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To successfully complete this assignment, first read the following exercises from the Laboratory Manual: Exercise 7 The Integumentary System.
Student Discussion Assignment:
- Briefly describe the functions of each labeled section of the skin model found in your text.
- Briefly identify and discuss the structural features of skin found in the epidermal layer of skin.
- Discuss what would happen if a large percentage of the skin was damaged or lost.
Write your responses in a minimum of 250 words in APA format.
As in all assignments, cite your sources in your work and provide references for the citations in APA format. Support your work, using your course lectures and textbook readings. Helpful APA guides and resources are available in the South University Online Library. Below are guides that are located in the library and can be accessed and downloaded via the South University Online Citation Resources: APA Style page. The American Psychological Association website also provides detailed guidance on formatting, citations, and references at APA Style.
To successfully complete this assignment, first read the following exercises from the Laboratory Manual: Exercise 7 The Integumentary System. Student Discussion Assignment: Briefly describe the functi
Basic Structure of the Skin The skin has two distinct regions—the superficial epidermis composed of epithelium and an underlying connective tissue, the dermis (Figure 7.1). These layers are firmly “cemented” together along a wavy border. But friction, such as the rubbing of a poorly fitting shoe, may cause them to separate, resulting in a blister. Immediately deep to the dermis is the hypodermis, or superficial fascia, which is not considered part of the skin. It consists primarily of adipose tissue. The main skin areas and structures are described below. Figure 7.1 Skin structure. Three-dimensional view of the skin and the underlying hypodermis. The epidermis and dermis have been pulled apart at the right corner to reveal the dermal papillae. Tactile corpuscles are not common in hairy skin, but are included here for illustrative purposes. Figure 7.2 The main structural features in epidermis of thin skin. (a) Photomicrograph depicting the four major epidermal layers (4303). (b) Diagram showing the layers and relative distribution of the different cell types. Keratinocytes (orange), melanocytes (gray), dendritic cells (purple), and tactile (Merkel) cells (blue). A sensory nerve ending (yellow) extending from the dermis is associated with a tactile cell, forming a tactile disc (touch receptor). Notice that the keratinocytes are joined by numerous desmosomes. The stratum lucidum, present in thick skin, is not illustrated here. Activity 1 Locating Structures on a Skin Model As you read, locate the following structures in the diagram (Figure 7.1) and on a skin model. Epidermis Structurally, the avascular epidermis is a keratinized stratified squamous epithelium consisting of four distinct cell types and four or five distinct layers. Cells of the Epidermis Keratinocytes (literally, keratin cells): The most abundant epidermal cells, their main function is to produce keratin fibrils. Keratin is a fibrous protein that gives the epidermis its durability and protective capabilities. Keratinocytes are tightly connected to each other by desmosomes. Far less numerous are the following types of epidermal cells (Figure 7.2): Melanocytes: Spidery black cells that produce the brown-to-black pigment called melanin. The skin tans because melanin production increases when the skin is exposed to sunlight. The melanin provides a protective pigment umbrella over the nuclei of the cells in the deeper epidermal layers, thus shielding their genetic material (DNA) from the damaging effects of ultraviolet radiation. A concentration of melanin in one spot is called a freckle. Dendritic cells: Also called Langerhans cells, these cells play a role in immunity by performing phagocytosis. Tactile (Merkel) cells: Occasional spiky hemispheres that, in combination with sensory nerve endings, form sensitive touch receptors called tactile or Merkel discs located at the epidermal-dermal junction. Layers of the Epidermis The epidermis consists of four layers in thin skin, which covers most of the body. Thick skin, found on the palms of the hands and soles of the feet, contains an additional layer, the stratum lucidum. From deep to superficial, the layers of the epidermis are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum (Figure 7.2). The layers of the epidermis are summarized in Table 7.1. Dermis The dense irregular connective tissue making up the dermis consists of two principal regions—the papillary and reticular areas (Figure 7.1). Like the epidermis, the dermis varies in thickness. Papillary layer: The more superficial dermal region composed of areolar connective tissue. It is very uneven and has fingerlike projections from its superior surface, the dermal papillae, which attach it to the epidermis above. These projections lie on top of the larger dermal ridges. In the palms of the hands and soles of the feet, they produce the fingerprints, unique patterns of epidermal ridges that remain unchanged throughout life. Abundant capillary networks in the papillary layer furnish nutrients for the epidermal layers and allow heat to radiate to the skin surface. The pain (free nerve endings) and touch receptors (tactile corpuscles in hairless skin) are also found here. Reticular layer: The deepest skin layer. It is composed of dense irregular connective tissue and contains many arteries and veins, sweat and sebaceous glands, and pressure receptors (lamellar corpuscles). Both the papillary and reticular layers are abdundant in collagen and elastic fibers. The elastic fibers give skin its exceptional elasticity in youth. With age, the number of elastic fibers decreases, and the subcutaneous layer loses fat, which leads to wrinkling and inelasticity of the skin. Fibroblasts, adipose cells, various types of macrophages, and other cell types are found throughout the dermis. The abundant dermal blood supply allows the skin to play a role in the regulation of body temperature. When body temperature is high, the arterioles serving the skin dilate, and the capillary network of the dermis becomes engorged with the heated blood. Thus body heat is allowed to radiate from the skin surface. Any restriction of the normal blood supply to the skin results in cell death and, if severe enough, skin ulcers (Figure 7.3). Bedsores (decubitus ulcers) occur in bedridden patients who are not turned regularly enough. The weight of the body puts pressure on the skin, especially over bony projections (hips, heels, etc.), which leads to restriction of the blood supply and tissue death. The dermis is also richly provided with lymphatic vessels and nerve fibers. Many of the nerve endings bear highly specialized receptor organs that, when stimulated by environmental changes, transmit messages to the central nervous system for interpretation. Some of these receptors—free nerve endings (pain receptors), a lamellar corpuscle, and a hair follicle receptor (also called a root hair plexus)—are shown in Figure 7.1. (These receptors are discussed in depth in Exercise 22.) Table 7.1 Layers of the Epidermis Epidermal layer Description Stratum basale (basal layer) A single row of cells immediately above the dermis. Its cells are constantly undergoing mitosis to form new cells, hence its alternate name, stratum germinativum. Some 10–25% of the cells in this layer are melanocytes, which thread their processes through this and adjacent layers of keratinocytes. Occasional tactile cells are also present in this layer. Stratum spinosum (spiny layer) Several layers of cells that contain thick, weblike bundles of intermediate filaments made of a pre-keratin protein. The cells in this layer appear spiky because when the tissue is prepared, the cells shrink, but their desmosomes hold tight to adjacent cells. Cells in this layer and the basal layer are the only ones to receive adequate nourishment from diffusion of nutrients from the dermis. Stratum granulosum (granular layer) A thin layer named for the abundant granules its cells contain. These granules are (1) lamellar granules, which contain a waterproofing glycolipid that is secreted into the extracellular space; and (2) keratohyaline granules, which help to form keratin in the more superficial layers. At the upper border of this layer, the cells are beginning to die. Stratum lucidum (clear layer) Present only in thick skin. A very thin transparent band of flattened, dead keratinocytes with indistinct boundaries. Stratum corneum (horny layer) The outermost layer consisting of 20–30 layers of dead, scalelike keratinocytes. They are constantly being exfoliated and replaced by the division of the deeper cells. Figure 7.3 Photograph of a deep (stage III) decubitus ulcer. Skin Color Skin color is a result of the relative amount of melanin in skin, the relative amount of carotene in skin, and the degree of oxygenation of the blood. Carotene is a yellow-orange pigment present primarily in the stratum corneum and in the adipose tissue of the hypodermis. Its presence is most noticeable when large amounts of carotene-rich foods (carrots, for instance) are eaten. Skin color may be an important diagnostic tool. For example, flushed skin may indicate hypertension or fever, whereas pale skin is typically seen in anemic individuals. When the blood is inadequately oxygenated, as during asphyxiation and serious lung disease, both the blood and the skin take on a bluish cast, a condition called cyanosis. Jaundice, in which the tissues become yellowed, is almost always diagnostic for liver disease, whereas a bronzing of the skin hints that a person’s adrenal cortex is hypoactive (Addison’s disease).