Question

There are two major events in fetal development. Block to ployspermy and the transition of the corpus luteum control to the placenta. Explain how each of these events are important to child reproduction. Also, explain how if either of them failed what the repercussions would be.

Answer 1

1) Block to polyspermy:

Polyspermy is a condition where the egg can get fertilized by more than one sperm. Therefore block to polyspermy means inhibiting or stopping the second sperm to further fertilize the egg which has already been fertilized by one sperm.

There are two main types of block to polyspermy, namely-

• Fast block of polyspermy- This occurs when the electric charge is produced across the surface of the egg, which is caused by the fusion of the first sperm with the egg.
• Slow block of polyspermy- This occurs when there is a secretion reaction ( Cortical Reaction) modifies the extracellular coat of the egg and block the polyspermy.

Repercussions if polyspermy is not blocked: If polyspermy is not blocked, multipolar or extra mitotic spindles are formed which results in faulty segregationof chromosomes during cell division. This can also stop the development of the fetus further.

2) Transition of the corpus luteum to the placenta: Corpus luteum is a hormone secreting structure that develops in an ovary after an ovum has been discharged but degenerates after a few days unless pregnancy has begun. But if egg has been fertilized, corpus luteum continues to produce progesterone, thereby maintaining the thick lining of the uterus. Gradually the placenta takes over the production of progesterone and the corpus luteum degenerates into corpus albicans. Now the placenta (a temporary organ) produces estrogen along with progesterone . This estrogen is a hormone that helps maintain pregnancy and prepare the breasts for milk production (lactation). This milk will be the child's first nourishment after birth.

Repercussions if corpus luteum does not transit to placenta: If placenta does not take over the production of progesterone , it will effect the development of the fetus and production of breast milk.