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a succession or recurring series of events.
cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.
cell cycle the cycle of biochemical and morphological events occurring in a reproducing cell population; it consists of the S phase, occurring toward the end of interphase, in which DNA is synthesized; the G2 phase, a relatively quiescent period; the M phase, consisting of the four phases of mitosis; and the G1 phase of interphase, which lasts until the S phase of the next cycle.
citric acid cycle tricarboxylic acid cycle.
estrous cycle the recurring periods of estrus in adult females of most mammalian species and the correlated changes in the reproductive tract from one period to another.
hair cycle the successive phases of the production and then loss of hair, consisting of anagen, catagen, and telogen.
Krebs cycle tricarboxylic acid cycle.
menstrual cycle see menstrual cycle.
ovarian cycle the sequence of physiologic changes in the ovary involved in ovulation; see also ovulation and reproduction.
reproductive cycle the cycle of physiologic changes in the reproductive organs, from the time of fertilization of the ovum through gestation and childbirth; see also reproduction.
sex cycle (sexual cycle)
1. the physiologic changes that recur regularly in the reproductive organs of nonpregnant female mammals.
2. the period of sexual reproduction in an organism that also reproduces asexually.
TCA cycle tricarboxylic acid cycle.
tricarboxylic acid cycle the cyclic metabolic mechanism by which the complete oxidation of the acetyl portion of acetyl-coenzyme A is effected; the process is the chief source of mammalian energy, during which carbon chains of sugars, fatty acids, and amino acids are metabolized to yield carbon dioxide, water, and high-energy phosphate bonds. Called also citric acid cycle, Krebs cycle, and TCA cycle.
urea cycle a cyclic series of reactions that produce urea; it is a major route for removal of the ammonia produced in the metabolism of amino acids in the liver and kidney.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.
sexual cyclethe series of events in which generations are linked via GAMETES and MEIOSIS takes place. For example, in a DIPLOID (1) organism such as a human, HAPLOID (1) gametes are produced by meiosis and once fertilization has occurred the diploid number is restored in the ZYGOTE. In haploid organisms such as many fungi, meiosis is postzygotic, occurring after fertilization and with the function of restoring the haploid number.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005