According to NOVA online, the human body contains approximately 100 trillion cells. Cells in the human body constantly die and get replaced with new cells as part of the typical cell cycle. While the vast majority of cells in the human body perform as expected, a typical human cell may lose viability or become compromised.
Types of Human Cells
Many different types of human cells exist throughout the body. Each type has a specialized function depending on what the tissue is. The brain, skin, kidneys, lungs, and stomach cells are just some examples of organs that consist of differentiated cell types. The cells that make up tissues in these locations include epithelial cells, muscle cells, neurons and connective tissue cells. These cells divide and create new cells of the same type in each area to replace old and dying cells. One type of cells, adult stem cells, exists as undifferentiated cells. These cells can turn into any type of cell needed by the body.
Parts of a Cell
All human cells have components within them that are similar in structure and function, regardless of where the cell is located. The textbook "Microbiology (Sixth Edition)" notes that all human cells consist of a cell membrane, nucleus, ribosomes and many other membrane-bound organelles. Deoxyribonucleic acid (DNA), lysosomes, golgi apparatus, mitochondria, endoplasmic reticulum and centrioles all serve a variety of functions within a typical human cell.
Cell Division
Each cell exhibits a characteristic cycle of life, from initial growth to death. Human reproductive cells undergo a process called meiosis, in which the genetic material of the cell is doubled, then the cells are split in half two times, resulting in four cells, each with half of the original genetic material. When a sperm cell with half the original genetic material joins with an egg cell with half of its original genetic material, the resulting cell has the correct amount of genetic material.
Non-reproductive cells in the body undergo mitosis, in which a cell doubles the genetic material, then splits in half, creating two new cells of the correct amount of genetic material.
Eventually, a cell will undergo apoptosis, or programmed cell death, and is replaced with a new cell.
Cell Metabolism
A cell must have a source of energy to run all the processes necessary for growth. In human cells, oxygen is used as a final electron acceptor for creating energy. The breakdown of sugars and the byproducts from this breakdown are used to drive production of adenosine triphosphate, or ATP, which is the molecule that provides energy for many cellular processes in cells throughout the body.
Abnormal Growth
A human cell does not always divide as nature intended. Mutations can cause a cell to skip apoptosis, which often results in cancerous uncontrolled cell growth in the affected cell. Many other problems can occur within the cell that can result in death or abnormal growth of the cell.
References
- NOVA Online: Journey Into DNA
- "Microbiology: 6th Edition"; Lansing Prescott, John Harley and Donald Klein; 2005
