What is Blood Made Of? Blood Composition and Functions

Red Blood Cells (RBCs)

Anemia and Red Blood Cell Counts

White Blood Cells (RBCs)

Platelets

What is blood plasma?

Plasma is Mostly Made of Water

Blood plasma makes up 55% of blood and it is the largest amount of liquid in your body. Blood plasma is approximately 92% water and the remaining 8% contains a powerful mix of molecules that control many basic behaviors and emotions. When you feel hungry, anxious, sleepy, or sick, the microscopic bits that dissolve in your blood plasma are primarily responsible for these feelings. This is because blood plasma contains hormones, antibodies and clotting proteins, as well as nutrients such as fats, vitamins, electrolytes, and other digested food particles. Each of these components could have a full article dedicated to their function and importance, but the focus of this article is on the organs that interact with blood, so the information provided is brief. 

Plasma is 7% Protein

Around 7% of the stuff that is dissolved in the watery plasma are proteins that can be divided into three categories: albumin, globulins and fibrinogen. These proteins may not seem worth remembering due to their clunky names, but there are plenty of reasons to be grateful for these globs:

• Albumin is the most abundant type of plasma protein and it is a molecular taxi that can transport hormones, fatty acids, and drugs to different destinations throughout the body. For example, without albumin, the anti-inflammatory drug ibuprofen would not be efficiently transported to your tissues to relieve pain and reduce inflammation. 

• The globulin protein category also contains transport taxis, but it is best known for antibody proteins that are important for your immune system. Antibodies function as demolition stickers for bad bacteria and other pathogens that invade the bloodstream. Salmonella is a bacteria that is often found in undercooked meat and it can cause an infection that results in vomiting, fever and inflammation. When Salmonella moves into the blood from the intestines, at least three different types of antibodies can stick to the Salmonella surface. These antibody surface markers are destruction signals that are recognized by your white blood cell defense ninjas. When white blood cells come into contact with bacteria that have been labeled with antibodies, they respond by swarming, engulfing and dismantling the bacteria. Take a moment of gratitude to appreciate your fierce antibodies and white blood cells that protect your body.

• Last but not least, fibrinogens are large clotting proteins that make up a tiny percentage of the plasma. Fibrinogen proteins work with activated platelets to form scabs in injured tissue. Without fibrinogens, even scrapes and scratches would potentially result in life-threatening amounts of blood loss. 

Beyond each of their individual functions, all of these proteins are essential to maintain appropriate amounts of water within blood vessels. Due to their large size, most proteins cannot escape the blood vessel walls and therefore, they provide an incentive for water to enter the bloodstream. This incentive is due to osmosis and osmotic pressure, which determines the passive movement of water and other fluids in permeable systems.   

Osmosis is Essential to Keep Water in Your Bloodstream

One way to think about osmosis is to focus on how it influences the movement of water into and out of blood vessels. Think of water as an extroverted socialite—it flows toward the party with the most molecular guests. The bloodstream is a highly concentrated party due to the proteins and cells that are too big to exit the blood vessel walls. Therefore, water will flow into the blood vessels from surrounding tissues and tubes that are less concentrated, such as the kidneys and intestines. This osmosis party rule applies to the movement of water across all mammalian cell membranes and it is an essential process that supports the lives of all creatures and plants on this planet. Who knew that dihydrogen monoxide (H2O) had such a bustling social life?

Plasma is Made of 1% Tiny Molecules

The remaining 1% of blood plasma contains some of the most powerful effectors of your biology and well-being. These tiny components can be separated into three main groups: hormones, nutrients, and ions:

• Hormones are behavior bits that influence many feelings, such as love and fear, and they also regulate the basic desires for water, food, sleep, and sex. Different hormones are released into the bloodstream from many locations throughout the body and regulate your mood and behavior by causing biological cascades in different organ systems such as your digestive and nervous systems.

• Nutrients are primarily molecules that are broken down from food such as carbohydrates, proteins, vitamins, minerals, and fats that are broken down in your digestive track and are transferred into the bloodstream from your intestines and liver. But nutrients can also come from recycling your body’s old and defunct cellular machinery.

• Ions (also called electrolytes) are charged atoms that allow your body to send electrical impulses and they also maintain proper water and acid/base concentrations that keep your organs healthy and happy. 

Human blood anatomy summary

The next time that you donate blood, give a blood sample, or stop its flow from an injury, take a moment to reflect on the amazing microscopic material that is packed into every drop.