Integument Flashcards
What is Integument?
Outer covering of body, such as skin and related things such as hair and nails
What is the purpose of the integument?
Barrier for protection, sensation, excretion, thermoregulation, vitamin D3 synthesis
What is the integument made up of?
Epidermis (ectoderm) and dermis (dermatome of the paraxial mesoderm)
What is deep to the dermis layer and what is its function?
Hypoderm - loose connective tissue that binds skin to underlying tissues and corresponds to superficial fascia
What type of epithelium is the epidermis?
Keratinized stratified squamous epithelium
What is at the epidermal-dermal boundary?
Epidermal ridges and dermal papillae that form a zipper like structure that strengthens adhesion!
Describe the attributes of thick skin
Found on palms and soles of feet, 5 layers, fingerprints, 400-1400 microM thick
Describe the attributes of thin skin
Widespread over the body, 4 layers, glands and hair follicles, 75-150 microM thick
What are the epidermal layers from deep to superficial?
Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only thick skin), stratum corneum
What are the epidermal cell types?
Keratinocytes, melanocytes, merkel cells and langerhans cells
What is the most prominent cell type in the epidermis?
Keratinocytes
What do keratinocytes do?
Produce keratins that strengthen the epidermal water barrier and will produce cornufied cells full of keratin.
Also undergo keratinization and desquamation
What is keratinization?
Process of a keratinocyte maturing to the outer layer of epidermis
What is desquamation?
Shedding of keratinocytes
Stratum Basale defining features
Single layer of keratinocytes with stem cells interspersed; contains melanin
Bound basally by hemidesosomes and apically by desosomes - deepest layer of epidermis!
Stratum Spinosum defining features
Thickest layer!
Polyhedral cells with spiny processes; keratin filaments assemble into tonofibrils here - “prickle layer”
Stratum granulosum defining features
3-5 layers of flattened cells
Filled with keratohyaline granules and lamellar granules whose products create an almost impenetrable skin barrier
What is unique about keratohyaline granules?
They stain intensely basophilic and the granules then undergo terminal differentiation of keratinization
What do lamellar granules contain?
Lipids and glycolipids that undergo exocytosis and produce a lipid-rich layer that protects against water loss
Stratum lucidum defining features
ONLY IN THICK SKIN!
Thin, translucent layer of flattened keratinocytes and cytoplasm is mostly keratin filaments
Stratum corneum defining features
15-20 layers of squamous keratinized cells that are anucleate
What are squames
Fully keratinized “cornified” cells that are continuously shed as desosomes break down; housed in the stratum corneum
What do melanocytes do?
Produce melanin and transfer it to keratinocytes
What is melanin and where is it derived from?
Pigment protein that protects nuclei from UV radiation
NCC DERIVED
How many keratinocytes does 1 melanocyte associate with?
About 10
Describe the process of melanin being formed and transferred to keratinocytes
Tyrosinase converts tyrosine to melanin in premelanosomes
As the melanin accumulates the premelanosome turns into a melanosome where it can now be transferred to keratinocytes
What are langerhans cells?
Antigen presenting cells that phagocytose and present foreign materials to lymph node cells
Found in the stratum spinosum
What initiates epidermal cell replacement?
Stem cells in the stratum basale
What causes the number of epidermal ridges and dermal papillae to increase?
Sites of increased mechanical stress
What are the layers of the dermis?
Papillary layer and reticular layer
Describe the papillary layer
Loose CT beneath epidermis that contains vasculature and nerve endings
Describe the reticular layer
Dense irregular CT that forms regular lines of tension known as the Langer’s lines – cut along them to increase healing capablities
Subpapillary plexus
Capillary network between papillary and reticular layers that supplies nutrients to the epidermis
Deep plexus
Capillary network near dermis-subcutaneous (hypodermis) boundary that supplies nutrients to the dermis
What is the function of the hypodermis (subcutaneous) layer?
Loose CT that binds skin to subjacent organs
What is the clinical relevance of the hypodermis?
It contains varying numbers of adipocytes and an extensive vasculature promotes rapid uptake of injected drugs
What types of sensory receptors does the skin have?
Encapsulated and non-encapsulated
What are merkel cells?
Low threshold mechanoreceptors essential for sensing gentle touch; abundant in finger tips and hair follicles
How would you differentiate a merkel cell?
Lack melanosomes, contain small golgi-derived granules near the basolateral surface
What is merkel cell carcinoma?
A rare, aggressive, difficult to treat cancer
40X less common than malignant melanoma but it is 2X more deadly
Free nerve endings
Located in papillary dermis and lower epidermal layers; respond to temperature, pain, itching
Meissner’s corpuscle
Encapsulated receptors that respond to light touch or low freq. stimuli
Perpendicular to epidermis in dermal papillae; found in fingertips, palms, soles
Lamellated (pacinian) corpuscle
Large encapsulated receptors that respond to coarse touch, pressure, vibrations
Found deep in reticular dermis and hypodermis; also rectum wall and bladder
Sebaceous glands
Abundant in face and scalp; produce a lipid mixture = sebum via holocrine secretion
Lubricates skin, and discharged into hair follicle
Eccrine sweat glands
Found throughout skin, stratified cuboidal duct;
Myoepithelial cells facilitate expulsion
Temperature regulation via cooling
What is sweat made of?
H2O, salt, mucinogen, ammonia, uric acid
Apocrine sweat glands
USE MEROCRINE SECRETION - odorless until mixed with bacteria
Stratified cuboidal duct, myoepithelial cells facilitate expulsion, functional at puberty
What is the terminal dilation of the hair follicle and what inserts?
Hair bulb and dermal papilla inserts into that hair bulb to provide nutrients
What causes hair growth?
Keratinocytes dividing and differentiating
What does the follicular bulge contain?
Epidermal stem cells; near the insertion of arrector pili m.
Arrector pili m.
Smooth muscle that extends from midpoint of hair root to papillary layer in dermis and when contracts, hair stands up “goose bumps”
What are nails made of?
Highly keratinized cells on bed of epidermis
Nail root
Most proximal; covers nail matrix
Nail matrix
Stem cells divide and form keratinocytes, pushed forward by continuous growth
Cuticle
Extension of skin covering nail root
What is merocrine secretion?
secretion delivered via membrane bound vesicles that undergo exocytosis
What is holocrine secretion?
secretion delivered once secretion builds up within the cell and apoptosis releases the cell contents
