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The Corpus Luteum
- When the dominant antral follicle ovulates, slight localised haemorrhage occurs at the site of ovulation and fills the former cavity.
- The small amount of bloody tissue can be observed by the naked eye.
- Loss of fluid from the antral cavity causes the follicle to collapse into many folds.
- As a result, some granulosal and thecal layers are pushed into the apex of the ruptured follicle.
- This protrusion of tissue and ruptured blood vessels forms a structure known as the Corpus Haemorrhagicum.
- Following this, the theca interna and granulosa cells differentiate into large and small luteal cells.
- Luteal cells contain increased quantities of lipid droplets and the pigment 'lutein'.
- As the blood is resorbed, a solid Corpus Luteum is formed by proliferation of granulosa and theca intera cells as well as blood vessels. This remains on the surface of the ovary.
- In the non-pregnant animal, corpora lutea are transient structures.
- Cyclic corpora lutea undergo proliferation and vascularisation directly after ovulation.
- The corpora lutea then regress and degenerate into a connective tissue scar, the Corpus Albicans.
- If the ovum is fertilised, the corpus luteum remains fully developed and active throughout at least part of the pregnancy.
- Corpora lutea produce progesterone.
- Progesterone prepares and maintains the uterus for implantation of the fertilised ovum.
- The number of corpora lutea formed are directly related to the number of oocytes released.
Control of Progesterone Biosynthesis in the Corpus Luteum
- In most species, luteinization and progesterone synthesis is regulated principally by luteinising hormone (LH) in the non-fertile cycle.
- Further conversion to oestradiol is prevented.