Anatomy & Physiology

Anatomy & Physiology Study Guide • Difficult deliveries can include forceps deliveries and breech births—deliveries in which the legs or buttocks of the fetus, rather than the head, enter the vaginal canal first. Postnatal stages are the neonatal period, infancy, childhood, adolescence, maturity, and senescence: • Postnatal development involves a series of five life stages: the neonatal period, infancy, childhood, adolescence, and maturity. Senescence (aging) begins at maturity and ends in the death of the individual. • The neonatal period extends from birth to one month after. In the transition from fetus to neonate, the respiratory, circulatory, digestive, and urinary systems of the infant begin functioning independently. The newborn must also begin thermoregulation. Mammary gland cells produce protein-rich colostrum during the neonate’s first few days of life and then convert to milk production. These are released as a result of the milk let-down reflex. • Body proportions gradually change during infancy (from age one month to two years) and during childhood (from two years to puberty). • Adolescence begins at puberty, when the hypothalamus increases its production of GnRH, circulating levels of FSH and LH rise rapidly, and ovarian or testicular cells become more sensitive to FSH and LH. These changes initiate gamete formation, the production of sex hormones, and a sudden increase in the growth rate. The hormonal changes at puberty, especially changes in sex hormone levels, produce sex-specific differences in the structure and function of many systems; these differences will be retained. Adolescence continues until growth is completed. Further changes occur when sex hormone levels decline at menopause or the male climacteric. • Senescence begins, producing gradual reductions in the functional capabilities of all systems. Genes and chromosomes determine patterns of inheritance: • Every somatic cell carries copies of the original 46 chromosomes in the zygote; these chromosomes and their component genes constitute the individual’s genotype. The physical expression of the genotype is the individual’s phenotype. • Every somatic human cell contains 23 pairs of chromosomes; each pair consists of homologous chromosomes. Twenty-two pairs are autosomal chromosomes. The chromosomes of the twenty-third pair are the sex chromosomes; they differ between the sexes. • Chromosomes contain DNA, and genes are functional segments of DNA. The various forms of a given gene are called alleles. If both homologous chromosomes carry the same allele of a particular gene, the individual is homozygous; if they carry different alleles, the individual is heterozygous. • Alleles are either dominant or recessive, depending on how their traits are expressed. Combining maternal and paternal alleles in a Punnett square helps predict the characteristics of offspring. In simple inheritance, phenotypic characters are determined by interactions between a single pair of alleles. Polygenic inheritance involves interactions among alleles on several genes. Achieve Page 363 of 368 ©2018