People are aware of “concentrations” but may not be familiar with them on a chemical basis. Simply put, a concentration is described as the direct relationship between the amount of solute dissolved in a volume of solvent. A solute is the substance (ex. sugar, salt etc) that is to be dissolved in the solvent, which is typically a liquid, to create a homogenous mixture called a solution. As the amount of solute in a given solution increases, so does the overall concentration of the solution with respect to the amount of solvent present.
Concentrations aren't confined to the realm of chemistry experiments; in fact, they're present even in our own bodies! Our blood is a perfect example of why concentrations are so important. Different concentrations of different components in the blood enable our bodies to function properly. It brings up the question, what are the different components of blood, and how do they interact with one another to ensure the body is staying well?
Blood volume:
The average adult typically has 5 liters of circulating blood, but a more accurate approximation of the amount of blood circulating within an individual depends on his/her size and weight. To estimate the blood volume of a specific patient, scientists may use these equations down below. (R. Sharma and S. Sharma).
Blood composition:
As some may be able to recall from their biology courses, blood is composed of 4 parts: plasma, white blood cells, platelets (cells that help blood clot), and red blood cells. Here’s what the blood composition of a healthy person looks like:
(Photo provided by Freepik, and is copyright free)
As seen in the blood composition diagram above, plasma makes up the largest percentage of our blood. Plasma is composed of about 90% water along with salts, hormones, and rich proteins such as albumin, fibrinogen and immunoglobulins. White and red blood cells are suspended among plasma in the blood.
The plasma in blood performs a plethora of functions.
It transports blood cells and nutrients.
The immunoglobulins in plasma provide a defense against infections.
The protein albumin found in plasma regulates water within the body by retaining as much water as possible in the blood when the blood is being transported in narrow, water-permeable blood vessels known as capillaries (“Blood components”).
A deficiency in any of the proteins within the plasma can cause various health problems. For example, a lack of albumin can cause fluid to leak out of blood vessels, and a lack of immunoglobulins can weaken the body's defense against pathogens and eventually deteriorate the immune system. This is why doctors require a protein test from their patients to measure how healthy their blood is. Protein plasma tests can detect body dysfunctions such as bone marrow diseases, kidney failure, bowel problems, etc. (“Blood components”).
Blood To Plasma Ratio ( pharmacokinetic studies):
Pharmacokinetic studies refers to the study of the movement of medical drugs in the body. To assess for drug concentration, modern medical advancements have regarded the plasma as the matrix rather than the entirety of blood in order to have more effective matrix interference and protein binding. The blood to plasma ratio helps determine the concentration of the drug in whole blood and provides insight into fascinating statistics of the human body!
The blood-plasma ratio in the human body can be determined through a mathematical step by step process, which was broken down in the 2011 article “Blood or Plasma? Which Should You Assay for Drug Concentration?,” written by a leading drug development company called Certara. The process begins at step 1: collecting the evidence.
Blood, plasma and red blood cells
(Provided by Certara, in their article “Blood or Plasma? Which Should You Assay for Drug Concentration?”)
When measuring the drug concentration in plasma, a sample of whole blood is drawn from the patient, and the plasma is separated from the blood, while the RBC (red blood cells) is disregarded. This leaves us with this simple equation:
Equation 1
Equation 2
Here, C= concentration and V=volume. Remember, concentration * volume = number of moles in a given substance. To recall, moles are a unit measurement used in various studies to assess the number of particles, atoms or molecules in a given substance, with a ratio of 1 mole, or 6.02214076×10²³ of atoms/particles/molecules. Assume that the drug partitions, a ratio of concentrations of a compound disturbed in a mixture of two immiscible solvents at equilibrium, is equally parted into the RBC and plasma, it gives the following relationship:
Equation 3
The concentration in blood is equivalent to the concentration in plasma, which makes an easier conversion between blood and plasma concentrations. Assuming the drug is isolated in the plasma, the following relationship should be:
Equation 4
Substitute in Equation 2 and arrive at the following:
Equation 5
To clarify, hematocrit is the volume percentage of red blood cells in the blood and is used as an indication to identify any problems with the volume of red blood cells. Red blood cells carry a protein known as hemoglobin, which is known to carry oxygen throughout the body, so it is vital that the human body has a sufficient quantity of red blood cells in order to function properly, which typically means a patient’s hematocrit levels reach around 40-50% for males or 36-44% for females (Mathew et al.).
Equation 6
Equation 7
The volume of blood is larger than the volume of plasma, but the amount of drug in both blood and plasma is equivalent. This means that the concentration in the plasma will be higher than the concentration in blood by an adjustment factor of 1-Hct.
Equation 8 can only occur if the drug is concealed in the red blood cells
Equation 8
As stated before, all equation deviations have been provided by Certara, in their article “Blood or Plasma? Which Should You Assay for Drug Concentration?”.
Other Bodily Fluids:
Among the plasma, which is 90% water, there are other bodily fluids as well. What are the other types of bodily fluids that make up the total water composition in the body? Well, there are three main categories represented the following diagram:
(Figure 2. Fluid compartments in the human body. The intracellular fluid (ICF) is the fluid within cells. The interstitial fluid (IF) is part of the extracellular fluid (ECF) between the cells. Blood plasma is the second part of the ECF. Materials travel between cells and the plasma in capillaries through the IF.)
(Provided by Rice University, Anatomy and Physiology)
ICF fluids make up about 60% of the water in our body, which is equivalent to about 25 liters of fluid. The water suspended among this fluid is closely regulated, so it is a very stable volume in our body. However, if there is not enough water supply in the cell, the cytosol becomes too concentrated with solutes to perform normal cellular activities, which may destroy the cell. Furthermore, if the cytosol becomes too diluted with water intake by the cells, the cell membrane can be damaged, causing the cell to burst. As seen in this specific example, a carefully-measured diluted concentration is required for our cells to do their functions (“Body Fluids and Fluid Compartments”).
IF is part of the ECF (extracellular fluid between the cells), which takes up about ⅓ of the total water in the human body, and 20% of ECF fluids are mainly suspended within plasma. ECF fluids provide moisture to the brain, spinal cord, lymph, aqueous humour of the eye, etc. (“Body Fluids and Fluid Compartments”).
(Provided by Rice University, Anatomy and Physiology)
Each bodily fluid carries a composition of different ions in different concentrations that keep the body regulated. Here’s the different concentrations of different ions is in our bodily fluids:
(Provided by Rice University, Anatomy and Physiology)
If we take a closer look at some of the ions presented in the body, we can see that copper is very important. It enables the body to reproduce red blood cells, maintain healthy bones, blood vessels, and could be linked to preventing cardiovascular diseases. Another example is zinc concentration in the body, as zinc is an essential nutrient to help protect the body’s immune system, cell division, wound healing and the breakdown of other nutrients like carbohydrates (Mattew et al.).
How Solutes Are Affected By Hydrostatic Pressure and Osmosis
Research done by Rice University in BC, Canada, Anatomy and Physiology, states that the solutes in our body are also affected by the movement of cells that create hydrostatic pressure. The hydrostatic pressure of the blood is known to be pressure exerted by the blood against the walls of the blood vessels by the rhythmic and pounding action of the heart. This pressure forces plasma, other cells, and nutrients out of the capillaries and into surrounding body tissues, where these vital nutrients that our body needs to regulate are spread around.
The process of hydrostatic pressure can be best observed in the kidneys, which must ensure adequate filtering of the blood to form urine. There is a direct relationship between hydrostatic pressure and the amount of urine formation. As hydrostatic pressure in the kidneys increases, more urine filtrate is formed because the amount of water leaving the capillaries also increases as the force is entered on the blood vessels.
This active form of transportation allows cells to move a specific substance against its concentration gradient through a membrane protein. More passive transportation of an ion or molecule will depend on its ability to process osmosis (diffusion of water from higher contraction areas to lower concentration areas) and being able to pass through the membrane. Some states like gases and liquids can easily pass through the cell membranes, while other molecules such as amino acids and glucose can not do so. As a result, some of these solutes depend on using active transportation such as hydrostatic pressure, while other ions/molecules will move along a contraction gradient through specific channels in order to exist and enter the cell membrane (“Body Fluids and Fluid Compartments”).
Written By:
Elina J
References:
Certara. “Blood or Plasma? Which Should You Assay for Drug Concentration?” Certara,
19 Feb. 2011, www.certara.com/knowledge-base/blood-or-plasma-which-should-you-assay-for-drug-concentration/?ap.
Certara. “Blood, Plasma and Red Blood Cells.” Certara, 19 Feb. 2011,
Mathew, Joscilin, et al. “Physiology, Blood Plasma.” StatPearls [Internet]., U.S.
National Library of Medicine, 25 Apr. 2020, www.ncbi.nlm.nih.gov/books/NBK531504/.
Rice University. “26.1 Body Fluids and Fluid Compartments.” Anatomy and
Physiology, OpenStax, 6 Mar. 2013, opentextbc.ca/anatomyandphysiology/chapter/26-1-body-fluids-and-fluid-compartments/.
Rice University. “Figure 2. Fluid Compartments in the Human Body. The
Intracellular Fluid (ICF) Is the Fluid within Cells. The Interstitial Fluid (IF) Is Part of the Extracellular Fluid (ECF) between the Cells. Blood Plasma Is the Second Part of the ECF. Materials Travel between Cells and the Plasma in Capillaries through the IF.” ANATOMY AND PHYSIOLOGY, 6 Mar. 2013, opentextbc.ca/anatomyandphysiology/chapter/26-1-body-fluids-and-fluid-compartments/.
Rice University. “Figure 3. A Pie Graph Showing the Proportion of Total Body Fluid
in Each of the Body’s Fluid Compartments. Most of the Water in the Body Is Intracellular Fluid. The Second Largest Volume Is the Interstitial Fluid, Which Surrounds Cells That Are Not Blood Cells.” ANATOMY AND PHYSIOLOGY, OpenStax, 6 Mar. 2013, opentextbc.ca/anatomyandphysiology/chapter/26-1-body-fluids-and-fluid-compartments/.
Rice University. “Figure 4. The Concentrations of Different Elements in Key Bodily
Fluids. The Graph Shows the Composition of the ICF, IF, and Plasma. The Compositions of Plasma and IF Are Similar to One Another but Are Quite Different from the Composition of the ICF.” ANATOMY AND PHYSIOLOGY, OpenStax, opentextbc.ca/anatomyandphysiology/chapter/26-1-body-fluids-and-fluid-compartments/.
Sharma, Ragav, and Sandeep Sharma. “Physiology, Blood Volume.” StatPearls
[Internet]., U.S. National Library of Medicine, 25 Apr. 2020, www.ncbi.nlm.nih.gov/books/NBK526077/.
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