Corpus Luteum
Corpus Luteum is a transient, small endocrine gland formed after ovulation from the secretory cells of the ovarian follicles. Its primary function is in producing progesterone that is responsible in modulating different reproductive functions.
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Corpus Luteum Definition
The Corpus luteum is a temporary endocrine gland that is produced by the reminiscence of the Graafian follicle after ovulation. It secretes large amounts of progesterone and also some amounts of estrogen and inhibin A. The progesterone secreted by the Corpus luteum helps in maintaining the endometrium for implantation and pregnancy.
In the absence of fertilisation, the corpus luteum degenerates and another menstrual cycle starts due to the disintegration of the endometrium.
Structure and Development of Corpus Luteum
Image of Corpus luteum in the ovary
The Corpus luteum is formed from the fully mature Graafian follicle after ovulation. The size of the corpus luteum in humans ranges from 2 to 5 cm in diameter. It is formed from the follicular cells. Large luteal cells are formed from granulosa cells and the small luteal cells are formed from theca cells.
The Corpus luteum is formed in the luteal phase of the menstrual cycle. The ovarian follicle transforms into the corpus luteum after the release of a secondary oocyte from the fully matured ovarian follicle.
The corpus luteum remains in the ovary, whereas the secondary oocyte goes to the uterus through the fallopian tube. One corpus luteum is formed in each menstrual cycle.
The corpus luteum acts like an endocrine gland and produces progesterone in large amounts. Progesterone is synthesised from cholesterol by both large and small luteal cells.
Function of Corpus Luteum
The main function of the corpus luteum is to maintain the endometrium for implantation and pregnancy. Progesterone is essential for maintaining the endometrium.
In the absence of pregnancy, the corpus luteum disintegrates and stops making progesterone and transforms into corpus albicans after 10-14 days. This leads to endometrium disintegration and menstruation.
During pregnancy, secretion of hCG (human chorionic gonadotropin) signals the corpus luteum to continue secreting progesterone that ensures the maintenance of endometrium.
It also releases some amounts of estrogen and inhibin A. Estrogen inhibits the further secretion of GnRH (gonadotropin-releasing hormone) from the hypothalamus, therefore secretion of FSH and LH is also inhibited from the pituitary gland.
Ovarian Cycle and Corpus Luteum
In humans, the ovarian cycle can be divided into three phases –
- Follicular phase – It is distinguished by the activation of close to 20 primordial follicles to start the process of maturation. However, only one reaches the stage of complete maturity
- Ovulatory phase – Release of cumulus-oocite complex from the ovulating follicle
- Luteal phase – Development of corpus luteum from the walls of follicles and production of hormones
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In the event of no fertilization and no implantation of ovum in the walls of the uterus, the corpus luteum degenerates forming the corpus albicans.
In the event of implantation taking place, the developing placenta secretes chorionic gonadotrophin preventing the degeneration of the corpus luteum, prolonging the secretion of the progesterone. After 5-6 weeks in humans, the placenta is developed enough and becomes the main structure for the secretion of progesterone.
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Frequently Asked Questions on Corpus Luteum
Define corpus luteum.
Corpus Luteum is a transient, small endocrine gland established by the residual follicular wall cells following the process of ovulation. The main secretory product of corpus luteum is progesterone.
What happens to the corpus luteum at the termination of pregnancy?
When there is no implantation or towards the end of the pregnancy, the corpus luteum ceases to produce progesterone. Its tissue mass decreases in size followed by a loss in the cellular integrity. This permits the start of a new ovarian cycle.
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