Any organism is composed of various cells, each with its purpose. These cells all have different structural components to help them do their jobs. It’s actually quite amazing how all these cells work together to keep the organism alive!
Humans are relatively complex creatures, so their variety of cells is particularly impressive! These cells come in various shapes and sizes and with different features. You might wonder, what’s the largest cell in the human body?
What’s the Largest Human Cell?
The largest cell in the human body is the egg cell, or ovum. Its diameter is about 0.12 millimeters and, unlike the vast majority of cells, is actually visible to the naked eye!
Egg cells are only present in female humans, as well as other organisms. In humans and other mammals, a traveling sperm cell fuses with an egg cell. The egg cell is then activated and able to produce a new individual.
Even though human egg cells are significantly larger than other human cells, they are actually much smaller when compared to egg cells of other species. These cells can be one to two millimeters in fishes and frogs and many centimeters in reptiles and birds.
In all of these cases, the egg is really just one giant cell, which contains everything necessary for the early development of the embryo.
Egg cells actually have special mechanisms that they use to become so large. These include carrying extra gene copies within the cell, containing significantly more ribosomes than the average cell, and using the synthetic activities of other cells to help them grow.
What Are the Parts of the Largest Cell in the Human Body?
Egg cells contain many parts, but we will focus on the main ones.
The nucleus is the organelle that contains the majority of the genetic material of the cell. A human egg cell nucleus contains 23 chromosomes, as does a human sperm cell. When the two combine, the resulting human embryo has 46 chromosomes.
The cytoplasm is basically a gel-like compound that holds together all the structures (organelles) within the cell.
The egg wall, also known as the zona pellucida, is the egg’s outer membrane. It plays a role in the ability of the sperm to enter the egg through tough outer layers.
The corona radiata also surrounds the egg, consisting of layers of cells from the follicle. These layers provide vital proteins to the egg cell.
How Does the Largest Cell in the Human Body Develop?
Before an egg cell actually becomes an ovum, it has to develop. A developing egg is referred to as an oocyte, and the term for this developmental process is oogenesis.
Female humans contain all the eggs they will ever have at birth. Before birth, primordial germ cells travel to the forming gonad and become oogonia. The oogonia then differentiate into primary oocytes. Then, meiosis takes place, with the DNA replicating so that each chromosome includes two sister chromatids, which exchange material in a process known as crossing over.
At this point, the cell will stop developing and stay in prophase of the first division of meiosis. In human beings, this lasts for many years, basically until the sexual maturity of the female. At this point, the oocyte will be stimulated by hormones and resume its progress in the meiotic cycle.
At the end of meiosis I, each primary oocyte has divided into a small polar body and a large secondary oocyte. The secondary oocyte is the precursor of the ovum. At anaphase of meiosis II, the cytoplasm of the secondary oocyte will once again divide. This time, the division will create the ovum and a second small polar body. The polar bodies eventually degenerate.
In the majority of vertebrates, including humans, oocyte maturation will go all the way to the metaphase of meiosis II and then stop until fertilization takes place. When the female human ovulates, the secondary oocyte will be released from the ovary and rapidly mature into an egg that can be fertilized.
If fertilization occurs with a sperm cell, the egg will be stimulated to complete the meiotic process.
What’s the Smallest Human Cell?
Now that we know that egg cells are the largest cells in the human body, it’s interesting to note that the smallest cell is actually the sperm cell. The head of a sperm cell is about 4 micrometers long.
Both egg cells and sperm cells contain the same amount of genetic material that can be contributed to the creation of a human baby, yet egg cells are 20 times larger than sperm cells.
What’s the Largest Cell Universal to Humans?
Obviously, only female humans have egg cells. Now, you might be wondering, what’s the largest cell in the human body that’s universal to all people?
After the ovum, the nerve cell is considered to be the largest cell in the human body. More accurately, it’s the longest cell. Some nerve cells can be up to a meter in length. Of course, all humans, male and female, have nerve cells, making these the largest cells in the human body that everyone has.
Of course, we should keep in mind that nerve cells come in all lengths. Some are less than a millimeter long, but some are by far the longest cells in the human body. It isn’t the cell bodies that are long, but the axons. For example, the axon of a motor neuron whose cell body is located in the spinal cord can go through the entire leg to the foot and be the entire length of that person’s leg.
Nerve cells are made up of one cell body and multiple cell fibers. There is one extended axon, which is there for the purpose of sending impulses to other parts of the body. There are also often many branches, known as dendrites, which receive impulses from other locations of the body. Impulses travel from the cell body through the axon and into the dendrite of another cell.
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