SFP: histology of the skin Flashcards
What are the main functions of the epidermis
-Protection (physical barrier)
-Thermoregulation
-Sensory (interacting w environment)
-Metabolism (regulating electrolytes via sweat)
-Sexual signaling (visual indicator of health and attractiveness; pheromone production)
What are the layers of the skin
Epidermis, dermis, subcutis
Name the layers of the epidermis from superficial to deep
-Stratum corneum
-Stratum lucidum
-Stratum granulosum
-Stratum spinosum
-Stratum basale
Corny little grandpa sings badly
Which cells make up the majority of the epidermis
keratinocytes
Describe the stratum basale: general structure, connection to the basement membrane, function, other elements found
A single layer of cuboidal cells attached to the basement membrane via hemidesmosomes. They are the progenitor cells of the epidermis, so there is a lot of mitosis here. We can often find cytoskeletal keratins and melanocytes
Describe the stratum spinosum
Has lots of keratinocytes connected by desmosomes. Keratin is synthesized in the cytoplasm and assembled into tonofibrils
Describe the stratum granulosum
3-5 layers of flattened keratinocytes undergoing keratinization. The cytoplasm has keratohyaline granules with filaggrin and Golgi-derived lamellar granules containing lipids and glycolipids
Describe the stratum lucidem
Only found on thick skin and is composed of flattened eosinophilic keratinocytes held together by desmosomes
Describe the stratum corneum
15-20 layers of keratinized squamous cells with no nucleus. They’re filled with filamentous keratin and typically arranged in a basket weave pattern.
Describe melanocytes
They are dendritic cells found in the basal layer that make melanin to give to keratinocytes
What is the major function of melanin
Protect us from UV damage
What is eumelanin
Brown-black pigment
What is phaeomelanin
Melanin pigment found in red headed individuals
Describe melanin synthesis
-Tyrosine is converted to 3,4 DOPA
-DOPA is polymerized into melanin
-Melanin accumulates in vesicles to form melanosomes
-Melanosomes are transported via kinesin to tips of dendrites
-Keratinocytes phagocytose melanosomes and are transported to the nucleus by dynein
Describe Langerhans cells
They are dendritic cells that serve as antigen-presenters and are found in the stratum spinosum; they’re basically epidermal macrophages
Describe Merkel cells
They’re epithelial tactile cells that can sense gentle touch
Briefly describe the dermis
A layer of connective tissue that supports the epidermis, vasculature, and adnexal structures
What are the layers of the dermis
Papillary dermis and reticular dermis
Describe the papillary dermis
Loose connective tissue with type I and III collagen
Describe the reticular dermis
Thicker connective tissue with type I collagen and elastic fibers
What are the layers of the vascular plexus
Superficial: capillaries just below the epidermis
Deep: larger vessels and lymphatics
What are the unencapsulated receptors
Merkel cells, free nerve endings, and root hair plexus
meissner corpuscle: encapsulation and function
encapsulated and responds to light touch; found in the papillary dermis
pacinian corpuscle: encapsulation and function
encapsulated; pressure and vibration
krause end bulbs: encapsulation and function
encapsulated; low frequency vibration. found in the penis and clitoris
ruffini corpuscle: encapsulation and function
encapsulated; senses tissue distortion (ex: edema)
Describe the subcutis
Layer of fat between the dermis and superficial fascia; thickness is variable
Describe hair follicles
Specialized invaginations of the epidermis
What is the arrector pili muscle
Smooth muscle that can control hair position
Name the 3 phases of the hair growth cycle
-Anagen: growth, 2-7 year duration, 85% of hairs
-Catagen: 2-3 weeks duration, less than 15% of hairs
-Telogen: resting and shedding, 100 day duration, less than 1% of hairs
What is the dermal papilla
It inserts into the hair bulb at the base of the follicle. The cells here divide rapidly and keratinize here
Where does hair acquire melanin
cortex
What are the three layers of hair
-Medulla: in the center and made of moderately keratinized cells
-Cortex: heavily keratinized cells surrounding medulla
-Cuticle: thin outer layer of heavily keratinized squamous cells
What are sebaceous glands
Sweat glands associated with hair follicles; found everywhere but palms of hands and soles of feet. They’re acinar glands comprised of sebocytes that converge on a duct that empties into the follicle
What is the method of secretion in sebaceous glands
Holocrine; the cells proliferate, accumulate lipids, kill themselves and puke out their contents
Describe eccrine sweat glands
The most numerous; they’re responsible for sweating. They utilize merocrine secretion. Their ducts absorb sodium ions to prevent excessive water loss.
What are the cell types found in eccrine glands
Clear cells: product sweat
Dark cells: filled with eosinophilic granules that undergo merocrine secretion
Myoepithelial cells: contract to move secretions
Describe apocrine glands
Limited to the axilla and groin; associated with smelly sweat
Label the basic components of the nail unit
Nail plate: hard keratin derivative
Nail matrix: specialized cells divide and become keratinized and mature into nail plate
Nail bed: epithelium below nail plate
