SKIN Flashcards
What are the functions of skin?
- Protective: mechanical forces, pathogens, UV light, dehydration
- Sensory
- Thermoregulator
- Metabolic: Electrolytes, Vit. D
- Sexual signaling: pheromones and indicator of health
How do thick skin and thin skin differ?
- Thick skin
- Found on the palms of hand and soles of feet
- Lacks hairs, sebaceous gland, and accrine glands
- Contains sweat glands
- Melanin less abundant
- Ridges that hold epidermis to dermis are higher to resist shear.
- Has an extra layer- Stratum Lucidum
- Thin skin
- Layers are not clearly defined
List the layers of the epidermis from most deep to most superficial. What’s a defining characteristic of each?
- S. Basale – stem cells
- S. Spinosum – spiny-keratinization begins
- S. Granulosum – hydrophobic lipid envelope
- More pronounced in thick skin
- S. Lucidum – translucent appearance
- Only in thick skin
- S. Corneum – dead cells
What are the three layers of the skin? What is each layer made up of?
- Epidermis: stratified squamous epithelium
- Dermis: connective tissue
- Hypodermis: fatty, loose connective tissue
What kind of epitelium is found in the epidermis?
Keratinized Stratified squamous
The epidermis is composed mostly of _________cells that are generated in the __________ layer, and differentiate as they are pushed to the surface
keratinocyte; stratum basale
What cells are found in the S. Basale?
Stem cells
What cells are found in the S. spinosum?
Spiny-keratinization begins
What cells are found in the S. granulosum?
Hydrophobic lipid enveloped
What cells are found in the S. corneum?
Dead cells
How does a histo slide of thick skin differ from a histo slide of thin skin?
Layers of the epidermis are not clearly seen in thin skin.
Which epidermis layer is being described below?
- Highly mitotic
- Stem cells for all keratinocytes.
- Single layer of basophilic cuboidal cells attached to basement membrane.
- Contain intermediate filaments composed of keratin, bundled into tonofilaments.
- Site of synthesis of Vit D, in response to light.
S. Basale
Which epidermis layer is the site of Vit D synthesis?
S. Basale
S. Basale is also known as __________
S. Germinativum
The stratum basale is composed of a single layer of ___________ cuboidal cells attached to the basement membrane.
Basophilic
The keratin found in the stratum basale is bundled into ___________.
Tonofilaments
Keratinocytes are held together by ___________ and attached to the basement membrane by _____________.
Desmosomes; hemidesmosomes
Hemidesmosomes and desmosomes are attached to bundles of __________ fibers.
Collagen
What are the components of hemidesmosomes?
Tonofilaments
Plaque
Basal lamina
Anchoring filaments
Collagen Type I
Which molecules are involved in cell adhesion in skin?
Desmosomes
Keratin filaments
Hemidesmosomes
Anchoring filaments
Basal lamina
Type IV collagen
Anchoring fibrils (Type VII collagen)
Type I and III collagen
Anchoring plaques (Type IV collagen)
Which epidermis layer is being described below?
- Polyhedral cells attached by desmosomes.
- Shrinkage during fixation causes retraction in between desmosomes, to look like spines.
S. Spinosum
During the processing of polyhedral cells in s. spinosum layer, the cells contract and form spines, why is this?
They contract because they are held together by desmosomes
Which epidermis layer is being described below?
- Flatter keratinocytes fill with basophilic keratohyaline granules.
- The granules contain filaggrin, which links tonofibrils together to form dense bundles of keratin that fill the cell.
S. Granulosum
What type of granules are found in the stratum granulosom? What do these granules contain?
The keratinocytes in this layer are filled with basophilic kerahyalin granules that contain filaggrin.
Filaggrin links ____________ together to form dense bundles of __________ that fill the cell.
Tonofibrils; keratin
What do the keratohyaline granules promote?
Dehydration of the cell as well as aggregation and cross-linking of the keratin fibers.
How is profilagrrin converted to filaggrin?
The phosphate groups are cleaved
____________ crosslinks keratin.
Filaggrin
Which layer plays an important role in “waterproofing” the skin? How?
S. Granulosum cells also contain lamellar bodies: contain a lipid-rich secretion that is expelled into extracellular space and waterproofs the skin. Barrier is semi-permeable.
Why are the lamellar bodies found in the s.granulosum important in pharmocology?
Important in studying which kinds of drugs can penetrate the waterproof barrier of the skin
Which epidermis layer is being described below?
- Surface cells are flat, anucleate, filled with cross-linked keratins.
- The plasma membranes are thickened and “cornified”. Continuously shed, and replaced from beneath.
S. Corneum
What is the normal skin turnover time?
20-75 days
Describe the cells in the S. Corneum and plasma membranes within those cells.
Cells: Flat, anucleate, filled with crosslinked keratins
Plasma membrane: Thickened and “cornified”
Which epidermis layer is being describe below?
The keratinocytes do not feature distinct boundaries and are filled with eleidin, an intermediate form of keratin
S. Lucidum
An intermediate form of keratin
Eleidin
____________ helps stabilize the cell membrane of the dead keratinocyte.
Involucrin
involucrin is found in the ___________ layer but synthesized in the __________ layer.
S. Corneum; S. Lucidum
List specific abnormalties that can be found in epidermal keratinocytes. Describe each.
- Psoriasis: abnormal keratinocyte generation and differentiation
- Blistering Diseases: autoimmune diseases or keratin mutations
- Vitamin D Deficiencies : lack of sun, high latitudes, winter, poor diet
What is the mechanism by which psorasis occurs?
It occurs when you have abnormally fast keratinocyte generation, and it doesn’t take the time to differentiate before it comes to the surface.
Blistering diseases occur when?
In cases of autoimmune diseases or in cases of keratin mutation
What are some distinguishing characteristics of epidermis/ dermis in cases of psorasis?
- Thickening of the stratum corneum
- Microabcesses in the epidermis
- Elongation of the papillae
- Inflammatory cells in the dermis
- Cells in the S. corneum display nuclei
- Cells are usually flattened
Keratinocytes normally reach the surface in _________ days, but in cases of psorasis they reach the surface in __________ days.
30; 3-5
Bullous pemphigold
Autoimmune damage to the dermal-epidermal junction (eg hemidesmosomes) manifest
*Epidermis is lifting off the dermis
Mutations of keratins manifest as ______________ diseases.
epidermolysis
- Skin doesn’t hold well together and you have raw dermis
Pemphigus vulgaris
Autoimmune damage to intercellular adhesion molecules (eg desmosomes). Blisters between keratinocytes in skin and mucous membranes.
Bullous pemphigold results from damage to __________ (desmosome/hemidesmosome), while pemphigus vulgaris results from damage to ____________ (desmosome/hemidesmosome).
Hemidesmosome; desmosome
Lack of bone mineralization in adulthood is known as ___________. Lack of bone mineralization in childhood is known as _____________.
Osteomalacia; Rickets
*Results from Vitamin D deficiencies
Which trilaminar layer gives you epidermis?
Ectoderm
Which non-keratinocyte cells migrate into the epidermis?
Melanocytes
Langerhans cells
Merkel Cells
Melanocytes are dervied from the ___________.
Neural crest
Langerhans cells migrate from ___________
Bone marrow
Merkel cells migrate from ___________.
Neural crest
Melanocytes can make which two types of pigment?
Eumelanin- brown/black
Pheomelanin- red
Melanin is synthesized from __________ and packaged in ____________.
tyrosine; melanosomes
Melanosomes are transported along ___________ and phagocytized by ___________.
dendrites; keratinocytes
Melanosomes are stored over the nucleus to protect DNA and folic acid from UV light. How?
Melanosomes are able to protect DNA becuase the melanin absorbs the UV light and prevents it from getting to DNA
One melanocyte supplies approximately _______ keratinocytes.
30
Melanosomes are degraded within ___________
in upper layers of skin
lysosomes
Where are melanosomes degraded?
In upper layers of skin
UV light induces local __________
Melanocyte-stimulating hormone (MSH)
Melanocytes are always seen in what layer of the epidermis?
S. Basale
Are melanocytes connected to other cells?
Melanocytes are attached to the basment membrane by hemidesmosomes but aren’t attached to other cells becuase they’re not apart of structural support and they need to get their dendrites into as many cells as possible and deliver melanin everywhere.
The cell body of melanocytes are in the stratum basale but the dendrites make their way to the ______________ layer to export their melanin.
S. Granulosum
Albinism
Defects in melanin synthesis
- May have melanocytes but can’t synthesize melanin
- Varying degrees
- Could come from a sporadic mutation or other types of mutation
Waardenburg syndrome
- Patches of white skin or hair, wideset eyes of blue or different colors
- Deafness
- Defect of neural crest mutation
*Remember melanocytes migrate from neural crest cells
Addision disease
- Deficient adrenal gland causes bronzing of skin
- ACTH activates melanocytes
Vitiligo
- Depigmentation caused by autoimmune attack
Skin conditions
Defect in melanin synthesis: ___________
Defect in neural crest migration:__________
Defect in adrenal gland: ___________
Depigmentation: ______________
Albunism
Waardenburg Syndrome
Addison disease
Vitiligo
Outside of skin, where can you get melanomas?
Iris
Hair
Substantia nigra of brain
What are some characteristics of a melanoma?
Asymmetrical
Borders are uneven
Multiple colors
Larger the 1/4 inch
Changing in Size, shape, and color
In what layer of the epidermis are langerhans cells found?
S. Spinosum
What do langerhans cells and melanocytes have in common?
They both have light cytoplasms
Langerhans cells are antigen-presenting immune cells that bind antigens an present to _____________
T- Lymphocytes
Langerhans cells contain large granules called____________
Birbeck granules
What are birbeck granules?
Endosomes specialized for phagocytosis
- Shaped like tennis-rackets
- Facilitate uptake of microbial fragments
*It’s not enough to just phagocytize the antigen but you must also take it back to the lymph node, this is the importances of the endosome portion
The presence of Langerhans Cells is diagnostic of what?
Langerhans Cell Histocytosis
- A type of cancer involving clonal proliferation of Langerhans cells.
- Clinically, manifests from isolated bone lesions to multisystem disease
What function do langerhans cells play in immune function?
Langerhans cells breach the basement membrane, enter lymph vessels, and are transported to lymph nodes to activate T-cells. T lymphocytes then migrate back to skin to neutralize antigen.
Hansen’s disease (leprosy)
In Hansen’s disease (leprosy), it is Langerhans cells that pick up the bacterium. Activated T-cells then mistakenly target Schwann cells that surround peripheral nerves.
*Innervation is destroyed and area will become necrotic
In ________, Langerhans cells of vaginal mucosa and foreskin take up the virus.
HIV
langerhans cells actively migrate between __________ to exit the epidermis and reach lymph nodes
keratinocytes
What do merkel cells and melanocytes have in common?
- Found in stratum basale
- Migrate from neural crest cells
How do merkel cells and melanocytes differ?
- Merkel cells attached to keratinocytes by desmosomes. Melanocytes do not.
- Merkel cells do not contain hemidesmosomes but melanocytes do.
Merkel’s cells are especially frequent in what area of the body?
Palms and soles
Merkel cells are activated by _____________ and they release their granules of _________ onto the axon, which will transport the action potentail back to the dorsal root ganglion, whcih will go to the dorsal root.
Mechanical pressure; neurotransmitters
Actinic (solar) keratosis
- Precancerous
- Crusty scaly growth
- May progress to squamous cell carcinoma
2nd most common skin cancer
Squamous cell carinoma
Why is melanoma such a dangerous type of cancer?
Melanocytes can migrate and once they do they can colonize other areas easily
Most common type of skin cancer
Basal cell carcinoma
What two things attach the epidermis to the dermis?
Hemidesmosomes
Interdigitating ridges
Papillae are especially pronounced in _____________ skin, where shear forces are greatest.
Thick
What are the two layers of the dermis? What type of connective tissue is found in each layer?
Papillary dermis: loose connective tissue
Reticular dermis: dense irregular connective tissue.
What is the importance of the loose connective tissue found in the papillary dermis?
Loose connective tissue is important because you need a lot of room for capillaries to come in right next to the basement membrane to nourish the epidermis, which is avascular
Outside of dense irreguar connective tissue, what else is found in the reticular dermis?
Collagen type I
Elastic fibers
- Collagen accounts for our tough skin
- Elastic fibers account for the amount of movement that our skin does
Vasospasm
Sudden contriction of blood vessels, reducing its diameter and flow rate
Which layer of the dermis plays a role in thermoregulation? How?
Papillary dermis contains a rich supply of vessels to supply the epidermis (which is avascular).
What role do AV shunts play in thermoregulation?
Under cold conditions, blood is sent through arteriovenous shunts (AV shunt) ,so less blood reaches the surface and heat is retained. Especially common in extremities.
* If AV shunt goes into overdrive, you get Raynaud’s disease
Raynaud’s disease
Localized vasopasm in response to cold
What does anhidrotic mean?
It means you don’t sweat
How does the body release heat?
Body releases heat through evaporation of eccrine sweat and dilation of cutaneous blood vessels.
Anhidrotic ectodermal dysplasia
- No active sweat glands
- Vulnerable to overheating
- Symptoms:
- Delirum
- Death
What happens to skin as we age?
Naturally aged skin loses dermal papillae, collagen and elastin, and is thinner; more easily detached.
Photaged skin is also known as _____________
Solar elastosis
What is solar elastosis?
A disorder in which the skin appears yellow and thickened as a result of sun damage
- Skin thicker (epidermal layer is thicker but dermal papillae and epidermal ridges are flattened out)
- Defective collagen and elastin
- Wrinkes and fragility
- Loss of suppleness
Cutis laxa (elastolysis)
- Skin is inelastic and hangs in loose folds
- Excessive mobility of joints
Ehlers-Danlos
- Excessive stretching of skin and joints
- Defective collagen
Scleroderma
- Autoimmune
- Enlarged collagen fibers
- Hardening of skin and loss of circulation
In cases of scleroderma, what will happen to all of the capillaries and arterioles in the dermis?
They will get squished by the enlarged collagen, so you lose circulation and you can get nercrosis of the extremities
The hypodermis is also known as _____________.
Subcutaneous layer or superficial fascia
The hypodermis is composed of:
Loose connective tissue with copious fat
What makes the hypodermis a good injection site?
Rich supply of blood vessels
The fat in the hypodermis is important in_______
Thermoregulation
Energy storage
Ease of movement
What are the epidermal appendages?
A.Eccrine sweat glands
B.Apocrine glands
C.Hair follicles
- Sebaceous glands
- Arrector pili muscles
D. Nails
Eccrine sweat glands are found primarily in what layer of the skin?
Dermis
Eccrine sweat glands are activated by _____________that secrete ____________.
sympathetic nerves; acetylcholine
What kind of gland are eccrine sweat glands?
Simple coiled tubular
Everywhere else beside eccrine sweat glands, the neurotransmiter for sympathetic nerves is norepinephrine. But in eccrine sweat glands the neurotransmitter is ___________.
Acetylcholine
On histo slides, which is lighter, the eccrine ducts or glands?
The secretory portion of the gland is much lighter than the actual duct
What are components of the secretory portion of the eccrine sweat gland? What are the functions of each?
Dark cells
- Secrete antibacterial glycoproteins
Clear cells
- Secrete fluid sweat by transporting NaCl water
Myoepithelial cells
- Contract to discharge fluid
_______________ sweat glands are the only type of sweat gland found in soles and palms (thick skin).
Eccrine
What type of epithelium makes up the secretory portion of eccrine sweat glands?
Stratified cubodial epithelium
Which glycoproteins are secreted by dark cells of eccrine gland?
Dermicidin
Defensin
______________ between the light cells aid in the rapid extrusion of NaCl and water.
Intercellular canaliculi
*Help the light cells “communicate” with the lumen
What type of epithelium is found in eccrine ducts?
Stratified cuboidal epithelium
What is the normal tonic state of sweat? How is this state maintained?
Hypotonic
Eccrine ducts are active in resorbing NaCl
Sweat is carried from eccrine glands into epidermis by ducts, where it is trasnported in a _____________ cavity between keratinocytes that terminate upon the surface.
Spiraling
Apocrine glands are primarily found in places with hair. What is the exception?
Apocrine glands secrete usually into hair follicle, except for modified apocrine glands (ceruminous glands that produce earwax and tarsal glands of Moll in eyelids).
In what layers of the skin are apocrine glands found?
Dermis
Hypodermis
What type of gland are apocrine glands?
Simple coiled branching gland
Apocrine glands are activated by ____________ that secrete_______________.
Sympathetic nerves; norepinephrine
Apocrine glands develop at puberty under the influence of _____________.
Sex hormones
What tyoe of epithelium is found in apocrine glands?
Simple cuboidal epithelium
The odor that is produced from fluid secreted by apocrine glands is due to _____________
Bacterial decomposition
What do apocrine glands secrete?
- Lipid/protein ricj, viscous fluid
- Pheromones
What type of secretion do apocrine glands display?
Merocrine
*They secrete by exocytosis of secretory granules
What three things make up the pilosebaceous unit?
Hair follicles
Sebaceous glands
Arrector pili muscles
Hairs are produced only in _________ skin.
Thin
What intermediate filament makes up hair?
Keratin
Hair is develop from the _________
Epidermis but involutes into dermis, carrying stem cell keratinocytes with them
What roles do the dermal papillae and melanocytes play in hair?
A dermal papilla inserts into the base of the hair bulb, bringing capillaries (nourish hair) up to the keratinocytes of the hair root. Melanocytes contribute pigment to differentiating keratinocytes, which form the various layers of the hair.
Why does chemotherapy result in hair loss?
Because keratinocytes are rapidly deivign cells and chemotherapy destroys rapidly dividing cells
Male patterned baldness
- Heredity
- shrinking of the follicle
- response to testosterone
Alopecia areata
- autoimmune
- round bald patches
What are possible causes of hair loss?
- male pattern baldness: heredity; shrinking of the follicle; response to testosterone
- post-menopausal: thinning; hormonal changes
- alopecia areata: autoimmune; round bald patches
- sudden loss: physical or emotional shock; chemotherapy
- hormonal changes: pregnancy, thyroid problems
What type of gland are sebaceous glands?
Branched, acinar glands
What type of secretion do sebaceous glands display?
Holocrine secretion
*The whole cell becomes secretory product. The glands are filled to the brim with lipid droplets and they end up bursting and the whole cell becomes the secretory product
Sebaceous glands are stimulated by __________, that begins being dramatically expressed at puberty.
Testosterone
Sebaceous glands are more numerous where?
Scalp
Face
Vernix Caseosa
Sebaceous glands are highly active in the fetus, under the influence of maternal androgenic hormones, forming the vernix caseosa, a cheesy, waterproof covering that protects the skin from amniotic fluid. After birth, the glands subside until pubertal hormones activate them.
*This why babies aren’t so wrinkly even though they’ve been sitting in fluid for 9 months.
Arrector Pili Muscles
- Bundle of smooth muscle fibers
- Associated with hair follicle and sebaceous glands.
- Helps expel sebum
- Makes hair stand on end (piloerection) under sympathetic activation (fear, goose bumps).
Arrector pili muscles are made up of ___________ fibers.
Smooth muscle
Hair, nails, sweat glands, mammary glands, salivary glands, lacrimal glands and teeth all derive from _______________ interactions, using common developmental pathways.
epithelial-mesenchymal
Hypohidrotic ectodermal dysplasia
- Result from a defect in the cell signaling molecules involved (ectodysplasin) will include thin hair, hypoplastic nails and glands, dry skin, absent teeth.
- Life threatening because of inability to sweat.
When you don’t have epidermal appendages it’s becuase there is a signaling molecule called ____________ that is faulty and you’re not having a complete conversation between your epidermis and the underyling dermis.
Ectodysplasin
What are the stages to epithelial-mesenchymal interactions?
- Epidermis secretes signals that cause condensations in underlying dermal mesenchyme.
- The condensed dermal mesenchyme responds by secreting factors that cause epidermis to form regionally specific cutaneous structures.
*Epithelium can only make structures coded for in its own species DNA.
