Histology: epidermis, dermis, and hypodermis

What layer of skin?

keratinized stratified squamous epithelium; derived from ectoderm; attached to the basement membrane; avascular

epidermis

What layer of skin?

dense connective tissue; derived from mesoderm, vascular

dermis

What layer of the skin?

subcutaneous fascia composed of septta and adipose; vascular

hypodermis

Identify each layer of the skin (A-C)

A. Dermis

B. Hypodermis

C. Epidermis

What is thick versus thin skin? Where is it found, what makes the difference, and what layer is affected?

thick versus thin is based on the epidermis

thick is found on the palms and soles; thin is everywhere else

thick skin has stratum lucidum

glabrous versus non-glabrous skin

glabrous: hairless skin

non-glabrous: hairy skin

think being hairless is more glamorous

What is the predominant cell type of the epidermis?

they originate in the deepest layer of the epidermis and grow outward

keratonocytes (produce keratin)

What are the layers of the epidermis?

“can lauren get some bitches?”

strutum corneum, stratun lucidum (thick skin), stratum granulosum, stratum spinosum, stratum basale

Identify each layer of the epidermis: (A-D)

-Bonus: Is this thick or thin epidermis, why?

A: Stratum granulosum

B: Stratum spinosum

C: Stratum corneum

D: Stratum basale

This is thin epidermis because there is no stratum lucidum pictured

What layer and what sublayer?

outermost layer; made up of keratin-filled dead keratinocytes termed squames, layer that varies the most in thickness

epidermis: stratum corneum

What layer and sublayer?

thin layer of cells that is only evident in thick skin

epidermis: stratum lucidum

what layer and sublayer?

diamond shaped keratinocytes, contain keratohyalin granules

epidermis: stratum granulosum

What layer and sublayer?

irregular, polyhedral keratinocytes with desmosomes that link neighboring cells

epidermis: stratum spinosum

What layer and sublayer?

deepest layer, separated from the dermis by the basement membrane and attached by the hemidesmosomes/ cells are cuboidal to columnar and are mostly keratinocytes

epidermis: stratum basale

explain the role of the basement membrane and the hemidesmosomes

basement membrane: separates the stratum basale (deepest layer of epidermis) to the dermis

hemidesmosomes: attaches the stratum basale to the dermis

explain the development and migration of keratinocytes (include tonofilaments, keratohyalin granules, lamellar bodies, and tonofibrils)

they start at the deepest layer of the epidermis (basale) and go out to the stratum corneum

basal: the KC make tonofilaments that are bundles together to make tonofibrils

spinosum: they start to produce the keratohyalin granules and produce lamellar bodies

granulosum: they flatten some and accumulate the keratohyalin granules

corneum: lose the lamellar bodeis and nuclei. The keratohyalin granules turn tonofibrils into a homogenous keratin matrix

Explain the keratinocytes being desquamated. How is it triggered

the enzyme KLK (kallikrein-related serine peptidase) is triggered to break-down the desmosomes

the lymphoepithelial kazal-type inhibitors are what inhibit the KLK from breaking it down too early (not at the top)

the KLK are triggered to do the breakdown at the top because the pH is lower near the surface

Explain psoriasis and epidermal hyperplasia. Why is it happening, what layer is most affected, what do we see?

when there is accelerated maturation of the keratinocytes then they do not form properly (8-10 days) and there is insufficient development of tonofibrils and keratohyaline.

This causes the granular layer to not form properly

the skin surface has white flakes over a thick red epidermis

Explain the epidermia cell and lipid envelope. What is their purpose?

water barrier

cell envelope: insoluble proteins on the inner surface of the plasma membrane (loricrin)

lipid envelope: layer attached to the outer surface of the plasma membrane, lamellar bodies that contain a mixture of oils that get exocytized

What are the 3 major cell types in the epidermis?

keratinocytes, melanocytes, and langherhan’s cells

Identify each cell type (A-C)

A: Langerhan’s cell

B: Keratinocyte

C: Melanocyte

What type of cells are depicted on this histology slide?

Melanocytes

Where are the melanocytes located?

in the epidermis, specifically in the stratum basale

What is the condition where we have melanocytes but they do not produce melanin?

albinism

What is the condition where the melanocytes are targeted by the immune system and die? (autoimmune)

vitiligo

1. What type of cell is depicted on this histology slide?

2. What is the cellular component circled in pink? (and where is this located)

1. Langerhan’s cells

2. Birdeck’s granules (located in the Langerhan cell cytoplasm)

What cells serve as both APCs and macrophages? where are they located?

Langerhan’s cells

in the epidermis, specifically the stratum spinosum mostly

What is within the cytoplasm of the Langerhan cells and encloses the pathogens?

birdeck granules

What cells are involved in delayed-type hypersensitivity reactions like contact dermatitis?

langerhan’s cells

at the dermal-epidermal junction, ____ anchor cells to the hemidesmosome

____ bind the hemidesmosomes to the papillary dermis

tonofibrils go to hemidesmosome

loops of collagen go to papillary dermis

What layer houses the epidermal appendages and sensory neurons?

dermis

Identify each sublayer of the_______ (layer shown). (A,B)

The layer is the dermis.

A. Papillary dermis

B. Reticular dermis

What is the layer and sublayer?

outer layer connected to the basement membrane, composed of loose connective tissue (areolar), plentiful ground substance, type I and III collagen

dermis: papillary layer (top layer)

what layer and sublayer?

deeper and thicker layer, less cellular, consists of dense irregular connective tissue, bundles of type I collagen fibers and course elastic fibers

dermis: reticular layer (inner/bottom layer)

In addition to blood vessels (being vascularized) what is another component of the dermis that runs along near the vasculature?

lymphatics

what layer of the dermis has langer lines? what are they?

the reticular layer

the collagen and elastic fibers have a consistent orientation and form regular lines of tension. If incisions are made along these lines then there is less scarring

What layer?

also called the subcutaneous fascia, contains adipose lobules, skin appendages (hair follicles), sensory neurons, and lood vessels. is important for energy storage and delivering injections

hypodermis