Mammal, canine ovary (LM, High)

Structure List Secondary follicle Beginning antrum Granulosa cells Basement membrane Theca interna Theca externa Zona pellucida Cytoplasm of ova

SECONDARY FOLLICLES develop from primary follicles and are characterized by the formation of an antrum. The antrum is a fluid-filled space which begins as a number of small spaces between the granulosa cells. As the several spaces unite into a single fluid-filled chamber, the oocyte remains on a mound of granulosa cells, the cumulus oophorus, to one side of the follicle. A layer of granulosa cells remains surrounding the oocyte and is referred to as the corona radiata. The granulosa cells are surrounded by a capsule of modified stroma cells known as the theca folliculi. The theca folliculi is made up of two layers, the theca interna and theca externa. The theca interna is composed of aggregates of epithelioid cells with lipid droplets in the cytoplasm and surrounded by capillaries. The cells secrete the female sex steroids. The theca externa is made up of concentric layers of spindle-shaped stroma cells.