Mammal, canine ovary (LM, High)

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

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.