Cytoplasm

Definition - What does Cytoplasm mean?

Cytoplasm is the content within a cell excluding the nucleus and the cell membrane. Cytosol, the liquid medium of the cell is the primary constituent of the cytoplasm. In addition to the cytosol, the cytoplasm contains the cellular organelles such as the mitochondria, Golgi apparatus and the endoplasmic reticulum and the protein fiber network that forms the cell skeleton. The quality of an egg depends on the constitution of the cytoplasm. Abnormalities in the cytoplasm of the egg can interfere with development or fertilization of an egg and the development of the embryo, leading to infertility.

FertilitySmarts explains Cytoplasm

Eggs undergo a series of divisions in the ovaries before they are mature enough to be released during ovulation. When the cells divide in half, chromosomes in the cells carrying genetic material need to arrange symmetrically in the center of the cell so that both cells that are formed after cell division get an equal number of chromosomes. The cytoplasm plays a major role in this process. The protein fibers in the cell skeleton arrange themselves in a scaffold-like pattern, and they begin to contract, pulling the chromosomes and the cytosol apart forcing the cell to divide. Cell division also requires energy which is supplied by the mitochondria in the cytoplasm, the powerhouse of the cell. Abnormalities of the cell skeleton and mitochondria can prevent the eggs from properly dividing giving rise to abnormal eggs.

During fertilization, the nucleus of the egg has to fuse with the nucleus of the sperm cell and then start the process of cell division to develop into an embryo, which is a complex and energy consuming mechanism. The energy that is required for this is produced by the mitochondria and similar to the production of eggs, cell division requires the cellular skeleton. Cytoplasmic abnormalities including mitochondrial disorders can hinder fertilization and embryo development.

Cytoplasmic abnormalities are commonly seen in older women in their 40s. Checking the quality of the egg cytoplasm is difficult clinically or in a laboratory. Looking at the shape of the eggs through a microscope may give a rough understanding of the cytoplasm but proper assessment requires the use of an electron microscope which is extremely costly and has a limited availability, therefore infertility due to cytoplasmic abnormalities can remain undiagnosed. As a result, cytoplasmic abnormalities can cause high failure rates during in vitro fertilization (IVF).

Cytoplasmic transfer is a method used in IVF for women who have cytoplasmic abnormalities in the eggs. During the process, the cytoplasm is harvested from a healthy donor egg and injected into the egg that then undergoes fertilization with a sperm cell. Normal donor cytoplasm allows the egg to undergo fertilization and development into a fetus.

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