Histology Of The Integumentary System

Question 1

Epidermis layer

Answer 1

Is the outermost layer and is the physical barrier between internal and external environment
- dervived of surface ectoderm and stratified squamous keratinized epithelium

Consists of 4(or 5 if thick skin) layers

Possess melanocytes, merkel cells and langerhans cells

Question 2

Stratum basale layer of the epidermis

Answer 2

deepest layer of epidermis
Is composed of a single layer of cuboidal- low columnar basal stem cells in contact with a basement membrane
- possess abundant desmosomes which provides tight adherence to neighboring cells of the stratum spinosum
- stains basophilic on histology

Is the location site of melanocytes and Merkel cells

Also is the site of the majority of keratinocytes and keratin production

Question 3

Stratum spinosum layer of the epidermis

Answer 3

thickest region of the epidermis especially in regions of continuous friction and pressure (thick skin)

Basophilic keratinocytes in this multi-layered region are polyhedral with a centrally located nucleus.

• produce keratin filaments which assemble into larger microscopically visible bundles, tonofibrils (promote binding at desmosomes)
• **cells often shrink which makes the intracellular attachments look like little “spines” which is why this layer is nicknamed the spiny layer.
• **possess langerhans cells

Question 4

Stratum granulosum

Answer 4

Consists 3-5 layers of flattened keratinocytes that are nearing their terminal differentiation and have the most intense granular accumulation

Also stains basophilic due to dense keratohyaline granules

• *this is the last layer of live keratinocytes, above this are dead keratinocytes**
• in this layers, keratinocytes dump their contents into the extracellular space and produce a lipid rich impermeable layer around the cell which is the prime contributor to the skins barrier against water loss

Question 5

Stratum lucidum

Answer 5

Only found in thick skin

2-3 layers of dead flattened and anucleated cells, that are relatively translucent but still remain their desmosomes

Their eosinophilic cytoplasm has lost all of their organelles and is packed with keratin bundles.

In some preparations it has a “clear” appearance or refractive appearance

Question 6

Stratum corneum layer

Answer 6

Consists of 15-20 layers of dead squamous, fully keratinized keratinocytes

• cytoplasm has no cytosol and leaves on plasma membrane behind
• these cells are also called “squames” and are embedded in lipid-rich intercellular cement

the “squames” are constantly shed at the apical surface of the epidermis (dandruff)

Question 7

Melanocytes

Answer 7

Neural crest dervived cell that produces pigmentation molecules of the skin

• majority of them reside in the stratum basale and have a pale staining rounded cell body
• possess hemidesomoses to attach to basement membrane, but no desmosomes so dont adhere to each other

Eumelanin = brown/black

Pheomelnanin = reddish

melanin produced does not stay in melanocytes but rather accumulates in keratinocytes that are contacting the cytoplasmic projections

Question 8

How does melanin move from melanocytes?

Answer 8

1) melanin pigments accumulate within vesicles until they mature into melanosomes
2) melanosomes are transported to the distal tips of the melanocytes numerous cytoplasmic projections
3) adjacent keratinocytes phagocytize these tips to internalize the melanosomes and transport them toward the nucleus
4) internalized melanosomes accumulate to form a Supranuclear cap which protects DNA from harmful damage due to UV radiation

Question 9

What is skin color due to physiologically

Answer 9

It is NOT due to density of the melanocytes in the epidermis!

It is due to the RATE at which melanocytes produce melanosomes and the density of melanosomes that accumulate in the Supra nuclear cap

Question 10

Merkel cells

Answer 10

Epithelial tactile cells that act as specialized mechanoreceptors of the epidermis and form synaptic junctions with somatic afferent nerve endings

**Located within the stratum basale and have rounded cell bodies with pale-staining cytoplasms

Question 11

Langerhans cells

Answer 11

Monocyte derived cells that serve as APCs within the stratum spinosum layer

Account for 2-8% of epidermal cells

Stain pale and are distinguished via special immunohistochemistry

Question 12

Dermis layer over view

Answer 12

Is richly vascularized (compared to epidermis) and is innervated

Back dermis = paraxial mesoderm
head dermis = Paraxial mesoderm and neural crest cells
Body dermis = lateral plate mesoderm

Primary functions are to provide vascular action and innervation, as well as attach the epidermis to the hypodermis.

Question 13

Two sub layers of the dermis

Answer 13

1) papillary layer
- thin layer of areolar CT that directly underlies the basement of the epidermis and forms dermal papillae
- contains fibroblast cells that produce ECM and includes type 1 and type 2 and type 4 collagen fibers
- also numerous leukocytes, mast cells and APCs are found throughout

2) reticular layer
- thicker layer of dense irregular CT that is deep to the papillary layer
- has fewer cells and more fibers (mainly type 1 and elastic fibers)
- also abundant proteoglycans with GAGs (dermatan sulfates)
- THIS is the adherence layer of dermis to hypodermis

Question 14

What are the two vessel plexues within the dermis?

Answer 14

1) subpapillary plexus
- network of microvasculature that lies between the two dermal layers and gives rise to the capillary branches that extend into the dermal papillae
- forms nutritive network just below the epidermis

2) deep vascular plexus
- network of macro vasculature and lymph vessels near the interface of the dermis and hypodermis

Question 15

Arteriovenous anastomoses in the dermis

Answer 15

Connects the two plexus between each other and regulates blood flow via thermoregulation

Cold = vasoconstriction to subpapillary plexus
- reduces heat loss

Heat = vasodilation to subpapillary plexus
- increases heat loss

Question 16

Hypodermis layer

Answer 16

Composed of areolar CT with varying degrees of adipose tissues
- derived from somatic layer of lateral plate mesoderm

highly vascularized and is the site of drug injections and IV placement

Other functions:

• attached the skin to the deep investing fascia of the MSK system
• support small-medium cutaneous nerves and vessels that supply the skin
• houses and supports the secretory portion fo some cutaneous glands
• insulation, cushioning and movement of intersitital fluid

Question 17

Unencapsulated receptors of the skin

Answer 17

free nerve endings which the terminal portions of the neuronal projections are not invested with glial cells

1) tactile discs (merkel cells)
- low threshold tonic and slow mechanoreceptors
- sensitive to sustained logistical touch and is used to discern texture

2) root hair plexueses
- form network around hair follicle and act as mechanoreceptors that are sensitive to hair movement

3) epidermal free nerve endings
- free nerve endings in the epidermis that terminate in the stratum granulosum
- are sensitive to fine touch, pain, temperature and pruritis

Question 18

Encapsulated receptors

Answer 18

terminal portions of nerve endings are invested with Schwann cells

1) Tactile corpuscles
- located within dermal papillae and very concentrated in lips, fingertips, palms and soles of feet
- respond to light touch, low frequency stimuli against the skin that deforms their shape

2) lamellated (pacinian) corpuscles
- highly branched nerve endings that are composed of concentric lamellae of Schwann cells and collagen fibers
- respond to coarse touch, pressure and vibrations

3) ruffini corpsucles
- nerve endings are encapsulated by a thin, collagenous fusiform capsule that is anchored to surrounding CT. Act as mechanoreceptors in stretch and twisting of the skin (tension and torque respectively)

4) Krause end bulbs
- nerve endings that have a thin collagenous capsule
- respond to low frequency vibrations and thermoreceptors (especially temps below 20C)

Question 19

Phases of hair growth

Answer 19

1) anagen phase
- extended period of mitotic activity and growth

2) catagen phase
- brief period of arrested growth and regression of the hair bulb

3) telogen phase
- extended period of inactivity which leads to shedding of hair sometimes

Question 20

4 regions of hair follicles

Answer 20

1) hair bulb
- deepest region of the follicle that has vascularized loos CT around it (dermal papilla)
- during anagen phase this is the site of cell division that gives rise to different layers of hair
- also contains melanocyteswhcih produces melanosomes

2) follicular bulge
- serves as reservoir of epidermal stem cells and is near the arrector pilli muscle attachment site
- epidermal cells either go down to bulb and renew cells there or go up to sebaceous glands and renew cells there

3) isthmus (neck)
- site of sebaceous duct opening into follicle

4) infundibulum
- site of discharge of the sebum produced by sebaceous gland

Question 21

Arrector pili muscles

Answer 21

Smooth muscle that spans the superfical dermis layer to the hair bulb

Is innervated by postsynaptic sympathetic fibers. Contraction of the arrector pili causes hair to stand up “goosebumps”

Question 22

Sebaceous glands

Answer 22

Usually tied directly to hair follicles

Produces sebum on hair shaft and stratum corneum which has weak antibacterial and Funchal properties as well nutrients
- undergo holocrine secretion

Secretion increases in response to testosterone and adrenal androgens which is why teens get acne

Question 23

3 cell types within the eccrine (sweat) gland

Answer 23

1) clear cell
- pale staining cells that line the basement membrane and secrete majority of sweat

2) dark cells
- eosinophilic-staining cells that line the lumen and undergo merocrine secretion to release a mixture of glycoproteins used in anti-bacterial

3) myoepithelial cells
- flattened cells at the basement membrane and extend around the acini. Contract to move watery secretions into the ducts

Question 24

Apocrine glands of the skin

Answer 24

Found in the axillary and perineal regions

• dont become active until puberty
• secrete numerous secretory granules via apical bless that are released into the lumen
• is apocrine and merocrine secretion
• secretes pheromones primarily, but also earwax/cerumen, mammillary glands for milk and eyelid cebum (Moll glands)

Question 25

Skin repair steps

Answer 25

1) initiation of blood clotting within the wound and the release of PDGF, chemokines, cytokines and substance B 2) macrophages and neutrophils enter the wound and initiate an inflammatory response to remove bacteria and debris 3) epithelialization begins as keratinocytes at cut edges of the stratum basale proliferate and migrate beneath and through the blood clot - if too much is lost, new epithelial cells migrate from bulge in the hair follicle to help 4) blood clot gradually dries out to become scab 5) fibroblasts in the dermis proliferate and secrete new collagen fibers to form granulation tissue which replaces the scab/blood clot 6) epidermis reestablishes its continuity over the wound site 7) granulation tissue undergoes remodeling and produces scar tissues.

Question 26

Process of keratinization

Answer 26

1) synthesis and accumulation of keratin proteins by keratinocytes of the stratum basale and stratum spinosum 2) tonofibrils form as keratin filaments assemble in bundles. These tonofibrils bind to desmosomes to reinforce the cytoskeleton and intercellular adhesions 3) keratohyaline granules of the stratum granulosum are formed by linkage of tonofibrils by fillagrin proteins and other associated proteins 4) lamellar granules filled with various lipids and glycolipids are also present in keratinocytes of the stratum granulosoum and undergo exocytosis to produce a lipid-rich water-impermeable barrier that surrounds the cells 5) Autophagy of the nucleus and organelles is the final step which gives rise to the stratum lucodum (thick only) and stratum corneum. Cells are now “squames”

Question 27

Why does skin that is chronically exposure to friction and pressure have more dermal papillae?

Answer 27

To increase surface area and overall adhesion of the epidermal peg/ridge -> dermis

Question 28

Albinism vs vitiligo

Answer 28

Albinism (hypopigmentation) - a congenital disorder due to a defect in one of the enzymes involved in the melanin-producing pathway - **the most common enzyme deficiency = tyrosinase Vitiligo (depigmentation) - an acquired condtion that causes patches of skin pigmentation due to loss or decreased melanocyte activity - causes range from environmental, genetic or autoimmune

Question 29

Most common types of skin tumors (outside of merkel cell)

Answer 29

1) basal cell carcinoma - derived from cells of the stratum basale 2) squamous cell carcinoma - derived from cells of the stratum spinosum 3) melanocytes nevi/moles - benign proliferation of melanocytes 4) malignant melanoma - dysplasia of preexisting moles or nervus or de novo, proliferation is rapid and can quickly penetrate through the basement membrane into the dermis where they can metastasize into blood and lymph vessels 5) Merkel cell carcinomas - thought to arise from Merkel cells and are uncommon and very aggressive/difficult to treat. - is the most dangerous skin cancer (2x lethality of malignant melanoma)

Question 30

Friction blisters

Answer 30

Separation between epidermis and dermis of thick skin due to excessive rubbing that fills with lymph (interstitial) fluid - continued rubbing leads to thickening of the stratum corneum

Question 31

Pemphigoid

Answer 31

Autoimmune disorders that affect the dermal-epidermal junction and leads to TENSE filled blisters - most typically found in areas of friction or flexion

Question 32

Pemphigus

Answer 32

Autoimmune disorders that effects the intercellular junctions between keratinocytes that leads to FLACCID blisters and erosions

Question 33

Alopecia vs hypertrichosis

Answer 33

Alopecia = excessive hair loss due to reduction of hair follicles in a region of skin which hair generally was before - involves genetics and hormones and environmental factors Hypertrichosis = excessive hair growth over and above what is considered “normal” for the age sex and ethnic origins

Question 34

Psoriasis

Answer 34

Overactive keratinocyte production and inflammation causes dry overactive autoimmune T-cells Also produces redness,irritation and itching as well as desquamation of the skin

Question 35

Age changes in skin

Answer 35

Thickening of collagen fibers Less collagen synthesis Loss of GAGs Extensive crosslinking of collagen and loss of elastic fibers Solar elastosis (weakening fo collagen strength and flexibility with exposure to sun) Thin epidermis Increased skin and ligament extensibility caused by defective collagen fibril processing

Question 36

What receptors in the skin are lost in scleroderma?

Answer 36

Loss of meissner tactile corpuscles