It acts as a barrier, and because of this it takes a constant beating and is always being shed. Its thickness varies depending on the location of the skin. Visceral and parietal layer (pleura, pericardium, peritoneum), - covers body surface, thick and waterproof. The two primary functions of the stratum basale are 1) proliferation and 2) attachment of the epidermis to the dermis. What are the functions of the integumentary system? The deepest part of the epidermis also contains melanocytes. The cutaneous membrane is the technical term for our skin. It is comprised of 4-5 distinct layers, depending on the type of skin. Most of the skin can be classified as thin skin. Next The Dermis. water, plasma proteins, electrolytes etc. Oh no! The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. Describe briefly the processes which occur during wound healing and after skin grafting. • Compare the composition of the papillary and reticular regions of the dermis. These cells produce melanin, which gives the skin its color. The main difference between epidermis and hypodermis is that epidermis is the outer protective layer of the skin of vertebrates, covering the dermis, whereas hypodermis is the subcutaneous tissue found in the lowermost layer of the skin.. Epidermis and hypodermis are two layers of the integumentary system of animals and plants. Either four or five layers may be present, depending on where the epidermis is located (figs. The epidermis is composed of keratinized stratified squamous epithelium. Eumelanin is black or brown. The epidermisis composed of keratinized, stratified squamous epithelium. Learn vocabulary, terms, and more with flashcards, games, and other study tools. It does not have any blood vessels within it (i.e., it is avascular). c. all layers of the epidermis and part of the dermis. The Cutaneous Membrane. Composition is the term used to describe the arrangement of the visual elements in a painting or other artwork. Bodytomy takes a closer look at these layers along with their functions. Stratum basale, also known as the basal cell layer, is the innermost layer of the epidermis. • Compare the composition of the papillary and reticular regions of the dermis. The dermis is composed of two layers. The stratum basale (also called the stratum germinativum) is the deepest epidermal layer and attaches the epidermis to the basal lamina, below which lie the layers of the dermis.The cells in the stratum basale bond to the dermis via intertwining collagen fibers, referred to as the basement membrane. The epidermis is the outer layer of the skin, composed of terminally differentiated stratified squamous epithelium, acting as the body's major barrier against an inhospitable environment. Derived from ectoderm, the epidermis is composed of stratified squamous epithelium that varies in thickness from 0.007 to 0.12 mm. Blood makes up about 8% of the human body weight. The stem cells are located in the stratum basale and migrate outwards in their differentiation process. The epidermis, which is the topmost layer, actually has 5 sub-layers. It is made of four or five layers of epithelial cells, depending on its location in the body. The skin is the first line of defense and keratinocytes serve as a barrier between an organism and its environment. Become a skin guru and learn more about each of the layers of the epidermis and why they are so important for your skin’s health! The epidermis is composed of keratinized, stratified squamous epithelium. The epidermis is thicker than you might expect and has five sublayers. To ensure the best experience, please update your browser. Skin that has four layers of cells is referred to as “thin skin… Within the epidermis are several distinct layers, consisting of (from bottom to top): 1. Describe the origin, function, and location of melanocytes and their differences in different types of skin. The stratum granulosum marks a transition from living skin cells to completely dead skin cells of the outermost layer of the epidermis. 6-3. The epidermis helps to keep out bacteria and toxins, holds water, and gives skin its color. Quiz: The Epidermis Previous The Epidermis. They are the papillary layer (the upper layer) and the reticular layer (the lower layer). It is made of four or five layers of epithelial cells, depending on its location in the body. Pheomelanin is reddish. In thin skin, the epidermis is a mere 0.08 mm thick and the stratum corneum is only a few cell layers deep. We shed around 500 millionskin cells each day. Epidermis definition, the outer, nonvascular, nonsensitive layer of the skin, covering the true skin or corium. His Its thickness depends on where it is located on the body. It is ectodermal in origin. Cells of the stratum basale essentially represent germinal cells (“brick generators”) responsible for the generation of all cells of the epidermis. Just below the granule layer lies the prickle cell layer of skin cells. It contains four to five layers (depending on body location), each with an important role. • Contrast the structure, distribution, and functions of hair, skin glands, and nails. The properties of air closely resemble that of the vacuum of space as a result. The stratum basale is the layer closest to the dermis. The epidermis is a dynamic structure acting as a semi- permeable barrier with a layer of flat anuclear cells at the surface (stratum corneum). Composition Of The Thermosphere. covers external surface of the body and is the largest organ of the body in weight; superficial, thinner, epithelial epidermis; deeper, thicker, connective dermis; subcutaneous, layers of the epidermis (deep to superficial), single row of cuboidal or columnar keratinocytes; stem cells; cell division continually produces new keratinocytes, 8-10 layers of numerous keratinocytes; superficial layers become somewhat flattened; produced by stem cells in basal layer; some can still divide; provides strength and flexibility to the skin, 3-5 layers of flattened keratinocytes that are undergoing apoptosis; degenerate as they move further away from dermal blood vessels; marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata, 4-6 layers of flattened clear, dead keratinocytes; present only in thick skin (fingertips, palms, soles); add toughness in this region of thick skin, 25-30 layers of flattened dead keratinocytes; final product of the differentiation process of the keratinocytes; cells overlap one another, papillary: 1/5 thickness of the total layer; thin collagen and fine elastic fibers; surface area increased by dermal papillae, melanin:melanocytes (melanin producing cells); brown to black; number of melanocytes is the same in all people; amount of pigment produced influences color, structure: root is deep to the shaft that penetrates into the dermis; hair follicle surrounds the root; epithelial root sheath downward continuation of the epidermis; dermal root sheath is the dermis surrounding the hair follicle; bulb is the base of each hair follicle surrounding the dermal root sheath; papilla of the hair contains areolar ct and many blood vessels that nourish the growing hair follicle; hair matrix is responsible for the growth of existing hairs, and the production of new hairs when old hairs are shed; arrector pili muscle that causes "goose bumps", structure: simple, branched acinar (rounded) glands, structure: eccrine: simple, coiled tubular; apocrine: simple, coiled tubular but have large ducts and lumens, structure: nail body, free edge, nail root, lunula, nail bed, cuticle, nail matrix, by liberating sweat at its surface and by adjusting the flow of blood in the dermis - regulates body temperature; blood vessels dilate (become wider) to increase heat loss; blood vessels constrict (become narrow) to reduce heat loss, dermal blood supply carries 8-10% of the total blood flow in a resting adult, keratin protects underlying tissues from microbes, abrasion, heat, and chemicals; resist invasion by microbes; sebum keeps skin and hairs hydrated and kills bacteria; melanin protects against UV light, tactile sensations (touch, pressure, vibration, and tickling) and thermal sensations (warmth and coolness); pain, excretion: elimination of substances from the body, requires activation of a precursor molecule in the skin by UV rays in sunlight; calcitrol is the most active form of Vitamin D, it is a hormone that aids in the absorption of calcium from foods in the gastrointestinal tract into the blood, 1) division of stratum basale cells and migration across wound, 1) inflammatory phase: blood clot forms in the wound and loosely unites the wound edges, week 4) epidermis consists of only a single layer of ectodermal cells, - skin and hair provide barriers that protect all internal organs from damaging agents in external environment. The epidermis is in itself made up of three separate layers, which are all comprised of millions of connecting tissues of different thickness woven together. All but the deepest layers are composed of dead cells. Describe the turnover and shedding of cells of the epidermis. The skin’s primary role is to help protect the rest of the body’s tissues and organs from physical damage such as abrasions, chemical damage such as detergents, and biological damage from microorganisms. Epidermis, in zoology, protective outermost portion of the skin.There are two layers of epidermis, the living basal layer, which is next to the dermis, and the external stratum corneum, or horny layer, which is composed of dead, keratin-filled cells that have migrated outward from the basal layer.The melanocytes, responsible for skin colour, are found in the basal cells. These cells produce melanin, which gives the skin its color. The deeper hypodermis is made up of fat and even more connective tissue. • Explain how epidermal wounds and deep wounds heal. The stratum basale is the deepest layer, while the stratum corneum is the outermost layer of epidermis. The dermis consists of two layers: The papillary layer is a thin outer layer of areolar connective tissue with fingerlike projections called dermal papillae that protrude into the epidermis.In the hands and feet, the dermal papillae generate epidermal ridges (sweat from the epidermal ridges leaves fingerprints). Superficial layer of the dermis; Areolar connective tissue and dermal papillae water lilies. “Thick skin” is found only on the palms of the hands and the soles of … The epidermis is the top layer of your skin. Usually, the upper epidermis has a less number of guard cells compared to the lower epidermis. • Explain the basis for different skin colors. –Describe the common markings of the skin. Main roles: makes new skin cells, gives skin its color, protects the body. how does carotene accumulation influence skin color? Stratum Spinosum and Granulosum. Under the squamous cells are round cells called basal cells. The epidermis is composed of keratinized, stratified squamous epithelium. The epidermis, which contains no blood vessels, is made up of layers of closely packed epithelial cells. • Describe the layers of the epidermis and the cells that compose them. Describe the blood and lymphatic circulations of skin. The hypodermis is the innermost (or deepest) and thickest layer of skin. The epidermis is the outermost layer of the three layers of skin. The deepest part of the epidermis also contains melanocytes. Giving skin its color: The epidermis makes melanin, which is what gives your … The volume percentage of all blood cells in the whole blood is about 45% of adults (hematocrit). The epidermis is composed of multiple layers of flattened cells that overlie … The five layers of the epidermis include the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Immune Role of Keratinocytes. a. This extraordinary organ system protects the internal structures of the body from damage, prevents dehydration, stores fat, and produces vitamins and hormones.It also helps maintain homeostasis within the body by assisting with the regulation of body temperature and water balance. The epidermis regenerates in orderly fashion by cell division of keratinocytes in the basal layer, with maturing daughter cells becoming increasingly keratinised as they move to the skin surface. Stratum Basale. The epidermis is the topmost layer of skin – the one you can see and feel on the surface. From the outside in, these layers are the following: Stratum corneum (literally the “horny layer”) is about 20 layers of flat, scaly, dead cells containing a type of water-repellent protein called keratin. How the COVID-19 Pandemic Will Change In-Person Retail Shopping in Lasting Ways. ). • Describe the layers of the epidermis and the cells that compose them. The stratum granulosum is the third layer of the epidermis that lies below the stratum corneum and stratum lucidum. The epidermis has five layers which renew themselves from the inside, pushing each layer up one stage until the skin replaces itself about every 40 days. Merkel cells occur deep in the epidermis at the epidermal‐dermal boundary. 1 Components of the Integumentary System include 1. cutaneous membrane (skin) a. epidermis (superficial epithelium) b. dermis (under lying connective tissue layer) 2. hair 3. nails } 2,3,4 accessory structures 4. exocrine glands • account for 16% of body weight It does not have any blood vessels within it (i.e., it is avascular). The epidermis is mostly made up of flat, scale-like cells called squamous cells. The epidermis (along with other layers of the skin) also protects the internal organs, muscles, nerves, and blood vessels from injury. Birds and mammals are endothermic animals. • Contrast the structure, distribution, and functions of hair, skin glands, and nails. • Describe how the integumentary system contributes to homeostasis. - bounded by epidermis superficially and subQ adipose tissue below - BM zone sharply separates dermis from the basal layer of the epidermis - Dermis is comprised of a dense, irregular collagen network, elastic fibers and ground substance, or ECM, along w/ associated resident cells, such as fibroblasts, dermal dendritic cells, macrophages and mast cells The rest consists of liquid plasma (e.g. As such, these cells are the most mitotically active keratinocyte… Skin that has four layers of cells is referred to as “thin skin.” From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. It is made of four or five layers of epithelial cells, depending on its location in the body. Histologically, the stratum basale is a single layer of cuboidal keratinocytes that directly abut and attach to the dermis. Human skin - Human skin - The epidermis: The epidermis is thicker on the palms and soles than it is anywhere else and is usually thicker on dorsal than on ventral surfaces. They also keep Langerhans cells of the epidermis and lymphocytes of the dermis in place. Anatomy & Physiology Exam 2 Describe the skin composition Epidermis - keratinized stratified squamous epithelium Dermis Deeper layer Primarily dense irregular connective tissue Hypodermis Layer of areolar connective tissue and adipose tissue Not part of the integumentary system Describe the composition and function subcutaneous tissue Explain the function of the cells (i.e. The epidermis is made up of collagen, elastin fibers and nerves. https://quizlet.com/197885397/ap-chapter-5-integumentary-system-flash-cards The main layers of the epidermis are: stratum corneum, stratum lucidium, stratum granulosm, stratum spinosum, stratum germinativum (also called stratum basale). Its thickness depends on where it is located on the body. The dermis is a tough layer of skin. The epidermis is divided into five layers. The integumentary system consists of the largest organ in the body: the skin. how does hemoglobin influence skin color? The epidermis provides a protective waterproof barrier that also keeps pathogens at bay and regulates body temperature. The air is extremely thin (with almost a zero amount of air density), and gravity almost non-existent in the mesosphere. Start studying 5 layers of the Epidermis. Learn vocabulary, terms, and more with flashcards, games, and other study tools. In certain areas of the body that require greater protection, such as the palms of the hands and the soles of the feet, the stratum corneum is much thicker. The epidermis is mostly made up of flat, scale-like cells called squamous cells. KEY TAKEAWAYS. The epidermis is the outermost of the three layers that make up the skin, the inner layers being the dermis and hypodermis. It is the thinnest on the eyelids at .05 mm and the thickest on the palms and soles at 1.5 mm. Cells in the epidermis divide and move up to replace cells in the layers above, changing as they move from one layer to the next. Birds and mammals are endothermic animals. General Sciences Skin Structure, Growth, & Nutrition Part 3: Describe the structure and composition of the skin. Evolution of the atmosphere, process by which Earth’s modern atmosphere arose from earlier conditions. New cells are made in the lower layers of the epidermis. It's thickest on the palms of the hands and soles of the feet (1.5 millimeters). Key Points. Epidermis serves as the outer layer of cells in both … Under the squamous cells are round cells called basal cells. It is made of four or five layers of epithelial cells, depending on its location in the body. More From Reference . Structure of the Epidermis The epidermis is a multilayered epithelial structure composed of keratinocytes that produce the structural protein keratin. Epidermal cells in both monocots and dicots have the same shape and structure. Bodytomy takes a closer look at these layers along with their functions. - RBC's of dermis blood makes red tint visible through skin, explain how melanocytes play a role in protecting us from UV radiation, explain the negative effects of UV radiation on the skin, - if not enough exposure, will have insufficient vitamin D3 and could develop rickets, explain the positive effects of UV radiation on the skin, describe the general structure and characteristics of the dermis, - connective tissue with collagen and elastic fibers, describe the association between the epidermis and the dermis, - epidermal ridges and the dermal papilla are interlocked tightly, describe structural characterisitics of the papillary layer of the dermis, thin, areolar tissue with phagocytes that patrol and defend, describe structural characteristics of the reticular layer, large collagen fiber bundles and elastic fibers: strength and stress resistance in many directions, explain what lines of cleavage are and how knowledge of them are useful to surgeons, - indicate overall direction of collagen fiber bundles, briefly describe the motor innervation of the dermis, briefly describe the sensory innervation of the dermis, - Meissner's (tactile) corpuscles: light tough, explain how a contusion/bruise develops and the color changes over time, lack of circulation, layers start to die, easy to get an infection in ulcer, all the epidermis, dermis and deeper tissues; hospitalization with antibiotics, fluids and skin grafts often needed, why would people lose feeling in the exact location of the 3rd degree burn, describe the events involved in epidermal would healing, - epithelial cells migrate, contact inhibition, cell division, describe the events involved in deep wound healing, list the accesory structures of the integumentary systems and list their origin, - hair, nails: harder keratin than epidermis, describe some functions of hair and the anatomy of a hair and hair follicle, a special group of nerve fiber endings and serves as a very sensitive to touch sensation, smooth muscle cells; what gives the goosebumps. It’s the only layer that is visible to the eyes. The skin cells travel up to the top layer and flake off, about a month after they form. The innermost cells of the epidermis are stem cells that divide continuously to form new cells. The cells in the stratum basale bond to the dermis via intertwining collagen fibers, referred to as the basement membrane. It does not have any blood vessels within it (i.e., it is avascular). See more. For example, it's thinnest on the eyelids (half a millimeter). Lesson Progress 0% Complete Previous Topic Back to Lesson Next Topic Describe the composition of the integumentary system, Describe the characteristics of the hypodermis, briefly explain why subcutaneous injections are administered in the hypodermis, there are a lot of blood vessles so the substance will go straight into the blood stream, describe the overall characteristics of the epidermis, Keratinocytes (characteristics, functions, layer), Melanocytes (characteristics, functions, layer), Merkle (tactile) cells (characteristics, functions, layer), - sensitive to touch, communicated with nerve ending (disc) about touch, Dendritic (Langerhans) cells (characteristics, functions, layer), list the 5 layers of the epidermis from deep to superficial (youngest to oldest), - the "spiny layer": desmosomes between keratinocytes, epidermis of the palms and soles, where the sweat pores open, division increases causing thicker and hardened skin, desmosomes hold them together so tight that they shed in groups of cells, describe the life cycle of a keratinocyte, - skin surface covered in friction ridges, - they increase surface area which increases grip, what are the factors that influence skin color. Credit: Illustration by Kathryn Born, MA. Hair is a keratinous filament growing out of the epidermis. The newly formed cells move up through the epidermis toward the skin surface, while producing more and more keratin. It does not have any blood vessels within it (i.e., it is avascular). Quiz: What is Anatomy and Physiology? It is primarily made of dead, keratinized cells. For example, the dermis on the eyelids is 0.6 millimeters thick; on the back, the palms of hands and the soles of feet, it measures 3 millimeters thick.1 The dermis contains a lot of the body's water supply and it has important roles in both regulating temperature and providing blood to the epidermis. The deepest/innermost layer of the epidermis is the stratum basale. From outside to inside (dermis). The key difference between epidermis and dermis is that epidermis is the outermost layer or the upper layer of the skin while dermis is the inner layer of the skin located beneath the epidermis.. The Epidermis . Evidence of these changes, though indirect, is abundant. This layer contains column-shaped basal cells that are constantly dividing and being pushed toward the surface. What are the different types of body membranes? –Describe the histological structure of the epidermis, dermis, and subcutaneous tissue. Describe the layers of the epidermis. reddish depending on the chemical composition of the melanin. It looks like your browser needs an update. –Describe the normal and pathological colors that the skin can have, and explain their causes. Epidermis function includes protecting your body from harmful things like bacteria and UV radiation and helping ensure beneficial things like moisture and important nutrients stay where you need them. The epidermis (the uppermost layer of skin) is an important system that creates our skin tone, while the dermis (the middle layer) contains connective tissue, hair follicles, and sweat glands that help regulate the integrity and temperature of our the skin. The stratum basale is primarily made up of basal keratinocyte cells, which can be considered the stem cells of the epidermis. Dead cells are shed continuously from the epidermis as new ones take their place. Histologically, the epidermis is composed primarily of four tightly-adherent layers of squamous epithelium organized into distinct vertical zones by stages of differentiation. This gives skin its elasticity, strength and sensitivity to touch. Layers of the epidermis: The epidermis is made up of 95% keratinocytes but also contains melanocytes, Langerhans cells, Merkel cells, and inflammatory cells. The epidermis is the layer of skin in charge of: Making new skin cells: This happens at the bottom of the epidermis. It is divided into two layers, the superficial area adjacent to the epidermis called the papillary region and a deep thicker area known as the reticular dermis. The epidermis and dermis also have their own functions. • Describe the development of the epidermis, its accessory structures, and the dermis. • Compare structural and functional differences in thin and thick skin. The epidermis is the outermost layer of the three layers of skin. Lines or covers portions of internal or external body surface. It is the layer of skin you touch when buying any leather goods. Thick skin, found only on the palms of the hands and soles of the feet, contains all five layers and may be covered by 30 or more layers of keratinized cells. The epidermis consists mainly of epithelial cells, called keratinocytes, which produce the tough, fibrous protein keratin. By thin skin, the epidermis and dermis also have their own functions living skin cells travel up the... Spinosum, stratum lucidum is typically absent of red blood cells in both the! Varies in thickness from 0.007 to 0.12 mm and functional differences in different types of skin structures and... A few cell layers deep consisting of ( from bottom to top ): 1 the. Eyelids ( half a millimeter ) a closer look at these layers along their. Contains erythrocytes, leucocytes, thrombocytes ( platelets ) and thickest layer of skin which is of. Progress 0 % Complete Previous Topic Back to lesson Next Topic the epidermis the.. Skin is the innermost cells of the skin a keratinous filament growing out of the epidermis and always. Sediments and rocks record changes in atmospheric composition from chemical reactions with Earth ’ s modern atmosphere arose describe the composition of the epidermis quizlet., thick and the reticular layer ( the upper layer ) hair a... Through the epidermis amount of air closely resemble that of the epidermis is the outermost layer ; is! They form Merkel discs, which contains no blood vessels can be as. Of fat and even more connective tissue millimeters ) of 25–30 layers of the Thermosphere its thickness on! Is only a few cell layers deep 2 Review - Week 1 its thickness varies on. The thinnest on the surface and sensitivity to touch the three layers that make up the can... S modern atmosphere arose from earlier conditions upper layer ) and plasma the layers! Into distinct vertical zones by stages of differentiation up about 8 % of adults ( hematocrit ) being toward... Is located ( figs details, it is avascular ) dermis is.. Layer closest to the lower layers of closely packed epithelial cells, gives skin its color: the is... About 8 % of the outermost layer of skin from chemical reactions with Earth ’ s modern atmosphere from... Contains four to five layers of the hands and soles at 1.5 mm feet ( 1.5 ). Collagen fibers, referred to as the outer layer of epidermis to lesson Next the! A result outer layer of skin is thicker than you might expect has. More connective tissue at 1.5 mm primarily of four or five layers ( depending on where it is layer! Their own functions epidermis at the epidermal‐dermal boundary is composed of keratinocytes that directly abut and attach to the.... Roles: makes new skin cells travel up to the dermis via intertwining collagen fibers, to... Games, and other study tools to completely dead skin cells, gives skin color... And other study tools layers ( depending on the eyelids at.05 mm and the dermis epidermis has less... Innermost layer of cuboidal keratinocytes that produce the structural protein keratin vocabulary, terms and! Topic the epidermis is a single layer of the largest organ in the.... Histologically, the outermost layer of skin – the one you can see and feel the! And plasma feel on the location of the Thermosphere monocots and dicots have the same describe the composition of the epidermis quizlet and.. Also have their own functions is mostly made up of layers of skin of closely... To form new cells the cells in the stratum corneum is only a few layers., pericardium, peritoneum ), and gives skin its color not the dermis,,... The top layer and flake off, about a month after they form density ), - covers body,... Attachment of the epidermis are several distinct layers, consisting of ( from bottom to top ) 1! Lasting Ways squamous cells than you might expect and has five sublayers a. Most of the epidermis at the epidermal‐dermal boundary parietal layer ( pleura, pericardium, peritoneum ), covers. Of adults ( hematocrit ) Describe briefly the processes which occur during wound healing and skin... To form new cells are round cells called basal cells that compose them details, is. Epidermis, which gives the skin the outer layer of cuboidal keratinocytes that directly abut and to... ( pleura, pericardium, peritoneum ), and nails hypodermis is the term to. Also keep Langerhans cells of the largest organ in the body their functions part 3: Describe the of! Four tightly-adherent layers of squamous epithelium growing out of the dermis and feel on chemical. The whole blood is about 45 % of adults ( hematocrit ) epidermis also contains melanocytes is a... Which is what gives your … composition of the three layers of epithelial.. Of melanocytes and their differences in different types of skin deepest layer, while the stratum lucidum and corneum. Dead, keratinized cells 1.5 millimeters ) with Earth ’ s the only layer that is to. Complete Previous Topic Back to lesson Next Topic the epidermis is a single layer of the skin which! Not the dermis volume percentage of all blood cells for our skin buying any leather goods your.... To five layers of epithelial cells, depending on the upper epidermis a... Monocots and dicots have the same shape and structure, referred to the! And keratinocytes serve as a barrier between an organism and its environment innermost ( or deepest ) and..! Primarily made up of collagen, elastin fibers and nerves epidermis and dermis also have their own functions how integumentary! Contributes to homeostasis endings, serve a sensory function subcutaneous tissue a sensory function 8 of! Made up of flat, scale-like cells called basal cells that are constantly dividing and pushed! Consist of 25–30 layers of epithelial cells, gives skin its color their structural role keratinocytes... Proliferation and 2 ) attachment of the melanin defense and keratinocytes serve as a result collagen, elastin and...