LAB 3 Tissues 2022 PDF

LAB 3 HISTOLOGY I TISSUES At the end of this exercise, you should be able to: 1. Identify microscopic samples of epithelial, connective, muscle and nervous tissue, and the components of each tissue type. 2. Describe the general characteristics of each of...

LAB 3 HISTOLOGY I TISSUES At the end of this exercise, you should be able to: 1. Identify microscopic samples of epithelial, connective, muscle and nervous tissue, and the components of each tissue type. 2. Describe the general characteristics of each of the tissues, including structure, function, and location. 3. Identify at least two locations in the body for each tissue type. Lab introduced you to the general structure and function of the parts of the cell. Groups of similar cells that work together to carry out a specialized function are called tissues. To perform specific body functions, various tissue types are organized into organs. The arrangement of these tissues within an organ determines the organ's structure and function. Tissues are divided into four major categories based on cell arrangement, shape, and function: epithelial, muscular, connective and nervous. Histology is the microscopic study of tissue structure and function. When viewing slides it is important that you begin by scanning each slide at low power (4x) to examine the entire tissue. A slide may have only one tissue on it, or may have several tissues, of which you want to see only one. Once you have located the tissue you want to view, increase the magnification to medium (10x) then to high power (40x) to observe individual cells. At high power, rotate the fine focus knob back and forth an eighth of a turn to see the details of finer structures, like cilia and cell membranes. It is strongly suggested that you make your own sketches of the slides, and include any features in bold or other structures that will assist with subsequent identification. You should include at least two locations for each of these tissues in the tables below. PART A: EPITHELIAL TISSUE Epithelial tissues cover external body surfaces, line cavities and hollow organs, and form glands. The functions of epithelial tissue can include protection, absorption, secretion, filtration, and excretion. Some characteristics that distinguish them from other tissues are: They do not have a direct blood supply, but get their nutrients by diffusion from blood vessels located in the underlying connective tissue. The tissue always attaches to the basement membrane (the basal surface) and always has one free surface (the apical surface), where cells are exposed to the lumen. The cells can regenerate by mitosis. May produce specialized secretions. 1. Covering and Lining Epithelia Epithelial cells are classified based on whether the cells are arranged in layers and the shape of the cells in the surface/apical layer. A single layer of cells is a simple epithelium. Two or more layers of cells are called stratified epithelium. In a stratified epithelium, only the cells of the basal layer attach to the basement membrane while the cells of the apical layer face the lumen. Pseudostratified epithelium is a modified simple epithelium – all the cells attach to the basement membrane (farthest from the lumen) though not all reach the lumen. Flattened, irregular cells are squamous. Cuboidal cells are cube-shaped; the height and width are about equal. Columnar cells are taller than they are wide. 3-1 Figure 3.1 Cell shapes and arrangement of layers of epithelial tissues. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. The slides in your slide box are numbered in the same order as the information in the lab manual. Observe each of the slides listed below. Unless otherwise indicated, use the 40x objective lens to see individual cells. Pay attention to which organelles are visible, the cell shape, and any other structures indicated in the list for you to find. In general, the nucleus of a cell stains darker than the cytoplasm. Since it can sometimes be difficult to see plasma membranes, you should practice scanning for the shape of the nucleus to help you identify the shape of the cell. Once you have found a representative section on your slide, showing cells that resemble those in photomicrographs, sketch what you see and label as many structures as possible. 3-2  Description: A single layer of flattened cells with a central nucleus 1. simple squamous (nucleus looks flattened and oval from side, oval or round from epithelium above). slide may be called Locations: Lines blood and lymphatic vessels, alveoli, glomerular cheek cell capsule, inner surface of tympanic membrane, and forms serous membranes. Functions: thinness allows passage of materials by diffusion and filtration in areas where protection is not important; secretes serous fluid within serous membranes. simple squamous drawing Figure 3.2 Whole mount slide of simple squamous epithelium, magnified 240x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 12th Ed., Copyright © 2009 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-3  Description: A single layer of cube-shaped cells with a large, 2. simple cuboidal central nucleus. epithelium slide may be called Locations: kidney slide Functions: simple cuboidal drawing Figure 3.3 Simple cuboidal epithelium, magnified 100x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-4  Description: A single layer of cells which are taller than they are 3. simple columnar wide, with an oval-shaped nucleus found in the lower half of cell. epithelium Find goblet cells, may see microvilli. Locations: Functions: simple columnar drawing Figure 3.4 Simple columnar epithelium showing goblet cells and microvilli, magnified 675x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-5  Description: As in simple ciliated columnar. Not all cells reach the 4. pseudostratified lumen; nuclei are seen at different levels in the cells. Look for ciliated columnar goblet cells and cilia. epithelium Locations: Functions: pseudostratified ciliated columnar drawing Figure 3.5 Pseudostratified ciliated columnar epithelium, magnified 500x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-6  Description: Several layers of cells. Find squamous at the apical 5. stratified surface and cuboidal or columnar at basal surface of the tissue. squamous epithelium Locations: see slide of vagina Functions: stratified squamous drawing Figure 3.6 Stratified squamous epithelium, magnified 200x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-7  Description: When relaxed, cells at the apical surface look large and 6. rounded. Not all cells reach the apical or basal surface. Cells can be a variety of shapes and sizes. Locations: slide may be called ureter slide Functions: drawing Figure 3.7 , magnified 400x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. Compare the functions of simple epithelium with that of stratified epithelium. Name two types of epithelial tissues that have goblet cells. 3-8 2. Glandular Epithelia Many epithelial tissues contain single-celled or multicellular glands that produce secretions. If the secretions are released into the surrounding interstitial tissue and distributed by the blood stream, the glands are called endocrine glands. Endocrine glands such as the thyroid and pituitary secrete hormones, and will be covered extensively in Biol 1191. If the secretions are released via ducts onto an epithelial surface, the gland is considered to be an exocrine gland. Examples of exocrine secretions are milk, sebum and the enzymes in the digestive system. The unicellular exocrine gland that produces mucus was seen in the slide of pseudostratified ciliated columnar epithelium (goblet cells). Identifying multicellular glands on a slide can be complicated by the angle of the section taken. In many cases the lumen of the duct is not visible in the center of the tubule or at the epithelial surface. Look for groupings of cells that are cuboidal, short columnar or pizza-shaped with a round nucleus. Description: Darker purple clusters of cells (acini) make up the 7. pancreas majority of the pancreas. The ducts are not usually visible. Light pink areas are connective tissue and blood vessels. The larger group of lighter purple cells (in inset photo) is an endocrine islet. Location: Function: pancreatic acini and islets drawing Figure 3.8 Pancreas showing islets and acini, inset image magnified 200x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-9  Description: Prominent ducts with visible lumen and acini. 8. salivary gland Appearance of acini varies with type of salivary gland (serous fluid or mucus secreting). Location: Function: salivary gland drawing Figure 3.9 Submandibular salivary gland showing mucous acini on right and serous acini on left, magnified 350x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-10  Description: Located beside the hair follicle. Acinar cells are tear 9a. sebaceous drop in shape. Lumen very narrow, if visible. gland (on hairy skin slide) Location: Function: sebaceous gland drawing Figure 3.10 Hair, hair follicle and associated sebaceous gland, magnified 60x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-11  Description: Are coiled, tubular glands located in the deep dermis 9b. sudoriferous or upper subcutaneous region. Lumen can be seen in the coiled gland regions, rarely seen leading to the surface. (on hairy skin slide) Location: Function: Sudoriferous gland drawing Figure 3.11 Cross section through the secretory portion of a sweat gland, magnified 400x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-12 PART B: CONNECTIVE TISSUE The most common functions of connective tissues are to protect, support or bind together other tissues. They also insulate, transport, and act to store energy as fat. The characteristics of connective tissues are: A non-living extracellular matrix produced by the cells of the connective tissue. Have many types of cells that are scattered throughout the tissue. Most are highly vascularized. The extracellular matrix between the cells consists of two major components: 1) A ground substance that may be fluid, semi-fluid, gelatinous or very hard. 2) A combination of three different types of fibers, whose function is to strengthen and support the tissue. Collagen fibers often occur in parallel bundles, adding strength but not stiffness. Collagen fibers are found in bone, cartilage, tendons and ligaments. Elastic fibers are strong, yet can be stretched up to 150x their relaxed length without breaking. Elastic fibers are found in skin, blood vessel walls and in the lungs. Reticular fibers form a branching network, providing support and strength. They form the framework for many soft organs like the spleen and lymph nodes, and form part of the basement membranes of epithelial tissues. Figure 3.12 Representative cells and fibers present in connective tissues. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. When observing connective tissue slides, all of the material on the slide is the tissue you want to see, except for the hyaline cartilage slide. Scan the whole slide at 4x and 10x to find a clear view, then focus at 40x. Use the arrangement and size of the fibers, the shape and placement of the cells within the ground substance, and the shape of the nucleus when identifying each type of connective tissue. 3-13  Description: Has all three types of fibers and many different types 10. areolar of cells, with a loose, irregular arrangement. connective tissue Locations: Functions: areolar drawing Figure 3.13 Areolar connective tissue, magnified 300x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-14  Description: Nucleus and cytoplasm are displaced peripherally due 11. adipose to a large internal fat droplet. Matrix is sparse and the cells are connective tissue closely packed. Locations: Functions: adipose drawing Figure 3.14 Adipose tissue, magnified 200x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-15  Description: A network of dark reticular fibers with many cells 12. reticular containing small, round nuclei. connective tissue Locations: Functions: reticular drawing Figure 3.15 Reticular connective tissue, magnified 225x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-16  Description: Wavy bundles of parallel collagen fibers. Note the 13. dense regular darkly stained cells between bundles of light pink fibers. connective tissue slide may be called Locations: tendon Functions: dense regular drawing Figure 3.16 Dense regular connective tissue, magnified 250x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-17  Description: Sparse numbers of chondrocytes lie in lacunae. The 14. hyaline matrix is made up of fine collagen fibers that are not visible. cartilage Locations: Functions: hyaline drawing Figure 3.17 Hyaline cartilage, magnified 200x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-18  Description: The matrix (collagen fibers and mineral salts) is 15. bone organized into layers called lamellae. Osteocytes sit in lacunae that are connected by canaliculi. Best seen using the 10x objective lens. Locations: Functions: compact bone at 10x drawing Figure 3.18 Compact bone, magnified 550x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-19  Description: Cells are found in a fluid matrix (plasma). Fibers are 16. blood smear observed only during clotting. Find nucleated white blood cells (leukocytes), red blood cells (erythrocytes) which lack a nucleus, and platelets (thrombocytes). Locations: Functions: erythrocytes, leukocytes, platelets drawing Figure 3.19 Blood, magnified 1230x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. How do connective tissues differ from epithelial tissues? 3-20 PART C: MUSCULAR TISSUE Muscle tissue contracts to provide body movements, to pump blood, and to control movement of materials through the viscera. The skeletal and smooth muscle slides may have both longitudinal and cross section samples of the cells you are looking for. Be sure you are observing the longitudinal views. Scan the slides to find the view which best shows the structures listed below. The cardiac muscle slide has been cut from a section of curved tissue. Find an area of the tissue where the cells are large and close together to see the identifying structures. Figure 3.20 Microscopic appearance of the three types of muscle tissues. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-21  Description: Long, cylindrical, striated, multinucleate muscle 17. skeletal muscle fibers. Nuclei are located on the periphery of the cells. Considered to be voluntary. Locations: Functions: skeletal muscle fibers drawing Figure 3.21 Skeletal muscle tissue, magnified 400x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-22  Description: Short, branched cells that typically have a single, 18. cardiac muscle centrally located nucleus. Have intercalated discs and striations. Considered to be involuntary. slide may be called Location: intercalated disc Functions: cardiac muscle drawing Figure 3.22 Cardiac muscle tissue, magnified 600x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-23  Description: Short, spindle-shaped cells with a single, centrally 19. smooth muscle located nucleus. Considered to be involuntary. Locations: Functions: smooth muscle drawing Figure 3.23 Smooth muscle tissue, magnified 350x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. Smooth muscle fiber, magnified 500x, from Tortora and Derrickson, Principles of Anatomy and Physiology, 14th Ed., Copyright © 2014 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. 3-24 How are smooth muscle cells and skeletal muscle fibers similar to each other? How are they different? SIMILARITIES DIFFERENCES smooth + skeletal How are skeletal muscle fibers similar to cardiac muscle cells? How are they different? SIMILARITIES DIFFERENCES cardiac + skeletal What is the function of intercalated discs? PART D: NERVOUS TISSUE Nervous tissue consists of cells that can convert chemical or mechanical stimuli to electrical signals (neurons), and cells with important support functions (neuroglia). Neurons have three basic parts – a cell body containing a nucleus and other organelles, dendrites and axons. On most slides, it is difficult to distinguish between axons and dendrites, though axons may appear thicker. 3-25  Description: Large cell body with multiple extensions. 20. neurons Locations: Functions: Description: Much smaller and more numerous than neurons. neuroglia Locations: Functions: neurons, neuroglia drawing Figure 3.24 Neuron from spinal cord and glial cells, magnified 430x. From Tortora and Derrickson, Principles of Anatomy and Physiology, 11th Ed., Copyright © 2006 by Biological Sciences Textbooks, Inc. and Bryan Derrickson. This material is used by permission of John Wiley & Sons, Inc. What are the basic functions of nervous tissue? How is nervous tissue involved in maintaining homeostasis? 3-26 II THE INTEGUMENTARY SYSTEM At the end of this exercise, you should be able to: 1. Discuss the functions of the integumentary system. 2. Identify and discuss the functions of the epidermis, the dermis and the hypodermis. 3. Identify and describe the functions of the accessory structures of the skin. 4. Differentiate between apocrine and eccrine sweat glands, and distinguish between sudoriferous and sebaceous glands. The integumentary system consists of the skin and its accessory structures – glands, nails, hair, muscles and nerves. It is involved in protection against mechanical stress, regulates water and heat loss, and is the site of Vitamin D synthesis. The integument has two distinct regions. A superficial epidermis, composed of stratified squamous epithelium, and a deeper dermis, composed of a layer of connective tissue. The hypodermis or subcutaneous layer below the dermis is not part of the skin, but will be studied here. The epidermis is made of keratinized stratified squamous epithelium (non-keratinized stratified squamous was studied earlier). In thick-skinned areas like the palmar and plantar surfaces there are five layers in the epidermis: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum and stratum basale. In thin-skinned areas, the stratum lucidum is not present. The dermis has finger-like projections, the dermal papillae, attaching it to the epidermis. Numerous collagen and elastic fibers attach the dermis to the subcutaneous layer. Unlike the epidermis, the dermis is highly vascularized. A number of cutaneous sensory receptors are found in the dermis. When stimulated by environmental changes (a touch, cold temperature, or a pinch) they transmit messages to the brain (CNS) for interpretation. The hypodermis attaches the dermis to the underlying structures. It is composed primarily of adipose and areolar connective tissue, contains large blood vessels that supply the dermis, and stores fat. A variety of accessory structures, such as finger and toe nails, sweat glands and hair, are found in the skin. Hair and hair follicles are derived from the stratum basale but can extend from the surface of the skin to project into the dermis and hypodermis regions. Arrector muscle of the hair (arrector pili muscle) attached to the hair follicles cause the hairs to stand upright. Several exocrine glands, which are also epidermal in origin, are found in the skin. Sebaceous glands produce oil and are connected to the hair follicles, while sudoriferous glands produce sweat. 3-27 Identify the following structures on the skin models, and label Figure 3.25. LAYER/STRUCTURE DESCRIPTION FUNCTION epidermis stratum corneum outermost layer, undergoes exfoliation stratum lucidum stratum granulosum stratum spinosum stratum basale next to basement membrane, single layer of cuboidal or columnar cells dermis dermal papillae tactile corpuscle/ detect the onset of the Meissner corpuscle sensation of touch and low frequency vibration detect high frequency lamellar corpuscle/ vibrations Pacinian corpuscle subcutaneous layer hair follicle hair arrector muscle of the hair (arrector pili muscle) 3-28  LAYER/STRUCTURE DESCRIPTION FUNCTION sebaceous glands connected to hair follicles sudoriferous glands eccrine apocrine axillary and genital areas Figure 3.25 Sectional view of the Figure 3.26 Layers of the epidermis skin and subcutaneous layer. From of thick skin. From Tortora and Derrickson, Tortora and Derrickson, Principles of Anatomy and Principles of Anatomy and Physiology, 14th Ed., Physiology, 14th Ed., Copyright © 2014 by Biological Copyright ©2014 by Biological Sciences Textbooks, Inc., Sciences Textbooks, Inc. and Bryan Derrickson. This and Bryan Derrickson. This material is used by material is used by permission of John Wiley & Sons, Inc. permission of John Wiley & Sons, Inc. 3-29 1. Observe the slide of thick skin (palm or sole of foot) on the side bench. Using the 4x objective lens scan the slide, from superficial to deep, and observe the epidermis, dermis and subcutaneous regions. The epidermis typically stains darker than the dermis. Dermal papillae can be seen at the junction between the epidermis and dermis. The dermis is a mass of connective tissue and large blood vessels. Your slide may not show the hypodermis, deep to the dermis. At 10x and 40x, observe the layers of the epidermis. The stratum corneum of thick skin is made of many layers of darkly stained, dead, anucleate, flattened, keratinocytes. The stratum lucidum appears as a pale layer, sandwiched between the corneum and darker stained granulosum. Deep to the stratum granulosum is the stratum spinosum and the stratum basale. The stratum basale is a single row of columnar or cuboidal keratinocytes. Sketch and label the slide of thick skin at 4x or 10x. Estimate the thickness of the stratum corneum of thick skin, in millimeters. Use the 10x objective lens. __________ mm. slide of thick skin drawing Most of the cells forming the epidermis are keratinocytes. Where would you expect to find the thinnest keratinized epidermis? Give two functions of keratinocytes. What is the function of the capillary networks in the dermis? 3-30 2. Observe the slide of hairy skin on the side bench. Scan the slide with the low power objective lens to see the three regions of the skin and the dermal papillae. On this slide, only the stratum corneum and stratum basale are easily identified. Estimate the thickness (in millimeters) of the corneum layer using the 10x lens. __________ mm. Identify the hairs and hair follicles that sit at an angle to the skin surface. Depending on the angle of the section, not all follicles or hairs appear to be connected to the surface. Notice that the cells of the hair follicles stain the same colour as the epidermis, darker than the dermis. Find a hair follicle on your slide that has an arrector pili muscle. What type of muscle tissue are the arrector pili made of? You may need to switch to the 40x objective lens to identify the muscle cells. Find sebaceous (oil) glands connected to the hair follicles, approximately ⅔ of the way up the follicle. Using the 40x objective lens, note the round nuclei and irregularly shaped cells of the gland. Are the lumens of the acinar glands visible? There are two types of sudoriferous (sweat) glands. Your slide likely contains only eccrine sweat glands, commonly seen as a cross section of coiled tubules at about the same height as the base of the hair follicles. The duct of the gland and the pore opening at the skin surface are not usually visible. Apocrine sweat glands are found mainly in the axillary and genital areas, and can be seen on the skin model. Sketch and label the slide of hairy skin at 4x or 10x. Include as many structures from the list on page 3-29 as possible. slide of hairy skin drawing What regions of the body do not have hair? 3-31 3. Observe the slide of pigmented skin on the side bench. The brown keratinocytes visible in this slide show an accumulation of the pigment melanin in their cytoplasm. Melanin is produced by melanocytes scattered throughout the stratum basale and is transferred to other cells in the epidermis. Which layers of the epidermis have accumulations of melanin in their cells? What is the function of melanin in the skin? The presence of a second pigment, carotene, may also influence skin colour. What is the origin and function of carotene in the stratum corneum? As a review, compare and contrast keratinized (e.g. skin slide) and non-keratinized (e.g. vagina slide) stratified squamous epithelial tissue with respect to structure and function. STRUCTURE FUNCTION keratinized non-keratinized 3-32