Integument Flashcards
What is the integumentary system?
Skin and its epidermal derivatives
What are the skin (cutis, integument) layers?
Epidermis
Dermis
What are the epidermal derivatives of skin?
Hair follicles and hair
Sebaceous glands
Sweat (sudoriferous) glands - eccrine and apocrine
Nails
Mammary glands
What is the hypodermis made up of?
Subcutaneous fascia
Mostly white fat
Also has CT septa, sensory receptors, vessels, and nerves
What are the functions of the skin?
Barrier that protects the body
Homeostasis - regulates body temperature and water loss
Sensory organ
Excretion of exocrine products
Endocrine organ
Selective absorption
What are the characteristics of thin skin?
Most skin is thin skin
Epidermis is thin and has 4 layers (strata)
Thicker dermis than thick skin
Has eccrine and sometime apocrine sweat gland, sebaceous glands, hair.
Surface lacks alternating ridges and grooves
Fewer nerve endings and fewer sensory receptors than thick skin
What are the characteristics of thick skin?
Skin of palms and soles
Epidermis is thick and has 5 layers. Thinner dermis than thin skin
Only has eccrine sweat glands
Lacks sebaceous glands, hair
Surface has alternating ridges and grooves
Always sensitive - many nerve endings and sensory receptors
What is the function of thick skin?
Protects against damage
Increased ability to grip surfaces and objects
Increased sensitivity for object manipulation and where our body weight contacts ground
What are characteristics about epidermis?
Keratinized stratified squamous epithelium - avascular, from ectoderm, and 4-5 strata
Grows continuously, but thickness is consistent - new cells added to basal layers via mitosis at same rate cells are lost from superficial layers (desquamation)
Contact with dermis is very distinct - locks both layers in place and reduces risk of epidermal delamination
What are the 5 epidermal strata?
Stratum corneum - thin/thick, flaky, superficial layer
Stratum lucidum - thick skin only
Stratum granulosum - thin/thick
Stratum spinosum - thin/thick
Stratum basale - thin/thick, basalmost layer
What are the cells of the epidermis and their function?
Keratinocytes
Synthesize a type of keratin called soft keratin
Help form the epidermal water barrier by synthesizing and secreting lipids and soft keratin also contributes
What are the names and functions of other keratinocytes?
Basal cells - stem cells that generate new keratinocytes (stratum basale)
Prickle cells - synthesize keratin protein (stratum spinosum)
Granular cells - synthesize lipids and undergo keratinization (stratum granulosum)
Keratinized cells - forms a physical barrier of dead cells (stratum lucidum and stratum corneum), in stratum corneum they are called squames
What are the characteristics of the stratum basale?
Single layer of cells in contact with BM
Deepest layer of epidermis
Cells are mainly basal cells - stem cells of epidermis and are cuboidal and divide to create new keratinocytes
Other cells include melanocytes that make melanin and Merkel cells that are mechanoreceptors
What are the characteristics of the stratum spinosum?
second thickest stratum
Several to many layers of tightly linked cells
Spiny appearance
Most cells are prickle cells that make lots of keratin that aggregate into tonofilaments
Intercellular bridges extend between adjacent cells
Other cells include Langerhans cells (dendritic cells) which are antigen presenting cells
What are the characteristics of the stratum granulosum?
3-5 layers of flattened cells - cells in most layers are alive, cells in superficial layer are dying and those that finish dying cross into stratum lucidum/corneum
All cells are granular cells
What is the function of granular cells in the stratum granulosum?
Undergo keratinization - named for intensely basophilic keratohyalin granules in cytoplasm
Synthesize lipid components of epidermal water barrier - has organelles called lamellar bodies that synthesize and store lipids that help waterproof skin
What are the characteristics of stratum lucidum?
Only in thick skin
1-2 indistinct, homogenous layers of cells
Cells lack visible organelles/granules - stains acidophilic or is unstained
All cells in this layer are dead keratinocytes called keratinized cells - fully keratinized with no visible nuclei, granules, or other organelles
What are the characteristics of stratum corneum?
Most superficial stratum
Several to many layers of flattened and desiccated dead cells
Change in pH moving from basal layers to the surface
All cells are dead keratinocytes called keratinized cells or squames (horny cells) that are fully keratinized with no visible nuclei/organelles and no desmosomes
Where is stratum corneum thickest?
Areas subject to higher amounts of friction, shearing forces, or focal pressure (calluses and corns)
What is desquamation or exfoliation?
Cells on surface are sloughed off or worn off by abrasion
Describe the process of keratin synthesis
All living keratinocytes of the epidermis synthesize a type of keratin called soft keratin
Prickle cells synthesize LOTS of keratin protein and aggregate it into bundles called tonofilaments
Granular cells are where keratinization occurs - as apoptosis begins, filaggrin and tricohyalin surrounded and crosslink keratin tonofilaments and form water insoluble tonofibrils
What are keratohyalin granules?
Clusters of proteins filaggrin and tricohyalin in the cytoplasm of granular cells
What is keratinization?
Process of converting all keratin tonofilaments into tonofibrils
Keratinized cell cytoplasm is mostly tonofibrils and other water insoluble proteins that create a mechanically strong barrier
How is the epidermal water barrier formed?
Lamellar bodies synthesize and store lipids that help waterproof skin
Granular cells secrete lamellar body contents into ECM of stratum granulosum and deepest corneum
Lipids form waterproof barrier but also prevent nutrient diffusion to cells so superficial layer of stratum granulosum starve and it initiates apoptosis
Proteases are activated by low pH in superficial layer of stratum corneum which degrades desmosomes and allows desquamation
What are the functions of melanocytes?
Cell bodies in basale and long processes extend into spinosum
Synthesize melanin (endogenous pigment) in specialized organelles called melanosomes (melanin granules)
Multistep process that involve oxidation of tyrosine
Melanin absorbs UV radiation
Where does melanin migrate to after being made?
Melanosomes synthesize melanin and migrate to tips of melanocyte cell processes
Tips of processes exocytosed into ECM of spinosum and phagocytosed by prickle cells
Melanosomes released into prickle cell cytoplasm and aggregate along superficial side of nucleus
Forms dark umbrellas of melanin that shield nuclear DNA in dividing cells from UV radiaiton
How do we get differences in skin pigmentation?
Melanocyte number and ratio of melanocytes to prickle cells vary in different part of the body
Melanocyte number and ratio of melanocytes to keratinocytes very similar across all people
Exposing skin to sunlight promotes melanin synthesis in melanosomes
Differences in baseline skin pigmentation among people of different skin tones and races results from difference in the number, size, and distribution of melanosomes, and rate of melanin breakdown
In darker skin tone, melanosomes are ______
Larger and more numerous
Distributed throughout prickle cell cytoplasm
Present in more cells/layers of the stratum spinosum
Rate of melanin breakdown is slower
In lighter skin, melanosomes are ______
Smaller and less numerous
Only accumulate in umbrella of cytoplasm above nucleus
Not in superficial layer of stratum spinosum
Rate if melanin breakdown is faster
If sun exposed (tanned), melanosome distribution becomes similar to darker skin
What are Merkel cells?
In stratum basale
Mechanoreceptors that likely transmit fine/detailed touch sensation about shape and texture
Associated with sensory nerve endings with flat, expanded ends (merkel discs)
What is the Merkel cell + nerve ending?
Merkel corpuscle
Both parts are the mechanoreceptor
What are Langerhans cells and their function?
In stratum spinosum
Antigen presenting cells and part of immune response to contact allergens - they present epitopes to T lymphocytes to initiate delayed type hypersensitivity reactions
Actively defend the skin versus the bacteria that causes leprosy
What is the function and characteristics of the dermis?
Strong tissue layer that provides structural support to the skin
Vascularized CT and rich in collagen I fibers and elastic fibers
Contains most sensory receptors of skin as well as motor ends that supply vessels, arrector pili, and glands
Derived from mesoderm
Dermal papillae form boundary with epidermal ridges/pegs of epidermis
2 layers - papillary layer and reticular layer
What are the characteristics of the papillary layer?
Superficial and thinner layer of dermis
Named for dermal papillae
Loose CT: mainly elastic and reticular fibers
Well vascularized with abundant capillary loops in dermal papillae
Cells in papillary layer are CT cells (fibroblasts, macrophages, mast cells)
Sensory receptors in papillary layer - Meissner corpuscles
What are Meissner corpuscles?
Encapsulated mechanoreceptors local in dermal papillae
Detect light touch on skin surface
What is the function of the papillary layer of the dermis?
It is well vascularized so it helps with thermoregulation and supplies oxygen and nutrition to papillary layer and epidermis
What are the characteristics of the reticular layer?
Deeper and much thicker dermis
Refers to appearance of collagenous CT that contains collagen I fibers
Dense irregular collagenous CT that contains collagen I and elastic fibers ONLY
Cells of reticular layer are CT cells (fibroblasts, lymphocytes, white adipocytes)
Sensory receptors are all encapsulated and include Pacinian corpuscles, Ruffini corpuscles, and Krause end bulbs
What is the function of the collagen I fibers and elastic fibers and ECM in the reticular layer of the dermis?
Collagen I fibers - provide structural support and allow dermis to resist tensile forces from multiple direction
Elastic fibers give the skin elasticity
ECM rich in GAGs that drive hydration of the tissue
What are the functions of the sensory receptors in the reticular layer?
Pacinian corpuscles - mechanoreceptors that detect deep pressure and vibration on skin surface
Ruffini corpuscles - mechanoreceptors that detect stretching and torque of skin
Krause end bulbs - thermoreceptors that detect the cold
What are the characteristics and function of the hypodermis?
Hypodermis is subcutaneous or superficial fascia of gross anatomy and is transition zone between dermis and deep fascia
Technically not part of the skin
Mostly white fat that provides insulation and energy storage
Some CT
Vascularized and inenrvated
Contains some Pacinian corpuscles
What are the skin glands?
Sweat (sudoriferous) glands which include eccrine sweat glands (thin and thick skin) and apocrine sweat glands (thin skin)
Sebaceous glands - thin skin
What are the characteristics of eccrine sweat glands?
Thin and thick skin
Serous glands that use merocrine secretion
Secretions are hypotonic, water, and low in protein. Contain sodium chloride, urea, uric acid, and ammonia
Glands are tubular glands that do not branch - both secretory units and ducts are tubular and coiled
Located deep in dermis of skin of entire body, except lips and parts of external genitals
What is the function of eccrine sweat glands?
Secrete regular sweat in order to regulate body temperature
What are the characteristics of apocrine sweat glands?
Thin skin only
Serous glands that use merocrine secretion
Only in the axilla, areola, nipple, anal region, skin near external genitals
Secretions vary in color, content, and viscosity depending on region - typically a mix of proteins, carb, ammonia, and lipids
Coiled tubular glands that sometimes branch - much larger lumens than eccrine glands and ducts usually empty hair follicles
What are the functions of apocrine sweat glands?
Secrete protein rich secretions that contain pheromes
What are the characteristics and function of sebaceous glands?
Thin skin only
Sebaceous glands use holocrine secretion
Always associated with hair follicles
Acinar glands with short ducts that open directly into the hair follicle
Secrete an oily/waxy substance called sebum which coats the surfaces of hairs and skin surface
What are the parts of hair?
Hair follicles
Hair bulbs
Hair root
What is the function of hair follicles and their characteristics?
Produce and grow (lengthen) hair
Contain epidermal stem cells and melanocyte stem cells
What is the hair bulb?
Base of hair follicle
Hair bulb = hair toot + 1 dermal papilla
What is the hair roots and its function?
Contains hair matrix cells that migrate to the bottom of the hair and differentiate into keratinocytes that form 3 layers of the hair shaft
What are the 3 layers of the hair shaft?
Medulla (inner)
Cortex (middle)
Cuticle (outer)
Keratinocytes in all 3 layers and synthesize a more compact form of keratin called hard keratin
What does hair color depend on?
Depends on specific type/color of melanin contained in the hair
Melanocytes in the hair roots transfer melanosomes to keratinocytes in the cortex and in the medulla of the hair shaft
What structures are associated with the hair below the skin
Each hair shaft surrounded by internal and external roots sheaths
Each hair follicle has 1 or more sebaceous glands who ducts open into the follicle
Arrector pilli muscles - smooth muscle that attaches obliquely to hair follicle. When muscle contract, pulls hair follicle and raises hair. Also around sebaceous glands so contraction forces sebum into lumen of hair follicle
What are the parts of the nails?
Nails (nail plates)
Lunula
Nail bed
Nail root
Hyponychium
What are the nail plates made of?
Dead, fully keratinized keratinocytes containing hard keratin
Translucent but red because of capillaries beneath
Do not desquamate
What is the lunula of the nails made of?
White, crescent shaped area at base of nail
Derives white color from partially keratinized cells in this region
What is the nail bed?
Contains softer tissues - dermis, stratum basale, and stratum spinosum
Nail and lunula rest on it
What is the nail root?
Most proximal part of the nail hidden under a fold of stratum corneum called the eponchium (cuticle)
What is the function of the cuticle?
Prevents pathogens, dirt, and debris from getting into deeper tissues under the nail
What is the hyponychium and its function?
Anchors the underside of the nail to the skin of the fingertip
Part of nail distal to the hyponychium is the free edge of the nail
Prevents pathogens, dirt, and debris from getting into deeper tissues under the nail
How do nails grow?
Nail root overlies the nail matrix which contains the epidermal stem cells
Stem cells in the nail matrix divide, migrate to nail root, and differentiate into keratinocytes that make hard keratin and become keratinized
Nails grow by constantly adding keratinocytes to the proximal end of the nail root
Adding new cells to the proximal end pushes older keratinocytes distally across nail bed
