What technology would enable a fetus born in the fourth month to survive in a laboratory setting? (This is not yet possible.)

Why is it important for a middle-aged adult who has neglected physical activity for many years to have a physical examination before beginning an exercise program?

If an aged relative came to live with you, what special provisions could you make in your household environment and routines that would demonstrate your understanding of the changes brought on by aging?

Review Exercises

1. Define growth and development.

2. Describe the process of cleavage.

3. Distinguish between a morula and a blastocyst.

4. Describe the formation of the inner cell mass, and explain its significance.

5. Describe the process of implantation.

6. List three functions of hCG.

7. Explain how the primary germ layers form.

8. List the major body parts derived from ectoderm.

9. List the major body parts derived from mesoderm.

10. List the major body parts derived from endoderm.

11. Describe the formation of the placenta, and explain its functions.

12. Define placental membrane.

13. Distinguish between the chorion and the amnion.

14. Explain the function of amniotic fluid.

15. Describe the formation of the umbilical cord.

16. Explain how the yolk sac and the allantois are related, and list the functions of each.

17. Explain why the embryonic period of development is so critical.

18. Define fetus.

19. List the major changes that occur during the fetal stage of development.

20. Describe a full-term fetus.

21. Compare the properties of fetal hemoglobin with those of adult hemoglobin.

22. Explain how the fetal cardiovascular system is adapted for intrauterine life.

23. Trace the pathway of blood from the placenta to the fetus and back to the placenta.

24. Distinguish between a newborn and an infant.

25. Explain why a newborn's first breath must be particularly forceful.

26. List some of the factors that stimulate the first breath.

27. Explain why newborns tend to develop water and electrolyte imbalances.

28. Describe the cardiovascular changes that occur in the newborn.

29. Describe the characteristics of an infant.

30. Distinguish between a child and an adolescent.

31. Define adulthood.

32. List some of the degenerative changes that begin during adulthood.

33. Define senescence.

34. List some of the factors that promote senescence.

35. Cite evidence of passive aging and active aging.

chapter objectives

After you have studied this chapter, you should be able to

1. Explain how gene discoveries are relevant to the study of anatomy and physiology and to health care.

2. Distinguish between genes and chromosomes.

3. Define genome.

4. Define the two types of chromosomes.

5. Explain how genes can have many alleles (variants), but a person can have only two alleles of a particular gene.

6. Distinguish among the modes of inheritance.

7. Explain how gene expression varies among individuals.

8. Describe how genes and the environment interact to produce complex traits.

9. Describe how traits are transmitted on the sex chromosomes and how gender affects gene expression.

10. Explain how deviations in chromosome number or arrangement can harm health and how these abnormalities are detected.

11. Explain how conditions caused by extra or missing chromosomes reflect a meiotic error.

12. Explain how gene therapy works.

Understanding ^Vo rds chromo-, color: chromosome—a "colored body" in a cell's nucleus that includes the genes. hetero-, other, different:

heterozygous—condition in which the members of a gene pair are different. hom-, same, common: homologous chromosomes—pair of chromosomes that contain similar genetic information. karyo-,nucleus: karyotype—a chart that displays chromosomes in size order. mono-, one: monosomy—

condition in which one kind of chromosome is present in only one copy. phen-, show, be seen:

phenotype—physical appearance that results from the way genes are expressed in an individual. tri-, three: trisomy—condition in which one kind of chromosome is triply represented.

he year is 2006. With completion of the human genome

T project—the determination of the sequence of all of the DNA within a human cell—the focus of health care has shifted, becoming predictive. Devices called DNA ml-croarrays, also known as DNA chips, can rapidly Identify many genes In a cell, providing profiles that Indicate which diseases a person Is at highest risk of developing and even how that person will likely react to particular drug treatments. Young people are encouraged to take such tests—if they want to—because they have time to try to prevent illnesses that have controllable environmental components. This is the choice that two college freshmen, Laurel and Peter, face. Each selects DNA microarray tests based on family background.

Laurel's brother, sister, and father smoke cigarettes, and her father's mother, also a smoker, died of lung cancer. Two relatives on her mother's side had colon cancer, and older relatives on both sides have Alzheimer disease. Laurel's DNA panel tests for gene variants that predispose her to developing addictions, such as genes that regulate her circadian (daily) rhythms and encode the receptor proteins on nerve cells that bind neurotransmitters; genes that cause colon or lung cancer; and genes associated with inherited forms of Alzheimer disease. Later in life, she may elect to have a prenatal DNA microarray test to detect inherited conditions in a fetus, or undergo a "toxicogenomics" screen to identify chemical sensitivities if she might encounter chemicals at her job that are dangerous to susceptible individuals.

Peter requests a different set of tests, appropriate for his family history. Each winter he suffers from bronchitis and sometimes pneumonia, and his doctor once suggested that he might have mild cystic fibrosis (CF), especially since Peter's sister and mother also get bronchitis often. Unlike Laurel, Peter refuses a test for Alzheimer disease, even though his paternal grandfather died of it—he feels he could not bear knowing that the condition lay in his future. Because previous blood tests revealed elevated cholesterol and several relatives have suffered heart attacks or have hypertension, Peter takes a panel of tests to track cardiovascular disease risk, including gene variants that control blood clotting, blood pressure, homocysteine metabolism, and cholesterol synthesis, transport, and metabolism.

The DNA microarray tests are easy, for the patient. After completing a family history, each student provides a DNA sample by collecting cells from the inside of the cheek with a cotton swab. At a laboratory, DNA in the cells is extracted, cut into pieces, tagged with molecules that fluoresce under certain types of light, and finally the pieces are applied to a glass or nylon chip and the light applied. Once results are in—a pattern of colored dots on a square—a genetic counselor explains the findings.

Laurel learns that she is genetically predisposed to addictive behaviors and has a high risk of developing lung cancer—a dangerous combination. She knows that more than most people, she must avoid

A DNA microarray, or "chip," identifies genes that are active in a particular cell. DNA microarrays will be used to confirm diagnoses based on signs and symptoms; predict future diseases that have a genetic basis; identify sensitivities to environmental agents; and predict which drugs will be effective to treat certain conditions in particular individuals.

A DNA microarray, or "chip," identifies genes that are active in a particular cell. DNA microarrays will be used to confirm diagnoses based on signs and symptoms; predict future diseases that have a genetic basis; identify sensitivities to environmental agents; and predict which drugs will be effective to treat certain conditions in particular individuals.

cigarettes and alcohol and other addictive drugs. Happily, she does not have genes that increase her chances of developing colon cancer or inherited Alzheimer disease.

Peter does have mild cystic fibrosis. He takes a different DNA mi-croarray test that indicates which antibiotics will most effectively treat the frequent bronchitis and pneumonia. He might even be a candidate for gene therapy—periodically inhaling a preparation containing the normal version of his mutant gene delivered in a "disabled" virus that would otherwise cause a respiratory infection. Peter has several gene variants that elevate serum cholesterol level and blood pressure. By following a diet low in fat and high in fiber, exercising regularly, and having frequent cholesterol checks, he can help keep his cardiovascular system healthy. A third DNA microarray panel identifies the most effective cholesterol-lowering drug for him.

The genetic tests that Laurel and Peter take will become parts of their medical records, and they will add tests as their interests and health status change with age. But these medical records are confidential. Laws prevent employers and insurers from discrimination based on genetic information.

Although the scenario of Laurel and Peter is in the near future, each test described exists today. Human genome information promises to provide a wealth of new predictive and diagnostic tests and treatments for rare as well as common disorders. In the years to come, thanks to the avalanche of new genetic information, we will be learning what our own blueprints are and how they work to assemble a human body.

The Emerging Role of Genetics and Genomics in Medicine

Genetics (je-net'iks), the study of inheritance of characteristics, concerns the transfer of information from generation to generation, which is termed heredity. That information is transmitted in the form of genes (jenz), which consist of sequences of nucleotides of the nucleic acid DNA (see fig. 4.19). Genes are carried on rod-shaped structures called chromosomes, introduced in chapter 3 and revisited in figure 24.1. The transfer of genetic information between generations occurs through the nuclei of eggs and sperm, via the process of meiosis discussed in chapter 22 (pp. 884-887).


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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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  • rosamunda
    Why are newborns first breath forceful and why do they develop water and electrolyte imbalances?
    6 years ago

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