Answers to Mastering Concepts Questions

23.1
1. What is the difference between anatomy and physiology?

Anatomy is the study of the physical arrangement of the body’s parts; physiology explains how those parts function.

2. What is the relationship among cells, tissues, organs, and organ systems?

Specialized cells form tissues.  Multiple tissues working together form organs, and organ systems are groups of related organs that interact to produce a specific body process.

23.2
1. List the four main tissue types in animal bodies.

The four main tissue types are connective, epithelial, nervous, and muscle tissue.

2. Where do epithelial tissues occur, and how are they named?

Epithelial tissues line the interior and exterior surfaces of the body.  These tissues are named for their cell shapes and number of layers.

3. List and describe six types of connective tissue.

The six types of connective tissue are:

• Loose connective tissue:  cells in a loose matrix of elastin and collagen fibers
• Dense connective tissue:  cells in a dense matrix of elastin and collagen fibers
• Adipose tissue:  fat cells embedded in a small amount of extracellular matrix
• Blood:  red and white blood cells and platelets suspended in a liquid matrix called plasma
• Cartilage:  cells in a network of fine collagen fibers
• Bone:  bone cells in a matrix of collagen and minerals

4. Explain the similarities and differences among the three types of muscle tissue.

All three types of muscle tissue contract by sliding actin filaments across myosin.  Differences between the three muscle types include:

• Skeletal muscle:  cells have many nuclei and have a striated appearance. Skeletal muscle is under voluntary control, and most of it attaches to bone.
• Smooth muscle:  each cell has one nucleus and no striations. Smooth muscle forms part of many internal organs and is under involuntary control.
• Cardiac muscle:  cells are striated and each contains one nucleus. Cardiac muscle cells are connected electrically so that they contract simultaneously. Cardiac muscle forms much of the heart and is under involuntary control.

5. What are the two main cell types in nervous tissue?

The two main cell types in nervous tissue are neurons and neuroglia.

23.3
1. Which organ systems contribute to each of the five general functions of life?

• Communication:  nervous and endocrine systems
• Movement and support: skeletal and muscular systems
• Acquiring energy:  digestive, circulatory, and respiratory systems
• Protection: urinary, integumentary, immune, and lymphatic systems
• Reproduction: reproductive system (although all systems contribute indirectly to this function)

2. What are some examples of interactions between organ systems?

Examples of interactions between organ systems include:

• The circulatory system carries blood to the urinary system, where the blood is cleansed.  Fluids then return to the circulatory system. The functions of the urinary system are monitored by endocrine glands and controlled by hormones.
• The respiratory system exchanges gases with the bloodstream. The nervous system monitors the breathing rate, which is under the control of voluntary muscles and involuntary muscles. The breathing rate is also influenced by hormones.
• The digestive system breaks food down into particles that are absorbed into the bloodstream and carried to cells that need nutrients (or stored in the liver and in fat deposits). The digestive system is controlled by hormones and influenced by the nervous system.

23.4
1. Which fluids are part of the body’s internal environment?

Interstitial fluids that bathe the body’s cells form part of the body’s internal environment.

2. What is homeostasis?

Homeostasis is the state of internal constancy in the face of a changing environment.

3. What happens to an organism that fails to maintain homeostasis?

An organism that fails to maintain homeostasis will stop functioning and will eventually die.

4. Distinguish between negative and positive feedback.

In negative feedback, the product of a process turns off its own production.  In positive feedback, the product of a process stimulates its own production.

23.5
1. How does the integumentary system help the body maintain homeostasis?

The integumentary system blocks the entry of foreign organisms and foreign objects into the body. It also prevents the loss of body fluids, and helps to maintain body temperature through the constriction and dilation of blood vessels and erection of hair or feathers in animals that have them. The production of vitamin D in skin helps to keep the skeleton strong.

2. What tissue types occur in each layer of human skin?

The epidermis is composed of stratified squamous epithelium.  The dermis consists mostly of dense connective tissue, but also includes nerve endings, muscle tissue, blood vessels, and glands.

23.6
1. Describe how folic acid and vitamin D nutrition might explain the variation in human skin pigmentation.

Deficiencies in vitamin D can cause death or pelvic deformities.  Deficiencies in folic acid can lead to infertility in men or birth defects in pregnant women.  Therefore, deficiencies in both vitamins affect a population through the reproductive years when selective pressures have an effect.  Because UV light affects concentrations of the two vitamins in opposite ways (low UV results in lower vitamin D concentrations, but higher folic acid concentrations), selection for pigmentation probably represents an evolutionary trade-off between maximizing the two vitamins.  As populations migrated to more northern latitudes, the selective pressure on melanin production lessened while selection for vitamin D synthesis increased.

2. Why do you think people who migrate from the tropics to urban areas in northern latitudes are at high risk for vitamin D deficiency? How might they decrease this risk?

People originally from the tropics most likely have a high concentration of melanin in their skin.  This melanin blocks their absorption of the little UV present at high latitudes, hindering the production of vitamin D.  They could lower their risk for vitamin D deficiency by taking supplements and exposing themselves to special UV lamps.

3. Suggest a specific prediction related to folic acid that follows from the nutritional trade-off hypothesis.

People with dark skin living in northern areas should have a greater concentration of folic acid in their blood as compared to people with lighter skin.

Answers to Write It Out Questions

1. Distinguish between:
a. organs and organ systems.
b. simple squamous and stratified squamous epithelial tissue.
c. loose and dense connective tissue.
d. skeletal and cardiac muscle tissue.
e. neurons and neuroglia.
f. negative and positive feedback.

(a) Organs and organ systems: multiple organs interact in an organ system. 
(b) Simple squamous and stratified squamous epithelial tissue: simple squamous epithelium contains just one layer of flattened cells, whereas stratified squamous epithelium contains multiple cell layers.
(c) Loose and dense connective tissue: loose connective tissue binds tissues together and fills spaces, whereas dense connective tissue builds ligaments and tendons.
(d) Skeletal and cardiac muscle tissue: skeletal muscle tissue is voluntary and has long cells, whereas cardiac muscle is involuntary, and has electrically connected short cells.
(e) Neurons and neuroglia: neurons are the communicating cells of the nervous system, whereas neuroglia are the supporting cells.
(f) Negative and positive feedback: negative feedback counteracts an existing condition, whereas positive feedback exacerbates the condition.

2. Marfan syndrome (see chapter 10) and osteogenesis imperfecta are two examples of heritable disorders of connective tissue. Use the Internet to learn about these two diseases. Why do people with connective tissue disorders have many interrelated symptoms?

Connective tissue disorders cause many symptoms because connective tissues occur throughout the body. 

3. What is homeostasis, and how is it important?

Homeostasis is a state of internal constancy. Cells and tissues must maintain conditions within a certain range if they are to function.  If the body system cannot maintain homeostasis, it may stop functioning, and the organism may die.

4. When a person gets cold, he or she may begin to shiver. If the weather is too hot, the heart rate increases and blood vessels dilate, sending more blood to the skin. How does each scenario illustrate homeostasis?

Shivering is the involuntary contraction of skeletal muscles; the muscle movement produces heat, which helps increase the body temperature.  In the second scenario, blood passing near the skin surface releases heat to the atmosphere, which helps cool the overheated body.  Both examples illustrate how the body maintains a constant temperature.

5. Observe what happens to the size of your eye’s pupil when you leave a dark room and enter the sunshine. What happens in the opposite situation, when you enter a dark room? How do the opposing reactions of your eye illustrate negative feedback?

When the light levels reaching the eye’s sensory cells are very high, the pupil constricts.  This lets in less light and counters the original stimulus.  If you enter a dark room where less light reaches the eye, then the pupil will dilate.  This will let in more light and, again, counters the original stimulus.

6. Which tissues make up skin, the largest organ of the body? How do these tissues interact to provide each of the functions of skin? Describe one interaction between skin and each of the other organ systems (see figure 23.6).

The epidermis contains stratified squamous epithelial tissue; the dermis contains connective tissue, smooth muscle tissue, and nervous tissue.  These tissues allow the body to maintain temperature homeostasis as nerves in the skin detect temperature and send the information to the hypothalamus.  For example, if the body is too hot, then blood vessels will dilate and sweat glands will open.  This will bring the body temperature back to normal.  The skin also plays a role in water balance, nutrition, and defense against disease.  Interactions between the skin and the other organ systems include:

• Nervous—sensory receptors in the skin detect stimuli.
• Endocrine—the endocrine system produces the hormone that stimulates melanin production in the skin.
• Skeletal—the skin absorbs UV light and produces vitamin D, which indirectly influences bone structure.
• Muscular—muscle fibers that attach to the dermis produce facial expressions.
• Digestive—vitamin D in the skin helps regulate calcium and phosphorus needed for proper nutrition.
• Circulatory—blood vessels in the skin constrict and dilate to maintain temperature homeostasis.
• Respiratory—the respiratory system exchanges the needed O2 with the CO2 waste from skin cells.
• Urinary—the loss of body water through the skin is countered by water retention in the urinary system.
• Immune/lymphatic—the skin acts as first line of defense to keep out pathogens.
• Reproductive—mammary glands in the skin produce the milk necessary for lactation.

7. How would you design an experiment to determine whether a new brand of artificial skin is safe for use in humans?

A group of human volunteers could be divided into two groups.  One group would receive a small square of artificial skin; a control group would receive a similar surgery, but without artificial skin.  Researchers could test for toxicity to nearby tissues, allergic reactions, or immune system rejection. 

8. Make a chart that compares and contrasts the organization of the animal body with that of a plant (see chapter 21).

Answers to Pull It Together Questions

1. What features distinguish the four types of tissue?

Epithelial tissue forms layers that surround all the organs.  Connective tissue consists of cells that are scattered within an extracellular matrix. The cells that make up muscle tissue are elongated and synchronize their activity to contract. Nervous tissue consists of networks of cells that use electrical impulses in rapid communication.

2. Add the specific types of epithelial, connective, muscle, and nervous tissue to this concept map.
“Epithelial” connects with “includes” to “Simple squamous”, “Simple cuboidal”, “Simple columnar”, and “Stratified squamous”. “Connective” connects with “includes” to “Loose connective tissue”, “Dense connective tissue”, “Adipose tissue”, “Blood”, “Cartilage”, and “Bone”. “Muscle” connects with “includes” to “Skeletal muscle”, “Cardiac muscle”, and “Smooth muscle”. “Nervous” connects with “includes” to “Neurons” and “Neuroglia”.

3. Add the names of the 11 organ systems to this concept map.
All connections made with “is carried out by”.
“Communication” connects to “Nervous system” and “Endocrine system”.
“Support and movement” connects to “Skeletal system” and “Muscular system”.
“Energy acquisition” connects to “Digestive system”, “Circulatory system”, and “Respiratory system”.
“Protection” connects to “Urinary system”, “Integumentary system”, and “Immune/Lymphatic system”.
“Reproduction” connects to “Reproductive system”.

4. Describe examples of organ system interactions that maintain homeostasis.

Organ systems interact in a variety of ways to maintain homeostasis. For example, the brain monitors levels of carbon dioxide in the blood. When these levels are too high, the autonomic nervous system stimulates an increase in the breathing rate, returning the carbon dioxide concentration to normal.