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Skin Fill in the Blanks...

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Integumentary System Reference pages: 488-502 “Histology a Text and Atlas” Dr. S. McLean, [email protected], MSB 203 Office hours: Mondays 9-11 am LEARNING OUTCOMES: By the end of this lecture you should be able to: 1. List the functions of the skin 2. Compare and contrast the layers of the skin: epidermis, dermis, hypodermis 3. Differentiate between the different layers of the epidermis in terms of structure and function 4. Explain the processes of epidermal water barrier formation and pigment donation 5. List the different cell types in the skin CASE STUDY Rupert McLean:

OVERVIEW OF OUR SKIN

Layers of the Skin: Epidermis: stratified squamous epithelium- derived from Dermis: connective tissue (loose and dense irregular)- derived from Hypodermis: loose CT….mainly

tissue. (called superficial fascia in gross

anatomy). Derivatives of skin include sweat glands, hair, sebaceous glands and nails.

Functions of the skin: 1) Barrier: protects against physical, chemical, and external environmental biologicals 2) Immunologic: Langerhans cells 3) Homeostasis: 4) Sensory information: 5) Endocrine functions- hormones and cytokines, vitamins 6) Exocrine functions- sweat, sebum

NOTES/QUESTIONS:

Thick Skin

Thin Skin

Location in body Presence of hair? Epidermis- thick or thin? Dermis- thick or thin?

Layers of the Skin The epidermis is made up of layers of keratinocytes that become more differentiated as they reach the skin’s surface. Thick skin has 5 layers, whereas thin skin has 4 layers. 5 LAYERS OF THE EPIDERMIS 1) stratum basale=stratum germinativum Made of progenitor cells that constantly renew epithelium. Made up of a single layer of low columnar/cuboidal basophilic cells resting on the . 2) stratum spinosum aka “prickle cells” Several layers of cells thick. Nodes of Bizzozzaro = desmosomes 3) stratum granulosum 1-3 cells thick. “Granular” looking because contains keratohyalin molecules. The keratoyhyalin molecules contain the protein which works to aggregate keratin. 4) stratum lucidum Poorly staining part of stratum corneum only found in thick skin. Eosinophilic refractile cells containing large amounts of . Nuclei not visible. 5) stratum corneum Anucleate, flattened cells with no cytoplasmic organelles. Cell membranes coated with glycolipid (acylglucosylceramide). This layer gets thicker when exposed to more wear and tear: callus formation. LAYERS OF THE DERMIS Epidermal ridges/ rete ridges: where the epidermis projects into the Dermal papillae: projections of dermis into the

. .

Interpapillary pegs: down growth of epidermis into dermis where sweat duct passes from dermis to epidermis Dermal ridges: form basis for - basal cells attach to dermis via hemidesmosomes: attach to basementmembrane via anchoring filaments- anchoring fibrils run from basal lamina to the dermis below.

NOTES/QUESTIONS: Question: What is the purpose of the epidermal ridges/dermal papillae? LAYERS OF THE DERMIS 1. Papillary layer: loose C.T. carrying blood vessels and nerves – form dermal papillae. Collagen type I/III. 2. Reticular layer: deep C.T. dense irregular CT. Variable thickness but ALWAYS thicker than papillary layer. Type I collagen. HYPODERMIS Layer of adipose tissue called the storage and insulation.

. Has roles in energy

Cells of the Epidermis Keratinocytes: Melanocytes: melanin production Langerhans’ cells: antigen presentation Merkel’s cells: sensation (PNS)

KERATINOCYTE DIFFERENTIATION Keratinocytes are the main cell type in epidermis. 1. In the stratum basale, keratinocytes have the standard synthetic machinery. They are basophilic due to large numbers of ribosomes. 2. In the stratum spinosum, the keratinocytes become eosinophilic as the tonofilaments (intermediate filaments) are formed. Keratinocytes in the stratum spinosum begin making keratohyalin granules and lamellar bodies. 3. In the stratum granulosum, you get a large accumulation of keratohyalin granules and lamellar bodies. keratohyalin granules + = soft keratin 4. In the stratum corneum peptidases break apart desmosomes that are holding adjacent cells together- this leads to the sloughing off of this layer. EPIDERMAL WATER BARRIER Made of 2 layers: 1. Cell envelope- made primarily of proteins deposited on inner surface of plasma membrane 2. Lipid envelope- made primarily of lipids attached to cell surface. The most important component is

NOTES/QUESTIONS: EPIDERMAL WATER BARRIER CONT’D Lamellar bodies are formed by the Golgi apparatus in the keratinocytes of the stratum spinosum and stratum granulosum. They are responsible for making pro-barrier lipids as well as lipid-processing enzymes. The lamellar bodies are released by into the space between cells of the stratum granulosum and stratum corneum.

MELANOCYTES Dendritic in appearance, skin pigment producing cells make The primary function of melanin is to protect cells against non-ionizing UV radiation. Usually in stratum basale and their processes reach into keratinocytes into the stratum spinosum. melanosomes tyrosinase

Tyrosine

DOPA

Melanin

Enzymes (tyrosinase) convert tyrosine to 3,4 dihydroxyphenylalanine (DOPA) DOPA converted to melanin in melanosomes (membrane bound structures in melanocytes) Melanosomes transferred to keratinocytes by process called “pigment donation”. Question: What is the difference between melanosomes in lighter skin vs. melanosomes in darker skin?

LANGERHANS’ CELLS Found in the stratum spinosum. i. Macrophage-like cell that present antigens to recirculating T-cells ii. Nucleus very basophilic, cytoplasm clear.

MERKEL’S CELLS Function in cutaneous sensation. Found in the stratum basale and are joined to adjacent keratinocytes by desmosomes. Closely associated with afferent myelinated nerve cells. Identified by the presence of neurosecretory granules

NOTES/QUESTIONS:...