Corpus luteum — temporary endocrine gland in the ovary:

• is formed as a result of differentiation of the follicular epithelium and the cells of the theca of the tertiary ovulated follicle;
• synthesizes a hormone of a steroid nature progesterone (to a lesser extent — estrogens, androgens and oxytocin);
• the average duration of the development cycle of the corpus luteum in the absence of pregnancy (includes phases of proliferation and vascularization, glandular metamorphosis, blossom, reverse development) is 2 weeks and corresponds to 14–28 days of 28-day of ovarian cycle;

Corpus luteum in blossom stage (menstrual corpus luteum):

• a rounded structure in the thickness of the ovary, surrounded by connective tissue membrane #1, #2,
• consists of luteal cells (luteocytes) #1, #2 — large cells of rounded or polygonal shape with cellular cytoplasm (steroid inclusions dissolve in alcohols during histological treatment and look like voids #1, #2),
• between luteal cells there are thin layers of loose connective tissue, numerous capillaries #1, #2 and larger vessels (arterioles and venules).