In this video, we're going to talk about the composition of blood. Blood can actually be separated out into three components that we have numbered down below in the text, 1, 2, and 3. Now before we cover each of these three components of blood, let's first recall from our previous lesson videos that blood is a type of specialized liquid connective tissue. And like all tissues, it consists of living cells and a nonliving extracellular matrix. Notice, this is exactly what we're indicating on the right side, that these three components of blood are either considered living cells or cell fragments that we call formed elements, or they are considered part of the nonliving extracellular matrix.
The very first component of blood listed in our lesson is the erythrocytes, commonly known as red blood cells and abbreviated as RBCs. Erythrocytes are the most numerous type of cell in the blood, making them the main cell type. As their name implies, their components give them a reddish color. Because they are the most numerous cell type in the blood, this is what gives our blood that reddish color. Functionally, these erythrocytes are adapted for gas transport, specifically oxygen (O2 gas) and carbon dioxide (CO2 gas) transport.
The term hematocrit is highly linked to erythrocytes. The hematocrit represents the percentage of the total blood volume that is composed of red blood cells. It is an important value because it can give medical professionals insight into the overall health of their patients. If the value falls outside of the normal range, that could indicate a problem with the patient. The normal range for the hematocrit is somewhere between 36-50, and males tend to have a higher hematocrit than females. Let's say that the hematocrit value for a specific patient is about 45. This means that 45% of the total blood volume is made up of red blood cells.
The second component of blood is the buffy coat, named after its color since it has this light buff type of color. The buffy coat consists of white blood cells, also known as leukocytes, which are important for providing immunity, and platelets, also known as thrombocytes. These are cell fragments that are important for the blood clotting process, which helps to reduce blood loss during an injury.
Lastly, the third and final component of the blood is the plasma, the nonliving extracellular matrix. Plasma is a liquid extracellular matrix, consisting of 90% water, with electrolytes such as sodium ions and chloride ions, and various proteins dissolved in it, such as albumin, globulins, and fibrinogen, which are plasma proteins that we'll talk more about later in our course.
Notice that initially, the blood is pretty homogeneous, meaning that the components of the blood are evenly distributed throughout the tube. After being inserted into a centrifuge, which spins the sample very fast, it can separate the blood components based on their densities, where more dense components end up closer toward the bottom of the vial. Now, visually distinguishable, we can see the erythrocytes at the bottom in red. The hematocrit, represented here as 45%, indicates the volume percentage of red blood cells for this particular patient. Above it, the thin layer represents the buffy coat, making up less than 1% of the total blood volume. At the top, we see the plasma in yellow, making up about 55% of the total blood volume. This concludes our brief lesson on the composition of blood, and I'll see you all in our next video.