![]() Biology of Reproduction Summers |
text: Human Reproductive Biology2nd Edition - Richard E. Jones & Kristin H. Lopez,: Read pages 73 - 74 for this lecture acronyms end |
XVI. Reproductive Cycling back to XV. Puberty A. during Puberty the neuroendocrine regulatory mechanisms necessary for female cyclicity develop B. Periodic fertility 1. pattern and rough timing regulated by biological rhythms a. suprachiasmatic nucleus (hypothalamus) generates circadian (about a day) pattern in mammals b. in many species female and male reproductive activity is circannual i. ovarian and testicular size and activity are reduced (quiescent) most of the year (1) reduces energy expended maintaining ovaries (a) vitellogenin for yolk is energy rich c. other important rhythms for reproduction include: circalunar, circatidal, ultradian (= pulsatile for hormones) 2. pattern and rough timing are also regulated by reproductive physiology a. negative and positive feedback b. copulation, pregnancy & lactation 3. environmental stimuli, from seasonal variations, adjusts timing a. zeitgeibers entrain rhythms b. light - especially in birds, mammals and reptiles i. direct optic innervation of SCN (retino-hypothalamic tract = Glu) (1) SCN is a part of the hypothalamic region (APS) which stimulates GnRH and LH surges (2) SCN also projects to the pineal ii. some reptiles have a 3rd eye (= parietal eye) with direct innervation of the pineal gland iii. pineal secretes melatonin during scotophase (darkness ) (1) helps coordinate rhythms (2) usually inhibits reproduction (a) scotophase is longest during non-reproductive seasons (b) melatonin may stimulate reproduction for short-day breeders c. temperature i. poikilotherms often require warmer temperatures for gonadal recrudescence (growth and activation) d. food/water/shelter e. tides i. many fishes and invertebrates have reproduction tied to the tides (1) they may also have circannual reproductive rhythms f. social environment i. protandrous sequential hermaphrodites may depend on group zoography to become female C. Reproductive cyclicity is the neural integration of biological clock, reproductive physiology 1. rhythms may be set in utero a. affected by hormonal rhythmicity 2. rhythms set hormonal patterns 3. hormones (as neuromodulators) modify rhythms via feedback 4. environmental cues influence rhythms and hormone secretion a. neurally mediated 5. hypothalamus, limbic system, & senses are all reciprocally innervated D. Seasonal cycles coordinates male and female effort at times which fitness