In addition to keratinocytes, the stratum spinosum contains the immunologically active Langerhans cells. Spiny cellular projections form between the keratinocytes and hold them together. The keratinocytes in this layer have begun to accumulate keratin, and they have become tougher and flatter. This is the thickest of the four epidermal layers. Just above the stratum basale is the stratum spinosum. The Merkel cells are especially numerous in touch-sensitive areas, such as the fingertips and lips. Melanocytesno post and Merkel cells are also found in the stratum basale. As more keratinocytes are produced, previously formed cells are pushed up through the stratum basale. When keratinocytes first form, they are cube-shaped and contain almost no keratin. The stratum basale contains stem cells - called basal cells - which divide to form all the keratinocytes of the epidermis. It is separated from the dermis by a membrane called the basement membrane.
The stratum basale is the innermost (or deepest) layer of the epidermis. This diagram illustrates the five layers that exist on the palms and soles of the feet. Figure 10.3.2 The epidermis has multiple layers, and structures (such as hairs from the dermis below it) pass through them. The layers of the epidermis are shown in Figure 10.3.2, and described in the following text. A fifth layer occurs in the palms of the hands and soles of the feet, where the epidermis is thicker than in the rest of the body. The epidermis in most parts of the body consists of four distinct layers. Less than one per cent of epidermal cells are Merkel cells, which respond to light touch and connect to nerve endings in the dermis.These are immune system cells that detect and fight pathogens entering the skin. About one per cent of epidermal cells are Langerhans cells.These cells produce the pigment melanin that protects the dermis from UV light. Another eight per cent of epidermal cells are melanocytes.Near the top of the epidermis, these cells are also called squamous cells. These cells make up at least 90 per cent of the epidermis. The epidermis consists mainly of stacks of keratin-producing epithelial cells called keratinocytes.All of the cells are necessary for the important functions of the epidermis. There are several different types of cells in the epidermis. It has a variety of cell types and multiple layers. However, as thin as it is, the epidermis still has a complex structure. Without blood to bring epidermal cells oxygen and nutrients, the cells must absorb oxygen directly from the air and obtain nutrients via diffusion of fluids from the dermis below. There are no blood vessels and very few nerve cells in the epidermis. Chapter 1 - Nature and Processes of Scienceġ.1 Case Study: Why Should You Learn About Science?ġ.7 Pseudoscience and Other Misuses of Scienceġ.8 Case Study Conclusion: To Give a Shot or NotĢ.1 Case Study: Why Should You Study Human Biology?Ģ.6 Case Study Conclusion: Our Invisible InhabitantsĤ.14 Case Study Conclusion: More Than Just Tiredĥ.10 Mendel's Experiments and Laws of Inheritanceĥ.12 Sexual Reproduction, Meiosis, and Gametogenesisĥ.18 Case Study Conclusion: Cancer in the FamilyĦ.1 Case Study: Our Similarities and DifferencesĦ.4 Human Responses to Environmental StressĦ.9 Case Study Conclusion: Your Genes May Help You Save a Lifeħ.9 Case Study Conclusion: Under PressureĨ.1 Case Study: The Control Centre of Your Bodyġ0.1 Case Study: Skin, Hair, and Nails - Decorative but Functionalġ0.2 Introduction to the Integumentary Systemġ0.8 Case Study Conclusion: Wearing His Heart on His Sleeveġ1.8 Case Study Conclusion: A Pain in the Footġ2.7 Case Study Conclusion: Needing to Relaxġ3.1 Case Study: Respiratory System and Gas Exchangeġ3.2 Structure and Function of the Respiratory Systemġ3.7 Case Study Conclusion: Cough That Won't Quitġ4.1 Case Study: Your Body's Transportation Systemġ4.2 Introduction to the Cardiovascular Systemġ5.2 Introduction to the Digestive Systemġ5.7 Disorders of the Gastrointestinal Tractġ5.8 Case Study Conclusion: Please Don’t Pass the Breadġ6.5 Ureters, Urinary Bladder, and Urethraġ6.7 Case Study Conclusion: Drink and Flushġ7.7 Case Study Conclusion: Defending Your Defensesġ8.2 Introduction to the Reproductive Systemġ8.3 Structures of the Male Reproductive Systemġ8.4 Functions of the Male Reproductive Systemġ8.5 Disorders of the Male Reproductive Systemġ8.6 Structures of the Female Reproductive Systemġ8.7 Functions of the Female Reproductive Systemġ8.9 Disorders of the Female Reproductive Systemġ8.12 Case Study Conclusion: Trying to ConceiveĬhapter 1 Answers: Nature and Processes of ScienceĬhapter 2 Answers: Biology: The Study of LifeĬhapter 7 Answers: Introduction to the Human BodyĬhapter 14 Answers: Cardiovascular System
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