CHAPTER 29 Development, Growth, Aging, and Genetics

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9. The lungs form as evaginations of the digestive tract. These evagina-tions undergo repeated branching.10. The urinary system develops in three stages—pronephros, mesoneph-ros, and metanephros—from the head to the tail of the embryo. Theducts join the allantois, part of which becomes the urinary bladder.11. The reproductive systems develop in conjunction with the urinarysystem. The presence or absence of certain hormones is very impor-tant to sexual development.

2. Suckling stimulates prolactin and oxytocin synthesis. Prolactinstimulates milk production, and oxytocin stimulates milk letdown.

29.5 First Year After Birth (p. 1108)

1. The number of neuron connections and glial cells increases.2. Motor skills develop gradually, especially head, eye, and handmovements.

Growth of the Fetus

1. The embryo becomes a fetus at 60 days.2. The fetal period, from day 60 to birth, is a time of rapid growth.

29.6 Aging and Death (p. 1109)

1. Loss of cells that are not replaced contributes to aging. ■ A loss of neurons occurs. ■ Loss of muscle cells can affect skeletal and cardiac musclefunction.2. Loss of tissue plasticity results from cross-link formation betweencollagen molecules. The lens of the eye loses the ability to accom-modate. Other organs, such as the joints, kidneys, lungs, and heart,also have reduced efficiency with advancing age.3. The immune system loses the ability to act against foreign antigensand may attack self-antigens.4. Many aging changes are probably genetic.5. Death is the loss of brain functions.

29.2 Parturition (p. 1098)

The total length of gestation is 280 days (clinical age).

Stages of Labor

Uterine contractions force the fetus out of the uterus during labor.

Hormonal Stimulation of Parturition

1. Increased estrogen and decreased progesterone help initiateparturition.2. Fetal glucocorticoids act on the placenta to decrease progesteronesynthesis and to increase estrogen and prostaglandin synthesis.3. Stretch of the uterus and decreased progesterone levels stimulateoxytocin secretion, which stimulates uterine contraction.

29.7 Genetics (p. 1110)

1. Genetics is the study of heredity, the characteristics children inheritfrom their parents.2. Genomic medicine uses an understanding of the biochemical relation-ship between genes and disease to diagnose and manage disease.

29.3 The Newborn (p. 1104)

Shortly after birth, the newborn baby experiences several dramaticchanges when it is separated from the maternal circulation and transferredfrom a fluid to a gaseous environment.

Mendelian Genetics

1. The genes an organism has for a given trait is called the genotype.The expression of the genes is called the phenotype.2. Alleles are alternate forms of genes. A dominant allele masks theeffects of a recessive allele for the same trait.3. An organism homozygous for a trait has two identical alleles for thetrait, whereas an organism heterozygous for a trait has two differentalleles for the trait.

Respiratory and Cardiovascular Changes

1. The foramen ovale closes, separating the two atria.2. The ductus arteriosus closes, and blood no longer flows between thepulmonary trunk and the aorta.3. The umbilical vein and arteries degenerate.

Digestive Changes

1. Meconium is a mixture of cells from the digestive tract, amnioticfluid, bile, and mucus excreted by the newborn.2. The stomach begins to secrete acid.3. The liver does not form adult bilirubin for the first 2 weeks.4. The neonate can digest lactose, but other foods must be graduallyintroduced.

Modern Concepts of Genetics

1. Chromosomes ■ Somatic cells have a diploid number of chromosomes, whereasgametes have a haploid number. In humans, the diploid number is46 and the haploid number is 23. ■ Humans have 22 pairs of autosomal chromosomes and 1 pair ofsex chromosomes. Females have the sex chromosomes XX, andmales have XY. ■ A karyotype is a display of the chromosomes of a somatic cell dur-ing metaphase of mitosis. ■ Chromosome pairs are called homologous chromosomes.2. The genome consists of all the genes found in the haploid number ofchromosomes from one parent.3. Each gene occupies a specific locus, or location, on a chromosome.4. Alleles exist in many different forms, called multiple alleles.5. Gene dominance ■ In complete dominance, the dominant allele masks the effects ofthe recessive allele. ■ In codominance, two alleles at the same locus are expressed, sothat separate, distinguishable phenotypes occur at the same time. ■ In incomplete dominance, the dominant allele does not completelymask the effects of the recessive allele.6. Polygenic traits result from the interaction of many genes.

Apgar Scores

1. Apgar represents appearance, pulse, grimace, activity, and respira-tory effort.2. Apgar and other methods are used to assess the physiological condi-tion of the newborn.

Congenital Disorders

1. Congenital disorders are abnormalities present at birth.2. Teratogens are environmental agents that cause some congenitaldisorders.

29.4 Lactation (p. 1107)

1. Estrogen, progesterone, and other hormones stimulate the growth ofthe breasts during pregnancy.