How Much Blood is in the Human Body?

October 27, 2022

4 mins

Almost every organ in the human body plays a role in normal bodily function, but few components touch every physical aspect in the same way that your blood does.

Blood is classified as connective tissue, and it acts as the transportation highway for many processes, including delivering oxygen to tissues, transporting important molecules among organs, and much more. 

So how much blood is in the body, what are all the functions of blood, and how is blood measured? 

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What is Blood?

We think of blood as a single fluid, but the reality is that blood is made up of many components. 

Blood is a mixture of plasma, erythrocytes, leukocytes, platelets, and much more. Blood is a heterogeneous mixture, and in measuring these components, a blood sample is placed in a centrifuge that spins this fluid and separates blood based on the density of each component. 

The layers that are formed from the centrifuge process are plasma, red blood cells, and a layer with white blood cells and platelets. 

Below is a breakdown of the components of blood, what they contain, and what they do in the body. 

Plasma

Plasma makes up the majority of blood’s constituents and encompasses around 55% of blood volume. 

Plasma is the component of blood that is home to most liquid parts of blood. Plasma contains mostly water, which allows it also to house other materials that are dissolvable. Blood plasma contains water, electrolytes, enzymes, antibodies, albumin, lipids, hormones, and fibrinogen. 

White blood cell and platelets

The next layer seen in centrifugal separation includes white blood cells and platelets. 

White blood cells, also known as leukocytes, are a part of your immune system and play an important role in your active immune response. These immune cells help to fight foreign invaders and keep you healthy. 

Platelets, also known as thrombocytes, are cells that help to clot blood and stop bleeding. When you cut or sustain an injury to your blood vessels, blood will leak through — thrombocytes help plug this hole and stop bleeding. 

Red blood cells

Red blood cells, also known as erythrocytes, are the cellular component of blood that are responsible for gas exchange throughout the body. These red cells contain a protein known as hemoglobin which has a unique ability to bond with gaseous oxygen. Red blood cells also are able to help eliminate carbon dioxide from the body. 

Red blood cells also contain antigens that determine your blood type. There are type A and type B antigens. Some individuals can have both types of antigens, which yields type AB blood, or no antigens, which is type O blood. 

Blood type is important if an individual is donating blood or receiving a blood transfusion, as foreign antigens will be recognized by immune cells as pathogens and will not be accepted by the recipient.

How Much Blood is in the Body?

The amount of blood in your body depends on several factors, including age, weight, and sex. 

The average adult will have anywhere from eight to 12 pints (one to one and a half gallons) of blood, which makes up approximately 10% of an individual's body weight. 

A newborn baby may have just 1 cup of blood in their body!

Studies have found that most adults can tolerate blood loss of up to 14% without experiencing substantial physical symptoms. This figure is an upper limit, and most blood donation centers don’t take any more than 8% of your blood during a blood donation. 

Losing more than 30% of your blood is when significant physical effects are seen.

Your blood regenerates quickly, and most people will have their full blood volume within a couple days of making a donation.

What is the Purpose of Blood in the Body?

Blood is a multipurpose tissue, with duties including gas exchange, hydrating tissues, providing the vehicular highway system within the body, and more. 

Gas exchange

Most people consider your lungs the most important aspect of your respiratory system, but blood plays an equally vital role in getting oxygen gasses into your body and properly distributed. 

The lungs contain small capillaries that allow for gaseous oxygen to be exchanged from red blood cells to the environment. With each inhale, red blood cells take oxygen from the air you breathe, releasing carbon dioxide with each exhale. 

Oxygenated blood travels throughout your body and gradually deposits the oxygen to cells that then utilize it for cellular respiration. On its way back, the blood picks up the waste carbon dioxide, which is then released into the lungs during exhale.

Hydration

Hydration is another important job of your blood. Blood is mainly made up of water, which plays a central role in keeping your body properly hydrated. The water in blood can be taken in by cells needing water and can act as a drain for cells that need to eliminate excess water.

The water also acts as a means of carrying nutrients to cells and waste products away from cells. 

The urinary system and the kidneys closely monitor the amount of water in your blood. If you are over-hydrated, the kidneys eliminate excess water and filter out cellular waste products like urea from blood. 

Facilitate immunity

Blood plays a crucial role in immune function. 

Blood acts as a highway throughout your body; immune cells constantly circulate through your blood, patrolling for foreign invaders and pathogens. Not only does blood help these specific immune cells to find foreign invaders, but it also can act as a means of fighting infection by transporting antibodies throughout the body to where they’re needed.

Hormone delivery

Hormones are the body's chemical messengers. Some hormones you may have heard of include testosterone, insulin, growth hormone, melatonin, and adrenaline. These chemicals evoke changes in various tissues, and blood allows these chemical messages to be conveyed throughout the body. 

Blood vessel dilation and contraction

One important function of blood that is frequently overlooked is how its flow is manipulated throughout the body. The blood vessels within your body can dilate and increase blood flow to a given area, or contract and restrict blood flow. 

This has many uses in the body. One example is heat regulation. If you’re too hot, blood vessels near the skin's surface will dilate and increase blood flow to allow heat to be more readily dissipated form the surface of the skin. This is akin to a car’s radiator.

Another function for dilation is in relation to erections. Increasing blood flow to the penis and restricting flow from the penis allows the capillaries to fill and for an erection to be obtained. 

If you're struggling to achieve and maintain an erection, it may be because of an underlying condition affecting your blood flow. It's important to see a doctor to treat this potential cause, and thus resolve your ED.

While issues pertaining to blood flow are often the cause of ED, there are other factors that may be contributing to erectile dysfunction, including performance anxiety.

That's why Rex MD offers men medications like Viagra® and Cialis® that can help you get back to a happy sex life that both you and your partner will benefit from. 

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