Anatomy & Physiology

Anatomy & Physiology Study Guide Many body systems alter their activities in response to circulating sex hormones and to the presence of growth hormone, thyroid hormones, prolactin, and adrenocortical hormones, so sex-specific differences in structure and function develop. At puberty, endocrine system changes induce characteristic changes in various body systems. After puberty, the continued background secretion of estrogens or androgens maintains the foregoing sex-specific differences. In both sexes, growth continues at a slower pace until age 18–21, by which time most of the epiphyseal cartilages have closed. The boundary between adolescence and maturity is hazy because it has physical, emotional, and behavioral components. Adolescence is often said to be over when growth stops, in the late teens or early twenties. The individual is then considered physically mature. Senescence Changes occur when sex hormone levels decline at menopause or the male climacteric. All these changes are part of the process of senescence, or aging, which reduces the functional capabilities of the individual. Even in the absence of such factors as disease or injury, senescence-related changes at the molecular level ultimately lead to death. The elderly are less able to make homeostatic adjustments in response to internal or environmental stresses. The risks of contracting a variety of infectious diseases are proportionately increased as immune function deteriorates. This deterioration leads to drastic physiological changes that affect all internal systems. Death ultimately occurs when some combination of stresses cannot be countered by the body’s existing homeostatic mechanisms. 26.3 Genetics and Inheritance Genes and chromosomes determine patterns of inheritance. Chromosomes contain DNA, and genes are functional segments of DNA. Each gene carries the information needed to direct the synthesis of a specific polypeptide. Every nucleated somatic cell in your body carries copies of the original 46 chromosomes present when you were a zygote. Those chromosomes and their component genes constitute your genotype . The instructions contained in your genotype determine the anatomical and physiological characteristics that make you a unique individual. Those anatomical and physiological characteristics constitute your phenotype . Specific elements in your phenotype, such as eye and hair color, foot size, and skin tone, are called phenotypic characters, or traits. Your genotype is derived from the genotypes of your parents. Patterns of Inheritance The 46 chromosomes carried by each somatic cell occur in pairs: every somatic cell contains 23 pairs of chromosomes. The two members of each pair are known as homologous chromosomes . Twenty- two of those pairs are called autosomal chromosomes . Most of the genes of the autosomal chromosomes affect somatic characteristics, such as hair color and skin pigmentation. The chromosomes of the 23rd pair are called the sex chromosomes; one of their functions is to determine whether the individual is genetically male or female. The two chromosomes in a pair may not carry the same form of each gene, however. The various forms of a given gene are called alleles . These alternate forms determine the precise effect of the gene on your phenotype. If the two chromosomes of a homologous pair carry the same allele of a particular gene, you are homozygous for the trait Achieve Page 358 of 368 ©2018