Name________________________________________
LAB
SKIN & MEMBRANES
The skin can be considered to be an organ system called the integumentary system. It does much more than
cover the body exterior. The skin has several functions, most, but not all concerned with protection.
BASIC SKIN STRUCTURE
The skin has two distinct regions, the upper epidermis composed of epithelial cells and underlying connective
tissue called the dermis. The layers are firmly cemented together along a wavy border. Deep to the dermis is the
subcutaneous tissue, also known as hypodermis. The hypodermis is composed mostly of adipose cells and is not
considered part of the skin.
Layers of epidermis. The epidermis is avascular and composed of stratified squamous epithelial cells. It consists
of five layers.
Locate these layers on a model or diagram.
1.
2.
3.
4.
5.
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum
Stratum corneum
Layers of the dermis. Dense connective tissue makes up the bulk of the dermis. Collagen and elastic fibers are
found throughout the dermis along with adipose cells, fibroblasts, and phagocytes. The dermal blood supply
allows the skin to regulate temperature. There are two principal regions of the dermis.
1. Papillary layer
2. Reticular layer
Activity - visualizing changes in skin color due to continuous external pressure
Obtain a small glass plate. Press the heel of your hand firmly against the plate for a few seconds and then
observe and record the color of your skin in the compressed area by looking through the glass. Note the color of
compressed skin. What is the reason for color change? Record responses on answer sheet.
The dermis also has a rich nerve supply. Many of the nerve endings bear specialized receptor organs that
respond to pain, pressure, or temperature extremes and transmit messages to the central nervous system for
interpretation. For example, Meissner’s corpuscle responds to light touch and is composed of connective tissue
located in a dermal papilla. The much larger Pacinian corpuscle responds to deep pressure and resembles a tiny
onion.
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The density of the touch receptors varies significantly in different areas of the body. In general, areas having the
greatest density of tactile receptors have a heightened ability to “feel.” These areas are typically areas of fine
motor control.
Activity - testing tactile localization
Tactile localization is the ability to determine which portion of the skin has been touched. Each receptor has a
corresponding touch field in the brain.
1. Subject should close eyes. The experimenter touches the palm of the subject’s hand with a pointed
black marker. The subject should try to touch the exact point with her or his own marker of a different
color. Measure the discrepancy of localization in millimeters.
2. Repeat in the palm again, average the results, and record in the chart on the answer sheet.
3. Repeat the procedure on a fingertip, the ventral forearm, and the back of the hand. Record the
averaged results in the chart.
Activity - demonstrating adaptation of touch receptors
In many cases, when a stimulus is applied for a prolonged period of time, the rate of receptor response slows,
and our conscious awareness of the stimulus declines. This phenomenon is called adaptation. Touch receptors
adapt rapidly so that we, for example, are not aware of our clothing rubbing against our skin.
1. Subject should close eyes. Place a coin on the anterior surface of the subject’s forearm and determine
how long the sensation persists for the subject.
Duration of sensation = _________ seconds.
2. Repeat the test, placing the coin at a different location on the forearm. How long does the sensation
persist? ________ seconds.
3. After awareness of the sensation has been lost at the second site, stack three more coins on top of the
first one. Does the pressure sensation return ? If so, for how long is the subject aware of the pressure in
this instance? ______ seconds. Are the same receptors being stimulated when the four coins, rather
than one coin are used?
APPENDAGES OF THE SKIN
Appendages of the skin include hair, nails, and cutaneous glands. These are all derived from the epidermis but
reside in the dermis. We will look at cutaneous glands here.
Cutaneous glands
Cutaneous glands fall into two categories – sebaceous (oil) glands and sweat (sudoriferous) glands. Sebum, a
combination of oils and fragmented cells, is the product of the sebaceous glands. It acts like a natural skin
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cream. Sweat glands are of two types, eccrine producing clear perspiration (containing water, salts, and urea),
and apocrine, producing milky protein and fat rich substance (including water, salts, and urea). Apocrine glands
occur in the axillary and genital areas. Sweat glands are controlled by the nervous system and are part of the
body’s heat regulating system.
Activity - plotting the distribution of sweat glands
For this experiment, you will need two squares of bond paper (1cm x 1cm), adhesive tape, and a betadine swab.
Using the betadine solution, paint an area of the medial aspect of your left palm (avoid the crease lines) and a
region of your left forearm. Allow the solution to dry thoroughly. The painted area in each case should be
slightly larger than the paper squares.
1. Mark one piece of ruled bond paper with a “H” (for hand) and the other “A” (for arm). Have your lab
partner securely tape the appropriate square of paper letter side up over each iodine-painted area.
Leave the squared in place for 10 minutes. While waiting to determine the results, continue with other
sections of this lab.
2. Remove the squares and count the number of blue-black dots on each square. The appearance of a
blue-black dot indicates an active sweat gland. The iodine in the pore dissolves in the sweat and reacts
with the starch in the bond paper to produce the blue-black color producing “sweat maps.”
Hair
A hair is also an epithelial structure. The part of the hair enclosed within the follicle is called the root. The
portion of the hair projecting from the skin is called the shaft. Hair is formed by mitosis of the cluster epithelial
cells at the base of the follicle. This cluster is called the hair bulb. As the daughter cells are pushed away from
the growing region, they become keratinized and die. The bulk of the hair shaft is dead material.
View the drawing or microscope slide provided and sketch or label these structures, providing your results on
the answer sheet:
1.
2.
3.
4.
5.
6.
Epidermis
Hair follicles
Sloughing stratum corneum cells
Hair shaft
Dermis
Hair bulb
BODY MEMBRANES
Body membranes cover surfaces, line body cavities, and form protective sheets around organs. Body
membranes fall into one of two categories; epithelial membranes or connective tissue membranes. There are
three types of epithelial membranes, one being cutaneous membranes. Cutaneous membranes form the skin,
also known as the integumentary system. The skin serves to protect underlying organs and tissues in the body.
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In general, we can use the term “membrane” to refer to any thin layer or layers covering or surrounding
something. You have seen the term “plasma membrane” as the phospholipid layer surrounding every cell. Now
we have tissue membranes consisting of several layers of tissue sandwiched together that surround body
cavities, organs, or entire organ systems.
Describe these membranes, including a location for each, and record on your answer sheet.
1.
2.
3.
4.
Serous membranes
Mucous membrane
Synovial membrane
Cutaneous membrane
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Name______________________________
LAB – THE SKIN & MEMBRANES
Questions & Answer Sheet
1. List five agents skin protects against, and list five other functions besides protection.
2. Tell one unique characteristics of each layer of epidermis.
3. Into which layer is a hypodermic injection given?
4. What is a second-degree burn?
5. How do dermal blood vessels help regulate body temperature?
6. From visualizing changes in skin color activity:
a. What was the color of compressed skin?
b. Why do you think the color changed?
c. What would happen if in this area the pressure was continued for an extended period?
7. In the tactile location exercise, which area had the smallest error of localization (is most sensitive to
touch)?
8. Duration of sensation in sensory adaptation exercise _______ seconds.
9. When this test was repeated, placing the coin at a different location on the forearm, the sensation
persisted _______ seconds.
10. In the duration of sensation exercise, were the same receptors being stimulated when the four coins,
rather than one coin are used? Explain.
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11. After awareness of the sensation had been lost at the second site, and three more coins were stacked
on top of the first one. Does the pressure sensation return?
12. If so, for how long is the subject aware of the pressure in this instance? ______ seconds.
13. Which skin area tested for the most sweat glands? How many glands per cubic centimeter for each
area?
14. What is the function of sebum?
15. Define the term “keratinization.”
16. What is an arrector pili and how does it function?
17. Label this figure of skin and hair.
18. Describe these membranes, including a location for each.
a. Serous membrane
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b. Mucous membrane
c. Synovial membrane
d. Cutaneous membrane
19. Average Discrepancy Between Subject and Experimenter Touch Points (in mm)
Palm
Average
Fingertip
Average
Forearm
Average
Back of
Hand
Average
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