Biomedical science paid surprisingly little attention to a remarkable change in human biology during the 20th century—the marked increase of human life expectancy N62-1 in developed nations. Life expectancy is the projected mean length of life of those born in…
The earth and its atmosphere provide environments that are compatible with an extraordinary number of diverse life forms, each adapted to its particular ecological niche. However, not all the earth's surface is equally friendly for human survival, let alone comfort…
Physical exercise is often the greatest stress that the body encounters in the course of daily life. Skeletal muscle typically accounts for 30% to 50% of the total body mass. Thus, with each bout of muscular activity, the body must…
Heat and Temperature: Advantages of Homeothermy Homeotherms maintain their activities over a wide range of environmental temperatures The ability to regulate internal body temperature has provided higher organisms independence from the environment. Because the rates of most physical and chemical…
Metabolism encompasses all chemical reactions in the body's cells, necessary to sustain life. These chemical processes allow the body to grow, reproduce, maintain structure, and respond to changes in its environment. These processes can be anabolic, in which energy is…
Fetal development is a highly organized process. The most rapid phase of growth transpires in at a degree of hypoxemia that mimics ascent to Mount Everest, while nutrients reach the fetus indirectly, from the maternal circulation. The transition to the…
Transport of Gametes and Fertilization Cilia and smooth muscle transport the egg and sperm within the female genital tract Following ovulation, the fimbriae of the fallopian tube sweep over the ovarian surface and pick up the oocyte—surrounded by its complement…
The female reproductive system functions to (1) produce haploid gametes— ova, (2) facilitate syngamy —or fertilization—between an ovum and a spermatozoon, (3) supply a site for implantation of the embryo (if syngamy occurs) and the establishment of pregnancy, (4) provide…
The male reproductive system consists of two essential elements: the gonads (in this case the testes) and the complex array of glands and ducts that constitute the sex accessory organs ( Fig. 54-1 A, B ). Open full size image…
Reproduction is a fundamental process of life. All living organisms must reproduce either asexually (e.g., bacteria) or sexually (e.g., mammals). Asexual reproduction is highly efficient and produces large numbers of genetically identical offspring in a relative short amount of time.…