Laboratory 4 The Integument

Transcription

1 Laboratory 4 The Integument Goals: Identify the three layers of the skin. Identify and describe the layers of the epidermis and the tissue type(s) present. Describe the two layers of the dermis. Identify the tissue types that form each layer. Identify the receptors for sensation in the skin and describe their function. Identify and describe the distribution of sebaceous glands, eccrine and apocrine sweat glands, and hairs. Be able to identify the major structures in hair. Describe sensory adaptation and descrimination. Integument, from the Latin integere meaning to cover, refers to the outer enveloping layer of an organism. In humans, the organs of the integumentary system are the skin, hair, and nails. The skin is the largest organ in the human body. It forms a hardened, waterproof, cushioning, bacteria- and chemical- resistant outer layer. Other functions include roles in body temperature regulation, excretion of wastes and water, synthesis of the hormone Vitamin D, and housing the receptors for our sense of touch. 1. Layers of the Skin The skin proper has two distinct layers, the epidermis composed of epithelial tissue and the dermis composed of connective tissue. Immediately deep to the skin is a layer of adipose tissue called the hypodermis, or superficial facia. Epidermis The epidermis (epi-, upon and derme, skin) is comprised on stratified squamous epithelial tissue. As an epithelial tissue, it is avascular. Depending upon the area of the skin, the epidermis consists of either four or five distinct layers. Cells of the Epidermis The predominant cell type in the epidermis is a keratinocyte which produce large quantities of the tough fibrous protein keratin. These cells are connected to each other by desmosomes. The cells begin as cubiodal- shaped cells that flatten as they mature. The outer layers of keratinocytes in the epidermis are dead. Melanocytes are located in the innermost layer of the epidermis. These cells produce melanin which helps protect the skin from damage due to ultraviolet radiation and contribute to skin color. The color imparted from melanocytes can be seen in slides of pigmented skin. Dendritic cells, also called Langerhans cells, are phagocytic cells derived from white blood cells found in the epidermis. These cells help protect the skin from microorganisms. 41 Figure 1. The two layers of skin and the hypodermis.

2 Merkel cells are slow adapting touch receptors that are found in abundance in the finger tips. These cells are located at the dermal- epidermal junction. Layers of the Epidermis: The epidermis consists of four layers in skin thin, which covers most of the body and five layers in thick skin found on the palms of the hands and soles of the feet. The layers are: Stratum basale, or basal layer, is a single layer of cubiodal- shaped cells found of the basolateral surface of the tissue. Cells found in this layer include heavily mitotic keratinocytes, melanocytes, and Merkel cells. Stratum spinosum, or spiny layer, consists several layers Figure 2. Melaninocytes of the epidermis. of keratinocytes connected by desmosomes with some scattered dendritic cells. Stratum granulosum, or granular layer, has three to five layers of mature keratinocytes containing abundant granules of keratin fibrils and glycolipids. Stratum lucidum, or clear layer, is a thin, clear layer of flattened, dead keratinocytes found only in the thick skin of the soles of the feet, fingertips or palms of the hand. Stratum corneum, or horny layer, is twenty to thirty layers of dead keratinocytes that have lost their organelles and are completely filled with keratin. This is the major bulk of the epidermis. These cells are continually shed and must be replaced. Dermis The dermis is immediately deep to the epidermis and is most of the thickness of the skin. The dermis is primarily connective tissue with blood vessels and nerves running through it. Cell types found in the dermis include fibroblasts, adipocytes, and macrophages. Also present are collagen and elastic fibers. Accessory structures of the skin are also found in the dermis such as sebaceous (oil) glands, sweat glands, and hair follicles. There are two layers in the dermis. Figure 3. Layers of the Epidermis. The most superficial layer is the papillary layer and is areolar connective tissue. It is uneven and has fingerlike projections from the superficial surface. An extensive capillary network in the papillary layer nourishes the epidermis. This layer also contains tactile receptors known as Meissner s corpuscles that are especially dense in the lips and fingertips. The reticular layer of the dermis is dense irregular connective tissue. This is the most deep skin layer sitting directly atop the hypodermis. The layer contains arteries and veins, sweat glands, sebaceous glands, and Pacinian corpuscles, touch receptors for pressure. 42

3 Figure 4. Structure of the skin. Hypodermis The hypodermis (hypo-, below) is a layer of adipose tissue, often called subcutaneous fat that is located deep to the dermis and superficial to the connective tissue sheath of the mucles. The hypodermis functions as cushioning, insulation, and as site of chemical energy storage. Additionally, the larger blood vessels providing for the skin are located in the hypodermis. Activities Using charts and the skin model, locate the structures on your laboratory study list. Look at pigmented thin skin and thick skin under the microscope. Draw: o pigmented thin skin at 40X. Label the dermis, hypodermis, and epidermis. o both pigmented and thick skin at 400X. Label the layers of the epidermis. Note the differences between thick and thin skin. What chemical is responsible for the color seen in pigmented skin? 2. Accessory Structures of the Skin: Accessory structures of the skin include hair, nails and cutaneous glands. Cutaneous Glands There are three categories of cutaneous glands: sweat glands, sebaceous (oil) glands, and ceruminous (wax) glands. Sebaceous glands: These glands produce secum, an oily substance that lubricates the hair and skin. These glands are abundant except for on the thick skin on the palms and soles. Many of these glands empty into hair follicles although some empty directly onto the skin. Sebaceous glands are holocrine glands meaning that the secretory product contains entire cells. The periphery is comprised of a single layer of cuboidal cells with the bulk of the gland being large, pale- staining cells that are secreted into the duct. 43

4 Sweat glands, also known as sudoriferous glands, are coiled tubular structures located in the dermis that secrete sweat through a sweat pore or into a hair follicle. There are two types: eccrine and apocrine. The tubular structure of both types is composed of simple cuboidal with the excretory duct being stratified cuboidal. Ecrine, or merocrine, sweat glands are the most abundant and function in regulation of body temperature. Ecrine sweat glands secrete sweat directly onto the skin through a sweat pore. In contrast, apocrine sweat glands are located in the genital and axillary areas and open into hair follicles. Apocrine sweat glands are larger. The composition of the sweat also differs between the two types of sweat glands with apocrine sweat containing many fats in addition to the components of eccrine sweat. Figure 5. Sebaceous and sudoriferous glands. Hair Hairs are keratinized structures that grow from follicles deep in the dermis out through the surface of the epidermis. Hair growth is found over the entire human body excepting the palms, soles, lips, and portions of the external genitalia. Most of the human body is covered in fine, non- pigmented vellus hair. The hair found on the scalp, axillary and anal areas, as well as facial hair on men is called terminal hair. The hair follicle is a tubular invagination that anchors the hair. The deepest portion of the follicle expands into the hair bulb, which contains the mitotically active cells that provide for hair growth. Sensory nerve endings wrap around each hair bulp serving as touch receptors, the hair root plexus. You should be able to feel if someone moves your hair even if they don t touch your skin. The hair papilla at the base of the follicle provides nourishment for the growing hair. Sebaceous glands are associated with the hair follicle. Figure 6. Structures associated with hair. 44

5 A small muscle, the arrector pili, associates with each follicle. These muscles literally raise the hair and are responsible for goose bumps. This occurs due to cold temperatures or fear. Lifting the hair can trap a greater layer of insulating hair next to the body of furred animals. Activities 2A. Using the available slides, draw: o a sebaceous gland at 40X. Label the secretory cells. o a sudoriferous gland at 100X. Label the secretory cells and the lumen. o a hair follicle with the arrector pili at 100X. Label the arrector pili, hair shaft, hair bulb, and hair follicle. 2B. Compare the density of sweat glands on your forearm and on your palm. 1. Hypothesize which area would have the greater density of sweat glands. Record this on your lab report sheet. 2. Obtain two squares of bond paper about 1cm 2, some adhesive tape, and iodine. 3. Using a cotton swab, paint a small area of your palm and forearm with the iodine solution. The painted area should be slightly larger than the paper. Be generous while painting. 4. Let the solution dry completely. 5. Tape the bond paper over the dried iodine by placing adhesive tape around the edges of the bond paper and securing it to the skin. 6. Wait 20 minutes. 7. Remove the bond paper and determine the density of sweat glands. 8. The bond paper contains starch that reacts with the iodine solublized by your sweat. 3. Sensory Receptors in the Skin: The skin houses many sensory receptors. Some of these receptors allow for our tactile sense by acting as mechanorecptors, converting pressure or motion into nerve impulses. Others sensory receptors in our skin respond to termperature or pain. Merkel cells are located in the deep epidermis. These cells are slow- adapting tactile receptors. Adaptation refers to decrease in response to constant stimuli. Slow- adapting receptors will desensitize to a continued stimulus more slowly. These cells, therefore, can detect continued touch. Meissner s corpuscles are located in the papillary layer of the dermis. These are fast- adapting tactile receptors. Since Meissner s corpuscles adapt rapidly they detect initial sensation well, but not continued stimulus. Pacinian corpuscles are located in the deep reticular layer of the dermis. These are extremely fast- adapting receptors for pressure. They are particularly suited to detecting vibration. Nerve endings associated with the hair root as part of the hair root plexus also contribute to our tactile senses. These rapidly- adapting receptors detect movement of the hairs. Free nerve endings terminate in the dermis and epidermis. These can respond to touch, pain or temperature. 45

6 The density of touch receptors varies significantly across different regions of the skin. The areas with higher densities of receptors have a greater ability to differentiate between closely localized stimuli. Decreased ability to discriminate between two points can signify nerve damage. Activities 3A. Two- point dicrimination threshold 1. Bend a metal paperclip into a U- shape with the points 10mm apart. 2. Have the volunteer close their eyes. 3. Randomly touch the volunteer on the indicated body region with one or both points of the paperclip. The touching with one is to control for expectation bias of the volunteer. Touch two or three times for each distance. 4. Move the paperclip edges closer together to determine that the closest points that the volunteer can discriminate on the fingertip, palm of the hand, back of the hand, and back of the neck. Use a ruler each time you move the paperclip edges closer together to determine the distance. 3B. Adaptation of temperature receptors: 1. Obtain 3 beakers. 2. Fill one with cold water, one with lukewarm water, and one with very hot, but not painful water. 3. Place one hand in the cold water and one in the hot water. 4. Describe the sensation on the lab report sheet. 5. Keep you hands in the cold and hot water for one minute. 6. Describe the sensation in each hand at the end of one minute. 7. Remove and immediately place both hands in the lukewarm water. 8. Compare the sensation in each hand on the lab report sheet. Attribution of images used in this document: Figure 1Lutz S. (2009). [Two layers of skin and the hypodermis]. Blue Histology. Retrived May 7, 2012 from: Figure 2. Lutz S. (2009). [Melaninocytes of the epidermis]. Blue Histology. Retrived May 7, 2012 from: Figure 3. Gray, H. (1918). [Layers of the epidermis] from Gray's Anatomy, 20th ed. Figure 4. Madhero88. (2011). [Skin layers]. WikimediaCommons retrieved May 7, 2012 from Figure 5. Lutz S. (2009). [Sebaceous and sudoriferous glands]. Blue Histology. Retrived May 7, 2012 from: 46

7 Laboratory 4 Name: Section: 1. Using the following terms, correctly label this drawing. Arrector pili Blood vessels Dermis Epidermis Hair follicle Hair papilla Hypodermis Meissner s corpuscle Nerve fiber Pacinian corpuscle Sebacous gland Sweat gland 2. Histology Drawings from part 1 and 2 activities: Tissue Name: Tissue Name: Tissue Source: Tissue Magnification (TM)= Tissue Source: TM= 47

8 48

9 3. State you hypothesis as to which area to be tested will have the greatest density of sweat glands. 4. Which area had the greatest density of sweat glands? 5. Complete the following table based on your results from Activity 3A: Body Region Two-point threshold (mm) Palm Back of hand Fingertip Back of neck 6. Which area of the skin had the best two-point discrimination? The worst? What differences in the skin receptors would account for this? 49

10 7. Record your observations from activity 3B. Cold water hand: First submerged After 1 min When placed in lukewarm water - Hot water hand: First submerged After 1 min When placed in lukewarm water - 8. Define adaptation with respect to sensory receptors. 50