In mammalian females, yellow body refers to the corpus luteum. It is formed from the remnants of the Graafian follicle after it has ruptured to release the secondary oocyte. This occurs during the luteal phase of the ovarian cycle. It is called the yellow body because it contains the lutein protein and carotene pigment. The transformation of the Graafian follicle into corpus luteum occurs under the influence of Luteinising hormone (LH).
The main purpose of corpus luteum is to release progesterone. Progesterone is required for the maintenance of pregnancy.
Corpus luteum doesn’t produce hCG (human chorionic gonadotropin). HCG is produced by the placenta. In fact, corpus luteum is under the regulation of hCG to produce progesterone during pregnancy.
Luteinising hormone and follicle stimulating hormones are secreted by the anterior lobe of the pituitary. FSH acts on the ovarian follicles and stimulates their development.
Progesterone, FSH, and hCG don’t trigger the formation of corpus luteum.