Corpus luteum

CORPUS LUTEUM

  • Corpus luteum is 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
    • maintain pregnancy
    • preparation endometrium for implantation
    • 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 starts (Days from ovulation)
    • Cow – 14 – 15
    • Ewe – 12 – 14
    • Sow – 13
    • Mare - 17
  • The regression changes are
    • Microscopic – Cytoplasmic Vacule
    • Pyknotic nuclei
    • Decreased progesterone in luteal cells
    • Degeneration of capillaries
    • Gradual replacement of luteal cells by fibroblasts
    • Macroscopic – The whole organ decreased in size suddenly within short interval
  • 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 - PGF2α is secreted by myometrial tissue
  • Ovarian artery and utero ovarian vein are intertwined and in close apposition. This vascular arrangement favors diffusion of PGF2α into ovarian arterial blood.
  • several mechanism are proposed for luteolysis.
    • Constriction of blood vessels supplying luteal cells causing ischemia and starvation of luteal cells
    • Interference with progesterone
    • Competition with LH for receptor site
    • 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.

Corpius luteum
Picture showing corpus luteum on the ovary
(Courtesy: Dr.S.Selvaraju, Scientist, NIANP, Bangalore)
Last modified: Wednesday, 20 June 2012, 5:45 AM