Germ Cells: Structure, Function & Diseases

Germ cells are the basis of life. There are male as well as female germ cells, which after fusion are responsible for creating an embryo. In this regard, germ cells have crucial differences compared to all other body cells.

What are germ cells?

A woman’s germ cell is the egg, and a man’s is the sperm. When the cells are combined, fertilization and pregnancy occur in the woman. In this process, the germ cells are created in the body’s own processes. Before the germ cell can perform its function, it divides in a maturation process called meiosis. This consists of two phases in which the diploid chromosome set is transformed into a haploid one. The background of this event is that each cell has 46 chromosomes. After maturity division germ cells have only 23 chromosomes. When the egg and sperm fuse, they complement each other. A cell with 46 chromosomes is formed again, 23 of which come from the mother and 23 from the father. The germ cells of the woman are located in the ovary. Approximately every four weeks one of them grows. Either it is fertilized after ovulation, or menstruation occurs. The sperm, the male germ cells, are formed in the testicles. In the process, the development of the haploid cells takes only a few hours.

Anatomy and structure

The egg cell is the largest cell in the human body. Its average is about 0.11 to 0.14 millimeters. The egg cell is surrounded on the outside by the zona pellucida. This has a particularly important function: it consists of certain proteins that enable the sperm to bind to the envelope. The egg membrane is followed by the perivitelline space. During meiosis, in addition to a functional egg cell, polar bodies are formed. DNA, which is no longer utilized, is stored in these. The polar bodies also float in the perivitellin space. Opposite to the space is the inner egg membrane. It is the cell membrane of the oocyte. The oocyte is filled with ooplasm, in which the nucleus is also stored. This is the location of DNA. Sperm is formed and stored in the testicles of the male. It consists of a head, the middle piece and flagellum. The head of the sperm contains the genetic material, while the middle part contains many mitochondria. Spermatozoa belong to the smallest occurring cells. They measure an approximate size of 0.06 millimeters.

Function and tasks

The most important function of germ cells is human reproduction. During the sexual act or artificial insemination, the egg and sperm are combined. The fertilized egg is called a zygote. It divides several times within a short time frame, resulting in a larger accumulation of cells. The uterus prepares to implant the fertilized egg. At a certain point, the zygote moves through the fallopian tube into the uterus. A new division occurs, in which the placenta as well as the embryo are formed. In addition to the pregnancy itself, the DNA of the mother and father is also passed on via the germ cell. This is in the form of chromosomes in the cell nucleus. Of the 46 chromosomes, 23 come from each parent. They consist of two halves. For each possible characteristic of the child, two pieces of information are available. Which one finally prevails is subject to certain rules. Pregnancy can only occur within a certain time window. This is the ovulation. Within one day, the egg cell travels through the fallopian tube into the uterus. If the egg was not fertilized at this time, menstruation occurs.

Diseases and medical conditions

The germ cells can become diseased in different ways. For example, in women with PCO syndrome, ovulation may not occur, which also prevents fertilization. The basis for this disease is hormonal imbalances. In the case of pregnancy, it can also not be ruled out that the egg does not get back into the uterus due to stuck fallopian tubes. If this process occurs, an ectopic pregnancy follows. This is associated with serious risks and is therefore terminated in most cases.In addition, the speed and quality of sperm is greatly reduced by regular tobacco and alcohol consumption. It has also been demonstrated that the aforementioned groups produce more defective sperm. Serious problems arise with diseased germ cells, especially for the embryo. Complications can arise during the maturation of the egg and sperm. For example, it is possible that after cell division an additional chromatid, half of a chromosome, is present in the cell. Due to this process, the cell is not haploid, instead there are two chromatids in it. This can have severe consequences because fertilization adds another chromosome half. The result is diseases such as Down syndrome. The basis of this disease is the triple occurrence of the 21st chromosome. The child is born with mental as well as physical limitations. Diseases or disorders of the germ cells almost always affect the genetic material in different ways. Besides missing or additional chromosomes, there can also be an incorrect base combination of the DNA. In the end, such processes do not result in any consequences for the carriers of the germ cell. The disease usually affects the embryo exclusively.