Skin and Skin Appendages Histology PDF

Integumentary System (Skin and Skin Appendages) Histology University of Northern Philippines College of Medicine Department of Medici...

Integumentary System (Skin and Skin Appendages) Histology University of Northern Philippines College of Medicine Department of Medicine MD 103 Laboratory Microscopic Body Structure Skin and Skin Appendages Module Tutor: Ana Patricia Villanueva-de Grano, MD, FPAPRAS OBJECTIVE: By the end of the module student must complete the following objectives: 1. Know the layers of the skin 2. Understand how the components of the serve its various functions. 3. Correlate the histological structure of the skin and its appendages with their functional significance as well as the resulting functional impairment when structural abnormalities occur. To Do List: 1. Read Junqueira's Basic Histology, 15th ed, McGraw Hill - Lange, 2018 by A.L. Mescher. Chapter 18 “Skin” 2. Read Wheater’s Functional Histology, 6th ed., Elsevier, 2014 by B. Young et al. Chapter 9 “Skin” 3. Read Lab manual 4. Attend class 5. Take Quiz 6. Pass assignment on week after module (Microsoft Word/Place name and Section/Arial 12/1.5 spacing) Lectures 1. The Histology of the Skin and Skin Appendages (Integumentary System) Activities 1. Synchronous class on scheduled date 2. Asynchronous learning with individual readings 3. Assignment: Answer the questions in the manual. Laboratory Module INTEGUMENTARY SYSTEM Skin is the largest organ in the body, typically accounting for 15%-20% of total body weight. It possesses regional variation, from from 0.5mm thick on the eyelids to 4.0mm thick on the heels of your feet. Also known as integument or the cutaneous layer, skin consists of three main layers. The surface layer of the skin, or the epidermis, is nonvascular and lined by keratinized stratified squamous epithelium of ectodermal origin. The dermis is a layer of mesodermal connective tissue which supports the epidermis. At the irregular junction between the dermis and epidermis, projections called dermal papillae interdigitate with invaginating epidermal ridges to strengthen adhesion of the two layers. Epidermal derivatives include hairs, nails, and sebaceous and sweat glands. Beneath the dermis lies the subcutaneous tissue or hypodermis, a loose connective tissue layer consisting of adipose tissue with supporting fibrous bands. The subcutaneous tissue binds the skin loosely to the underlying tis- sues and corresponds to the superficial fascia of gross anatomy. The various functions of skin (protective, sensory, thermoregulatory and metabolic) are mediated by one or more of its major regions—the epidermis, dermis, and hypodermis. CELLS OF THE EPIDERMIS 1. Keratinocytes are the most numerous cells of the epidermis and undergo a terminal differentiation process called keratinization. The form and function of these cells change as they pass from basal to superficial locations. The layers of the epidermis from basement membrane to skin surface include: a. Stratum basale or germinativum is one layer of mitotically active cuboidal cells attached by hemidesmosomes and integrins to the basement membrane and to each other by desmosomes. Cells of all the layers are generated from the keratinocytes in this layer. Therefore, you may see mitotic figures. The keratinocytes in this and the overlying layers contain melanin granules that have been transferred to them by melanocytes. b. Stratum spinosum has several layers of polyhedral cells attached to each other by desmosomes at the tips of short projections containing bundled keratin, or tonofibrils. Because the cells pull apart during preparation, the attachment sites give the cells a spiny appearance. The stratum basale and the stratum spinosum are collectively known as stratum malphigii. c. Stratum granulosum is a thinner layer of keratinocytes, now flattened and are recognizable by their basophilic keratohyalin granules containing filaggrin and other proteins binding tonofibrils. d. Stratum lucidum consists of non-nucleated cells with eleidin droplets and is only found in thick skin. e. Stratum corneum consists of superficial layer of dead, flattened, anucleate, keratin-filled keratinocytes Cells divide in the basal layer, and move up through the layers above, changing their appearance as they move from one layer to the next. It takes around 2-4 weeks for this to happen. This continuous replacement of cells in the epidermal layer of skin is important. The epidermal layer of the skin is directly exposed to the outside world, and therefore is vulnerable to its damaging effects. There is constant proliferation of cells in the bottom layer (stratum  basale) which constantly move up to the top where they are lost. This means damaged cells are continually shed, and replaced with new cells. 2. Melanocytes are found in the stratum malphigii and they are capable of synthesizing melanin pigments which they transfer to neighboring cells through process. The cytoplasm of melanocytes does not stain with H&E, giving the appearance of a halo. They are best appreciated through the use of DOPA reagent. 3. Langerhans Cells are stellate cells in the stratum spinosum and perform immune function as they trap surface antigens. 4. Merkel Cells are found in the stratum germinativum and function as mechanoreceptors for reception of tactile stimulus. DERMIS The dermis is a dense irregular type of connective tissue made up of two layers: Papillary layer: more superficial, with loose connective tissue underlying the basal layer of the epidermis containing blood vessels (subpapillary vascular plexus), nerves, and lymphatic vessels. Dermal papillae may contain sensory nerve endings called Meissner’s corpuscles. Reticular layer: deeper layer with dense, irregularly arranged connective tissue, containing coarse bundles of collagenous and some elastic fibers, with hair follicles, sebaceous glands, sweat glands, nerves and deep plexus of blood vessels. SUBCUTANEOUS LAYER The subcutaneous layer consists of loose connective tissue that binds the skin loosely to the subjacent organs, making it possible for the skin to slide over them. This layer, also called the hypodermis or superficial fascia, contains adipocytes that vary in number in different body regions and vary in size according to nutritional state. CUTANEOUS SENSORY RECEPTORS 1. Free nerve endings which detect pain and temperature 2. Merkel cells are light-touch or tactile receptors associated with sensory fibers 3. Meissner corpuscles are encapsulated elliptical mechanoreceptors that surround sensory axons and also detect light touch 4. Lamellated or pacinian corpuscles are located deeper in the dermis and subcutaneous layer which are ovoid and much larger than Meissner corpuscles, for detection of pressure or firm touch SKIN APPENDAGES 1. Hair follicle is an invagination of the epidermis made up of an external dermal root sheath and an epidermal root sheath internally. It is expanded basally to form the hair bulb. 2. Sebaceous gland is a simple or branced saccular gland whose duct opens into the hair follicle. Together with the hair follicle, it forms the pilo-sebaceous unit. 3. Sweat gland is a convoluted tubular gland whose duct opens independently into the surface of the skin. It is important for thermoregulation. 4. Nails are horny plates on the dorsal surfaces of fingers and toes and are made up of clear cells containing hard keratin characterized by clear, shrunken, nuclei. 5. Arrectores pilorum muscle is a strip of smooth muscle attaches to the base of the hair follicle. Its contraction causes the hair to stand on its end known as the goose flesh appearance. THICK AND THIN SKIN Thick skin is found in the palms and soles, and is characterized by a considerable thickness of the stratum corneum, with abundant sweat glands, thicker and taller dermal papillae, prominent surface ridges, abundant blood vessels and absent pilosebaceous unit. Thin skin is found notably on the face, and is characterized by a fine checker board pattern of ridges and moderate number of pilosebaceous units and sweat glands. Its stratum corneum is not considerably thickened. Layers of the Skin (LPO, H&E) PHOTO CREDIT: http://histology.med.yale.edu/skin/home.php E= Epidermis K= Keratin PD= Papillary Dermis Epidermis (HPO, H&E) The cell layer that occupies the deepest location is the stratum basale (SB). This is one cell deep. Just above this is a layer several cells in thickness, the stratum spinosum (SS). It consists of cells that have spinous processes on their surface. These processes meet with spinous processes of neighboring cells and, together, appear as intercellular bridges (arrows, inset). The next layer is the stratum granulosum (SGr), whose cells contain keratohyalin granules (arrowhead, inset). On the surface is the stratum corneum (SC). This consists of keratinized cells, i.e., cells that no longer possess nuclei. The keratinized cells are flat and generally adhere to other cells above and below without evidence of cell boundaries. Pigment (P) PHOTO CREDIT: HISTOLOGY A TEXT AND ATLAS 6th ed p 515 In thick skin, a fifth layer, the stratum lucidum, is seen between the stratum granulosum and the stratum corneum. PHOTO CREDIT: https://www.ouhsc.edu/histology/Text%20Sections/Integument.html Identify the pointed structure: (2 pts) __________________________ What is the main function? (1pt) __________________________ Identify the pointed structure: (2 ts) __________________________ What is the main function? (1 pt) __________________________ Identify and differentiate the pointed layers: (5 pts) A: __________________________ ____________________________ ____________________________ B: __________________________ ____________________________ ____________________________ What are the structures present? (4 pts) 1)__________________________ 2)__________________________ A special stain that is used to visualize the structures: (1 pt) ____________________________  Identify the parts of a hair follicle: (6 pts) A: ______________________ B: ______________________ C: ______________________ DRAW AND DIFFERENTIATE ECCRINE GLAND AND APOCRINE GLAND: (10 pts) ECCRINE GLAND APOCRINE GLAND Identify: (3 pts) A: ______________________ B: ______________________ C: ______________________ What structure is formed? (1 pt) ________________________ DIFFERENTIATE THIN SKIN AND THICK SKIN: (10 pts) Thick Skin Thin Skin __________________________________ _________________________________ __________________________________ _________________________________ __________________________________ _________________________________ __________________________________ _________________________________ __________________________________ _________________________________ __________________________________ _________________________________ __ Identify the pointed structure: (1 pts) __________________________ What is the lining of the nail bed? (1 pt) __________________________ QUESTIONS 1. What are the cell junctions in the stratum spinosum? (1 pt) 2. Where are the melanocytes located? (1 pt) References & Photo credits: 1. Junqueira's Basic Histology, 13th ed, McGraw Hill - Lange, 2013 by A.L. Mescher. Chapter 18 “Skin” 2. Wheater’s Functional Histology, 6th ed., Elsevier, 2014 by B. Young et al. Chapter 9 “Skin” 3. Hill, M.A. (2020, August 29) Embryology Neonatal nail.jpg. https://embryology.med.unsw.edu.au/ 4. Netter’s Essential Histology, 2nd edition 5. “Adapted from Skin and Skin Appendages histogy lab manual (by Dr. Eugenio R. Pipo III)