Integument Flashcards
The skin and derivations/appendages make up the __ and ___ organ in the body
largest and heaviest
What % total body weight is the skin?
16
What are the 7 main functions of the skin? (dont need to explain)
- protective
- Immunological
- Sensory
- Exocrine
- Endocrine
- Homeostasis
- Communication
How is the skin protective?
water resistant barrier that protects against dehydration, abrasions, UV light, and toxins
How is the skin immunological?
acts as a passive barrier to pathogens but also contains APCs
What kind of exocrine activity does the skin have? (4 kinds)
Eccrine sweat glands for excretion and cooling
Apocrine sweat glands for signalling
Sebaceous glands for lubrication
Mammary glands for nutrition
What is an endocrine function of the skin?
part of the vitamin D synthesis pathway occurs here
What are some homeostatic functions of the skin?
Thermoregulation, water conservation, gas exchange, and excretion
What are some “communication” roles of the skin?
Non-verbal signals like changes in coloration and goosebumps
The most superficial later of the skin is the…?
epidermis
What is the predominant cells type of the epidermis?
Keratinocytes (90%)
Besides keratinocytes, what 3 other cell types make up the epidermis?
- Melanocytes
- Langerhans cells
- Merkel cells
regeneration of the epidermis occurs approximately every…
30 days
The epidermis is avascular, how then is it nourished?
Receives nourishment from vessels in the underlying dermis
What is the only kind of innervation that the epidermis receives?
Unencapsulated (free) nerve endings
the epidermal layer is further subdivided into how many strata?
5
What is the order of the epidermal strata from outer to inner?
- Stratum corneum
- Stratum lucidum
- Stratum granulosum
- Stratum spinosum
- Stratum basale
Which strata isn’t always present in the epidermis?
the stratum lucidum
Where does the division of the keratinocytes occur?
in the stratum basale
what are two main divisions of types of skin? where is each found
thick and thin
- depends on location
- thick is only on the palms of hands and the soles of feet
What is the difference between thick and thin skin in terms of layers? in terms of functions?
the thick skin has all 5
- has abundant sweat glands
- more squamous stratum spinosum cells
thin skin has 4 layers
- stratum lucidum not always detectable
- has hairs
The turnover of the skin surface is made up of 4 overlapping processes: what are they?
- Cell renewal (mitosis)
- Differentiation (keratinization)
- Cell death
- Exfoliation
How long does the keratinization process take? is it totally synchronized?
takes about 15-30 days and occurs in waves
cell layer produced by a mitotic wave in the basal layer undergoes keratinization in synchrony
What is the stratum basale comprised of and what does it rest on?
Single later of columnar cells that sit on the basal lamina
What 3 cell types are in the stratum basale?
- mitotically active keratinocytes
- Melanocytes
- Merkel cells
How are kertinocytes linked together and to the basal lamina?
Linked together by desmosomes and to the basal lamina by hemidesmosomes
What 4 parts make up the structure of the desmosome? what do they do?
- Adaptor proteins that attach keratin filaments to the cytoplasmic plaque
- Transmembrane linkers that connect adjacent cells
- Cytoplasmic domain which binds the adaptor
- Extracellular domain which associates with linkers on the opposing cell
Keratin filaments are also called two other things..?
Tonofilaments and intermediate filaments
Hemidesmosomes are only found in the ___ and the intercellular proteins are ___ as opposed to ___
only found in the stratum basale
intercellular proteins are integrins instead of cadherins
What is the morphology of the cells in the stratum spinosum layer? What do they have?
Cuboidal to squamous cells with central nuclei
Have aggregates of keratin called tonofilaments
What are the cells in the stratum spinosum responsible for?
responsible for the mechanical strength of the epidermis
What are the layers of cells like in the stratum spinosum? single or multiple?
variable number depending on location
What is the Malpighian layer?
layer including the stratum basale and the stratum spinosum
Nearly all of what occurs in the Malpighian layer and when?
mitotic activity and at night
What gives the stratum spinosum the “spikey” appearance?
the tonofilaments that are linked cell to cell by desmosomes
the intercellular bridges of the keratinocytes (prickle cells) bind the cells of this layer together strongly and resist..
abrasion
In the stratum granulosum, the keratinocytes are mainly…
squamous
What do the keratinocytes in the stratum granulosum layer contain (2 things)
- membraneless keratohyalin granules
2. Membraned lamellar granules
Is there divisional capacity in the stratum granulosum?
Nope but the cells are still alive and making lots of keratin
What do lamellar granules do? What does this accomplish
Fuse with the plasma membrane and release their contents into the intercellular spaces
these glycosaminoglycans and phospholipids may be important in sealing the deeper layers of the skin from the external environment/protect from dehydration
What layer sits on top of the stratum granulosum?
the stratum lucidum but only in thick skin
What is the morphology of the stratum lucidum?
a narrow, acidophilic, translucent band of flattened keratinocytes
What are not visible in the keratinocytes of the stratum lucidum?
Nuclei, organelles, and intercellular borders
What is found in the cytoplasm of the keratonocytes of the stratum lucidum?
dense cytokeratin aggregates embedded in an amorphous, electron dense matrix derived from keratohyalin granules
What makes up the stratum corneum?
many layers of dead, plate like keratinocytes
What are the keratonocytes of the stratum corneum like (mophologically)
have thickened plasma membranes and lack nuclei
Filled with almost pure keratin
What is the function of the stratum corneum?
acts as the permeability barrier of the skin
What acts as a sealant between the cells of the stratum corneum?
epidermal lipids
What does differentiation of a Keratinocyte entail?
- accumulation of keratin filaments
- aggregation of filaments into tonofibrils
- synthesis of lamellar granules
- Release of lamellar granules at cell surface
In what layer do the nuclei of the keratinocytes begin to degenerate?
In the outer layer of the stratum granulosum
What else degrades in the stratum granulosum? Why?
Intracellular organelles do as a result of release of lysosomal enzymes
Melanocytes make up what % of cells in the epidermis?
about 5
Where are melanocytes found?
in the stratum basale
How are melanocytes attached and to which cells?
Attached to the basal lamina via hemidesmosomes
Not attached to neighboring keratinocytes
Where is skin pigment made?
In melanosomes
How is skin pigment dispersed?
Melanosomes aggregate as granules and are delivered in small packaged to each basal cell by dendrites to other keratinocytes
What does the pigment do /where does it go in each cell?
Sit over the nucleus of each cell
protects against UV damage
What is required to make melanin?
Tyrosinase is required for melanocytes to produce melanin from the amino acid tyrosine
this enzyme is lacking in people who are albino
Where is the highest concentration of melanin?
In the cells that are most deeply localized and actively dividing
- the DNA is therefore more sensitive to damage
- other layers don’t have proliferative cells so it doesn’t matter is the DNA is damaged
Skin colour is conferred by which two pigments?
melanin and carotene
What other factors besides pigment affect skin coloration?
- Thickness of epidermis
- Number of dermal blood vessels
- Colour of the blood (hemoglobin) in the vessels
the amount of melanin you produce is …
hereditarily conferred
What is carotene?
yellowish pigment found in corneum and dermis. It is a plant pigment that enters the body via food and helps yield the yellow and red skin colours
Which pigment is responsible for darker or lighter skin colourations?
More melanin leads to dark-skin colouration
Caucasians have more carotene than melanin
Does the number of melanocytes differ between people of different skin colours?
No, the keratinocyte processing of melanosomes differs OR the activity of the melanocytes
What are the two steps in skin darkening following exposure to UV radiation ?
- Physiochemical reaction darkens pre-existing melanin and releases it rapidly into the keratinocytes
- this happens immediately - Increased rate of melanin synthesis by melanocytes
- occurs after a couple days
What does Melanin absorb to protect DNA?
some rays directly and some free radicals produced
What does melanin not protect against?
the deeper penetrating UVA rays
- these get into the dermis
The youthfulness of skin is attributed to which layer?
the dermis
What 3 things happen as skin ages?
- Thinning of the epidermis and dermis
- Disorganization and loss of collagen
- Reduced vascularization
What is UVB required for?
synthesis of previtamin D from 7-dehydrocolesterol
What are langerhans cells? where are they located?
Star shaped APCs located int the stratum spinosum
What do the langerhans cells do?
present any antigenic material that penetrates the skin to the lymphocytes
where do Langerhans cells present antigenic material to lymphocytes?
local lymph nodes
- so they need to migrate out of the epidermis and into the lymphatic vessels
Langerhans cells are important in which kind of response?
contact allergic responses by recruiting and stimulating other myeloid cells
Merkel cells make up what % of epidermal cells?
<1%
Where are Merkel cells found?
in the basal layer of the epidermis
How are Merkel cells attached to keratinocytes?
via macula adherens junctions
Where are Merkel cells most commonly found throughout the body?
most on the palms of hands and soles of feet
What is thought to be the function of merkel cells?
sensory or neuroendocrine
What is the purpose of the ridges of the dermal-epidermal junction?
ridges formed that promote the strength of the skin AND allow for nutrients to get into the epidermis more readily
What is each dermal ridge further subdivided into?
Two secondary dermal ridges
What separates the two secondary dermal ridges?
a downgrowth of the epidermis called an interpapillary peg
the dermis is a layer of variable thickness ___ tissue?
Vascular connective tissue
What are 4 typical cells found within the dermis?
Fibroblasts, lymphocytes, macrophages, and mast cells
What are some typical skin structures that arise in the dermis?
Sweat glands, sebaceous glands, and hair follicles
What kind of cell is NOT found in the dermis
epithelial cells lol
What are two layers of the dermis?
- Papillary layer
2. Reticular layer
What is the morphology of the dermal papillary layer like? What is it composed of?
Uneven and forms dermal papillae which increase contact area with epidermis
Composed of loose connective tissue
What touch receptors are found in the dermal papillary layer? What kind of receptors are they?
Meissner corpuscles which are fine touch receptors
What kind of tissue makes up the reticular layer of the dermis?
Dense irregular connective tissue
What kind of property does the reticular layer confer to the skin?
overall strength and elasticity
What two things are housed in the reticular layer of the dermis?
glands and hair follicles
What two kinds of nerves supply the reticualr layer of the dermis
both free and encapsulated ends
What features control the amount of blood reaching the papillary capillaries? what else does this accomplish?
Arteriovenous anastomoses/shunts
also aid in the regulation of heat loss and blood pressure
What is not actually a true layer of skin but is attached to it?
Hypodermis - subcutaneous layer of fascia
What is the function of the hypodermis?
allows for movement of skin over the body proper
What is the hypodermis composed of?
fat cells, fibroblasts, lymphocytes, macrophages, and mast cells
glands, hair, and nails arise from…
epidermal downgrowths into the dermis during embryonic development
what are the parts of the hair shaft?
Inner medulla, cortex, outer cuticle of the hair
The hair bulb is…
the terminal expanded region of the hair follicle in which the hair is rooted
Where is the internal root sheath located?
lies deep to the entrance of the sebacous gland
What is the external root sheath a direct continuation of?
the surrounding malpighian layer of the epidermis
What is the glassy membrane of the hair?
Non cellular layer which is a thickening of the basement membrane separating the hair follicle from the surrounding dermal sheath
the contraction of which muscle is responsible for the formation of goose bumps?
the arrector pili muscle
Where does the arrector pili muscle attach?
to the dermal sheath surrounding the hair follicle
Contraction of the arrector pili muscle also results in…
compression of sebaceous glands and the pushing out of their contents to the surface of the skin
Hair only occurs in which type of skin?
thin skin
What are the 4 types of hair?
- Lanugo
- Vellus
- Intermediate
- Terminal
What is lanugo?
Neonatal hair present from month 7 to 8 in utero
- soft, fine, without a medulla
What is vellus hair?
short, fine shafted hair present post natally
What is intermediate hair and when is it present?
post natal to 2 years of age
intermediate between vellus and terminal hair
What is terminal hair like?
long, course, medullated and most common visible hair
What makes up the nail root? what do these make?
the stratum basale and the spinosum of the epidermis
synthesize the nail plate/body
What is the nail bed made from? Does this contribute to nail synthesis?
Stratum basale and stratum spinosum of nail and doesn’t contribute to nail synthesis
What is the nail plate? what layer of the nail is this
a closely compacted keratin structure enriched with hard interfibrillar material
stratum corneum of the nail
What is the eponychium ?
aka the cuticle
junction between the skin stratum corneum and the base of the nail plate
What causes nail growth?
keratinocytes in the nail (matrix cells) proliferate, grow, synthesize hard keratin and die to form the plate of the nail
What are the 3 epidermal derived glands in the skin?
- Eccrine
- Apocrine
- Sebaceous
Where are Apocrine sweat glands located?
in the axilla and groin only
When do apocrine glands become active? What do they secrete?
become active at puberty and secrete glycoproteins
Where are eccrine glands found?
these are basic sweat glands found all over the body
What do eccrine sweat glands secrete?
Water, ions, urea
Sebaceous glands are essentially part of what other structure?
hair follicles
What secretory product do sebacous glands secrete onto the hair follicle?
sebum
What is sebum composed of?
lipids, triglycerides, waxes, squalene, cholesterol and cell remnants
What controls secretions from sebaceous glands?
Testosterone in men and androgens in women
What is the function of secretions from the sebaceous glands?
antibacterial or antifungal effects
Mammary glands are modifications of what type of glands? What are they?
Apocrine sweat glands
Milk producing glands that develop during pregnancy and lactation
Free nerve endings sense..
pain and temperature
Hair follicle receptors sense?
hair motion and its directions
Merkel cell endings sense?
edges, corners, and curvatures
- pins and needles
What sensory structures sense slipping of surface over skin?
Meissner’s corpuscles
What are Krauses end bulb ? what do they sense?
Golgi tendon organ
senses tension/force
What do pacinian corpuscles sense?
are mechanoreceptors
sense any kind of mechanical stimulus or pressure
What do ruffini endings sense?
Displacement/tension in collagen fibres in the dermis
pressure
Meissner’s corpuscles are… what kind of response do they have?
encapsulated unmyelinated nerve ending in the dermal papilla of skin, sense dynamic deformation of skin with high sensitivity but poor special resolution
What is the distribution of meissner’s corpuscles like throughout the skin?
distributed throughout the skin but concentrated in areas sensitive to light touch
Pacinian corpuscles are located in which layers of the skin?
deep in the dermis and hypodermis
in some mucous membranes and joints
What is dermatitis
any inflammation of the skin
usually used to refer to eczema
What is contact hypersensitivity? what happens?
Allergic reaction where haptens are absorbed through the skin and bind langerhans cells which then migrate to draining lymph nodes
What is psoriasis?
Chronic reoccuring skin disease that produces red, scaly, and well defined patches of skin on the body
What produces the scaly lesions in psoriasis?
Very quick regeneration of epidermal skin cells which results in poorly formed skin cells that tend to pile up on the skin and produce the scale
What is hyperkeratosis?
thickening of the stratum corneum
What is parakeratosis?
retention of nuclei in the stratum corneum
What is Ehlers-Danlos syndrome?
rare genetic disorder caused by defective collagen synthesis
What are some of the effects of Ehlers-Danlos syndrome?
Fragile ski
Hyperentensible joints
What is bullous pemphigoid?
chronic blistering of the skin
What kind of disease is bullous pemphigoid?
Autoimmune disorder prevalent in the elderly
What causes bullous pemphigoid?
loss of attachment of basal keratinocytes to the underlying basement membrane
Deposition of immunoreactants at the dermal-epidermal junction
What is vitiligo?
loss of skin colour
What causes vitiligo?
loss or malfunction of melanocytes
What are the ABCDEs of skin cancer?
A= asymmetry B = border, rough or not C = colour, continuous or not? D = diameter ? Bigger than the eraser head of a pencil should be check out E = evolving. Is it changing over time?
skin cancer is a malignant growth of skin developing in the…
epidermis
what are three predisposing factors to developing skin cancer?
- Sunburn or excessive sun damage
- Chronic non healing wounds
- Genetic predisposition
- “Congenital Melanocytic Nevi Syndrome”
What are the 3 most common types of skin cancer?
- Basal cell carcinoma
- Squamous cell carcinoma
- Melanoma
Which one of the 3 common skin cancer types tends to metastasize?
melanoma
Where does basal cell carcinoma originate?
In the stratum basale
Where does squamous cell carcinoma originate?
in the stratum spinosum
What is different about melanoma that allows it to metastasize?
develops in melanocytes that have dendrites
Where do most breast cancers start?
in the ducts
Ductal carcinoma in situ means that the breast cancer lesion is..
non invasive/non metastatic
What does it mean if you have an invasive ductal carcinoma?
breast cancer cells have spread beyond the basement membrane of the ductal walls
