biology

<I ~ _____ _, ---- _ ~--- ~ ...... -- J ........ -- .-. -J ___ ...... u -..&.• .. :n .• ·u.~"'· "" .I..U4L """u~""~ U11o3 Ulo3~a~~! Cl.UW UUC~ ll

affect the baby? Is there a cure? 1 14. Read "Coloring Organisms" page 47 and answer "Questions to Consider" 1 and 2

Chapter 4 (Part 1) A. Computer Homework B. Text Read Pages 67-77 1-5. Answer studying the concepts- page 89, 1-5 6. What are four types of cancers? From which tissue are they derived? 7. Describe the different types of fibers found in connective tissue. 8. List the different types of connective tissues. 9. What makes cartilage unusual? Where is cartilage located? What is its function? 10. Describe bone. Where is compact bone found? Where is spongy bone found? What is their function? Where are blood cells made? 11. Using the textbook page 188,254-255,274, and internet sources, discuss osteoporosis, and the risk factors for developing the disease. What life style changes can you make to prevent it. 12. Describe blood. What are the different types of cells that make up blood? What is their function? 13. What is lymph fluid? What does it do? 14. What is a gland? Compare and contrast endocrine and exocrine glands. 15. What is the function of junctions between cells? Compare and contrast the different types of junctions

(Chapter 4- part 2 will be in Joumal2)

B106joumall mader 13 fall2013

l

Biology 106 Journal2 (Mader 13 ed )

Chapter 4 (part 2) 1. What are four types of cancers? From which tissue are they derived? 2. How does the skin help to maintain bomeostasis? 3 .. Answer: check your progress, page 77, questions 1-3 4.Text page 90 answer questions 6-8 5 a) Describe the structure and function of human skin. b) compare the function of the epidermis and dermis c) identify the function of the accessory organs associated with the skin

6. a) What are the effects of Botox injections b) Why would someone have a laser treatment c) Is tanning safe for your skin? Explain. d) Are tanning beds safe? Explain

7 .. Using the article;"The Evolution of Skin Color", discuss a) What kind of a cooling system has the human animal developed? b) What is the relationship between dark skin coloring and folate? c) What is the relationship between light skin coloring and vitamin D d) Why do the researchers believe that skin color is "largely a matter of vitamins"?

5. Read "Not an Old Person's Disease, Learning about Skin Cancer" and briefly answer the questions in the article.

6. Read: Textbook chapter 4 and

http://www.mayoclinic.comlhealthlskin-cancer/DS00190 Look at entire site

a) What are the risk factors of skin cancer? What are the A,B, C's of skin cancer? b) What does a skin cancer look like? c) Compare basal cell, and squamous cell carcinomas. What is actinic keratosis? Which type of skin cancer is the most common and easily cured? ?.What is a melanoma? When should you worry about it? 8. How can you protect yourself from skin cancers?

--=;

F

Stem cell research and Cloning

Read Text pg 63, 74, 410-411(cloning)

Handout

http://www .mayoclinic.comlhealthls tem-cells/CA00081

http://www .stemcells. wisc.edu/patients/

http://learn.genetics.utah.edu/

http:/ /learn. genetics. utah.edu/content/tech/cloning/whatiscloning/

http://learn.genetics.utah.edu/content/techlcloning/clickandclone/ ( Clone MIMI the mouse)

1. What is a stem cell? 2. Compare and contrast totipotent and pleuripotent stem cells. 3. How are totipotent stem cells obtained? Pleuripotent? 4. List some possible uses of pleuripotent stem cells. 5. What are multipotent stem cells? How are multipotent stem cells obtained? Give

examples. Why are they so important for blood production? 6. Do adult stem cells have the same potential as pleuripotent stem cells? 7. Why not just use the adult stem cell? 8. What is the ethical controversy about the methods currently available to obtain stem

cells? 9. From the article "Life in Print" and our movie, describe the process that we might use

to make new organs in the future, 10. What diseases do scientists believe could be cured with the use of stem cells? Using

the articles, "Body Regenerate Thyself', and "Stem Cells the Hope and the Hype" and "Stem cell discovery", What are the potentials and risks of stem cell use.

11. What are induced pleuripotent stem cells (iPS)? What is there potential? 12. What is the current government position on developing new stem cell lines? 13. Answer questions 1-3 on page 61 14. What was government policy under the Bush administration? Under the Obama

administration? If you were President, what would be your policy and why? 15. Read and Answer questions 1-4, page 411 16. What is a clone? 17. Who is Dolly? How was she created? 18. What is reproductive cloning? 19. What is therapeutic cloning?

-J

188 Unit 2 Maintenance of the Human Body

Minerals Minerals are divided into major minerals and trace minerals. Major minerals are needed at quantities greater than 100 mil- ligrams (mg) per day. Trace minerals are needed at levels less than 100 mg per day. Table 8.5 lists the selected minerals and gives their functions and food sources.

The major minerals are constituents of cells and body flu- ids and are structural components of tissues. The trace miner- als are often part of larger molecules. For example, iron (Fe 2 +) is present in hemoglobin, and iodine en is a part ofhormohes produced by the thyroid gland. Zinc (Zn2 +), copper (Cu2 +), and manganese (Mn 2 +) are present in enzymes that catalyze a variety of reactions. As research continues, more and more elements are added to the list of trace minerals considered essential. During the past three decades, for example, very small amounts of selenium, molybdenum, chromium, nickel, vanadium, silicon, and even arsenic have been found to be essential to good health. Table 8.5 also provides signs of defi- ciency and toxicity for the selected minerals.

Occasionally, individuals do not receive enough iron (especially women), calcium, magnesium, or zinc in their diets. Adult females need more iron in their diet than males (15 mg

i§ij§=ii Mineral Functions

Major (More than 100. mg/Day Needed) Calcium Strong bones and teeth, nerve (Ca2+) conduction, muscle cOntraction,

blood clotting Phosphorus Bone and soft tissue growth; (POl-l part of phospholipids,

ATP, and nucleic acids Potassium Nerve conduction, (K+) muscle contraction Sulfur (S2-) Stabilizes protein shape,

neutralizes toxic substances Sodium (Na+) Nerve conduction,

pH and water balance Chloride (Ca-) Water balance Magnesium Part of various enzymes (Mg2+J for nerve anQ muscle

contraction, protein synthesis , Trace (Less than 100 mg/Day Needed) Zinc (Zn2+) Protein synthesis, wound healing,

fetal development and growth, immune function

Iron (Fe2+) Hemoglobin synthesis

Copper (Cu2+)

Iodine (II Selenium (SeOl-l Manganese (Mn2+)

Hemoglobin synthesis

Thyroid hormone synthesis Part of antioxidant enzyme

Part of enzymes

Food Sources

Dairy products, leafy. green vegetables

Mea~·dairy products, sunflower seeds, tood additives Many fruits a(ld vegetables, bran Meat, dairy products, legumes Table salt

Table salt Whole grains, leafy green vegetables

Meats, legumes, whole grains

Whole grail-Is, meats, prune juice Meat, nuts, legumes

Iodized table salt, seafood Seafood, meats, eggs

Nuts, legumes, green vegetables

compared with 10 mg) because they lose hemoglobin each month during menstruation. Stress can bring on a magnesium deficiency, and due to its high-fiber content, a vegetarian diet may make zinc less available to the body. However, a varied and complete diet usually supplies enough of each type of mineral.

Calcium Calcium (Ca2 +) is a major mineral needed for the construction of bones and teeth. It is also necessary for nerve conduction, muscle contraction, and blood clotting. Many people take cal- cium supplements to prevent or counteract osteoporosis, a degenerative bone disease that afflicts an estimated one-fourth of older men and one-half of older women in the United States. Osteoporosis develops because bone-eating cells called as teo- clasts are more active than bone-forming cells called osteo- blasts. Therefore, the bones are porous, and they break easily because they lack sufficient calcium. Recommended calcium intakes vary by age, but in general 1,000 mg a day is recom- mended for men and women. After age 50 in women, and 70 in men, this increases to 1,200 mg a day. For many people, calcium supplements are needed to obtain these levels.

Deficiency

Stunted growth in children, tow bone. density in adults.

... Weakness, confusion, paih iri bones and joints.

• Paralysis; irregular·· heartueat, eventu"al death Not likely

Lethargy, muscle cramps, loss of appetite Not likely Muscle spasm, irregular heartbeat, convulsions, confusion, personality changes

Delayed wound healing, stunted growth, diarrhea, rnentall~thargy

Anemia, physical and mental sluggishness Anemia, stunted growth in children Thyroid deficiency Vascular collapse, possible cancer development Weakness and confusion

fnAnimatlon ~Osteoporosis

~

~

~----

· · ·- • -· • ·-· ,., ~• •- ... n.AtJtJ\JI L Ill I IUIJIOII:l

Bone Remodeling and Calcium Homeostasis Bone is constantly being broken down by osteoclasts and re- formed by osteoblasts in the adult. As much as 18% of bone is recycled each year. This process of bone renewal, often called bone remodeling, normally keeps bones strong (Fig. 11.13). In Paget's disease, new bone is generated at a faster-than-normal rate. This rapid remodeling produces bone that's softer and weaker than normal bone and can cause bone pain, deformi- ties, and fractures.

Bone recycling allows the body to regulate the amount of calcium in the blood. To illustrate that the blood calcium level is critical, recall that calcium is required for blood to clot (see section 6.4). Also, if the blood calcium concentration is too high, neurons and muscle cells no longer function. If calcium falls too low, nerve and muscle cells become so excited that convulsions occur. They are also necessary for the regulation of cellular metabolism by act- ing in cellular messenger systems. Thus, the skeleton acts as a res- ervoir for storage of this important mineral-ifthe blood calcium rises above normal, at least some of the excess is deposited in the bones. If the blood calcium dips too low, calcium is removed from the bones to bring it back up to the normal level.

You Can Avoid Osteoporosis Osteoporosis is a condition in which the bones are weakened due to a decrease in the bone mass that makes up the skeleton. The skeletal mass continues to increase until ages 20 to 30. After that, there is an equal rate of formation and breakdown of bone mass until ages 40 to 50. Then, reabsorp- II' . . . Animation t10n begms to exceed formatiOn, and the total • osteoporosis

bone mass slowly decreases (Fig. llC). Over time, men are apt to lose 25% and women to lose 35%

of their bone mass. But we have to consider that men-unless they have taken asthma medications that decrease bone formation-tend to have denser bones than women anyway. Whereas a man's testoster- one (male sex hormone) level gener- ally declines slowly after the age of 45, estrogen (female sex hormone) levels in women begin to decline significantly at about age 45. Sex hormones play an important role in maintaining bone strength, so this difference means that women are more likely than men to suffer a higher incidence of fractures,

Figure 11( Preventing osteoporosis. Weight-bearing exercise, when we are

young, can help prevent osteoporosis when

we are older. a. Normal bone. b. Bone from a person with osteoporosis.

Two hormones in particular are involved in regulating the blood calcium level. Parathyroid hormone (PTH) stimulates osteoclasts to dissolve the calcium matrix of bone. In addition, parathyroid hormone promotes calcium reabsorption in the small intestine and kidney, increasing blood calcium levels. Vitamin D is needed for the absorption of Ca2 + from the diges- tive tract, which is why vitamin D deficiency can result in weak bones. It is easy to get enough of this vitamin, because your skin produces it when exposed to sunlight, and the milk you buy at the grocery store is fortified with vitamin D.

Calcitonin is a hormone that acts opposite to PTH. The female sex hormone estrogen can actually increase the num- ber of osteoblasts; the reduction of estrogen in older women is often given as reason for the development of weak bones, called osteoporosis. Osteoporosis is discussed in the Health feature, "You Can Avoid Osteoporosis." In the young adult, the activity of osteoclasts is matched by the activity of osteoblasts, and bone mass remains stable until about age ~Video 45 in women. After that age, bone mass starts to 11111 ::~~s decrease.

Bone remodeling also accounts for why bones can respond to stress. If you engage in an activity that calls upon the use of

involving especially the hip, vertebrae, long bones, and pelvis. Although osteoporosis may at times be the result of various dis- ease processes, it is essentially a disease that occurs as we age.

How to Avoid Osteoporosis

Everyone can take measures to avoid having osteoporosis when they get older. Adequate dietary calcium throughout life is an important protection against osteoporosis. The National Osteo- porosis Foundation (www.nof.org) recommends that adults

b. Osteoporosis

,__,;

'~

.J

..._...

"'-'

~

under the age of 50 take in 1,000 mg of calcium per day. After the age of 50, the daily intake should exceed 1,200 mg per day.

A small daily amount of vitamin D is also necessary for the body to use calcium correctly. Exposure to sunlight is required to allow skin to synthesize a precursor to vitamin D. If you reside on or north of a "line" drawn from Boston to Milwaukee, to Minneapolis, to Boise, chances are you're not getting enough vitamin D during the winter months. Therefore, you should take advantage of the vitamin D present in fortified foods such as low-fat milk and cereal. If you are under age 50, you should be receiving 400-800 IU of vitamin D per day. After age 50, this amount should increase to 800-1,000 IU of vitamin D daily.

Very inactive people, such as those confined to bed, lose bone mass 25 times faster than people who are moderately active. On the other hand, moderate weight-bearing exercise, such as regular walking or jogging, . is another good way to maintain bone strength (Fig. UC).

Diagnosis and ~Treatment

Postmenopausal women with any of the following risk factors should have an evaluation of their bone density:

• white or Asian race • thin body type • family history of osteoporosis • early menopause (before age 45) • smoking • a diet low in calcium, or excessive alcohol consumption

and caffeine intake • sedentary lifestyle

Chapter 11 Skeletal System 255

Figure 11.13 Bone remodeling. Diameter of a bone increases as bone absorption occurs inside the shaft

and is matched by bone formation outside the shaft.

-~':'- bone formation

•. · ~. medullary cavity

compact bone

Bone density is measured by a method called dual-energy X-ray absorptiometry (DEXA). This test measures bone den- sity based on the absorption of photons generated by an X-ray tube. Soon there may be blood and urine tests to detect the biochemical markers of bone loss. Then it will be made eas- ier for physicians to screen older women and at-risk men for osteoporosis.

If the bones are thin, it is worthwhile to take all possible measures to gain bone density because even a slight increase can significantly reduce fracture risk. Although estrogen therapy does reduce the incidence of hip fractures, long-term estrogen therapy is rarely recommended for osteoporosis. Estrogen is known to increase the risk ofbreast cancer, heart disease, stroke, and blood clots. Other medications are available, however. Cal- citonin, a thyroid hormone, has been shown to increase bone density and strength, while decreasing the rate of bone frac- tures. Also, the bisphosphonates are a family of nonhormonal drugs used to prevent and treat osteoporosis. To achieve optimal results with calcitonin or one of the bisphosphonates, patients should also receive adequate amounts of dietary calcium and vitamin D.

Questions to Consider

l. How may long-term digestive system problems promote the chances of developing osteoporosis?

2. Why are individuals at risk for osteoporosis encouraged to increase their exercise regimes, including load-bearing exercises?

Exercise, Exercise, Exercise Exercise programs improve muscular strength, muscular endurance, and flexibility. Muscular strength is the force a muscle group (or muscle) can exert against a resistance in one maximal effort. Muscular endurance is judged by the ability of a muscle to contract repeatedly or to sustain a contraction for an extended period. Flexibility is tested by observing the range of motion about a joint.

Exercise also improves cardiorespiratory endurance. The heart rate and capacity increase, and the air passages dilate so that the heart and lungs are able to support prolonged muscu- lar activity. The blood level of high-density lipoprotein (HDL) increases. HDL is the molecule that slows the development of artherosclerotic plaques in blood vessels (see Chapter 5). Also, body composition-the proportion of protein to fat-changes favorably when you exercise.

Exercise also seems to help prevent certain types of can- cer. Cancer prevention involves eating properly, not smoking, avoiding cancer-causing chemicals and radiation, undergoing appropriate medical screening tests, and knowing the early warning signs of cancer. However, studies show that people who exercise are less likely to develop colon, breast, cervical, uterine, and ovarian cancers.

Physical training with weights can improve the density and strength of bones and the strength and endurance of muscles in all adults, regardless of age. Even men and women in their eighties and nineties can make substantial gains in bone and muscle strength that help them lead more independent lives. Exercise helps prevent osteoporosis, a condition in which the bones are weak and tend to break (see Chapter ll). Exercise promotes the activity of osteoblasts in young as well as older people. The stronger the bones when a person is young, the less chance of osteoporosis as that person ages. Exercise helps pre- vent weight gain, not only because the level of activity increases

'dbNf¥1 1

but also because muscles metabolize faster than other tissues. As a person becomes more muscular, the body is less likely to accumulate fat.

Exercise relieves depression and enhances the mood. Some people report that exercise actually makes them feel more energetic. Further, after exercise, particularly in the late aftern.oon, people sleep better that night. Self-esteem rises because of improved appearance, as well as other factors that are not well understood. For example, vigorous exercise releases endorphins, hormonelike chemicals known to allevi- ate pain and provide a feeling of tranquility.

A sensible exercise program is one that provides all of these benefits without the detriments of a too-strenuous program. Overexertion can be harmful to the body and may result in sports injuries, such as lower back strains or torn ligaments of the knees. The beneficial programs suggested in Table 12A are tailored according to age.

Dr. Arthur Leon at the University of Minnesota performed a study involving 12,000 men, and the results showed that only moderate exercise is needed to lower the risk of a heart attack by one-third. In another study conducted by the Institute for Aerobics Research in Dallas, Texas, which included lO,OOll men and more than 3,000 women, even a little exercise was founa to lower the risk of death from cardiovascular diseases and cancer. Increasing daily activity by walking to the corner store instead of driving and by taking the stairs instead of the elevator can improve your health.

Questions to Consider 1. At the level of the muscle fiber, how does exercise increase

muscle strength? 2. How might an overly ambitious workout damage muscle

fibers?

Exercise

Amount

Children, 7-12 Teenagers, 13-18 Adults, 19-55

Purpose

Organized

Group

Family

Vigorous activity 1-2 hr daily

Free play

Build motor skills through team sports, dancing, or swimming

Enjoy more exercise outside of physical education classes

Participate in family outings: bowling, boating, camping, or hiking

Vigorous activity 1 hr, 3-5 days a week; otherwise, h hr daily moderate activity

Build muscle with calisthenics

Continue team sports, dancing, hiking, or swimming

Pursue sports that can be enjoyed for a lifetime: tennis, swimming, or horseback riding

Take active vacations: hike, bicycle, or cross- country ski

Vigorous activity 1 hr, 3 days a week; otherwise, V2 hr daily moderate activity

Exercise to prevent lower back pain: aerobics, stretching, or yoga

Do aerobic exercise to control buildup of fat cells

Find exercise partners: join a running club, bicycle club, or outing group

Initiate family outings: bowling, boating, camping, or hiking

several layers, whereas only one exists. The lining of the wind- pipe, or trachea, is pseudostratified ciliated columnar epithe-

_. lium. A secreted covering of mucus traps foreign particles. The upward motion of the cilia carries the mucus to the back of the throat, where it may either be swallowed or expectorated (spit out). Smoking can cause a change in the secretion of mucus and can inhibit ciliary action, resulting in a chronic inflamma- tory condition called bronchitis.

--

-----~

In some cases, columnar and pseudostratified columnar epithelium secretes a product. In this case, it is said to be glan- dular. A gland can be a single epithelial cell, as in the case of mucus-secreting goblet cells, or a gland can contain many cells. Glands with ducts that secrete their product onto the outer sur- face (e.g., sweat glands and mammary glands) or into a cavity (e.g., salivary glands) are called exocrine glands. Ducts can be simple or compound:

_.l; Example: Sweat gland Example: Mammary gland I Example: Pancreas

Glands that have no ducts are appropriately known as the ductless glands, or endocrine glands. Endocrine glands (e.g., pituitary gland and thyroid) secrete hormones directly into the bloodstream.

Stratified Epithelia Stratified epithelia have layers of cells piled one on top of the other (Fig. 4.8). Only the bottom layer touches the base- ment membrane. The nose, mouth, esophagus, anal canal, the outer portion of the cervix (adjacent to the vagina), and vagina are lined with stratified squamous epithelium. Cancer of the cervix is detectable by doing a pap smear. Cells lining the cervix are smeared onto a slide later examined to detect any abnormalities.

As we shall see, the outer layer of skin is also stratified squamous epithelium, but the cells have been reinforced by keratin, a protein that provides strength. Stratified cuboi- dal and stratified columnar epithelia also are found in the body.

Transitional epithelium was originally named because it was thought to be an intermediate form of epithelial cells. Now the term is used to imply changeability, because tis- sue changes in response to tension. It forms the lining of the urinary bladder, the ureters (tubes that carry urine from the kidneys to the bladder), and part of the urethra (the single tube that carries urine to the outside). All are organs that may need to stretch. When the bladder is distended, this epi- thelium stretches, and the outer cells take on a squamous appearance.

Chapter 4 Organization and Regulation of Body Systems 77

C:-tECK YOUR PROGRESS 4.5 ~,

List the functions of epithelial tissue.

escribe the structure of each major type of epithelial

'Summarize how the structure of some epithelial tissue relates to its function. Give some specific examples.

CONNECTING THE CONCEPTS

Epithelial tissue is involved in the operation of most organs of the body. For more information, refer to the following discussions:

Section 8.3 describes how specialized epithelial cells in the stomach secrete hydrochloric acid.

Section 9.6examines how gas exchange occurs across the epitheliat cells of the lungs. Sectlo1'115.1: provides 'More information on the endoc~ and exocrine glands of the body.

4.6 Integumentary System

LEARNING

Upon completion of this section, you should be able to

1. Describe the structure and function of human skin. 2. Compare the function of the epidermis and dermis. 3. Identify the function of the accessory organs associated

with the skin.

In some cases, a tissue is associated with a particular organ. For example, nervous tissue is typically associated with the brain. But an organ is composed of two or more types of tissues working together to perform particular functions. The skin is an organ comprised of all four tissue types: epithelial, connective, muscular, and nervous tissue. An organ system contains many different organs that cooperate to carry out a process, such as the digestion of food. The skin has several accessory organs (hair, nails, sweat glands, and sebaceous glands) and, therefore, is sometimes referred to as the integumentary system.

Skin is the most conspicuous system in the body because it covers the body. In an adult, the skin has a surface area of about 1.8 square meters (m2) (over 19.5 square feet [ft2]). It accounts for nearly 15% of the weight of an average human. The skin has numerous functions. It protects underlying tissues from physical trauma, pathogen invasion, and water loss. It also helps regulate body temperature. Therefore, skin plays a signifi- cant role in homeostasis, the relative constancy of the internal environment. The skin even synthesizes certain chemicals that affect the rest of the body. Skin contains sensory receptors such as touch and temperature receptors. Thus it helps us to be aware of our surroundings and communicate with others.

flfiMP3 KfJ Skin and Its Tissues

5. How are epithelial tissues classified? Describe each major type, and give at least one location for each type and the reason why it is found in that location. (pages 75-77}

Explain why the skin is sometimes referred to as the integumentary system. (page 77}

7 .!Referring to Figure 4.13, list each organ system, the major rgans, major functions of each, and how each aids in omeostasis. (pages 82-84)

at organs of the body are found in the thoracic cavity? The abdominal cavity? (pages 83-84)

9. List the types of membranes found in the body, their functions, and their locations. (pages 82-84)

10. Why is homeostasis defined as the "relative constancy of the internal environment"? Does negative feedback or positive feedback tend to promote homeostasis? Explain. (pages 84-86)

11. Which of the following is not a type of fibrous connective tissue? a. hyaline cartilage c. tendons and ligaments b. areolar tissue d. adipose tissue

12. Blood is a(n) tissue because it has a ___ _

a. connective; gap junction b. muscular; ground substance c. epithelial; gap junction d. connective; ground substance

13. This type of muscle contains striations. a. smooth muscle b. skeletal muscle c. cardiac muscle d. Both b and c are correct. e. All of these are correct.

14. Which of the following forms the myelin sheath around nerve fibers outside the brain and spinal cord? a. microglia c. Schwann cells b. neurons d. astrocytes

15. Which of these is not a type of epithelial tissue? a. simple cuboidal and stratified columnar b. bone and cartilage c. stratified squamous and simple squamous d. pseudostratified and transitional e. All of these are epithelial tissues.

16. What type of epithelial tissue is found in the walls of the urinary bladder to provide it with the ability to distend? a. simple cuboidal epithelium b. transitional epithelium c. pseudostratified colUmnar epithelium d. stratified squamous epithelium

17. Without melanocytes, skin would a. be too thin. c. nottan. b. lack nerves. d. not be waterproof.

18. Which of the following is a function of skin? a. temperature regulation b. manufacture of vitamin D c. protection from invading pathogens d. All ofthese are correct.

19. The skeletal system functions in a. blood cell production. c. movement. b. mineral storage. d. All of these are correct.

20. Which system helps control pH balance? a. digestive c. respiratory b. urinary d. Both b and c are correct.

21. Which type of membrane is found lining systems open to the outside environment, such as the respiratory system? a. serous c. synovial b. mucous d. meningeal

22. Which allows rapid change in one direction and does not achieve stability? a. homeostasis c. negative feedback b. positive feedback d. All of these are correct.

23. Which of the following is an example of negative feedback? a. Uterine contractions increase as labor progresses. b. Insulin decreases blood sugar levels after a meal is eaten. c. Sweating increases as body temperature drops. d. Platelets continue to plug an opening in a blood vessel until

blood flow stops.

ENGAGE

Thinking Critically About the Concepts In the hierarchy of biological organization, you have learned that groups of cells make tissues and two or more tissue types compose an organ. In this chapter, the four types of tissues (connective, muscular, nervous, and epithelial} have been discussed in detail. The skin is an organ system referred to as the integumentary system that contains all four tissue types. In addition to the epidermis and dermis, the integumentary system also includes accessory structures such as nails, sweat glands, sebaceous glands, and hair follicles. Each ofthese components of the skin aids in the various functions ofthe integumentary system. In the case study, Kristen has burns severe enough to need artificial skin treatment. This treatment will help Kristen's skin repair itself while mimicking some of the functions the integumentary system does for homeostasis.

1. The doctor diagnosed Kristen's burn as severe. Which of the following best describes a severe burn versus a superficial burn? a. Superficial burns include the epidermis, dermis, and

hypodermis layers. b. Severe burns only include the layers of the epidermis. c. Severe burns include anything including and below the

dermis. d. Superficial burns occur on the limbs only.

2. What accessory structures and tissues are damaged in a severe burn? Why?

3. What types of functions will the artificial skin perform while Kristen's own skin is repairing itself?

4. What effects can a severe burn have on overall homeostasis of the body? Give a few examples.

5. Which structures in the dermis will have the slowest repair time compared to others? Which might never repair themselves fully? Why?

6. Without the integumentary system, what might happen to the functions of the cardiovascular system? The nervous system?

. --~

___ /

"-'

.._,

Chapter 3 Cell Structure and Function 63

"' / ~ 'li "~, ~.~·' '* ., ,c, ,, ,, ,,, , A1iJIJ',Jt'rilllf '""" • . .' :r ;.1' ~"!'~~~t~~ J ~-' ',*' ,"if,'ti),'¥;~~11,;;~! ,.,, ~~~ SCIence ' ' ' ' ' ' ' t '"1\{J~% , !~ '~t" ,.,~ .. ,~~

"1\f l"' i(ji '~',,"' " f > i~ '""•· ltl •

Stem-Cell Research

In the human body, stem cells are analogous to immortal "parents:' Their "offspring;' called daughter cells, can remain as stem cells and potentially divide indefinitely. However, most daughter cells differentiate further, forming mature cells called end cells. Research using stem cells has remained a source of controversy since 1998, when scientists discovered how to iso- late and grow human stem cells in the laboratory.

There are primarily two different types of stem cells: embry- onic and adult. Advantages and disadvantages exist for each type. Embryonic stem cells are derived from fertilized embryos at various stages of development. Fertilized human ova stored in infertility clinics are often used as the source of embryonic stem cells. The use of these cells for research has sparked tre- mendous controversy, because many people believe these cells have the potential to become a human. Adult stem cells are undifferentiated cells found in various body tissues, whose pur- pose is to repair or replace damaged tissues. The use of adult stem cells is generally accepted. However, adult stem cells lack the flexibility of embryonic stem cells, because adult stem cells form far fewer types of end cells.

With all the time and money spent on stem-cell research, how close are we to using stem cells for the cure of disease? Advances in stem-cell therapy are being announced all the time. For example, in 2012, researchers announced that they had successfully used stem cells to produce a neuron cell that could be used as a model for producing drugs to treat Alzheimer disease. Some of the most successful uses of stem cells have involved Parkinson disease. Parkinson disease is a progressive motor control disorder, triggered by the death of certain neurons in the brain. These neurons are responsible for releasing the neurotransmitter dopamine onto specific brain cells that control movement. (This is why Parkinson patients are often treated with L-dopa, which is converted into dopa- mine.) It is now possible to cause stem cells in the laboratory to

C A S I S T U D Y. C 0 N C L U S I 0 N

Over the next fe~ months, both Kevin and Mary dedicated hours to understanding the causes and treatments of Tay-Sachs disease. They learned that the disease is caused by a recessive mutation that limits the production of an enzyme called beta-hexosaminidase A. This enzyme is loaded into a newly formed lysosome by the Golgi apparatus. The enzyme's function is to break down a specific type of fatty acid chain called gangliosides. Gangliosides play an impor- tant role in the early formation of the neurons in the brain. Tay-Sachs disease occurs when the gangliosides overaccu- mulate in the neurons.

differentiate into neurons that produce dopamine. To be used for transplant purposes, however, the stem cells must produce enough end cells for transplant. Further, the cells must survive after the transplant and function correctly for the remainder of the patient's life. Finally, transplanted cells must not harm the patient. The usual risks of surgery would still exist for the trans- plant recipient: damage to healthy tissue, bleeding, infection.

A possible solution was introduced in 2008 when research- ers first developed the use of induced pluripotent stem cells, or iPS cells. These cells are normal cells of the body that have been chemically "convinced" to return to an undifferentiated state. In other words, it is now possible to induce adult cells of the body to form stem cells. By doing so, researchers hope to be able to bypass some of the controversies surrounding the use of embryonic stem cells and, in the process, develop a more rapid and effective method of obtaining stem cells to fight specific diseases. For this groundbreaking work, Science Maga- zine was awarded its 2008 Breakthrough of the Year Award.*

Questions to Consider

~ VIdeo Heart Stem Cells

~ VIdeo Making Brain Cells

I. How much time and money should be spent on a therapy that may work only after "years of intensive research"? Would this money be better spent on therapies that have a higher likelihood of success?

2. Should the president remove the ban on certain types of stem cells so that this research can proceed faster?

3. What criteria and ethical considerations should be used to select Parkinson patients for stem-cell therapy?

• "Breakthrough of the Year: Reprogramming Cells;• Science 322, no. 5909 (2008), http:/ /www.sciencemag.org/cgi/content/full/322/5909/1766 (accessed February 22, 2012).

Though the prognosis for their child was initially poor..,-very few children with Tay-Sachs live beyond the age of four, the parents were encouraged to find out what advances in a form of medicine called gene therapy might be able to prolong the life of their child. In gene therapy, a correct version of the gene is intro- duced into specific cells in an attempt to regain lost function. Some initial studies using mice as a model had demonstrated an ability to reduce ganglioside concentrations by providing a work- ing version of the gene that produced beta-hexosaminidase A to the neurons of the brain. Though research was still ongoing, it was a promising piece of information for both Kevin and Mary.

74 Unit 1 Human Organization

' " : ' ~~ ' ' ' '' " ' ' ' ~ ,,, , , ,,, ,~'IA:s-""'' Science ~,,'

' " '£.,;,.. ' ' ' ' ,. ' '· *

Nerve Regeneration and Stem Cells

In humans, axons outside the brain and spinal cord can regenerate-but not those inside these organs (Fig. 4A). After injury, axons in the human central nervous system (CNS) degenerate, resulting in permanent loss of nervous function. Interestingly, about 90% of the cells in the brain and the spinal cord are not even neurons. They are glial cells. In nerves outside the brain and spinal cord, the glial cells are Schwann cells that help axons regenerate. The glial cells in the CNS are oligodendrocytes and astrocytes, and they inhibit axon regeneration. F"

4 A

~""" ____... '("~, New Schwann fl1 Axon cells form a "''j regenerates.

.pathway .•

Regeneration of nerve cells. The spinal cord does contain its own stem cells. •gure Wh h

. 1

d . . . d . . 1

Outside the CNS, nerves regenerate because new neuroglia called Schwann cells en t e spma cor ts mJure m expenmenta .

. 1

h II d n . d form a pathway for axons to reach a muscle. In the CNS, comparable neuroglia called amma s, t ese stem ce s 0 pro 1 erate. But mstea oligodendrocytes do not have this function. of becoming functional neurons, they become glial cells. Researchers are trying to understand the process that triggers the stem cells to become glial cells. In the future, this understanding would allow manipulation of stem cells into neurons.

In early experiments with neural stem cells in the labora- tory, scientists at Johns Hopkins University caused embryonic stem (ES) cells to differentiate into spinal cord motor neu- rons, the type of nerve cell that causes muscles to contract. The motor neurons then produced axons. When grown in the same dish with muscle cells, the motor neurons formed neuro- muscular junctions and even caused muscle contractions. The cells were then transplanted into the spinal cords of rats with spinal cord injuries. Some of the transplanted cells survived for longer than a month within the spinal cord. However, no improvement in symptoms was seen and no functional neuron connections were made.

APPLICATIONS AND• MISCONCEPTIONS

How fast is a reflex?

A reflex is a built-in pathway that allows the body to react quickly to a response. One example, the knee-jerk, or patel- lar reflex, is tested b)( tapping just below the kneecap. The lower leg will then involuntarily kick forward. The reaction is designed to protect the thigh muscle from excessive stretch. The knee-jerk reflex is an example of a simple stretch reflex. There is only one pathway required: the stretch sensation (caused by tapping the knee), to the spinal cord, to the leg muscle. The whole circuit is complete within a millisecond- or 1/1,000 second!

In later experiments by the same research group paralyzed rats were first treated with drugs and nerve growth factors to over- come inhibition from the central nervous system. These tech- niques significantly increased the success of the transplanted neurons. Amazingly, axons of transplanted neurons reached the muscles, formed neuromuscular junctions, and provided par- tial relief from the paralysis. Research is being done on the use of both the body's own stem cells and laboratory-grown stem cells to repair damaged CNS neurons. While many questions remain, the current results are promising.

Questions to Consider 1. Why do you think that neurons cannot simply be trans-

planted from other areas of the body? 2. How might this research also help patients who suffer from

neurodegenerative diseases such as Parkinson disease?

CHECK YOUR PROGRESS 4.4 l 0 Describe the structure and function of a neuron. E) Discuss the different types of neuroglial cells and the

function of each.

E) Explain how the neurons and neuroglial cells work together to make nervous tissue function.

CONNECTING THE CONCEPTS

Nervous tissue plays an important role in transmitting the signals needed to maintain homeostasis. For more informa- tion on how neurons work, refer to the following discussions:

Section 13.1 provides a more detailed examination of how neurons function.

Section 14.1 discusses how neurons are involved in sensation.

________ /

__/

~"~~'-L", ,·' "'. .,. . . ~ ·-;., ealth

62

The Metabolic Fate of Pizza Obviously our diets do not solely consist of carbohydrates. Because fats and proteins are also organic nutrients, it makes sense that our bodies can utilize the energy found in the bonds of these molecules. In fact, the metabolic pathways we have discussed in this chapter are more than capable of accessing the energy of fats and proteins. For example, let's trace the fate of a pepperoni pizza, which contains carbohy- drates (crust), fats (cheese), and protein (pepperoni).

We already know that the glucose in the carbohydrate crust is broken down during cellular respiration. When the cheese in the pizza (a fat) is used as an energy source, it breaks down to glycerol and three fatty acids. As Figure 3B indicates, glycerol can be converted to pyruvate and enter glycolysis. The fatty acids are converted to an intermediate that enters the citric acid cycle. An 18-carbon fatty acid results in nine acetyl CoA molecules. Calculation shows that respiration of these can produce a total of 108 ATP molecules. This is why fats are an efficient form of stored energy-the three long fatty acid chains per fat molecule can produce considerable ATP when needed.

Proteins are less frequently used as an energy source, but are available ifnecessary.The carbon skeleton of amino acids can enter glycolysis, be converted to acetyl groups, or enter the citric acid cycle at another point. The carbon skel- eton is produced in the liver when an amino acid under- goes deamination, or the removal of the amino group. The amino group becomes ammonia (NH3), which enters the urea cycle and becomes part of urea, the primary excretory product of humans.

In Chapter 8, "Digestive System and Nutrition," we will take a more detailed look at the nutritional needs of humans, including discussions on how vitamins and min- erals interact with metabolic pathways, and the dietary guidelines for proteins, fats, and carbohydrates.

Questions to Consider I. How might a meal of a cheeseburger and fries be pro-

cessed by the cellular respiration pathways?. 2. While Figure 3B does not indicate the need for water, it

is an important component of our diet. Where would water interact with these pathways?

1-lupothesize what would happen to homeostasis if each three major steps of cellular respiration were missing.

t ~;)t"'i glucose glycerol fatty

~ 1 acids

Glycolysis

~ t pyruvate

~

Figure 38 The use of fats and proteins for energy. Carbohydrates, fats, and proteins can be used as energy sources, and their monomers (carbohydrates and proteins) or subunits (fats) enter degradative pathways at specific points.

CONNECTING THE CONCEPTS

For additional information on the processing of nutrients for energy, refer to the following discussions:

, Sections 2.3 to 2.5 provide a more detailed look at carbohydrates and other energy nutrients.

Section 8.3 explores how the small intestine processes nutr1ents for absorption. · Section 8.6 aescribes the importance of carbohydrates, fats, and proteins in the diet. · ·

~ .. _ _/

._/