thick and thin

Thick and Thin 75 1998 Center for Image Processing in Education. Limited classroom reproduction rights are granted under the notice appearing earlier in this work.

GoalStudents will compare andcontrast thick and thin skinstructures, and relate skinstructures to their function.

Topics Integumentary System Histology

Science Process Skills Observation Measurement Analysis

IPTechnique Sheets Drawing & Text Windows Measuring Density Slicing

TeachingNotesThick and Thin

Evaluating layers of the skin

OverviewUnderstanding the layered structure of skin is essential to understanding how itfunctions. The focus of this lesson is for students to discover and investigate the layersof the skin. Using light micrograph images of skin sections, students observestructural differences between thick and thin skin and make measurements toquantify those differences. They compare the structure of the dermis to the epidermisand observe and quantify differences in pigment in the stratum basale of pigmentedversus nonpigmented skin. Using this information, students are asked to hypothesizeabout the relationships between structure and function.

In the first two sections of the lesson, students are asked to find and draw boundariesbetween layers in a section of thin skin, and specifically identify the border betweendermis and epidermis. They then compare two composite images of thick and thinskin, comprising deep dermis to outermost epidermis. Each image is really a stackof two images, with important structures identified by arrows on the first slice of eachstack and labels on the second. Students identify and measure the thickness of thedermis and epidermis in both the thick and thin skin images to determine which layergives thick skin its name.

After observing and identifying the sublayers of the epidermis, a quantitative com-parison of pigmented and nonpigmented skin is also performed. Students select thedarker pixels found in the melanocytes of the stratum basale by density slicing andmeasure the area of this layer in both pigmented and nonpigmented skin. A ratio iscalculated to determine the relative difference in area of pigmentation.

In the More exploration section, students can study micrographs of epidermalappendages such as sweat glands, sebaceous glands, and hair follicles. Thought-provoking questions are included to promote reasoning skills and understanding ofcontent.

ObjectivesStudents 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 protectiveadvantages

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.

PrerequisitiesPrior to this lesson, students should

be able to recognize the major tissue types, especially epithelial and connectivetissues

Related Activities The Tissue Study lesson is an introduction to basic histology.

AcknowledgmentsLesson developed by Paul Johnson and Deborah Alongi.

Digital photomicrographs created by Paul Johnson.

Answers1. 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 lighterpink tissue at the bottom of the image (dermis) and the darkly stained layer aboveit (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 0.61-0.98 0.56-0.84

Thin skin 0.07-0.16 0.78-1.26

4. 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 hairfollicles 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 theybecome progressively flattened.

9. Answers will vary. Apoptosis (cell death) occurs as the basal cells move towardthe outer layers of the epidermis. As they die, organelles degenerate and thecells 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 elementsin the outside environment such as water, microorganisms, chemicals, andinjury.

11. Outer epidermal layers are cut, but not the dermis where blood vessels andnerve endings are found.

12. The lack of blood supply results in diminishing nutrient supply contributing tothe 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 damagingultraviolet (UV) radiation. DNA in the actively dividing cells of the stratum basaleis particularly susceptible to damage. The amount of melanin in the cells of thestratum basale controls the amount of ultraviolet light reaching these cells andthe cells of the dermis below.


15. The intercellular matrix is made of collagen.

16. The dermis is composed mostly of collagen bundles with a few fibroblastswhereas the epidermis is composed almost entirely of cells.

17. The function of the intercellular matrix is to provide strength and durability tothe 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 thenonpigmented skin.

22. Answers may vary. In conditions of prolonged intense sunlight, increasedpigmentation protects the skin cells from damage from ultraviolet radiation.

23. In this image of malignant melanoma there are abnormally large numbers ofmelanocytes in the dermis.

24. In this image of basal cell carcinoma, large numbers of cells from the stratumbasale have invaded the dermis.

25. Malignant cells in the dermis can easily enter the blood supply because thedermis is vascularized. This allows the cancerous cells to metastasize to the vitalorgans 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. Thehypodermis 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 bloodvessels.

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. Shampooscannot 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 dissemi-nation of pheromones by the armpit and groin hair.

F. Sebaceous glands are made up of epithelial tissue. Sebum reaches the skinsurface 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 fingerprintridge and Guess what this is #2 shows a Pacinian corpuscle.


LessonThick and ThinEvaluating layers of the skin

The skin is the most visible but perhaps most underappreciated organ in thehuman body. In the average adult it covers about 18 square feet and makesup 15% of total body weight. The skin is not just a boundary between internaland external environments, but is a vital organ responsible for maintainingbody homeostasis in many important ways. Temperature regulation, fluidbalance, sensation, protection and excretion are only some of its functions.

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 indigital photomicrographs.

Open Skin layers. This is an image of the skin magnified 100 undera microscope.

Use the 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?

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 andepidermis. The epidermis is the most superficial of the two and is made upof stratified epithelial cells. The dermis is deep to the epidermis and iscomposed of connective tissue containing collagen and elastic fibers.

2. Based on your observations of the layers, where is the boundary betweenthe epidermis and dermis?

Close Skin layers.

Thick versus thin skinThe human body is covered mostly with thin skin (perhaps making usoverly sensitive to criticism). The thickness of skin varies from about 0.5-4.0millimeters depending upon body location. However, thick and thin skinare not defined merely by total measured thickness.

In the Thick and thin folder, open Thick skin 100x and Thin skin100x. Each of these images is actually a stack of two images.

Arrange the images so you can see both at once. Use the tool toscroll each image from top to bottom if necessary.

Use the > key to move to the next slice of each stack to study the labeledlayers and parts. Use the < key to move back to the first slice.

Lets investigate differences in thick and thin skin using the measuring toolsof NIH Image.

Locate the dermis and epidermis in both the thick and thin skinimages.

File/Open

File/Close

See the Drawing & TextIPTechnique Sheet if you needhelp.

File/Open/ Open All

Windows/Tile Images

More than 50% of victims diewhen more than 70% of the skinis destroyed by a third degreeburn.

See the Windows IPTechniqueSheet for more informationabout managing windows.


Choose Analyze/Options and set your measurement options toonly Perimeter/Length.

Use the tool to select the thickness of the epidermis in the Thickskin 100x image, as shown in the margin.

Measure the thickness by choosing Analyze/Measure. ChooseAnalyze/Show Results to see your measurement recorded by thecomputer (length). The scale on the image has been set to measure inmillimeters.

3. Record the measurement in the table on your Data Sheet.

Use the same technique to measure the dermis and epidermis of boththick and thin skin and record the results in the data table.

4. Which layer gives thick skin its name?

Observe the epidermal derivatives, such as hair and glands, in eachimage carefully. Compare and contrast the structures found in eachtype 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 thebody?

The base of the dermis is attached to deeper tissues and organs by the areolartissue of the hypodermis or superficial fascia.

7. What structures are found primarily in the hypodermis?

Close both images.

A closer look at the epidermisThere are four cell types in the epidermis. The most common is thekeratinocyte, 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% ofthe cells.

In the Epidermis folder, open Thick skin inner epidermis andstudy 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 ofthe epidermis to the outer layers?

9. What do you think causes this change?

Open Thick skin outer epidermis. This image shows the outer-most layer of epidermis, called the stratum corneum.

Study the images and labels on each slice of this stack.

10. The cells in the stratum corneum are extremely flattened, filled withkaratin and have no nucleus. What do you think is the purpose of thislayer? Explain your answer.

11. In the past you have probably experienced very shallow cuts into yourskin that did not hurt or bleed. Explain why.

12. How does the lack of blood supply in the outer layers of the epidermisaffect the cells there?

Open Thin skin epidermis.

Compare the structures in the thick and thin skin images.

Use the > and < keys tomove from slice to slice.

File/Close

See the MeasuringIPTechnique Sheet if you needextra help.

Selection ofthickness ofepidermis

File/Open

Other cells found in the epider-mis include Langerhans cells, atype of macrophage thatingests foreign objects thatenter the skin, and Merkelscells, which are sensitive totouch.


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 concen-trated at the base of the epidermis?

Close all images.

A closer look at the dermisThe dermis is the thickest and strongest part of the skin. It contains manyblood vessels and nerve endings.

In the Dermis folder, open Papillary layer of dermis.

15. This slide has been stained to emphasize the intercellular matrix. What isit made of?

Use the > key to study the labeled image until you can identify theparts.

16. What is a major difference in composition that you can see between theepidermis 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?

Close Papillary layer of dermis.

Variability in skin pigmentationAcross 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 D3 is also synthesized in the epidermiswhen skin is exposed to ultraviolet rays in sunlight. However, ultravioletradiation can also damage DNA in the nuclei of cells.

Open Pigment comparison and study the images. The skin sectionon the left is from a person with light skin. The section on the right isfrom a person with darker skin.

Activate density slicing.

Density slicing is a technique that highlights (in red) a range of pixel valuesin the LUT and any pixels in the image that have those same values. The areaof the highlighted pixels can then be measured. Lets compare the area ofpigmentation in non-pigmented skin to that in pigmented skin.

Adjust the red range in the LUT to highlight only the dark areas ofmelanin 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 orbottom edge of the red bar

slide red range up and down click and drag red bar inLUT from middle

Choose Analyze/Options and set your measurement optionsto show only Area.

Use the tool to make a box around the non-pigmented image on theleft. See the example in the margin (showing a box around thepigmented skin image).

File/Close

Options/Density Slice

See the Density SlicingIPTechnique Sheet for detailedinformation about densityslicing.

File/Open

pigmented areashighlighted red

rectangular selection


Measure the area of pigmentation in the non-pigmented skin.

20. Record the area measurement (in pixels) in the table on your Data Sheet.

Use the tool to select the pigmented image on the right andmeasure the area of pigmentation in the pigmented skin. Record thearea in the data table.

21. Calculate a ratio of the relative amount of pigment in the pigmentedversus the non-pigmented skin.

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 havelarge amounts of pigment in the skin?

In the Skin cancer folder, open Condition A. Study the imagecarefully. Locate the epidermis and dermis.

23. What is abnormal about the tissue in Condition A?

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?

Close all images.

More exploration

Epidermal appendages

Hair, sweat and sebaceous (oil) glands are accessory structures associatedwith skin.

Open all the images in the Skin appendages folder. Study theimages until you can name the structures.

Use your observations of the images, your notes or textbook and yourown 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? Wheredo 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 thistissue found?

D. When a hair shaft extends beyond the surface of the epidermis, are thecells 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 sebumreach the surface? Water without soap will not remove sebum. What doesthis indicate about the chemical composition of sebum?

Mystery images

Open both images in the Mystery images folder. Consider magni-fication as you try to determine what these structures are.

Close all images.

Pixels are tiny square pictureelements that make up a digitalimage.

Hint: Most cancers kill whenthey spread, or metastasize, toother parts of the body. How docancer cells spread?

Analyze/Measure andAnalyze/Show Results

File/Close

File/Open/ Open AllIf you dont have enoughmemory, open the imagesone at a time.

Hint: These structures arelocated on the fingertips.


DataSheet

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.

Thick and ThinName(s) Class

Date

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 doyou think is the purpose of this layer? Explain your answer.

Skin type Thickness of epidermis, m m Thickness of dermis, m m

Thick skin

Thin skin


11. In the past you have probably experienced very shallow cuts into your skin that did not hurt or bleed. Explainwhy.

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.


22. Under what environmental conditions would it be an advantage to have large amounts of pigment in theskin?

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 makethe 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? Manyshampoos 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 withoutsoap 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?

thick and thin

Documents