Hormonal Control of Timing of Reproductive Cycles
Endocrine Events
That Orchestrate
Reproduction
Hormonal Control of Timing of Reproductive Cycles
From fish to mammals, reproduction in vertebrates is usually a seasonal or cyclic activity. Timing is crucial, because the young should appear when food is available and other environmental conditions are optimal for survival. The sexual reproductive process is controlled by hormones, which are regulated by environmental cues, such as food intake, and seasonal changes in photoperiod, rainfall, or temperature, and by social cues. Neurosecretory centers of the brain (hypothalamus) regulate the release of anterior pituitary gland hormones, which in turn stimulate tissues of the gonads (neurosecretion and the pituitary gland are described in Chemical Coordination. This delicately balanced hormonal system controls development of the gonads, accessory sex structures, and secondary sexual characteristics (see the following text), as well as timing of reproduction.
The cyclic reproductive patterns of mammals are of two types: estrous cycle, characteristic of most mammals, and menstrual cycle, characteristic only of the anthropoid primates (monkeys, apes, and humans). These two cycles differ in two important ways. First, in estrous cycles, females are receptive to males only during brief periods of estrus, or “heat,” whereas in the menstrual cycle receptivity may occur throughout the cycle. Second, a menstrual cycle, but not an estrous cycle, ends with collapse and discharge of the inner portion of the endometrium (uterine lining). In an estrous animal, each cycle ends with the uterine lining simply reverting to its original state, without the discharge characteristic of the menstrual cycle.
Hormonal Control of Timing of Reproductive Cycles
From fish to mammals, reproduction in vertebrates is usually a seasonal or cyclic activity. Timing is crucial, because the young should appear when food is available and other environmental conditions are optimal for survival. The sexual reproductive process is controlled by hormones, which are regulated by environmental cues, such as food intake, and seasonal changes in photoperiod, rainfall, or temperature, and by social cues. Neurosecretory centers of the brain (hypothalamus) regulate the release of anterior pituitary gland hormones, which in turn stimulate tissues of the gonads (neurosecretion and the pituitary gland are described in Chemical Coordination. This delicately balanced hormonal system controls development of the gonads, accessory sex structures, and secondary sexual characteristics (see the following text), as well as timing of reproduction.
The cyclic reproductive patterns of mammals are of two types: estrous cycle, characteristic of most mammals, and menstrual cycle, characteristic only of the anthropoid primates (monkeys, apes, and humans). These two cycles differ in two important ways. First, in estrous cycles, females are receptive to males only during brief periods of estrus, or “heat,” whereas in the menstrual cycle receptivity may occur throughout the cycle. Second, a menstrual cycle, but not an estrous cycle, ends with collapse and discharge of the inner portion of the endometrium (uterine lining). In an estrous animal, each cycle ends with the uterine lining simply reverting to its original state, without the discharge characteristic of the menstrual cycle.
Support our developers
