Integument Flashcards
what are the six functions of the skin?
barrier function, immunologic function (antigen processing), homeostasis, sensory function, endocrine function (hormones / conversation into vitamin D precursor), excretory function (sweat, sebaceous, apocrine glands)
What are the three layers of the skin, from top to bottom?
Epidermis, dermis, hypodermis (subcutaneous tissue or fascia)
What are the two types of skin and their characteristics?
- Thick skin - thick epidermis, hairless with no sebaceous glands. Found on palms and soles of feet
- Thin skin - thin epidermis, containing hair and sebaceous glands. Found everywhere else
What is the stratum basale / germinativum?
Single layer of small cuboidal cells resting on basal lamina. Contains mitotically active cells which give rise to keratinocytes, as well as melanocytes. Cells are attached to eachother by desmosomes and basal lamina by hemidesmosomes. They move up to next layer after mitosis
How do cells of the stratum basale appear?
Closely spaced nuclei (single layer of cuboidal epithelium) with basophilic cytoplasms from keratin production. Will contain varying amounts of melanin transferred from neighboring melanocytes.
What is the stratum spinosum?
Layer composed mainly of keratinocytes producing keratin, several cells thick. Cells are attached to eachother by desmosomes. Cells will increase in size and flatten out as they mature and move to surface.
How does the stratum spinosum appear?
Because the keratinocytes are connected by desmosomes, when the cells shrink during the fixation process there is an increase in intercellular space and the appearance of spines or prickles. -> why this is called the spinous or prickle cell layer
What is the most superficial layer of nonkeratinized portion of the epidermis? How do these cells appear?
Stratum granulosum. They appear to have intensely basophilic granules from the keratohyalin granules in the cytoplasm
What are in keratohyalin granules?
precursors of filaggrin and trichohyalin. They help aggregate keratin filaments in the stratum corneum
What is the stratum lucidum?
Layer above stratum granulosum but below stratum corneum seen only in thick skin and only sometimes. Eosinophilic cell layer in which keratinization is well advanced. Now considered a division of the stratum corneum.
What is the stratum corneum?
Outermost layer of epidermis - exposed to external environment. Flattened, desiccated, anucleate cells. Cells have no nucleus or organelles and are almost entirely filled with keratin filaments. Extremely thick layer in thick skin, also have epidermal water barrier
What makes the epidermal water barrier?
keratinocytes of stratum corneum have two components making this barrier:
- Cell envelope: 15 nm thick layer of insoluble proteins on inner surface of plasma membrane providing strength
- Lipid envelop: 5 nm thick layer of lipids extruded by lamellar bodies in stratum granulosum, imparts hydrophobicity
What are the two layers of the dermis?
Papillary layer (highest) and reticular layer
What are fingerprints?
to increase the SA between the epidermis and dermis, there are ridges where the two connect. Epidermal protrusions into the papillary dermis are called epidermal / rete ridges. Dermal protrusions into the epidermis are called dermal papillae. These dermal ridges make fingerprints
What is the papillary layer?
Superficial layer of dermis, consisting of loose connective tissue with Types 1 and 3 collagen and threadlike elastic fibers. Contains vasculation and even some nerve processes that terminate here or in epithelium
What is the reticular layer?
The deep layer of the dermis. It is dense irregular connective tissue -> thick, irregular type 1 collagen bundles and coarse elastic fibers
What are keratinocytes?
predominant cell type in the epidermis, originating from mitosis of stem cells in the stratum basale.
What are the two functions of keratinocytes?
- Produce keratin, which is the major structural protein of the epidermis (~85% of the cell)
- Participate in formation of epidermal water barrier
How do the cytoplasms of immature keratinocytes appear?
Basophilic, because of the numerous free ribosomes synthesizing keratin filaments (tonofilaments)
How do the keratinocytes change their appearance going up the epithelial layers
They become more eosinophilic because of the increasing concentration of keratin. At the level of the stratum granulosum, they have basophilic granules holding filaggrin and trichohyalin which promote the aggregation of keratin filaments to tonofibrils
What is keratinization?
The conversion of granular keratinocytes in the stratum granulosum to cornified cells in the stratum corneum. The keratin fibril formed in this process is called soft keratin
What is desquamation?
The sloughing off of cornified cells on the upper layer of the stratum corneum
What are lamellar bodies?
granules produced in stratum spinosum which lead to the release of lipids for the epidermal water barrier int he stratum granulosum. At the same level, the keratohyalin granules are begun to be produced by free ribosomes
What are the “dendritic cells of the epidermis”
Melanocytes, though they have no immune function. They stain clear with a rounded cytoplasm by H&E, and are scattered around the basal cells at the stratum basale. They have long cytoplasmic processes between keratinocytes which makes them resemble a dendritic cell.
How many melanocytes are there and how do they attach to surroundings?
There is a ratio of 1:4-1:10 melanocytes:keratinocytes across the body which is constant in all races. They do not form desmosomal attachments with neighboring keratinocytes. They can replicate, but slower than keratinocytes
What is the function of melanin and how is it produced?
Protects cells again nonionizing UV radiation.
Produced by oxidation of tyrosine to DOPA by tyrosinase, and transformation of DOPA into melanin. This occurs in melanosomes that are maturing as they go to be phagocytosed
What is a melanosome?
Released by Golgi apparatus as a pre-melanosome, they have lots of tyrosinase for melanin production. They become early and then late melanosomes, getting increasingly darker, as they travel through the melanocyte’s processes to get phagocytosed by keratinocytes.
What two factors control skin color?
- Melanin content - degradation of melanin by keratinocytes is more rapid in individuals with light skin
- Type of melanin - genetically determined (eumelanin or pheomelanin)
These are found in different places of the body
What is eumelanin
Common melanin -> brownish black pigment
What is pheomelanin
Rarer melanin -> reddish yellow pigment
What are Langerhans’ cells?
Antigen presenting dendritic cells of epidermis, resides in stratum spinosum. Detected by immunostaining. They migrate to lymph nodes after processing antigens that bind to surface and phagocytosing them.
What are Merkel’s cells?
Modified epidermal cells located in stratum basale which function in touch, most abundant in fingertips for acute sensory perception. Interacts with afferent (sensory) neuron via Merkel’s disc
What is a Merkel’s corpuscle?
Merkel’s cell + unmyelinated sensory neuron terminal interacting with the cell at Merkel’s disc. The neuron becomes unmyelinated when it stops interacting with Schwann cell before penetrating the basal lamina.
What is a hair follicle?
Invagination of epidermis in which hair is formed, extending deep into hypodermis. Only found in thin skin, associated with sebaceous glands
What is the base of a hair follicle?
Called a bulb - invaginated by vascularized loose connective tissue (the dermal papilla). The papilla is surrounded by matrix cells.
What is the germinative layer of the bulb?
Matrix cells adjacent to papilla. The layer also includes melanocytes which contribute melanosomes to developing hair. They differentiate into keratin-producing cells and the internal root sheath
What re-establishes the epidermis when trauma or surgery destroys it?
Germinating matrix cells in the deepest part of hair follicles will dive and migrate to re-establish it
What is the internal root sheath?
Multilayered cellular covering that surrounds the deep part of hair. Contains cells with SOFT keratin formed by germinative layer and ends around the level of the sebaceous gland
What is the external root sheath?
Downgrowth of epidermis extending the entire length of the follicle -> continuous with the epidermis
What is the connective tissue sheath?
Collar of dense irregular connective tissue surrounding the follicle
What is the arrector pili muscle?
Attaches to connective tissue sheath, responsible for goosebumps when contracted, also aids in sebaceous gland secretion. It is smooth muscle
What are the three layers of the deep hair (deep to internal root sheath)
- Cuticle - Outermost
- Cortex - Middle (or inner in thin hair)
- Medulla - Inner (thick hair only)
They are keratinized cells
How is deep hair formed?
Cells on apex of papilla produce medulla if it’s present. Basal stem cells of matrix produce cortex and cuticle. Keratinization occurs shortly after the cells leave the keratogenous zone. Melanocytes in the germinative layer give melanin pigment
How is keratin in the hair different than cornified cells?
Contains hard keratin. has high sulfur content, which is responsible for hardness. It does not involve keratohyalin granules and it does not desquamate!! (no peeling of hair)
Where are eccrine sweat glands and what do they secrete?
Distributed over the entire body except for lips and part of external genitalia, they secrete hypotonic sweat by merocrine secretion
They are located in deep dermis or hypodermis
What type of gland is an eccrine sweat gland? What epithelium lines the secretory and duct portions?
simple coiled tubular gland.
Secretory: coiled tubular secretory unit of pseudostratified cuboidal or columnar
duct: less coiled, narrow lumen that leads to surface. stratified cuboidal
What does the duct of an eccrine gland do?
Resorbs sodium and water from the secretion of the secretory cells which is like an ultrafiltrate of blood. Leads to hypotonic sweat
What is the function of an eccrine gland and what does it respond to?
Function: Thermoregulation - evaporation of hypotonic sweat cools the body.
Responds to heat and stress (emotional sweating) by SANS
What is the function of a clear cell of an eccrine gland?
Secretory epithelial cells which have abundant glycogen, produce the water component of sweat which travels to lumen via intercellular canaliculi
What is the function of a dark cell of an eccrine gland?
secretory epithelium characterized by abundant rough ER and secretory granules. Produce the proteinaceous component of sweat, have direct plasma exposure to the lumen
What is a myoepithelial cell of an eccrine gland?
Contractile cells that lie between secretory cells and basal lamina. The cytoplasm contains actin filaments which are deeply eosinophilic. Contraction -> rapid explusion of sweat from gland
What is an apocrine sweat gland? Where are they found in the body and what area of the skin?
They are glands releasing protein-rich secretion containing pheromones by MEROCRINE secretion. They are found in axilla, areola and nipple of mammary gland, skin around anus, and external genitalia. Development is dependent on sex hormones (start secreting during puberty). Located in upper dermis or hypodermis
What are the features of the apocrine ducts?
They are straight duct segments with narrow lumen and stratified cuboidal epithelium -> hard to distinguish from eccrine. They release into hair follicle just above the sebaceous gland. They do not resorb any material. They develop from same downgrowth of epidermis that gives rise to hair follicle and thus can re-establish the epithelium.
What type of gland is an apocrine sweat gland?
Merocrine gland with simple coiled tubular gland that may be branched.
What is the secretory unit of the apocrine sweat gland?
Coiled tubular with very wide lumen which is how you distinguish from secretory unit of eccrine. Epithelium is simple cuboidal or columnar
What is the function of apocrine sweat secretion and what does it respond to?
Pheromones are chemical signals important in sexual, maternal, and social behaviors in animals. Apocrine glands respond to emotional and sensory stimuli but NOT HEAT. Controlled by SANS
What are the two types of secretory cells in apocrine sweat glands?
Secretory - secretory epithelial cells contain secretory granules and numerous epithelia
Myoepithelial cells - same function as in eccrine gland
Where are sebaceous glands found?
Found in thin skin over entire body, and in the dermis emptying their products into hair follicle by help of arrector pili (no myoepithelial cells in these glands)
What do sebaceous glands secrete and why?
They secrete oily / fatty sebum by holocrine secretion (apoptosis). Role is unclear, may be bacteriostatic, have a barrier function, or pheromone function. Appears to play a role in development of acne (secretion increases at puberty) and linked to acne lesions
What are the cell types in the secretory segment of sebaceous glands?
- Secretory cells - cells moving towards opening of gland become filled with more and more lipid (washed out by H&E)
- Basal cells - small undifferentiated cells at the basal surface of secretory unit which are the source of secretory cells
What gland shape is a sebaceous gland?
Simple acinar / saccular
What is the duct portion of the sebaceous gland?
stratified squamous epithelium continuous with external root sheath. Makes sense because undifferentiated basal cells produce the secretory cells.
What is the function of free nerve endings in the epidermis or dermis?
These lack connective tissue or Schwann cell investment, and serve to feel fine touch, heat, cold, or other sensations
How does a hair mechanoreceptor work?
Free nerve ending surrounds hair follicles in dermis and attached to external root sheath, can sense hair movement
Where are Meissner’s corpuscles found and what is their function?
They are found in dermal papillae of papillary layer of hairless skin (lips, palmar and volar surfaces i.e. fingers and toes)
They function in response to touch of low-frequency stimuli through displacement of capsule
What is the structure of a Meissner’s corpuscle?
One or two unmyelinated nerve endings follow spiral patterns in cellular capsule. Flattened specialized Schwann cells form several irregular lamellae which axons course through. Looks like a piece of twisted wool
Where are Pacinian corpuscles found and what is their function?
Found in deep dermis or hypodermis of fingertips. Found in CT in general especially associated with joints + internal organs. They function as deep pressure sensory for mechanical and vibratory pressure.
What is the structure of a Pacinian corpuscle?
Myelinated nerve ending surrounded by a capsule. The axon becomes unmyelinated upon entering capsule, and is surrounded by concentric lamellae made by Schwann cells. Looks like a toothpick into a cocktail onion (Schwann cell capsule). The capsule being displaced causes axon depolarization
