Folliculogenesis and Steroidogenesis

The frequency of the menstrual/estrous cycle varies among species. For example, monoestrous species (e.g., dogs, cats) exhibit 1-2 cycles per year, whereas polyes-trous species (e.g., rodents, primates) exhibit more frequent cycles of shorter duration. Primordial follicles, each consisting of an oocyte surrounded by a single layer of flattened somatic cells known as granulosa cells, are recruited to become primary follicles, a transition marked by increased oocyte size, formation of a glycoprotein matrix (zona pellucida) around the oocyte, and transformation to cuboidal-shaped 

Basal lamina Fluid-filled antrum Thecal cells 

The enormous degree of cellular proliferation and differentiation, tissue remodeling, and biochemical and molecular changes involved in the transition of primor- 

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