They’re the smallest living organism and the building block of the body. Join Tidbits this week as we explore the basic unit of life.

The human body contains over 30 trillion cells – that’s the number 30 followed by 12 zeroes! This number can vary depending on age, gender, body size, and environment. About 200 different types of cell make up this total, including blood cells, skin, nerve, bone, and fat cells. Red blood cells are the most abundant, making up 80% of the total. Each cell contains an astonishing 100 trillion atoms!

The liver, kidneys, lungs, and scalp each contain about 100 billion cells, with another 10 billion in the pancreas, 300 million muscle cells, and an astounding 1 trillion nerve cells. There are about 170 billion cells in the average brain.    The skin’s 50 billion cells are dispersed to about 300 million per square inch.

There are a huge number of different functions of the cells. Some protect the body’s outer surface and internal organs. Bone cells build up bones, while others carry nutrients and oxygen throughout the body, while removing carbon dioxide.

    Cells are constantly dying and being replaced. Close to 300 billion new cells are produced every day, with new cells arising from pre-existing cells. A cell’s lifespan varies widely. White blood cells live for just 13 days, while red blood cells live for about 120 days. Liver cells can live up to 18 months. Some cells live for several years. The vast majority of the body’s brain cells stay alive throughout a person’s whole life. Unfortunately, when nerve cells in certain parts of the brain die off due to degenerative diseases like Parkinson’s and Alzheimer’s, they are not replaced.

    Each tiny cell has three distinct parts. The nucleus is the “headquarters” of the cell, delivering instructions to the cell to grow, divide, or die. The nucleus contains the majority of the cell’s DNA. Cytoplasm is a clear, semi-fluid substance that surrounds the nucleus. The nuclear membrane protects the DNA and separates it from the rest of the cell.

Cells have many different shapes – round, square, spindle-like, and star-shaped. They maintain their shape with the help of the cytoskeleton, a type of scaffolding within the cell’s cytoplasm. White blood cells, those that defend the body against infection and disease, can change their shape, enabling them to move through narrow spaces.

    A British scientist named Robert Hooke was the first person to observe cells in 1665. Hooke was looking at dead cork tissue using a compound microscope that he had built himself. He named the structures cells because they resembled the small simple rooms where monks slept in monasteries. The cork cells were dead, left behind after the death of the live cells. In the 1670s, Dutch microbiologist Anton van Leeuwenhoek was the first to observe living cells, recognizing them as red blood cells.

      Human cells aren’t the only cells in the body. There are also about 37 trillion bacteria cells in the average body as well, outnumbering the human cells.    Most types aren’t harmful, and in fact, help keep your body healthy. Good bacteria can be found on your skin, in your airways, mouth, digestive system, and urinary tract, and many other places. Bacteria in your gut absorb nutrients, break down food, and even prevent the growth of harmful bacteria. Other types can make you sick, such as streptococcus and staphylococcus, and are responsible for strep throat, whooping cough, staph infections, E.coli infections, urinary tract infections, and sepsis.