skin and its appendages Flashcards
Functions of skin
• Protection against physical, chemical and biologic agents in external environment
• Regulation of body temperature and water loss
• Reception of continual sensations from environment (touch, temperature and pain)
• Functions in excretion through the exocrine secretion of glands
• Absorption of ultraviolet light from the sun for synthesis of vitamin D
• Clinical uses: diagnosis of conditions such as jaundice, anemia and rash & medications- dermal patches, ointments and injection
What in hypodermis
▪Loose connective
tissue
▪Not part of the skin
adipose tissue with eccentric nucleus
What is epidermis
• Derived from ectoderm
• Lined by stratified squamous keratinized
• Consists of four population of cells
• Keratinocytes
• Non keratinocytes:
• Melanocytes
• Langerhans cells
• Merkel cells or epithelial tactile cells
What layers of keratinocyctes (from deep to superficial)
▪ Stratum basale or germinativum
▪ Stratum spinosum
▪ Stratum granulosum
▪ Stratum lucidum (seen only in thick skin)
▪ Stratum corneum
• Skin is classified as THICK and THIN according to the thickness of the epidermis & presence or absence of certain layers of keratinocytes and skin appendages.
diff of thick skin and thin skin
Thick
Presence of all five layers of keratinocytes
Presence of eccrine sweat glands
Thin
Lacks of stratum lucidum; other layers are thinner
Presence of hair follicles, arrector pili muscles, sebaceous glands, eccrine and apocrine sweat glands
Stratum basale or germinativum
• Deepest layer in epidermis
• Consist of a single layer of basophilic cuboidal to low columnar cells with a large nucleus
• Cells exhibit extensive cell junctions by desmosome and hemidesmosome
• Cytoplasm is rich in ribosomes; also contains various amounts of melanin is transferred from melanocytes
• Cells produce intermediate filaments or tonofilaments (cytoskeletal keratins)
• Serve as stem cells for cell regeneration or renewal, increased mitotic activity is seen in this layer
stratum spinosum
• Consists of several layers of polyhedral to flatten cells having central nuclei with nucleoli and eosinophilic cytoplasm; numerous cytoplasmic processes (spines)
• Cells are anchored to each other by spines that represent the attachment sites of desmosomes; also called as prickle cells
• Cells continuously produce tonofilaments which are grouped into bundles i.e. tonofibrils, more in upper layers
• Cells of stratum spinosum that just above the stratum basale are still actively dividing
what is malphigian layer
Malphigian layer: stratum basale & stratum spinosum
stratum granulosum
• Three to five layers of flattened cells
• Cells still retain their nuclei
• Cytoplasm contains large basophilic keratohyaline granules & lamellar granules formed by lipid bilayers
• Combination of tonofibrils with keratohyaline granule proteins produces keratin, the process is called keratinization
• Lamellar granules are discharged into the intercellular spaces between stratum granulosum and stratum corneum, as a lipid- rich impermeable water barrier around the cells
stratum lucidum
• Found only in thick skin, just above the stratum granulosum
• Consists of a lightly staining, thin layer of flattened dead cells without nuclei and organelles; cells are held together by desmosome, contains densely packed keratin
stratum corneum
• Most superficial layer
• Consists of numerous layers of flattened dead cells filled almost entirely with keratin, no nuclei and organelles
• These keratinized or cornified cells, called squames are continually shed or desquamated at the epidermal surface as desmosomes break down
Melanocytes
• Neural crest cell derivatives
• They have a rounded cell body with clear cytoplasm (arrow) which reside in stratum basale and extends long processes between cells keratinocytes (not seen in H&E stains)
• Secrete yellowish brown to black melanin pigment for skin colouration
• Melanosomes containing melanin form a supranuclear cap to protect the nucleus from excessive ultraviolet light
langerhans cells
• Antigen presenting cells
• Originate from bone barrow and migrate via bloodstream to enter epidermis
• Mainly found in stratum spinosum, also in upper dermis
• They are pale-staining cells with irregularly lobulated and almost clear cytoplasm in H&E stains, posses dendritic processes
• Function in immune system: they recognize, phagocytose, process and present antigens to T lymphocytes
merkel cells
• Found in stratum basale, numerous at finger tips and base of hair follicles
• They are rounded cells, cytoplasm contains dense core-neurosecretory granules
• Make synaptic junction with sensory nerve twigs in upper dermis
• Function as mechanoreceptors for light touch
dermis
• Derived from mesoderm
• Composed of connective tissue
• Its surface is irregular has many projections, dermal papillae that interdigitate with epidermal projections i.e. epidermal ridges
• Interdigitation of epidermal ridges with dermal papillae firmly interlocks the epidermis and dermis interface, mainly in the skin subject to frequent pressure e.g., palms & soles
Dermis, 2 layers
papillary (P) and reticular (R) layers
what papillary layer (dermis)
• Papillary layer:
• Consists of loose connective tissue with collagen, reticular, elastic fibres and cells of connective tissue, blood vessels, nerves, lymphatics
• Contains Meissner corpuscles (M),
the mechanoreceptors for light M touch, numerous in fingertips,
palms and soles
* capillary loops provide nutrients for the avascular epidermis and aid in regulating body temperature
what reticular layer (dermis)
Reticular layer (R):
• Consists of dense irregular connective tissue with more fibres and fewer connective tissue cells than the papillary layer (P)
• Contains Pacinian corpuscles (PC), the mechanoreceptors that detect pressure and vibration
eccrine sweat glands
•Develop as downgrowth of surface epithelium into dermis and hypodermis
• Found deep in dermis and hypodermis of both thick and thin skin throughout most of the body
• Glands begin to function soon after birth
• Play a role in thermoregulation & also serve as an excretory organ
eccrine sweat glands components
• Simple coiled tubular glands
• Secretory component (SS):
• Clear cells: large columnar or pyramidal cells
with central oval nuclei and pale eosinophilic SS cytoplasm; secrete watery sweat
• Dark cells: smaller darker-staining cells that contain secretory granules; best identified by a special stain; secrete mixture of glycoproteins with bactericidal activity
• Myoepithelial cells (arrows): spindle shaped cells that support the secretory component of the glands by forming a discontinuous layer between secretory cells and basement membrane; their contraction is responsible for excretion of sweat
• Duct component:
• Excretory duct (D) has a smaller diameter than secretory component & no myoepithelial cells
• Excretory ducts are lined by stratified cuboidal epithelium:
• Cells are smaller and appear darker (more acidophilic) than secretory cells consisting of a basal cell layer and a luminal cell layer
• Excretory ducts ascend through dermis and epidermis to the skin surface and open at the sweat pore
what method of secretion eccrine sweat glands
merocrine
apocrine sweat glands
• Develop from the epithelium of hair follicles
• Found in the deeper portions of the dermis and hypodermis of the thin skin in certain locations: axilla, areola of nipple, anal region
• Secretion is under the influence of sex hormones and does not begin until puberty
• Secretory product of apocrine glands is odourless upon secretion, but when metabolized by bacteria, it presents a distinctive odour.
components of apocrine sweat glands
• Simple coiled tubular glands
• Secretory components (S) have wider and dilated lumen than those of eccrine sweat glands
• Secretory cells: low cuboidal with eosinophilic cytoplasm, apical cells show a budding appearance (B); cells also surrounded by myoepithelial cells (My)
• Ducts (Ds) are similar to those of eccrine sweat glands, but open into hair follicle canal
• Secretion may contain protein-rich product
method of secretion apocrine sweat glands
merocrine
sebaceous gkands
• Simple branched acinar glands
• Secretory component: acini are composed of peripherally located flattened small basal cells surrounding a mass of larger rounded cells packed with lipid-filled vacuoles
• Ducts of sebaceous glands are short and open into the upper third of the canal of hair follicle, where they discharge their secretory product to coat the hair shaft
• In certain regions of body lacking hair follicles i.e. lips, glans penis, areola of nipples, labia minora, ducts open directly onto skin surface
• Secrete sebum to facilitate the maintenance of proper skin texture and hair flexibility
method of secretion sebaceous glands
holocrine
hair follicles
• Tubular structure formed of epithelium and perifollicular connective tissue (CT)
• At the base, there is the hair bulb, enclosing hair papilla (DP)
• Epithelial cells around the hair papilla proliferate to form layers of hair follicle
five concentric layers hair
• Five concentric layers:
• Hair [Cx: cortex, M: medulla, Cu: cuticle]
• Epithelial sheath [IRS: internal root sheath] • Epithelial sheath [ERS: external root sheath
what is arrector pili muscle
• Arrector pili muscle (AR), a small bundle of smooth muscle cells extending from connective tissue sheet surrounding the external root sheet of the hair follicle to the papillary layer of the dermis
• Contractions of these muscles depress the skin over their attachment and elevate the hair shaft and the skin around the hair shaft, forming tiny “goose bumps”
nails
• Hard plates of keratin on dorsal surface of distal phalanx
• Nail root develops from the nail matrix; is covered by cuticle (eponychium)
• Nail root matures and hardens as the nail plate
• Nail plate is bound to nail bed; continuous growth in the matrix pushes the nail plate forward over the nail bed
• Distal end of nail plate is free of nail bed at the epidermal fold called the hypochonium
what are innervation and nerve endings of skin
• Efferent: nonmyelinated fibres from sympathetic component of autonomic nervous system supplying blood vessels, arrector pili muscles and sweat glands
• Afferent: myelinated and nonmyelinated fibres that transmit impulses from various sensory nerve endings to CNS
• Free nerve endings
• Pacinian, Ruffini, Meissner corpuscles; Krause end bulbs
