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the period of development of the young in viviparous animals, from the time of fertilization of the oocyte (ovum) to birth; see also pregnancy.
gestation period the duration of pregnancy; in the human female, the average length, calculated from the first day of the last normal menstrual period, is 280 days, or 6 lunar months. The normal limits of the human gestation period are from 37 weeks (259 days) to 42 weeks (293 days); days and weeks are counted as completed days and weeks. If one counts from the moment of conception, the length of time is 266 days (280−14 days).
an interval or division of time; the time for the regular recurrence of a phenomenon.
absolute refractory period the part of the refractory period from phase 0 to approximately −60 mV during phase 3; during this time it is impossible for the myocardium to respond with a propagated action potential, even with a strong stimulus. Called also effective refractory period.
blanking period a period of time during and after a pacemaker stimulus when the unstimulated chamber is insensitive to avoid sensing the electronic event in the stimulated chamber.
effective refractory period absolute refractory period.
ejection period the second phase of ventricular systole (0.21 to 0.30 sec), between the opening and closing of the semilunar valves, while the blood is discharged into the aorta and pulmonary artery. Called also sphygmic period.
gestation period see gestation period.
incubation period see incubation period.
isoelectric period the moment in muscular contraction when no deflection of the galvanometer is produced.
latent period a seemingly inactive period, as that between exposure to an infection and the onset of illness (incubation period) or that between the instant of stimulation and the beginning of response (latency, def. 2).
refractory period the period of depolarization and repolarization of the cell membrane after excitation; during the first portion (absolute refractory period), the nerve or muscle fiber cannot respond to a second stimulus, whereas during the relative refractory period it can respond only to a strong stimulus.
relative refractory period the part of the refractory period from approximately −60 mV during phase 3 to the end of phase 3; during this time a depressed response to a strong stimulus is possible.
safe period the period during the menstrual cycle when conception is considered least likely to occur; it comprises approximately the ten days after menstruation begins and the ten days preceding menstruation. See the section on fertility awareness methods, under contraception.
sphygmic period ejection period.
supernormal period in electrocardiography, a period at the end of phase 3 of the action potential during which activation can be initiated with a milder stimulus than is required at maximal repolarization, because at this time the cell is excitable and closer to threshold than at maximal diastolic potential.
vulnerable period that time at the peak of the T wave during which serious arrhythmias are likely to result if a stimulus occurs.
Etymology: L, gestare, to bear; Gk, peri, near, hodos, way
the time span between conception and labor. In humans the period is approximately 38 weeks.
gestation periodThe period from fertilization of the egg (ovum) to the birth of the child. The human gestation period is 40 weeks, plus or minus 2 weeks.
the period of development of the young in viviparous animals, from the time of fertilization of the ovum to birth. See also pregnancy.
the duration of pregnancy in the domestic animal species are: cow—273 to 292 days (Bos taurus), 271 to 310 days (Bos indicus); mare—333 to 346 days; ass—365 to 375 days; ewe—143 to 147 days (meat sheep), 147 to 155 days (merino); goat doe—146 to 155 days; sow—111 to 116 days; bitch—58 to 68 days; queen—61 to 70 days.
In laboratory and quasi-pet animals: guinea pig 59-72 days, gerbil 24-26 days, hamster 15.5-16 days, mouse 19-21 days, rat 21-23 days, rabbit 29-35 days.
perpetual gestation chart
a table based on the average gestation period of the particular species, e.g. 63 days for bitches, that plots the anticipated date of parturition against the breeding (conception) date. Designed to be independent of the year so it is valid indefinitely.
see prolonged gestation.