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Your Body Makes 3.8 Million Cells Every Second. Most of Them Are Blood
Deep within, on a cellular scale, your body is in a constant state of activity to keep you alive. Among those processes is the turnover of cells, replacing the cells that die with fresh new ones so that you don’t crumble to bits like a zombie.
A new calculation reveals just how intensive that process is. According to biologists Ron Sender and Ron Milo of the Weizmann Institute of Science in Israel, your body replaces around 330 billion cells per day. At that rate, your body is making over 3.8 million new cells every second.
Most of those are blood cells, followed by cells in your gut. Less than 2 percent of your cell turnover is everything else. Confirming these numbers could help scientists better understand how the human body functions and the role cell turnover plays in both health and disease.
It’s a common myth that your body completely regenerates all its cells every seven years. The reality is a lot more complicated. Some cells live just a few days, while others – such as neurons in the cerebellum and lipids in the lenses of your eyes – are limited only by the lifespan of the host (you). So humans are very far from a Ship of Theseus situation.
However, while scientists have previously worked out estimates for how many cells are in the body, what kind they are, and what their lifespans are, very little work has been done to take a census of the cellular turnover rate.
There are about 200 different types of cells in the body. Here are just a few examples:
- red blood cells (erythrocytes)
- skin cells
- neurons (nerve cells)
- fat cells
Humans are multicellular, complex organisms. The cells inside our bodies are “specialized.” This means that each type of cell performs a unique and special function. For this reason, each of the 200 different types of cells in the body has a different structure, size, shape, and function, and contains different organelles.
- Cells in the brain may be longer in shape so they can transmit signals more efficiently.
- Cells of the heart have more mitochondria because they need a lot of energy.
- Cells in the respiratory system are responsible for taking up oxygen and releasing carbon dioxide.
All the cells work together to keep the human body running efficiently.
How many cells do we have in our body?
Great question! Amazingly, an adult human body contains about 50-100 trillion cells (that´s 100,000,000,000,000)! A lot of zeros, right!? So how do we get this number? Well it actually is not that complicated, mathematically.
First, we assume that an average eukaryotic (animal) cell is about 10 micro meters across (it has a diameter of 10 micro meters, also called microns). Then we assume that a human cell is a cube (as opposed to being a sphere or some other shape).
This allows us to calculate the volume of the cell as 10x10x10 cubic microns = 1000 cubic microns. Since there are one billion cubic microns in a cubic millimeter (mm, the smallest lines on a centimeter ruler), we can make the next calculation that there are one million cells in a cubic mm.
Ok, so now we can take it up another measurement as we know that there are one million million cells in a cubic decimeter, and one cubic decimeter is the same as one liter. In other words, there are one trillion cells in one liter of volume.
Next, we assume that 1 liter is about the same as 1 kilogram (kg) because this is the conversion that works for water (and we are mostly water after all). Now we know that there are roughly 1 trillion cells in one kilogram. How many kg are you? I´m about 53 kg, meaning I have about 53 trillion cells in me! How many trillion cells do you have in you?
How many blood cells are in the human body?
There are three types of blood cells: red blood cells, white blood cells, and platelets. Red blood cells (RBCs) are by far the most abundant type of cell in the human body, accounting for over 80 percent of all cells.
There are also about 147 million platelets and another 45 million lymphocytes (a type of white blood cell) in the body, based on recent calculations.
How many cells does the human body produce daily?
It’s difficult to measure exactly how many cells your body makes on any given day. The lifespan of each of the 200 types of cells varies considerably, so not every type of cell is produced at an equal rate.
A good start is to look at the number of RBCs that are produced each day, as RBCs are the most abundant type of cell in the body. RBCs live for about 120 days, at which point they are removed from circulation by macrophages in the spleen and liver. At the same time, specialized stem cells are replacing the dead red blood cells at roughly the same rate.
The average body makes about 2 to 3 millionTrusted Source red blood cells every second, or about 173 to 259 billion red blood cells per day.
How many cells in the human body die each day?
Most, but not all, cells in the body will eventually die and need to be replaced. Fortunately, a healthy human body is capable of maintaining a precise balance between the number of cells produced and the number of cells that die.
For example, as the body is producing between 173 and 259 billion RBCs per day, roughly the same number of RBCs are dying off.
It’s challenging to figure out exactly how many cells in the human body die each day. Cells aren’t created equal when it comes to the length of their life cycles. For example, white blood cells only live for about 13 days, whereas red blood cells live for about 120 days. Liver cells, on the other hand, can live up to 18 months. Cells in the brain will stay alive throughout a person’s life.
Using more sophisticated methods than before, new research estimates that there are about 30 trillion human cells in the average person. Red blood cells comprise the majority of these cells.
Of course, human cells are not the only cells in our bodies. New research has also learned that there are around 38 trillion bacteria in the average human as well. This brings the grand total to over 68 trillion cells (human or not).
Cell death: Is our health at risk?
The life and death of the cells in our bodies are tightly regulated. This is essential for normal function and limiting damage. But cell death can have side effects, and if it malfunctions, our health is at stake.
Every day, more than 50 billionTrusted Source cells die in our bodies. These are not random events, but part of a finely tuned biological mechanism called programmed cell death.
Multicellular organisms, including humans, need to keep a tight lid on the number of cells in their bodies. This would be easy if the cells never divided, but some areas – such as the blood, skin, and lining of the gut – are constantly producing new cells.
Cell death stops excessive and damaged cells from accumulating. This balance, or homeostasis, is essential to maintain a healthy organism and to prevent disease. It is also a crucial mechanism of defense against pathogens, as cells that are infected with bacteria or viruses are removed this way.
Under normal circumstances, dying cells are recycled by the immune system. But unfortunately, programmed cell death is not a foolproof mechanism.
When things go wrong, it can have dire consequences. Cancer, autoimmune conditions, and neurodegeneration are all linked to failures of normal cell death and cell clearance.
Many paths, one outcome
There are several different ways that a cell can die. Whatever is at the root of cell death, the corpse lodged in the tissue cannot stick around forever. Here, we enter the realm of the phagocytes, which are specialized white blood, or epithelial, cells that are able to swallow, or engulf, dying cells.
Phagocytes patrol our tissues on the lookout for “find-me” signals released by dying cells, and then engulf them when they encounter “eat-me” signals. They are also the gatekeepers of inflammation, and cell death can either be pro- or anti-inflammatory, leading to different outcomes.
Apoptosis is the most common form of cell death and is referred to as programmed cell suicide.
During apoptosis, a cell is broken up and packaged into small, self-contained pieces, which are easily recycled by phagocytes.
Apoptosis is often kick-started by an accumulation of stress signals, such as damaged DNA or low oxygen. This causes leaks in the membranes of mitochondria, which are the powerhouses that convert oxygen into energy in the cell. Once mitochondria are damaged, a cell is well and truly on its way to becoming a corpse.
Apoptosis can also be initiated by outside triggers. These activate so-called death receptors on the cell.
To make it easy for patrolling phagocytes to home in and engulf apoptotic cells, they release strong “find-me” and “eat-me” signals.