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appearance of follicles:
1. single squamous cell layer → flattened; little cytoplasm
2. single cuboidal cell layer
3. 2 cuboidal cell layers
4. contain fluid; many layers of cuboidal cells
characteristics of atretic follicles (4)
1. development of pycnotic nuclei → inside of the oocyte's nucleus gets "clumpy"
2. ↓ estradiol production
3. loss of gonadotropin receptors
4. changes in oocyte
changes in the oocyte of an atretic follicle (4)
1. size → oocyte shrinks
2. pseudocleavage → divisions that resemble divisions of an early embryo erroneously occur in the ovary
3. germinal vesicle breakdown → supposed to occur as part of the process of fertilization
4. degenerating zona pellucida
how long does it take for a follicle to develop?
1. 153 μM to 5000 μM in ~45 days
2. 130 μM to 8560 μM in 42.5 days
how to study development of small follicles (2)
1. radioactive labeling with thymidine
2. block cells in metaphase to establish mitotic index
factors affecting development of follicles
gonadotropins are not required for growth of prenatral follicles, but gonadotropins (especially FSH) will enhance their development
stages of follicular development (3)
1. Recruitment → signal goes to the ovary that says "I need X number of follicles to start the process of development"
2. Selection → as follicles develop, one gets a little bit ahead of the rest
3. Dominance → the dominant follicle causes the rest of the follicles in the group to become atretic & die off
waves of follicular development: cattle
in cattle, 2 or 3 dominant follicles can form during each estrous cycle → each dominant follicle that forms is described as belonging to a wave
hormonal requirements for recruitment, selection, & dominance (4)
1. both LH & FSH are needed for the recruitment & selection of follicles
2. one follicle becomes dominant → secretes increasing amounts of inhibin & estradiol resulting in ↓ FSH
3. decreasing FSH causes other follicles within the cohort to become atretic
4. demise of CL (& thus very low P4) allows ovulation
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