane
Glassy Membrane
- A small bundle of smooth muscle cells
- Extends from the midpoint of the fibrous sheath t the dermal papillary layer
- Contractions pulls the hair shafts to a more erect position
- Produced also by keratinization
- Hard plates of keratin on the dorsal surface of each distal phalanx
Arrector pili muscle
- proximal part of the
Nail root
- Covers the nail root
- An extension of the epidermal stratum corneum
Cuticle (Eponychium)
- Embedded in the dermis over most of the body
- Branched acinar glands converging at a short duct
SEBACEOUS GLANDS
- Filled with small fat droplets (sebum)
- Sebum covers the surfaces of both the epidermis and hair shafts.
Sebocytes
- Complex mixture of lipids
- Increases greatly at puberty, stimulated primarily by testosterone in men and ovarian and adrenal androgens in women.
- Maintains the stratum corneum and hair shaft
- Exerts weak antibacterial and antifungal properties
Sebum
Develop as long epidermal invaginations embedded in the dermis
SWEAT GLANDS
- Widely distributed, most numerous on foot soles.
- Produces sweat, a physiologic response to increased body temperature
- Both secretory and duct are coiled with small lumens
ECCRINE SWEAT GLAND
– located on basal lamina, have abundant mitochondria and microvilli
Clear cells
– filled with strongly eosinophilic granules
Dark cells
– contract to move watery secretion into the duct
Myoepithelial cells
- Largely confined to the axillary and perianal regions
- Development depend on sex hormones and is not complete and functional until after puberty.
APOCRINE SWEAT GLAND