Chapter 5 Assess What You Learned

17. How do sweat and sebum differ?

Sweat is a water-based secretion that functions primarily in thermo- regulation and is secreted via merocrine secretion. Sebum is a lipid- based secretion that provides a hydrophobic barrier and is secreted via holocrine secretion.

2. After Ramon's skin came into contact with a poison ivy plant in biology lab, he developed a painful, itchy rash. However, after the skin of his colleague Cathy came into contact with snake venom in lab, she developed no skin irritation. Poison ivy plants contain lipid-soluble oils, whereas snake venoms contain mostly water-soluble peptides. Explain why Ramon developed a rash, whereas Cathy did not.

The lipid-based toxins in poison ivy easily penetrate the epidermis and reach the cells of the deep epidermis and the dermis. However, the water-soluble toxins in venom cannot pass through the lipid- based substance that coats keratinocytes in significant amounts, and so the venom does not reach the deep epidermis and the dermis.

1. You are working in the emergency department when paramedics rush in with an unconscious patient. You notice that the patient is wearing athletic clothing and the skin on his face and elsewhere on his body is bright red. The paramedics tell you that he was picked up after collapsing during a bike race. What does the color of the patient's skin tell you about the probable cause of his illness? Explain.

The patient has likely suffered heat stroke. The bright red color of the skin is due to the body's attempt to release heat via dilation of the vessels in the dermis.

3. Nguyen comes to your clinic with a mole that has recently changed in appearance. You examine the mole and note that its borders are irregular, it has a deep blue-black color, and the color is unevenly distributed throughout the mole. a. What is your immediate concern? Why? b. Nguyen tells you that she has used a tanning booth once per week for the past several years, and that the tanning salon advertises it as safe. What do you tell her about the tanning salon's claim? How does any UV exposure affect keratinocytes and melanocytes? Explain.

a. The immediate concern is malignant melanoma, because her lesion has the characteristics of this particular cancer. b. Exposure to UV radiation mutates the DNA of cells in the skin. This DNA mutation is what triggers the production of more melanin by melanocytes. For this reason, any tanning, irrespective of the source, comes from the initial DNA damage and is therefore not completely safe.

6. Keratinocytes in the superficial strata of the epidermis die because: a. they are too far away from the blood supply in the dermis. b. they are surrounded by a lipid-based substance that makes them more permeable to water. c. they do not die. d. No keratinocytes in the epidermis are alive.

a. they are too far away from the blood supply in the dermis.

1. Why don't you bleed when you cut your nails? Why don't you bleed when a hair is pulled?

Both hair and nails are derived from the epidermis, which is avas- cular. Since these structures have no blood vessels, there is no bleeding when they are damaged unless the injury involves the underlying dermis.

2. Manufacturers of shampoos and conditioners often claim their products contain vitamins that are necessary to keep hair shafts healthy. Do hair shafts need vitamins? (Hint: Vitamins are

Hair shafts consist of dead keratinocytes. Dead cells do not carry out chemical reactions, and so they have no need of vitamins. For shampoos and conditioners to have any effect on the hair, the vita- mins would have to reach the cells in the hair matrix, and this is unlikely to happen. The claims are therefore very likely to be invalid.

18. Which type of burn involves the epidermis and all or part of the dermis? a. First-degree burn b. Second-degree burn c. Third-degree burn d. Fourth-degree burn

b. Second-degree burn

3. Which of the following is not a function of the integument? a. Protection from mechanical trauma b. Protection from the environment c. Thermoregulation d. Protection from acid-base imbalances e. Vitamin D synthesis

d. Protection from acid-base imbalances

16. Match each type of gland with its correct properties. _____ Eccrine sweat gland _____ Sebaceous gland _____ Ceruminous gland _____ Mammary gland _____ Apocrine sweat gland a. Branched gland that secretes sebum into a hair follicle b. Gland that secretes a protein-rich sweat into a hair follicle c. Simple coiled tubular gland found over most of the body that secretes sweat through a sweat pore d. Gland that secretes ear wax e. Modified sweat gland that produces milk

(c) Eccrine sweat gland (a) Sebaceous gland (d) Ceruminous gland (e) Mammary gland (b) Apocrine sweat gland a. Branched gland that secretes sebum into a hair follicle b. Gland that secretes a protein-rich sweat into a hair follicle c. Simple coiled tubular gland found over most of the body that secretes sweat through a sweat pore d. Gland that secretes ear wax e. Modified sweat gland that produces milk

4. Explain what happens to dermal blood vessels when heat needs to be conserved (i.e., due to a cold environment).

Dermal blood vessels constrict when in a cold environment, to direct heat to deeper tissues and minimize heat loss to the environment.

9. What are the functions of the dermal papillae?

Dermal papillae house capillary loops that provide oxygenated blood to the epidermal cells. They also house sensory receptors that detect changes in the environment.

6. Would a mild second-degree burn be likely to heal by regeneration or fibrosis? Would the same type of healing take place in a third-degree burn that involved muscle tissue? Why or why not? (Connects to Chapter 4)

A second-degree burn involves epithelium and connective tissue, which generally heal by regeneration unless the damage is extensive. However, muscle tissue generally heals by fibrosis, so healing of a severe third-degree burn will involve some degree of fibrosis.

1. Explain why the skin is considered an organ.

An organ by definition is two or more tissues that work together to achieve common functions. The skin consists of keratinized stratified squamous epithelium, loose connective tissue, and dense irregular connective tissue. These three tissues form a barrier between the environment and the internal body and perform a host of other

3. The hair and nails are sometimes called accessory organs. Are these structures technically organs? Why or why not?

An organ consists of two or more tissues. The hair and nails consist only of epidermal cells, and are therefore not organs. However, if the surrounding connective tissue is considered, they could be called organs.

5. Many anti-aging skin creams contain collagen and hyaluronic acid. Manufacturers claim that the collagen and hyaluronic acid applied to the surface of the skin will be absorbed into the dermis, where they will be incorporated into dermal tissue. a. What are collagen and hyaluronic acid, and what are their functions? (Connects to Chapter 4) b. Are these molecules polar or nonpolar? (Connects to Chapter 2) c. Predict whether or not these molecules are likely to be absorbed by the epidermis. d. Predict the effectiveness of the creams.

Many anti-aging skin creams contain collagen and hyaluronic acid. Manufacturers claim that the collagen and hyaluronic acid applied to the surface of the skin will be absorbed into the dermis, where they will be incorporated into dermal tissue. a. What are collagen and hyaluronic acid, and what are their functions? (Connects to Chapter 4) a. Both chemicals are components of the ECM. Collagen is a pro- tein fiber that gives the skin tensile strength, and hyaluronic acid is a glycosaminoglycan that traps water in the ECM and increases its firmness. b. Are these molecules polar or nonpolar? (Connects to Chapter 2) b. Most proteins are large polar molecules. c. Predict whether or not these molecules are likely to be absorbed by the epidermis. c. Since these molecules are large and polar, they are unlikely to penetrate the water-resistant lipid coating of the epidermis in significant amounts. d. Predict the effectiveness of the creams. d. The collagen and hyaluronic acid would need to reach the dermis in order to have any effect. Since they are unlikely to penetrate the epi- dermis in any significant amounts, they are not likely to be effective.

15. Fill in the blanks: Sebaceous glands secrete by __________ secretion; sweat glands secrete by __________ secretion.

Sebaceous glands secrete by (holocrine) secretion; sweat glands secrete by (merocrine) secretion.

4. What would happen to the skin if the oil produced by sebaceous glands was instead a polar covalent compound? (Connects to Chapter 2)

Sebum helps to repel water from the skin, along with the lipid- based substance produced by the keratinocytes. If sebum were water-soluble, the skin would be less water-resistant and more prone to gain or lose water to the external environment.

13. Fill in the blanks: The portion of the hair that projects from the surface of the skin is the __________, and the portion within the dermis is the __________, which is embedded in a(n) __________. The portion of the hair that contains cells that undergo mitosis during the growth stage of the hair is known as the __________.

The portion of the hair that projects from the surface of the skin is the (hair shaft), and the portion within the dermis is the (hair root), which is embedded in a(n) (hair follicle). The portion of the hair that contains cells that undergo mitosis during the growth stage of the hair is known as the (matrix).

5. Number the strata of thick skin epidermis from deepest (1) to most superficial (5). _____ Stratum spinosum _____ Stratum corneum _____ Stratum basale _____ Stratum lucidum _____ Stratum granulosum

___2__ Stratum spinosum ___5__ Stratum corneum ___1__ Stratum basale ___4__ Stratum lucidum ___3__ Stratum granulosum

7. Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. Melanocytes account for the bulk of the epidermis. b. Keratinocytes begin life in the stratum corneum and gradually are pushed into the stratum basale. c. Dendritic cells are phagocytes of the immune system that protect the skin and deeper tissues from invasion by pathogens. d. Merkel cells produce the pigment melanin.

a. False: Keratinocytes account for the bulk of the epidermis. b. False: Keratinocytes begin life in the stratum basale and gradually are pushed into the stratum corneum. c. T: Dendritic cells are phagocytes of the immune system that protect the skin and deeper tissues from invasion by pathogens. d. False: Melanocytes produce the pigment melanin.

11. Mark the following statements as true or false. If a statement is false, correct it to make a true statement. a. The primary skin pigment is melanin, which is derived from the amino acid tyrosine. b. Melanin is produced by melanocytes and covers the nuclei of neighboring dendritic cells. c. Carotene is a brown-black pigment that accumulates in the stratum corneum. d. Increased amounts of blood flowing through the dermis lead to pallor in the skin. e. Hemoglobin is a pigment found in red blood cells, and its color depends on the oxygen level of the blood.

a. True: The primary skin pigment is melanin, which is derived from the amino acid tyrosine. b. False: Melanin is produced by melanocytes and covers the nuclei of neighboring keratinocytes. c. False: Carotene is a yellow-orange pigment that accumulates in the stratum corneum. d. False: Decreased amounts of blood flowing through the dermis lead to pallor in the skin. e. True: Hemoglobin is a pigment found in red blood cells, and its color depends on the oxygen level of the blood.

2. Which of the following correctly describes the structure of the skin? a. It consists of the superficial epidermis, middle dermis, and deep hypodermis. b. It consists of the superficial epidermis and deep dermis. c. It consists of the superficial dermis and deep epidermis. d. It consists of the superficial dermis and deep hypodermis.

b. It consists of the superficial epidermis and deep dermis.

14. Nail growth occurs when: a. cells in the nail plate undergo mitosis. b. cells in the nail matrix undergo mitosis. c. cells in the eponychium undergo mitosis. d. cells in the medial and lateral nail folds undergo mitosis.

b. cells in the nail matrix undergo mitosis.

10. Epidermal ridges are caused by: a. the epidermal papillae. b. mounds of papillary dermis arranged into dermal ridges. c. gaps between collagen bundles in the reticular layer. d. tight binding of the reticular layer to deeper structures.

b. mounds of papillary dermis arranged into dermal ridges.

19. The type of skin tumor that involves the keratinocytes of the stratum spinosum is: a. basal cell carcinoma. b. squamous cell carcinoma. c. malignant keratocytoma. d. malignant melanoma.

b. squamous cell carcinoma.

8. Which of the following statements is false? a. Thin skin lacks the stratum lucidum, whereas thick skin has all five epidermal layers. b. Thick skin is located on the palms, the palmar surfaces of the fingers, the soles of the feet, and the plantar surface of the toes, whereas thin skin is located everywhere else. c. Thick skin has numerous hairs, whereas thin skin lacks hairs. d. Thin skin has a thin stratum corneum and the other layers are thinner than what we find in thick skin.

c

12. Which of the following is not a function of body hair in humans? a. Protection from the environment b. Sensation c. Protection from mechanical trauma d. Regulation of blood flow

d