Skin Histology PDF

# Skin and Skin Appendages (Integumentary System) ## Dr. Amal Abd El-hafez Associate professor of histopathology ## Objectives At the end of this lecture, you will be able to: 1. Define skin 2. Describe the structure of the epidermis 3. Describe the structure of the dermis 4. Compare between thi...

# Skin and Skin Appendages (Integumentary System) ## Dr. Amal Abd El-hafez Associate professor of histopathology ## Objectives At the end of this lecture, you will be able to: 1. Define skin 2. Describe the structure of the epidermis 3. Describe the structure of the dermis 4. Compare between thin & thick skin ## Introduction - The skin is the heaviest organ in the body (about 16% of body weight). - The skin consists of: 1. Epidermis 2. Dermis - Hypodermis is **NOT** a skin layer, and consists of loose C.T and fat cells. ## The junction of dermis and epidermis - The junction of dermis and epidermis is irregular. - It shows projections of the dermis called **dermal papillae** interdigitating with evaginations of the epidermis known as **rete ridges**. - **Skin appendages:** include nails, hairs, and sebaceous and sweat glands, all are derived from epidermis. ## Functions 1. Receptor organ. 2. Protection: (micro-organisms; Chemicals and ultraviolet rays) 3. Formation of Vitamin D3 4. Personal "forensic" identification (fingerprints). ## I - The Epidermis - Consists mainly of a **keratinized stratified squamous epithelium** resting on basement membrane. - It is formed of 5 layers (from deep to superficial): 1. Stratum basale 2. Stratum spinosum (spongiosum) 3. Stratum granulosum 4. Stratum lucidum (only in thick skin) 5. Stratum corneum ## Layers of The Epidermis ### 1 - Stratum basale: - Single layer of basophilic columnar cells perpendicular to the basement membrane. - Mitotically active, responsible for epidermal turnover. ### 2 - Stratum spinosum (spongiosum) - Polygonal cells, have surface spin-like projections (keratin filaments and desmosomes). ### 3 - Stratum granulosum - Three layers of flattened polygonal cells - Contain coarse basophilic keratohyaline granules and lamellar bodies formed of lipid to act as a barrier for skin sealing. ### 4 - Stratum lucidum - Only in thick skin. - Translucent layer, formed of flat cells. - No nuclei or organelles. ### 5 - Stratum corneum (horny layer) - Multiple layers of flattened non-nucleated eosinophilic cells filled with keratin. ## Cells of The Epidermis 1. Keratinocytes 2. Melanocytes 3. Langerhans "dendritic" Cells 4. Merkel's Cells ## Keratinocytes - These are epithelial cells that form the stratified squamous keratinized epithelium of the epidermis. - The most numerous cells found in the epidermis. - The basal layer divide to replace the superficial dead cells. - Bound together with various cellular junctions. ## Non-keratinocytes Include: 1. Melanocytes 2. Dendritic (Langerhans) cell 3. Merkel's cells ## Melanocytes - They give the skin its color. - They are present in stratum basal & spinosum. - Melanin granules migrate through the cytoplasmic extensions and enter keratinocytes. - Contain pigments: - Eumelanin (dark hair) - Pheomelanin (red hair) ## Langerhans "dendritic" Cells - Star-shaped cells, mainly in stratum spinosum - Derived from macrophages. - They are antigen-presenting cells (APC). ## Merkel's Cells - Generally found in thick skin - Similar to epidermal epithelial cells but show dense granules. - They are mechano-receptors. ## II - The Dermis - Consists mainly of dense irregular connective tissue, variable in thickness. - Arranged in 2 layers: - Superficial papillary dermis. - Deep reticular dermis. - Share in the formation of basement membrane. - Contains: fibroblasts, mast cells, macrophages and leukocytes - The dermis contains hair follicles, and sebaceous and sweat glands (collectively called skin appendages; derived from epidermis). ## Types of Skin ### 1 - Thin Skin - All over the body. - Irregular dermal papillae. - Contain skin appendages. - No stratum lucidum. ### 2 - Thick Skin - In palms and soles. - Regular dermal papillae. - No hair follicles or sebaceous glands. - Shows stratum lucidum. ## RECOMMENDED REFERENCES, WEBSITES - Junqueira's Basic Histology: Text and Atlas, Thirteenth Edition 2013 - ISBN-13: 978-0071780339 - ISBN-10: 0071780335 Edition: 13th - The histology tutor: http://www2.yvcc.edu/histologyzoomer/Histology Tutorials/histology_tutorials.htm ## THANK YOU!