Corpus Luteum

Corpus luteum is a temporary endocrine gland, functioning for few days in non pregnant cyclic animal and few months in pregnant animals.

The life span of corpus luteum varies with species depends primarily upon the fate of embryo.

Following ovulation, enough hemorrhage into follicular cavity from broken thecal vessels. It act as stopper sealing the residual cavity after discharge of oocyte

The blood filled follicle devoid of oocyte is called as ‘corpus haemorrhgium’

The blood clot serve as physical frame work and a nutritive medium for quick proliferate of granulosa cells. The intact vessel and connective tissue cells from the surrounding theca begins to proliferate

Granulosa layer folding towards the central portion of the residual cavity. Granulosa cells differentiated into luteal cells under the influence of LH and become corpus luteum.

The corpus luteum is one of the most vascular organs of the body. If animals are non–pregnant it is corpus luteum spurium and is destined to regress. If animal is pregnant, it is corpus luteum verum and corpus luteum is continues to function.

The function of corpus luteum is to secrete progesterone. During diestrus phase, maximum level of progesterone is produced which is necessary to –

1. maintain pregnancy
2. preparation endometrium for implantation
3. enable the blastocyst to implant

Following implantation of blastocyst, the corpus luteum undergoes extensive enlargement and continues synthesis and secrete hormone.

If fertilization does not occur, the CL regresses allowing other follicles to mature.

Regression of corpus luteum

Regression of corpus luteum starts (Days from ovulation) in different animals-

The degenerating a vascular non functional corpus luteum is corpus albicans. For several additional estrus cycle, a visible connective tissue scar remains on the ovary.

The corpora lutea of non – pregnant bitches and Queen continue to function approximately same length of time as for the pregnant animal.

The color of corpus luteum of cow and mare is intense than other species, due to lipochrome pigment- lutein. The ewe and sow are devoid of this pigment. Hence lighter color.

Natural luteolytic substance – PGF_2α is secreted by myometrial tissue

Ovarian artery and utero ovarian vein are intertwined and in close apposition. This vascular arrangement favors diffusion of PGF_2α into ovarian arterial blood.

There are several mechanism are proposed for luteolysis-

1. Constriction of blood vessels supplying luteal cells causing ischemia and starvation of luteal cells
2. Interference with progesterone
3. Competition with LH for receptor site
4. Destruction of LH receptor site

LH is necessary for luteotropic effect and for progesterone secretion which increases as CL matures. LH is luteotropic in ruminants and horse.

Prolactin is luteotropic in rat. In canines both LH and PRL are luteotropic. In rabbits and pigs oestrogen is luteotropic

Corpus luteum and pregnancy

Progesterone is necessary for maintenance of pregnancy. Progesterone increase resting membrane potential of myometrial cell.

Progesterone is serve as immediate precursor to other steroids that also necessary during pregnancy.