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− | <big><center>[[Female Reproductive Tract -The Ovary - Anatomy & Physiology|'''BACK TO THE OVARY''']]</center></big>
| + | {{review}} |
− | <big><center>[[Female_Reproductive_Tract_-The_Ovary_-_Anatomy_%26_Physiology#Processes_Taking_Place_In_The_Ovary|'''BACK TO PROCESSES TAKING PLACE IN THE OVARY''']]</center></big>
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− | * Prostaglandin F2 (PGF2) | + | == The Luteolytic Mechanism == |
− | * PGF2 from the uterus is transported to the ipsilateral ovary through a vascular counter-current exchange mechanism. | + | |
| + | * Prostaglandin F2α (PGF2α) |
| + | * PGF2α from the uterus is transported to the ipsilateral ovary through a vascular counter-current exchange mechanism. |
| * This involves two closely associated blood vessels in which blood from one vessel flows in the opposite direction to that of the adjacent vessel. | | * This involves two closely associated blood vessels in which blood from one vessel flows in the opposite direction to that of the adjacent vessel. |
| * Low molecular weight substances in high concentrations in one vessel cross over into the adjacent vessel, where they are low in concentration. | | * Low molecular weight substances in high concentrations in one vessel cross over into the adjacent vessel, where they are low in concentration. |
| * The ovarian artery lies in closs association with the utero-ovarian vein. | | * The ovarian artery lies in closs association with the utero-ovarian vein. |
− | * By counter-current exchange, PGF2 is transferred across the wall of the uterine vein into the ovarian artery by passive diffusion. | + | * By counter-current exchange, PGF2α is transferred across the wall of the uterine vein into the ovarian artery by passive diffusion. |
− | * This ensures a high proportion of PGF2 produced by the uterine glands will be transported directly to the ovary and corpus luteum without dilution in the systemic circulation. | + | * This ensures a high proportion of PGF2α produced by the uterine glands will be transported directly to the ovary and corpus luteum without dilution in the systemic circulation. |
− | * This is an important mechanism, because much PGF2 is denatured during one pass through the circulatory system. This is about a 90% loss in the ewe and cow. | + | * This is an important mechanism, because much PGF2α is denatured during one pass through the circulatory system. This is about a 90% loss in the ewe and cow. |
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| + | == Luteolysis in Ruminants == |
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| + | * The ruminant corpus luteum secretes large amounts of oxytocin as well as progesterone. |
| + | * In the late luteal phase, oxytocin receptors develop on the uterine endometrium. |
| + | * Binding of oxytocin to the receptors stimulates the pulsatile release of PGF2α. |
| + | * PGF2α secretion by the endometrium is almost non-existant during the first half of the luteal phase. |
| + | * During the late luteal phase, pulses of PGF2α secretion increase in frequency and amplitude as the end of the luteal phase approaches. |
| + | * A critical number of PGF2α pulses are required within a given time span to induce complete luteolysis. |
| + | ** In the ewe, this is ~5 pulses in 24 hours. |
| + | * During the first half of the cycle, progesterone prevents the secretion of PGF2α by blocking the formation of oxytocin receptors on the uterus. |
| + | * Oxytocin and PGF2α stimulate each other in a positive feedback manner. |
| + | * The greater the number of endometrial oxytocin receptors, the greater the ability of oxytocin to stimulate PGF2α synthesis. |
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| + | [[Category:Female Reproduction]] |
| + | [[Category:Bullet Points]] |