The mammalian egg is covered by a series of membranes that protect it and aid in fertilization. Immediately after ovulation, the egg is surrounded by a membrane known as the zona pellucida.

Explanation:

Zona Pellucida:

- The zona pellucida is a glycoprotein layer that forms around the mammalian egg immediately after ovulation.
- It is secreted by the egg as it travels through the oviduct towards the uterus.
- The zona pellucida is composed of three layers: an outer layer, a middle layer, and an inner layer.
- The outer layer is the thinnest and is composed of glycoproteins that help to bind sperm to the zona pellucida.
- The middle layer is the thickest and is composed of a matrix of glycoproteins and proteoglycans.
- The inner layer is the thinnest and is composed of glycoproteins that are involved in the sperm-binding process.

Functions of the Zona Pellucida:

- The zona pellucida plays a key role in fertilization, as it is the first barrier that sperm must penetrate in order to reach the egg.
- The glycoproteins on the surface of the zona pellucida bind to specific receptors on the surface of sperm, allowing them to attach and begin the process of fertilization.
- Once sperm have attached to the zona pellucida, they release enzymes that help to dissolve the outer layer, allowing them to penetrate to the egg.

Other Membranes Surrounding the Egg:

- In addition to the zona pellucida, the mammalian egg is also surrounded by a layer of follicle cells called the corona radiata.
- The corona radiata is composed of cells that have surrounded the egg within the follicle and are released along with the egg during ovulation.
- The corona radiata provides additional protection to the egg and helps to guide sperm towards the zona pellucida.

Conclusion:

In conclusion, immediately after ovulation, the mammalian egg is covered by a membrane known as the zona pellucida. This glycoprotein layer plays a key role in fertilization by allowing sperm to bind to its surface and penetrate to the egg. The corona radiata, another layer of follicle cells, also surrounds the egg and provides additional protection during fertilization.

Immediately after ovulation, the layer that forms around the ovum is called corona radiata. It is formed by the granulosa cells of cumulus oophorus. Corona radiata probably increases the likelihood that the ovum will be picked up in the uterine tube.