Thick and Thin Evaluating layers of the skin

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1 Overview Thick and Thin Evaluating layers of the skin Understanding the layered structure of skin is essential to understanding how it functions. The focus of this lesson is for students to discover and investigate the layers of the skin. Using light micrograph images of skin sections, students observe structural differences between thick and thin skin and make measurements to quantify those differences. They compare the structure of the dermis to the epidermis and observe and quantify differences in pigment in the stratum basale of pigmented versus nonpigmented skin. Using this information, students are asked to hypothesize about the relationships between structure and function. In the first two sections of the lesson, students are asked to find and draw boundaries between layers in a section of thin skin, and specifically identify the border between dermis and epidermis. They then compare two composite images of thick and thin skin, comprising deep dermis to outermost epidermis. Each image is really a stack of two images, with important structures identified by arrows on the first slice of each stack and labels on the second. Students identify and measure the thickness of the dermis and epidermis in both the thick and thin skin images to determine which layer gives thick skin its name. Goal Students will compare and contrast thick and thin skin structures, and relate skin structures to their function. Topics Integumentary System Histology Science Process Skills Observation Measurement Analysis IPTechnique Sheets Drawing & Text Windows Measuring Density Slicing Teaching Notes After observing and identifying the sublayers of the epidermis, a quantitative comparison of pigmented and nonpigmented skin is also performed. Students select the darker pixels found in the melanocytes of the stratum basale by density slicing and measure the area of this layer in both pigmented and nonpigmented skin. A ratio is calculated to determine the relative difference in area of pigmentation. In the More exploration section, students can study micrographs of epidermal appendages such as sweat glands, sebaceous glands, and hair follicles. Thoughtprovoking questions are included to promote reasoning skills and understanding of content. Objectives Students will: identify dermal and epidermal layers of thick and thin skin compare and contrast the structure of thick and thin skin relate the structure and position of skin layers to their function measure and compare differences in skin pigmentation to explore protective advantages 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work. Thick and Thin 75

2 Prerequisities Prior to this lesson, students should be able to recognize the major tissue types, especially epithelial and connective tissues Related Activities The Tissue Study lesson is an introduction to basic histology. Acknowledgments Lesson developed by Paul Johnson and Deborah Alongi. Digital photomicrographs created by Paul Johnson. Answers 1. Answers will vary with students ability to visualize microscopic structures. There are five layers visible in this image of thin skin: dermis, stratum basale, stratum spinosum, stratum granulosum and stratum corneum. 2. The boundary between the dermis and epidermis is between the fibrous lighter pink tissue at the bottom of the image (dermis) and the darkly stained layer above it (stratum basale). 3. Answers will vary. Representative measurements are show in the table below. Skin type Thickness of epidermis, mm Thickness of dermis, mm Thick skin Thin skin The epidermis in thick skin is much thicker than in thin skin. 5. Hair follicles and sebaceous glands. 6. Thick skin is found on the palms of the hands and soles of the feet where no hair follicles are found. 7. The sweat and sebaceous glands are found primarily in the hypodermis. 8. The cells in the basal layer are polygons. As they move to the outer layers they become progressively flattened. 9. Answers will vary. Apoptosis (cell death) occurs as the basal cells move toward the outer layers of the epidermis. As they die, organelles degenerate and the cells dehydrate, resulting in loss of volume and flattening. 10. Answers will vary. Owing to its many layers of dead cells filled with tough, water-proof keratin, the stratum corneum acts as an effective barrier to elements in the outside environment such as water, microorganisms, chemicals, and injury. 11. Outer epidermal layers are cut, but not the dermis where blood vessels and nerve endings are found. 12. The lack of blood supply results in diminishing nutrient supply contributing to the process of cell death. 13. The stratum lucidum is not apparent in thin skin. 14. The purpose of the melanin granules is absorption of potentially damaging ultraviolet (UV) radiation. DNA in the actively dividing cells of the stratum basale is particularly susceptible to damage. The amount of melanin in the cells of the stratum basale controls the amount of ultraviolet light reaching these cells and the cells of the dermis below. 76 A & P TECHNOLOGIST 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.

3 15. The intercellular matrix is made of collagen. 16. The dermis is composed mostly of collagen bundles with a few fibroblasts whereas the epidermis is composed almost entirely of cells. 17. The function of the intercellular matrix is to provide strength and durability to the dermis. 18. The fibroblasts are responsible for the synthesis of the collegen matrix. 19. Fibroblasts are not found in the epidermis. 20. Answers will vary. Representative measurements are shown in the table below. Skin type Area of pigmentation nonpigmented about 300 pixels pigmented about 2650 pixels 21. There is about nine times as much pigment in the pigmented skin than the nonpigmented skin. 22. Answers may vary. In conditions of prolonged intense sunlight, increased pigmentation protects the skin cells from damage from ultraviolet radiation. 23. In this image of malignant melanoma there are abnormally large numbers of melanocytes in the dermis. 24. In this image of basal cell carcinoma, large numbers of cells from the stratum basale have invaded the dermis. 25. Malignant cells in the dermis can easily enter the blood supply because the dermis is vascularized. This allows the cancerous cells to metastasize to the vital organs where they grow out of control, robbing the organs cells of nutrients, causing them to die. More exploration A. Most of the secretory portion of the sweat gland is found in the hypodermis. The hypodermis is not technically part of the skin. B. Cuboidal epithelial tissue lining the glands is responsible for secreting the sweat. The water to make the sweat is obtained through osmosis from the nearby blood vessels. C. The hair shaft is composed of cornified epithelial cells containing keratin. Cornified epithelial cells are found in the stratum corneum over the entire body. D. The cells in the hair shaft above the surface of the body are not alive. Shampoos cannot revitalize dead cells. E. Hair serves to provide warmth, tactile sensory input from the environment, shade from the sun, protection of the eyes by the eyebrows and eyelashes, recognition of age and sex by distribution and color of body hair, and dissemination of pheromones by the armpit and groin hair. F. Sebaceous glands are made up of epithelial tissue. Sebum reaches the skin surface by moving along the surface of the hair shaft. Sebum is not water soluble; it is a lipid. G. Guess what this is #1 shows a longitudinal section through a fingerprint ridge and Guess what this is #2 shows a Pacinian corpuscle Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work. Thick and Thin 77

4 78 A & P TECHNOLOGIST 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.

5 Thick and Thin Evaluating layers of the skin Lesson The skin is the most visible but perhaps most underappreciated organ in the human body. In the average adult it covers about 18 square feet and makes up 15% of total body weight. The skin is not just a boundary between internal and external environments, but is a vital organ responsible for maintaining body homeostasis in many important ways. Temperature regulation, fluid balance, sensation, protection and excretion are only some of its functions. More than 50% of victims die when more than 70% of the skin is destroyed by a third degree burn. To accomplish its many tasks, the skin is organized in layers. In this lesson, you will explore the structure and function of the layers of the skin as seen in digital photomicrographs. ì Open Skin layers. This is an image of the skin magnified 100 under a microscope. ì Use the ÿ tool to magnify the image to look more closely at the layers. 1. How many layers do you see in this image of the skin? ì Use the tool to draw lines along the boundaries of each layer. Change the color of the lines you draw by clicking on the or bars at the bottom of the LUT. Structurally, the skin is divided into two principal layers: the dermis and epidermis. The epidermis is the most superficial of the two and is made up of stratified epithelial cells. The dermis is deep to the epidermis and is composed of connective tissue containing collagen and elastic fibers. 2. Based on your observations of the layers, where is the boundary between the epidermis and dermis? ì Close Skin layers. Thick versus thin skin The human body is covered mostly with thin skin (perhaps making us overly sensitive to criticism). The thickness of skin varies from about millimeters depending upon body location. However, thick and thin skin are not defined merely by total measured thickness. ì In the Thick and thin folder, open Thick skin 100x and Thin skin 100x. Each of these images is actually a stack of two images. ì Arrange the images so you can see both at once. Use the tool to scroll each image from top to bottom if necessary. ì Use the > key to move to the next slice of each stack to study the labeled layers and parts. Use the < key to move back to the first slice. Let s investigate differences in thick and thin skin using the measuring tools of NIH Image.  File/Open See the Drawing & Text IPTechnique Sheet if you need help.  File/Close  File/Open /ï Open All  Windows/Tile Images See the Windows IPTechnique Sheet for more information about managing windows. ì Locate the dermis and epidermis in both the thick and thin skin images Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work. Thick and Thin 79

6 ì Choose Analyze/Options and set your measurement options to only ï Perimeter/Length. ì Use the tool to select the thickness of the epidermis in the Thick skin 100x image, as shown in the margin. ì Measure the thickness by choosing Analyze/Measure. Choose Analyze/Show Results to see your measurement recorded by the computer (length). The scale on the image has been set to measure in millimeters. 3. Record the measurement in the table on your Data Sheet. ì Use the same technique to measure the dermis and epidermis of both thick and thin skin and record the results in the data table. 4. Which layer gives thick skin its name? ì Observe the epidermal derivatives, such as hair and glands, in each image carefully. Compare and contrast the structures found in each type of skin. 5. What two major structures are found in thin skin and not thick skin? 6. Based on your observations, where do you think thick skin is found in the body? The base of the dermis is attached to deeper tissues and organs by the areolar tissue of the hypodermis or superficial fascia. 7. What structures are found primarily in the hypodermis? ì Close both images. A closer look at the epidermis There are four cell types in the epidermis. The most common is the keratinocyte, which makes up about 90% of the cells of the entire epidermis. Melanocytes make up 7-10% of the epidermal cells as a whole. However, they are more common in the basal layers where they may make up 25% of the cells. ì In the Epidermis folder, open Thick skin inner epidermis and study the images and labels on both slices of this stack. 8. What happens to the shape of the cells as you go from the basal layer of the epidermis to the outer layers? 9. What do you think causes this change? ì Open Thick skin outer epidermis. This image shows the outermost layer of epidermis, called the stratum corneum. ì Study the images and labels on each slice of this stack. 10. The cells in the stratum corneum are extremely flattened, filled with karatin and have no nucleus. What do you think is the purpose of this layer? Explain your answer. 11. In the past you have probably experienced very shallow cuts into your skin that did not hurt or bleed. Explain why. 12. How does the lack of blood supply in the outer layers of the epidermis affect the cells there? ì Open Thin skin epidermis. ì Compare the structures in the thick and thin skin images. Selection of thickness of epidermis See the Measuring IPTechnique Sheet if you need extra help. Â File/Close Other cells found in the epidermis include Langerhans cells, a type of macrophage that ingests foreign objects that enter the skin, and Merkel s cells, which are sensitive to touch. Â Use the > and < keys to move from slice to slice. Â File/Open 80 A & P TECHNOLOGIST 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.

7 13. Which layers of the thick skin epidermis are not found in thin skin? 14. Note the melanin-filled cells in the stratum basale. Why are they concentrated at the base of the epidermis? ì Close all images. Â File/Close A closer look at the dermis The dermis is the thickest and strongest part of the skin. It contains many blood vessels and nerve endings. ì In the Dermis folder, open Papillary layer of dermis. 15. This slide has been stained to emphasize the intercellular matrix. What is it made of? ì Use the > key to study the labeled image until you can identify the parts. 16. What is a major difference in composition that you can see between the epidermis and dermis? 17. What is the function of the intercellular matrix? 18. What cells are responsible for the synthesis of the matrix? 19. Are these cells found in the epidermis? ì Close Papillary layer of dermis. Â File/Open Variability in skin pigmentation Across the human population there is great variability in skin pigmentation. In most people, exposure to sunlight increases pigmentation in the skin. Although you cannot see it, vitamin D 3 is also synthesized in the epidermis when skin is exposed to ultraviolet rays in sunlight. However, ultraviolet radiation can also damage DNA in the nuclei of cells. ì Open Pigment comparison and study the images. The skin section on the left is from a person with light skin. The section on the right is from a person with darker skin. ì Activate density slicing. Density slicing is a technique that highlights (in red) a range of pixel values in the LUT and any pixels in the image that have those same values. The area of the highlighted pixels can then be measured. Let s compare the area of pigmentation in non-pigmented skin to that in pigmented skin. ì Adjust the red range in the LUT to highlight only the dark areas of melanin in cells of the stratum basale. Use the following techniques: To use this technique do this stretch or squeeze the red range click and drag the top or bottom edge of the red bar slide red range up and down click and drag red bar in LUT from middle ì Choose Analyze/Options and set your measurement options to show only ï Area. ì Use the tool to make a box around the non-pigmented image on the left. See the example in the margin (showing a box around the pigmented skin image) Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work. Â Options/Density Slice See the Density Slicing IPTechnique Sheet for detailed information about density slicing. rectangular selection pigmented areas highlighted red Thick and Thin 81

8 ì Measure the area of pigmentation in the non-pigmented skin. 20. Record the area measurement (in pixels) in the table on your Data Sheet. ì Use the tool to select the pigmented image on the right and measure the area of pigmentation in the pigmented skin. Record the area in the data table. 21. Calculate a ratio of the relative amount of pigment in the pigmented versus the non-pigmented skin. Â Analyze/Measure and Analyze/Show Results Pixels are tiny square picture elements that make up a digital image. area of pigmentation in pigmented skin area of pigmentation in nonpigmented skin = relative amount of pigmentation 22. Under what environmental conditions would it be an advantage to have large amounts of pigment in the skin? ì In the Skin cancer folder, open Condition A. Study the image carefully. Locate the epidermis and dermis. 23. What is abnormal about the tissue in Condition A? ì Open Condition B. Locate the epidermis and dermis. 24. What is abnormal about the tissue in Condition B? 25. Why are these cancers life-threatening? ì Close all images. Hint: Most cancers kill when they spread, or metastasize, to other parts of the body. How do cancer cells spread? Â File/Close More exploration Epidermal appendages Hair, sweat and sebaceous (oil) glands are accessory structures associated with skin. ì Open all the images in the Skin appendages folder. Study the images until you can name the structures. ì Use your observations of the images, your notes or textbook and your own reasoning skills to answer the following questions: A. In what layer is most of the secretory portion of the sweat gland found? Is this technically part of the skin? B. What type of tissue lines the sweat glands and secretes the sweat? Where do these cells get the water to make the sweat? C. What kind of tissue is the hair shaft made of? Where else in the skin is this tissue found? D. When a hair shaft extends beyond the surface of the epidermis, are the cells in the shaft alive? Many shampoos contain vitamins and proteins. Can these substances revitalize the cells in the hair shaft? E. What do you think is the function of hair in humans? F. What kind of tissue makes up sebaceous glands? How does the sebum reach the surface? Water without soap will not remove sebum. What does this indicate about the chemical composition of sebum? Â File/Open /ï Open All If you don t have enough memory, open the images one at a time. Mystery images ì Open both images in the Mystery images folder. Consider magnification as you try to determine what these structures are. Hint: These structures are located on the fingertips. ì Close all images. 82 A & P TECHNOLOGIST 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.

9 Name(s) Thick and Thin Class Date Data Sheet 1. How many layers do you see in this image of the skin? 2. Based on your observations of the layers, where is the boundary between the epidermis and dermis? 3. Record the measurement in the table below. Skin type Thickness of epidermis, µm Thickness of dermis, µm Thick skin Thin skin 4. Which layer gives thick skin its name? 5. What two major structures are found in thin skin and not thick skin? 6. Based on your observations, where do you think thick skin is found in the body? 7. What structures are found primarily in the hypodermis? 8. What happens to the shape of the cells as you go from the inner layers of the epidermis to the outer layers? 9. What do you think causes this change? 10. The cells in the stratum corneum are extremely flattened, filled with karatin and have no nucleus. What do you think is the purpose of this layer? Explain your answer Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work. Thick and Thin 83

10 11. In the past you have probably experienced very shallow cuts into your skin that did not hurt or bleed. Explain why. 12. How does the lack of blood supply in the outer layers of the epidermis affect the cells there? 13. Which layers of the thick skin epidermis are not found in thin skin? 14. Note the melanin-filled cells in the stratum basale. Why are they concentrated at the base of the epidermis? 15. This slide has been stained to emphasize the intercellular matrix. What is it made of? 16. What is a major difference in composition that you can see between the epidermis and dermis? 17. What is the function of the intercellular matrix? 18. What cells are responsible for the synthesis of the matrix? 19. Are these cells found in the epidermis? 20. Record the area measurement in the table below. Skin type Area of pigmentation nonpigmented pigmented 21. Calculate a ratio of the relative amount of pigment in the pigemented versus the non-pigmented skin. 84 A & P TECHNOLOGIST 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.

11 22. Under what environmental conditions would it be an advantage to have large amounts of pigment in the skin? 23. What is abnormal about the tissue in Condition A? 24. What is abnormal about the tissue in Condition B? 25. Why are these cancers life-threatening? More exploration Epidermal appendages A. In what layer is most of the secretory portion of the sweat gland found? Is this technically part of the skin? B. What type of tissue lines the sweat glands and secretes the sweat? Where do these cells get the water to make the sweat? C. What kind of tissue is the hair shaft made of? Where else in the skin is this tissue found? D. When a hair shaft extends beyond the surface of the epidermis, are the cells in the shaft alive? Many shampoos contain vitamins and proteins. Can these substances revitalize the cells in the hair shaft? 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work. Thick and Thin 85

12 E. What do you think is the function of hair in humans? F. What kind of tissue makes up sebaceous glands? How does the sebum reach the surface? Water without soap will not remove sebum. What does this indicate about the chemical composition of sebum? G. What skin structure is shown in each of the mystery images? 86 A & P TECHNOLOGIST 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.