Integumentary System Histology Flashcards
What are the 2 Main Components of the Integumentary System?
- Skin
2. Epidermal Derivatives
List the epidermal derivatives
- Hair follicles and hair
- Sweat (sudoriferous) glands
- Sebaceous (oil) glands
- Nails
What are the 6 major functions of the Integumentary System?
- protective (barrier against external factors / forces / biological agents)
- immunologic (antigen presenting cells that alert effector cells)
- homeostasis (body temperature and water loss)
- sensory (convey information about the external environment)
- endocrine
- exocrine
What are the 2 principle layers of the skin?
& an additional notable layer
- Epidermis
- Dermis
(additionally, the hypodermis or subcutaneous layer / subcutaneous fascia is deep to the skin)
Epidermis
1 of the 2 principle layers of the skin
- superficial layer
- keratinized stratified squamous epithelium
- embryologically derived from: ectoderm
- avascular (receives nourishment from dermis)
Dermis
1 of the 2 principle layers of the skin
- deep layer
- connective tissue
- derived from mesoderm
- highly vascularized
Hypodermis
Otherwise known as the subcutaneous layer / subcutaneous fascia
- deep to the skin (not a principle layer - the “3rd smaller layer”)
- made of adipose tissue
- vascularized
What are the histological terms for skin?
- Thick Skin
- Thin Skin
(these terms really aren’t accurate, because only the epidermis is being considered, while skin really consists of epidermis and dermis)
Thick Skin
(only referring to epidermal layer)
- found on palms of hands and soles of feet (areas that encounter and high degree of abrasive forces)
- skin is hairless
- much thicker epidermal layer than skin anywhere else
-5 layers/strata
Thin Skin
(only referring to epidermal layer)
- found everywhere except palms of hands and soles of feet
- much thinner epidermis
- hair follicles present in most locations
-4 layers/strata
When considering gross anatomy, where can you find the “thickest skin?”
The upper back (thin epidermis, very thick dermis)
List the Layers/Strata of the Epidermis
(from deep to superficial)
- Stratum Basale (basal layer)
- Stratum Spinosum (spinous layer)
- Stratum Granulosum (granular layer)
- Stratum Lucidum (thick skin only)
- Stratum Corneum
mnemonic: Bad Sprinters Get Leg Cramps
List the Cells of the Epidermis
- Keratinocytes (85%)
- Melanocytes (5%)
- Langerhans’ Cells (2-5%)
- Merkel’s Cells (6-10%)
Keratinocytes
epidermis cell (1/4)
- principle cell type of the epidermis
- produce keratins
- participate in the formation of epidermal water barrier via production of the lamellar bodies
Keratins
produced by keratinocytes
- a major structural protein of the epidermis
- form keratin filaments (intermediate filaments, commonly referred to as tonofilaments)
Lamellar Bodies
- produced by keratinocytes in order to form the epidermal water barrier
- tubular / ovoid-shaped membrane-bound organelle that contain lipids
- these are extorted into the extracellular space between the stratum granulosum and the stratum Corneum
- the epidermal water barrier is important for homeostasis and having dry epithelia)
Melanocytes
epidermis cell (2/4)
function: produce and secrete the pigment, melanin (synthesized and stored in melanosomes)
- have elongated nuclei surrounded by clear cytoplasm
- dendritic cells (rounded cell bodies in the stratum basle with long dendritic processes that extend upward and between keratinocytes in the stratum spinosum)
- Melanosomes will be transferred into adjacent keratinocytes (when they mature, they travel to the ends of dendritic process, accumulate, then go to the adjacent keratinocytes)
Langerhans’ Cells
epidermis cell (3/4)
antigen-presenting cells of the immune system
typically found within stratum spinosum
derived from bone marrow (originate from common lymphoid progenitor cells), then enter the blood stream and migrate into the epidermis, where they encounter and process antigens that enter through the skin
travel through the epidermis through regional lymph nodes where they present processed antigens to the T lymphocytes
in order to ID, must use immunostaining
Merkel’s Cells
epidermis cell (4/4)
mechanoreceptor cells associated with sensory nerve endings
location: stratum basale
contains neurosecretory granules (within cytoplasm)
base of these cells associate with expanded, plate-like terminal of afferent nerve fibers (Merkel’s Corpuscle)
have lobed nuclei
most abundant in areas of acute perception (fingertips)
Stratum Basale
deepest later of epidermis (located adjacent and superior to dermis)
- single layer of basophilic cells
- cells are small and cuboidal / low columnar
- mitotically active later that contains stem cells that give rise to keratinocytes (note that keratinocytes will migrate upwards and differentiate from here)
- this is where the production of intermediate (keratin) filaments begins
Stratum Spinosum
- keratinocytes exhibit numerous cytoplasmic processes (“spines”)
- cell processes are attached to those of adjacent cells via desmosomes (macula adherens)
Intermediate filaments (tonofilaments) are grouped into bundles (tonofibrils)
We see that keratohyalin granules and lamellar bodies will start to be produced here
Cytoplasmic Processes & Histological Prep
during histological prep, cells shrink which leaves expanded intercellular space between spines
this is what contributes to the spiny / prickly appearence
Keratohyalin Granules
Contain proteins that support the aggregation of tonofilaments into tonofibrils
These are produced in Stratum Spinosum, but are also found in other layers
Stratum Granulosum
- intensely basophilic
- varies in thickness (1-3 cell layers)
- keratinocytes contian keratohyalin granules, which will bundle tonofuilaments into tonofibrils
- keratinization is happening here (conversion of granular cells into cornfield cells)
- lamellar bodies are released in the intercellular space b/w stratum granulosum and stratum corneum
Stratum Lucidum
- only found in thick skin (palms of hands and soles of the feet)
- this is a thin, translucent layer of eosinophiloc cells (that are largely keratinized)
- nucleus and cytoplasmic organelles become disputed and disappear (as cells fill with more and more keratin
Stratum Corneum
this is the most superficial layer of epidermis
- cells lose nuclei and cytoplasmic organelle (flat, desiccated, a-nuclear cells)
- filled almost entirely (85%) with keratin
- cells of this layer are sloughed off at the surface
- this is the most differentiated cell layer
Key cell features of the Stratum Corneum
- most superficial layer
- most differentiated layer
- cells are dead
- represented only by flat membranous sacs filled with keratin
- glycolipids in extracellular space
Key features of the Stratum Granulosum
- cells are flattened and organelle are deteriorating
- cytoplasm full of lamellate granules (release lipids) & keratohyaline granules (continue to bundle the tonofilaments into tonofibrils)
Key features of the Stratum Spinosum
- cells contain thick bundles of intermediate filaments made of pre-keratin
- we start to see the synthesis of keratin, and start to see them bundled into tonifibrils into keritohyaline granules)
Key features of the Stratum Basale
- cells are actively mitotic stem cells
- some newly formed cells become part of the more superficial layers
- where we start to see synthesis of keratin
Melanin
within melanosomes, which are produced by melanocytes
melanin accumulates over nuclei to protect DNA from UV radiation (think of this as a nuclear umbrella)
List 3 types of skin cancer with epidermal origin
- Basal Cell Carcinoma
- Squamous Cell Carcinoma
- Malignant Melanoma
Basal Cell Carcinoma
most common and least aggressive type of skin cancer
resembles cells of stratum basale
slow-growing tumor
treatment: surgery
Squamous Cell Carcinoma
second most common, slightly more invasive
characterized by highly atypical cells at ALL levels of epidermis
treatment: varies depending on histological type, size, location
Malignant Melanoma
most serious form
originates from melanocytes
presents as irregularly pigmented, multicolor lesion
treatment: surgery and chemotherapy
List the two layers of the dermis
- Papillary Layer
2. Reticular Layer
Papillary Layer
more superficial layer of the dermis
loose (areaolar) connective tissue
characterized by dermal papillae, which project into the epidermis at the epidermal-dermal junction
Dermal Papillae
part of the papillary layer of the dermis
finger-like connective tissue protrusions
they project into the epidermis at the epidermal-dermal junction
has sensory nerve endings and blood vessels
Reticular Layer
the deeper layer of the dermis
dense irregular connective tissue
considerably thicker than papillary layer. but has fewer cells
Pacinian Corpuscles
large ovoid structures found in the dermis and the hypodermis
an encapsulated, mylenated nerve ending surrounded by a capsule consisting of concentric lamellae
inner core is made series of tightly packed, flattened Schwann cell lamellae surrounding unmyelanated axon
detects pressure and vibration changes across the skin surface
Meissner’s Corpuscles
tapered, cylindrical structures
located in the dermal papillae of hairless skin (fingertips and lips) - perpendicular to the skin surface
flattened Schwann cells form lamellae
unmyelinated nerve endings follow s[oroca; paths in corpuscle
detect light touch
Epidermal Skin Appendages
derived from down-growths fo epidermal epithelium during development
Includes:
- hair follicles & hair
- eccrine sweat (sudoriferous) glands
- apocine sweat (sudoriferous) glands
- sebaceous (oil) glands
Hair
elongated filamentous, keratinized structures that project from hair follicles
found along surface of almost the entire body (but NOT thick skin)
Hair Follicles
responsible for the production and growth of a hair
found along surface of almost the entire body (but NOT thick skin)
Arrector Pili Muscle
smooth muscle that extends from connective tissue sheath surrounding hair follicle to papillary layer of dermis
contraction of the arrestor pili m. causes hair to “stand at end” (goosebumps)
role in insulation (thermogenesis ) & “fright” response
receives sympthatic innervation
Eccrine Sweat (Sudoriferous) Glands
widely distributed (except the lips and portions of external genetalia)
simple coiled tubular gland
independent structures, not found in association with hair follicle
merocrine secretion (secretory product released via exocytosis)
role: thermoregulatory
excretes wastes and excess salts
has a secretory and a duct portion
Eccrine Sweat Glands - Secretory Portion
double layer of epithelial cells
secretory cells are larger and appear lighter than cells of the duct
located deep in the dermis or upper part of the hypodermis
Eccrine Sweat Glands - Duct Portion
narrower outside diameter and lumen than secretory portion
double layer of small cuboidal cells (stratified cuboidal epithelium)
cells are smaller and darker than cells of secretory potion
leads to the epidermal surface
Apocrine Sweat (Sudoriferous) Glands
localized to the axillary and perineal regions of the body
produce viscous, protein-rich sweat
product is secreted into hair follicles
merocrine secretion (misnomer)
coiled tubular glands with very wide lumens
become functional at puberty
body odor: bacterial breakdown of sweat
Aprocrine Sweat Glands - Secretory Portion
very wide lumen (much wider than eccrine sweat glands)
simple cuboidal epitherlium
eosinophilic cytpolasm
found in upper part of hypodermis (most commonly) or deep in dermis
apical portion - bleb-like protrusions, thought to be related to apocrine secretion, but TEM proved merocrin secretion
Apocrine Sweat Glands - Duct Portion
stratified cuboidal epithelium (2-3 layers thick)
narrow lumen; similar to eccrine sweat glands
empties into follicle canal rather than the skin surface
Subaceous (Oil) Glands
found everywhere except for thick skin
branched acinar gland
secretes SEBUM into hair follicles via holocrine secretion
Involved in acne development
Sebum
lipid-containing substance produced and secreted by sebaceous glands
Nails / Nail Plates
plates of keratinized cells rest on nail beds
nail is transparent (difficult to stain)
epithelium continues with stratum basle and stratum spinous of epidermis
