The amount of blood the human body makes per day has fascinated doctors and scientists for centuries. With advanced medical knowledge and technology, we now have a good understanding of the body’s blood production. This article will provide a comprehensive overview of how many milliliters (mL) of blood the body produces daily.
Quick Answer
The average adult human body makes around 2.4 million red blood cells per second. This equates to about 200 billion red blood cells produced each day. With an average volume of 90 fL per red blood cell, this results in approximately 2.16 trillion μL or 2.16 million mL (2.16 L) of new blood produced per day.
How Blood Cell Production Works
Blood cell formation is called hematopoiesis. It primarily occurs in the bone marrow, which produces red blood cells (erythrocytes), white blood cells (leukocytes), and platelets (thrombocytes). The process starts with hematopoietic stem cells that can develop into any type of blood cell. These stem cells divide and differentiate into blood cell precursors that further mature into fully functional blood cells. This complex process is regulated by various cytokines or growth factors.
Red blood cells have the vital role of carrying oxygen from the lungs to tissues throughout the body. They survive for around 120 days before they are removed from circulation by the spleen. The bone marrow must continuously produce new red blood cells to replace the old ones being destroyed.
The kidney hormone erythropoietin (EPO) is the main regulator of red blood cell production. When tissues become deprived of oxygen, the kidneys secrete more EPO to stimulate the bone marrow to produce more red blood cells. This boosts oxygen delivery to meet the body’s needs. The normal range for EPO levels is 4 to 30 mU/mL.
Rates of Red Blood Cell Production
Human red blood cells are small biconcave discs with a mean diameter of about 6-8 μm. Their volume ranges between 80-100 fL. The bone marrow produces around 2 million of these tiny red blood cells per second. This equates to the following daily production rates:
- 200 billion red blood cells made per day
- 16-20 trillion red blood cells circulating normally
- 1% of red blood cells renewed each day, or 200 billion destroyed and replaced daily
With an average red blood cell volume of 90 fL, simple math allows us to calculate the daily blood volume production:
- 90 fL per cell x 200 billion cells made daily = 18,000 trillion fL daily
- 18,000 trillion fL = 18 trillion μL = 18,000 mL = 18 L
Therefore, approximately 18 liters of new red blood cells are created by the bone marrow each day. However, the blood plasma volume also needs consideration.
Accounting for Blood Plasma Volume
While red blood cells transport oxygen, the pale yellow blood plasma carries nutrients, proteins, hormones, and waste throughout the body. Plasma makes up about 55% of total blood volume. The normal blood plasma volume is 3.5 to 5 liters for men and 2.5 to 4 liters for women. This plasma is constantly renewed by the liver and intestines to replace used components.
If we take the average plasma volume as 3 liters, then 45% or 1.35 liters consists of red blood cells. Combining the 18 liters of new red blood cells produced per day and the plasma volume gives us a total daily blood production of:
- New RBCs: 18 L
- Plasma: 3 L
- Total = 18 L + 3 L = 21 L
With some rounding, we can estimate the average adult human body produces about 2.16 million mL or 21 liters of new blood per day.
Blood Cell Lifespans
The numbers above reflect the high rate of red blood cell turnover. While they only live for about 4 months in circulation, white blood cells and platelets have much shorter lifespans:
- Red blood cells: 120 days
- Platelets: 8 to 10 days
- Neutrophils: 12 hours to 5 days
- Eosinophils: 8 to 12 days
- Basophils: Hours to days
- Lymphocytes: Days to months
- Monocytes: Days to months
This requires the constant daily production of billions of white blood cells and platelets along with the red blood cells. The coordinated process of blood cell formation is precisely regulated to meet the body’s continuous needs.
Blood Volume Relative to Body Weight
A person’s blood volume correlates closely with their body weight. Men tend to have higher blood volumes than women of the same weight due to having more muscle mass. Here are some general estimates:
| Body Weight | Total Blood Volume |
|---|---|
| 110 lbs (50 kg) | 4.7 liters |
| 150 lbs (68 kg) | 5.5 liters |
| 200 lbs (90 kg) | 6.4 liters |
Based on these values, a 150 pound person produces around 2.1 liters of new blood per day. A 200 pound person makes about 2.3 liters daily. Larger people generate more blood cells proportional to their size and metabolic needs.
Changes During Pregnancy
Blood volume increases dramatically during pregnancy to supply oxygen and nutrients to the developing baby. Plasma volume can increase up to 50% in pregnant women. The body boosts red blood cell mass by about 20-30% to carry more oxygen.
By the third trimester, the enlarged uterus compresses blood vessels and can decrease plasma volume despite the overall increase. The total blood volume expands by 30-50% over the course of a pregnancy. This increased production places extra demands on the bone marrow to rapidly generate additional blood cells.
Disorders That Affect Blood Cell Production
There are various medical conditions that can impair the bone marrow’s ability to produce healthy blood cells:
- Anemia – Inadequate RBCs, hemoglobin, or oxygen-carrying capacity.
- Leukemia – Cancer of the blood cells.
- Polycythemia – Excess RBC production.
- Neutropenia – Low neutrophil white blood cell count.
- Thrombocytopenia – Low platelet count.
These disorders may be inherited or acquired. They can result from nutritional deficiencies, autoimmune diseases, bone marrow damage, or cancers. Doctors can run blood tests to check cell counts and may recommend treatments like transfusions, medications, or bone marrow transplants in severe cases.
Key Points
To summarize the key points:
- The bone marrow produces around 2 million red blood cells per second or 200 billion per day.
- With an average volume of 90 fL per cell, approximately 18 liters of new red blood cells are created daily.
- Accounting for the plasma volume of ~3 liters gives a total daily blood production of ~2.16 million mL or 21 liters.
- Production rates correlate with body size and metabolic needs.
- Pregnancy significantly increases blood volume and cell generation.
- Disorders like anemia or leukemia can impair healthy blood cell formation.
Conclusion
The human body has an amazing capacity to continuously regenerate its blood supply. Roughly 2.16 million mL or 21 liters of new blood is produced daily to replace old cells and maintain homeostasis. This complex process involves the precise coordination of bone marrow, kidneys, hormones, and growth factors to meet the body’s ongoing demands for oxygen and nutrients.