cycle /cy·cle/ (si´k'l) a succession or recurring series of events.
cycle [si´k'l]
carbon cycle the steps by which carbon (in the form of carbon dioxide) is extracted from the atmosphere by living organisms and ultimately returned to the atmosphere. It comprises a series of interconversions of carbon compounds beginning with the production of carbohydrates by plants during photosynthesis, proceeding through animal consumption, and ending and beginning again in the decomposition of the animal or plant or in the exhalation of carbon dioxide by animals.
cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and intervening pause. 
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Events of the cardiac cycle.
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 c.
Cori cycle the mechanism by which lactate produced by muscles is carried to the liver, converted back to glucose via gluconeogenesis, and returned to the muscles.
γ-glutamyl cycle a metabolic cycle for transporting amino acids into cells.
Krebs cycle tricarboxylic acid c.
Krebs-Henseleit cycle urea c.
menstrual cycle the period of the regularly recurring physiologic changes in the endometrium, occurring during the reproductive period of female humans, culminating in partial shedding of the endometrium and some bleeding per vagina (menstruating). 
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Changes in the menstrual cycle in the human female. Solid lines indicate the course of events when the oocyte is not fertilized; dotted lines indicate the course of events when fertilization occurs. Arrows indicate the actions of hormones of the pituitary and the ovary in regulating the cycle.
mosquito cycle that period in the life of a malarial parasite that is spent in the body of the mosquito host.
nitrogen cycle the steps by which nitrogen is extracted from the nitrates of soil and water, incorporated as amino acids and proteins in living organisms, and ultimately reconverted to nitrates: (1) conversion of nitrogen to nitrates by bacteria; (2) the extraction of the nitrates by plants and the building of amino acids and proteins by adding an amino group to the carbon compounds produced in photosynthesis; (3) the ingestion of plants by animals, and (4) the return of nitrogen to the soil in animal excretions or on the death and decomposition of plants and animals.
ornithine cycle urea c.
ovarian cycle the sequence of physiologic changes in the ovary involved in ovulation.
reproductive cycle the cycle of physiologic changes in the female reproductive organs, from the time of fertilization of the oocyte through gestation and parturition.
sex cycle , sexual cycle
1. the physiologic changes recurring regularly in the genital organs of nonpregnant female mammals; in humans, the menstrual cycle.
2. the period of sexual reproduction in an organism that also reproduces asexually.
tricarboxylic acid cycle the final common pathway for the oxidation to CO2 of fuel molecules, most of which enter as acetyl coenzyme A; it also provides intermediates for biosynthetic reactions and generates ATP by providing electrons to the electron transport chain. 
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Tricarboxylic acid cycle. Diagrammatic representation of reactions by which carbon chains of sugars, fatty acids, and amino acids are metabolized to yield carbon dioxide. Water produced by the cycle and components of the high-energy phosphate pool generated by the associated electron chain are not shown.
urea cycle a series of metabolic reactions in the liver, by which ammonia is converted to urea using cyclically regenerated ornithine as a carrier. 
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Urea cycle. Diagrammatic representation of reactions by which excess nitrogen in the form of ammonia is converted to soluble urea, using l-ornithine as a recyclable carrier.
uterine cycle the phenomena occurring in the endometrium during the menstrual cycle, preparing it for implantation of the blastocyst.
visual cycle the cyclic interconversion of 11-cis- retinal and all-trans- retinal and association with opsins, creating an electric potential and initiating the cascade generating a sensory nerve impulse in vision. 
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Visual cycle of retinal rod cells; an analogous cycle occurs with iodopsins in the cones.
| ovarian cycle n. The normal sex cycle that includes development of an ovarian follicle, rupture of the follicle, discharge of the ovum, and formation and regression of a corpus luteum. |
cycle [si´k'l]
a succession or recurring series of events.
cardiac cycle a complete cardiac movement, or heart beat, including systole, diastole, and the intervening pause.
Cardiac cycle. From Applegate, 2000.
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.
Central pathways of metabolism: How the body produces energy from the energy-containing nutrients using the tricarboxylic acid cycle. From Davis and Sherer, 1994.
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.
cycle
a succession or recurring series of events.
cardiac cycle
a complete cardiac movement, or heartbeat, including systole, diastole, and the intervening pause.
The cycle includes eight separate phases: (1) isovolumetric contraction; (2) maximum ejection; (3) reduced ejection; (4) protodiastole (onset of ventricular relaxation); (5) isovolumetric relaxation; (6) rapid flow; (7) diastasis (onset of atrial contraction); (8) atrial systole.
cell cycle
the cycle of biochemical and morphological events occurring in a dividing cell population; it consists of the S phase, occurring toward the end of interphase, in which DNA is synthesized; the G2 phase, for gap 2, the interval between S and M; the M phase, for mitosis, consisting of the four phases of mitosis; and the G1 phase, which lasts from the end of M until the start of S phase of the next cycle. Fully differentiated cells are nondividing and are said to be in G0.
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Cell cycle. By permission from Booth DM, Small Animal Clinical Pharmacology and Therapeutics, Saunders, 2000
citric acid cycle
estrus cycle
see estrous cycle.
Krebs cycle
ovarian cycle
the sequence of physiological changes in the ovary involved in ovulation. See also ovulation and reproduction.
reproductive cycle
the cycle of physiological changes in the reproductive organs, from the time of fertilization of the ovum through gestation and parturition. See also reproduction.
sex cycle, sexual cycle
1. the physiological changes recurring regularly in the reproductive organs of female mammals when pregnancy does not supervene.
2. the period of sexual reproduction in an organism that also reproduces asexually.
tricarboxylic acid cycle
urea cycle
a cyclic series of reactions that produce urea, a major route for removal of the ammonia produced in the metabolism of amino acids in the liver and kidney. See also urea.
ovarian
pertaining to an ovary.
ovarian agenesis
one or both ovaries absent; usually accompanies defects of the tubular reproductive organs.
ovarian anomaly
includes ovarian dysgenesis (see below), agenesis (above) or hypoplasia, as in Swedish Highland cattle.
ovarian bursa
a pouch formed by the mesosalpinx and the mesovarium that encloses the infundibulum of the uterine tube and the ovary. It is shallow in the mare and does not enclose the ovary. It is capacious in sows and deep with a fat-filled wall in the bitch.
ovarian bursitis
inlammation of the ovarian bursa; likely to affect the function of the ovary and ovulation.
ovarian cycle
the cycle of follicle maturation and rupture, then luteinization and regression of the corpus luteum followed by recommencement of the cycle, unless pregnancy intervenes.
ovarian cyclicity
the regular appearance of estrus as an indication of the regular occurrence of estrous cycles.
ovarian cyst
see cystic ovarian disease (below).
cystic ovarian degeneration
persistent cysts derived from ovarian follicles which do not ovulate. Follicular cysts are thin-walled and fluctuant, and often multiple. Luteal cysts have a thick wall of luteal tissue about the cyst, are firm to palpate and do not rupture easily. There is abnormal estral behavior, either anestrus or nymphomania, and diminished fertility.
Cystic corpora lutea form after ovulation has occurred and do not interfere with reproduction. They have a characteristic ovulation papilla.
cystic ovarian disease
common disease of cows, less common in sows, characterized by gross abnormalities of estrus, either anestrus or more frequent and prolonged. In cows the cysts can be palpated per rectum.
ovarian dysgenesis
small, inactive ovaries lacking germ cells such as occur in mares lacking a second X chromosome.
ovarian follicle
see ovarian follicle.
follicular ovarian cyst
see cystic follicle.
ovarian hormones
estrogens, progesterone.
ovarian hypoplasia
functional hypoplasia in immature females and undernourished females of all ages are common findings; in the absence of these risk factors hypoplasia is genetic in origin in Swedish Highland and possibly white Ayrshire cattle.
ovarian imbalance
an alternative name of endocrine dermatoses caused by abnormalities of ovarian function in bitches. Type I, associated with cystic ovaries or functional ovarian tumors, consists of a bilaterally symmetrical alopecia, gynecomastia, enlargement of the vulva, and abnormalities of the estrous cycle. Type II is a bilaterally symmetrical alopecia, sometimes with seborrhea, in spayed bitches. It is responsive to treatment with estrogen. Called also estrogen-responsive dermatosis.
ovarian inflammation
see oophoritis.
intrafollicular ovarian hemorrhage
hemorrhage into an ovarian follicle occurs in all species during ovulation; also rarely in anovulatory follicles.
luteal ovarian cyst
see luteal cyst.
luteinized ovarian cyst
see luteal cyst.
ovarian neoplasms
includes mostly granulosa cell tumors, but also rarely carcinomas, fibromas, thecomas, sarcomas.
ovarian pain
a rare cause of colic in mares; identifiable by eliciting pain by rectal palpation of ovary.
premature ovarian failure
defective differentiation of ovarian tissue and the patient shows no signs of pubertal estrus until long past the customary age.
ovarian rebound
return of cyclical ovarian activity after a period of inactivity, usually pregnancy and parturition.
ovarian remnant syndrome
the return of estral activity in a desexed female; due to failure to remove all of the ovarian tissue or to dropping, and allowing to implant, a piece of the ovary.
rete ovarii ovarian cyst
a convoluted system of epithelial cell cords and tubules occupying part of the ovarian medulla; the cysts are found mostly in the hilar region of the ovary.
ovarian serous inclusion cyst
similar in size and appearance to, but distinguishable from, ovarian cysts by their intraovarian position; lined by cuboidal epithelium thought to be pinched off from indentations of surface epithelium.
tubular epithelial ovarian cyst
formed from epithelial cells from the surface of the ovary.
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