Difference between Zona Pellucida and Corona Radiata

What is Zona Pellucida?

Zona pellucida is a thick layer of glycoproteins that surrounds the plasma membrane of mammalian oocytes. The zona pellucida layer functions as a vital part of fertilisation. The incoming spermatozoa fuses with the membrane and the acrosome reaction is initiated. Acrosome reaction is the binding of the sperm’s membrane with the plasma membrane of the oocyte.

The layer is usually 13 μm thick and made up of cuboidal or columnar granulosa cells in humans. This layer has sperm binding proteins for easy adhesion of the sperm cells to the plasma membrane. It also prevents polyspermy. The zona pellucida layer is shed off as the embryo reaches the uterine wall for implantation.

What is Corona Radiata?

Corona radiata is a thick outer layer that surrounds the zona pellucida. It is a cellular layer that is composed of proteins, carbohydrates and hyaluronic acid. It is formed by the adhesion of follicle cells. It is made from squamous granulosa cells that enlarge to become cuboidal.

The hyaluronidase enzyme present on the head of sperm makes the dissolution of the layer easy, and hence the sperm can penetrate into the oocyte. It also supplies necessary proteins to the ovum.

Zona Pellucida vs Corona Radiata

Zona Pellucida

Corona Radiata

Description

Zona pellucida is a thick layer present around the plasma membranes of oocytes.

Corona radiata is a thick outlet membrane that is present outside the zona pellucida.

Composition

It is made up of glycoproteins.

It is made up of proteins, carbohydrates and hyaluronic acid.

Location

It is present just around the plasma membrane of the oocyte.

It surrounds the zona pellucida layer.

Function

It initiates acrosomal reaction of the sperms, and also prevents polyspermy.

It protects and supplies vital proteins to the ovum.

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Frequently Asked Questions on Difference between Zona Pellucida and Corona Radiata

What is the corona radiata of an oocyte?

Corona radiata is a cellular layer that is present on the oocyte and provides protection to them.

Which enzyme is responsible for dissolving corona radiata?

The enzyme hyaluronidase present in the head of sperm cells is responsible for dissolving corona radiata.

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