Integument Flashcards
What are some functions of the integument?
Barrier for protection, sensation and excretion, thermoregulation, and vitamin D3 synthesis
The integument contains epidermal derivatives including what?
Hair, nails and sebaceous gland
What is the integument composed of?
Epidermis and dermis
What is the epidermis?
Epithelial layer (ectoderm)
What is dermis?
Layer of CT (mesoderm)
What structure is deep to the dermis?
A loose CT layer known as the hypodermis which binds the skin to underlying tissues and corresponds to the superficial fascia
The epidermis consists mainly of what tissue type?
Stratified squamous keratinized epithelium composed of keratinocytes
What are examples of other less abundant cell types in the epidermis?
Melanocytes, Langerhans cells and Merkel cells
What are dermal papillae?
Irregular projections at epidermal-dermal junctions which interdigitate with epidermal ridges to strengthen adhesion
What are the two types of epidermis?
Thick and thin skin
What are characteristics of thick skin?
Palms and soles + fingerprints Five layers (with stratum lucidum)
What are some characteristics of thin skin?
Widespread all over the body
Four layers
Ex. Glands and hair follicles
What are the layers of the epidermis in order from most apical to basal?
Stratum corneum Stratum lucidum (thick skin only) Stratum granulosum Stratum spinosum Stratum basale
Describe the stratum corneum
15-20 layers of squamous keratinized cells filled with filamentous keratin
Cells are anucleated and coated by an extracellular layer of lipids
Fully keratinized cornified cells now called squames and are continuously shed as desmosomes break down
Describe the stratum lucidum
Thin, translucent layer of flattened eosinophilic keratinocytes
Held together by desmosomes
Nuclei and organelles have been lost
Cytoplasm is almost exclusively keratin filaments
Describe the stratum granulosum
3-5 layers of flattened cells
Filled with keratohyaline granules and lamellar granules
Keratinization + lipid rich layer = an almost impenetrable skin barrier
What are keratohyaline granules?
Granules = tonofibrils + flaggrin (bundling protein)
Undergoing terminal differentiation of keratinization
Stain intensely basophilic
What are lamellar granules?
Small ovoid structures containing lipids and glycolipids
Undergo exocytosis and produce lipid rich impermeable layer that protects against water loss
Describe the stratum spinosum
Typically the thickest layer
Polyhedral cells with central nuclei and spiny processes
What do keratin filaments assemble into in the stratum spinosum layer?
Into microscopically visible bundles of tonofibrils
Associate with desmosomes —> result in spiny appearance “prickle layer”
Describe the stratum basale
Single layer of keratinocytes with stem cells interspersed
Mitotically active
Cuboidal/low columnar cells
Contain melanin
What is the stratum basale bound apically by?
Desmosomes
What is the stratum basale bound basally by?
Hemidesmosomes
What is the predominant cell type of the epidermis?
Keratinocytes
What do keratinocytes produce?
Keratins and will produce cornified cells which are full of keratin
What do keratinocytes participate in?
Epidermal water barrier
What processes do keratinocytes undergo?
Keratinization (maturation) and desquamation (being lost or shed)
List characteristics of melanocytes
Produce melanin and transfers it to keratinocytes
Neural crest cell derived
Scattered along the stratum basale
What is melanin?
Pigment protein that protects nuclei from UV radiation
What is the epidermal melanin unit?
One melanocyte maintains an association with a specific number of keratinocytes (1:10)
Describe melanin production
Tyrosinase converts tyrosine to DOPA
DOPA is polymerized into melanin
Reactions occur in a membrane bound pre-melanosomes but as melanin production increases they transition into melanosomes
Ends with pigment donation
What is pigment donation?
The process of melanosomes being transferred to keratinocytes at the end of melanin production
What are Langerhan’s cells?
APCs that provide defense against pathogens
Develop from monocyte precursors
Pale cytoplasm with long processes
Found in the stratum spinosum
Explain epidermal differentiation and replacement
Epidermal cell replacement is initiated by the division of stem cells in the stratum basale
Move upward as they differentiate into keratinized cells
Eventually are lost by exfoliation on skin surface
What is the dermal-epidermal junction?
Uneven boundary with finger like dermal papillae that project into the dermis
Complemented by epidermal protrusions known as epidermal ridges
Hemidesmosomes provide tight interface
Focal adhesions are also present
The dermal-epidermal junction increases in size/number at sites of what?
Mechanical stress
What are the two layers of the dermis?
Papillary and reticular layer
Describe the papillary layer of the dermis
Loose CT immediately beneath the epidermis
Contains vasculature and nerve endings
Describe the reticular layer of dermis
Deep to papillary layer
Dense irregular CT with coarse elastic fibers
Form regular lines of tension called Langer’s lines
What is the subpapillary plexus?
Rich, nutritive capillary network located between the papillary and reticular layers
What is the deep plexus?
Lies near dermis-subcutaneous layer interface
Describe the hypodermis
Loose CT that binds the skin loosely to adjacent organs
Adipocytes vary in number and size based on body regions/nutritional state
The extensive vasculature within the hypodermis promotes what?
Rapid uptake of insulin or drugs injected into this tissue
Sensory receptors of the skin include?
Non-encapsulated and encapsulated receptors
What are Merkel’s cells?
Epithelial tactile cells that function as low threshold mechanoreceptors essential for sensing gentle touch
Abundant in sensitive skin (ex. Fingertips and hair follicles)
List characteristics of Merkel’s cells
Resemble surrounding keratinocytes but lack melanosomes
Contain small golgi derived granules concentrated near the basolateral surface
What are characteristics of Merkel cell carcinoma (MCC)?
Rare and aggressive
Difficult to treat
40x less common than malignant melanoma but 2x mortality rate
What are free nerve endings of the skin?
Located in the papillary dermis and extend into the lower epidermal layers
Respond primarily to high and low temperatures, pain and itching
May also function as tactile receptors
What are Meissner’s corpuscle?
Encapsulated receptors responsive to light touch or low frequency stimuli
Perpendicular to the epidermis in the dermal papillae
Numerous in the fingertips, palms and soles
What are lamellated (Pacinian) corpuscles?
Large encapsulated oval structures found deep in the reticular dermis and hypodermis
Specialized for sensing coarse touch, pressure (sustained touch) and vibration
What are some other locations where Pacinian corpuscles are found?
CT of visceral organs
Wall of the rectum and urinary bladder where they produce pressure sensations when distorted
Describe sebaceous glands
Produce a lipid mixture known as sebum via holocrine secretion (apoptosis) and is discharged into a hair follicle
Where are sebaceous glands abundant?
Face and scalp
Describe characteristics of the sebum produced by sebaceous glands
Waxy mix of triglycerides and cholesterol that lubricates, softens and waterproofs the skin
Describe eccrine sweat glands
Simple coiled glands with a stratified cuboidal duct
Found extensively throughout the skin
Method of secretion is merocrine which is facilitated by myoepithelial cells
What process do eccrine sweat glands participate in?
Temperature regulation via cooling
Evaporation of H2O from sweat on the body surface
What are the components of sweat?
H2O, salt, ammonia, uric acid and mucinogen granules
What are apocrine sweat glands?
Tubular glands with a large lumen and stratified cuboidal duct
Method of secretion is merocrine which is facilitated by myoepithelial cells
Explain the merocrine secretion of apocrine sweat glands
Protein, carb and ammonia rich secretion
Odorless until mixed with bacteria
Become functional at puberty
Describe the hair bulbs of hair follicles
The terminal dilation of a hair follicle
Dermal papilla insert into it providing nutrients via capillaries
What forms the hair matrix?
Keratinocytes which are continuous with the epidermis
Divide and differentiate leading to hair growth
Describe the follicular bulge of a hair follicle
Contains epidermal stem cells
Near insertion of the arrector pilli muscle
What are arrector pilli muscle?
A small bundle of smooth muscle that extends from mid point of the hair root to the papillary layer of the dermis
What causes goose bumps?
Contraction of the arrector pilli muscle which distorts the attached dermis
What are nails?
Highly keratinized cells on a bed of epidermis known as the nail bed
What is the nail root?
The most proximal region of the nail and covers the nail matrix
What is the nail matrix?
Contains stem cells that divide and form keratinocytes
Nail plate remains attached to nail bed
Pushed forward by continuous growth
What is the lunula of a nail?
Crescent shaped white area near the nail matrix
What is the cuticle of a nail?
Extension of the skin covering the nail root
What does it mean if a nail is black or purple that is not due to bruising?
Could be a sign of melanoma
