So how can organisms whose bodies require a near-neutral pH ingest acidic and basic substances (a human drinking orange juice, for example) and survive? Buffers are the key. Buffers readily absorb excess H+ or OH–, keeping the pH of the body carefully maintained in the narrow range required for survival. Maintaining a constant blood pH is critical to a person’s well-being. The buffer maintaining the pH of human blood involves carbonic acid (H2CO3), bicarbonate ion (HCO3–), and carbon dioxide (CO2). When bicarbonate ions combine with free hydrogen ions and become carbonic acid, hydrogen ions are removed, moderating pH changes. Similarly, as shown in Figure 1, excess carbonic acid can be converted to carbon dioxide gas and exhaled through the lungs. This prevents too many free hydrogen ions from building up in the blood and dangerously reducing the blood’s pH. Likewise, if too much OH– is introduced into the system, carbonic acid will combine with it to create bicarbonate, lowering the pH. Without this buffer system, the body’s pH would fluctuate enough to put survival in jeopardy. Show
Figure 1. This diagram shows the body’s buffering of blood pH levels. The blue arrows show the process of raising pH as more CO2 is made. The purple arrows indicate the reverse process: the lowering of pH as more bicarbonate is created. Other examples of buffers are antacids used to combat excess stomach acid. Many of these over-the-counter medications work in the same way as blood buffers, usually with at least one ion capable of absorbing hydrogen and moderating pH, bringing relief to those that suffer “heartburn” after eating. The unique properties of water that contribute to this capacity to balance pH—as well as water’s other characteristics—are essential to sustaining life on Earth. In Summary: BuffersThe pH scale is a measure of acidity/alkalinity and provides information about how substances tend to act in aqueous solutions. All living processes occur in an ideal pH range. Buffers act together to keep the pH within a certain range, based off the release or absorption of hydrogen ions. Acidity and alkalinity describe a property of chemicals based upon relative concentration of hydrogen ions in a solution. The pH scale measures this value and ranges from 0 to 14. A pH of 7.0 is considered neutral. A pH value greater than 7 is basic, and a pH less than 7.0 is acidic. The pH scale is defined as the negative log of the hydrogen ion concentration of a solution (figure 1). This means each pH value on the scale represents a ten-fold difference in hydrogen ion molarity than the next value. For instance, a solution with pH of 8.0 is one-hundred times more basic than a solution with a pH of 6.0. Similarly, a solution with a pH of 5.0 is ten times more acidic than a solution with a pH of 6.0. Figure 1. pH scale showing relative hydrogen ion concentrations. Examples of solutions with their pH listed, and concentration of Hydrogen ions compared to distilled water. For comparison, other biologically relevant solutions include the pH of pancreatic juice, which is 8.8, and seminal fluid, which has a pH of 7.8. By ChemEd DL (pH Scale)/CC-BY-SA.In biological systems, it is important to keep the pH of a solution within a narrow range of values. To accomplish this, buffers are used. Buffers resist changes in the pH of a solution when hydrogen ions or hydroxide are added (or removed). Buffers dissociate in solution and neutralize extra hydrogen ions or hydroxide ions by participating in reactions with them. Normal blood pH is 7.4, and arterial pH may only vary between 7.35 and 7.45 without being pathological. The Carbonic Acid-Bicarbonate buffer system is the most important buffer for maintaining the pH homeostasis of blood. In this system, gaseous metabolic waste carbon dioxide reacts with water to form carbonic acid, which quickly dissociates into a hydrogen ion and bicarbonate (see below). CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3– Besides the carbonic acid-bicarbonate buffer system, there are other buffers in whole blood, including the phosphate buffer system. Additionally, some proteins have buffering capacity, such as hemoglobin and blood serum albumin (a common carrier protein in blood). These have a lesser effect than the carbonic acid-bicarbonate system on maintaining blood pH homeostasis. In this week’s activity, you will test whether five solutions behave as buffers:
Part II: Blood Glucose HomeostasisBlood sugar homeostasis is important 1.) to consistently provide body cells with the necessary glucose to sustain metabolic reactions and 2.) to protect cells against damage that can occur when circulating blood glucose levels are too high for too long. For healthy individuals, the American Diabetes Association recommends a fasting (no food or drink, except water, for 8 hours) plasma glucose level of less than 100 mg/dL and, 2 hours after meals, a concentration less than 140 mg/dL. In order to tightly control blood glucose levels, α- and β-cells of the endocrine pancreas secrete two hormones – insulin and glucagon. When eating a meal, the surge in blood sugar is detected directly by receptors on the pancreatic islet β-cells. These cells then secrete insulin, which binds to insulin receptors on various body tissues. Occupied insulin receptors signal body cells to increase the number of glucose transporters, special proteins that shunt glucose from the blood, through cell plasma membranes, and into the cell. The increase in transporters results in quick internalization of blood glucose by the cells. When blood glucose levels are too low, e.g., less than 70 mg/dL or lower, the body may not have enough circulating blood glucose to sustain the body’s chemical reactions. Symptoms of low blood sugar (hypoglycemia) can be severe and include: nervousness, shaking, fatigue, blurry vision, trouble thinking, and even the loss of consciousness. Low blood sugar is detected by the α- cells of the pancreas, which increase glucagon secretion. Glucagon activates liver enzymes, which then convert the glucose storage molecule, glycogen, into glucose. Glucagon also initiates the endogenous synthesis of glucose from other biomolecules like amino acids. The newly released or synthesized glucose passes into the blood stream and raises blood glucose levels. Diabetes is a condition in which the body fails to respond to insulin, resulting in the body’s inability to control glucose homeostasis. Typically, in Type I diabetes, pancreatic β-cells are destroyed by an autoimmune reaction resulting in low or absent insulin in the body. Type II diabetes is also called “insulin resistance.” Generally, in this disease, the body manufactures insulin, but there is a problem that prevents insulin receptors from sending signals that increase the presence of glucose transporters in the plasma membranes of cells. In Lab this week, your TA may test your Blood Glucose using a Contour Blood Glucose Monitoring System. A blood sample will be obtained from the side of your middle or ring finger using an Accu-Chek Safe-T-Pro Lancet. It delivers a quick, almost painless pinprick and only a small amount of blood is needed. Figure 2. Blood glucose homeostasis. Figure shows pancreatic signaling in response to high blood sugar. Figure courtesy of Anatomy & Physiology (Open + Free) CC BY-NC 4.0.Laboratory MethodsThe following text describes the laboratory methods for analysis of blood buffering and blood glucose. In this experiment, students will determine the buffering capabilities of a variety of solutions by measuring the pH of the solutions when they are treated with a weak base. Each group of students will measure the pH changes that occur in Saline, Phosphate Buffered Saline (PBS), 5% Albumin in PBS, Blood Plasma diluted 1/10 with PBS, and Whole Blood diluted 1/10 with PBS.
Equipment Required
Safety Precautions! Students working with solutions in this lab must wear safety googles and gloves. Practice using the micropipetteTo draw up a specific amount of a solution, set the dial on the micropipette to the appropriate volume, then depress the plunger, and immerse the pipette tip in the solution. The micropipette plunger has a first “soft” stop. When the plunger is pushed to the first stop, it allows the pipette to draw up the programmed amount as the plunger is gently returned to the original position. To discharge the drawn-up solution, the plunger is pushed all the way down to the second “hard” stop. To practice, place a plastic tip on the pipette, push the plunger to the first stop, submerge the pipette tip into the distilled water and gently allow the plunger to return to its original position. Look at the plastic tip and note how much distilled water has been taken into the tip. Discharge the distilled water back into the container of distilled water and repeat. Did you get the same amount of distilled water drawn into the tip as the first time? Continue practicing until you feel confident that you are operating the pipette properly. PART I. Set up the computer
PART II: Calibrate the pH ElectrodeNote: electrodes are delicate and expensive sensors, which can easily crack. Do not tap or drop it. When placing it in a beaker, do so carefully.
Units Conversion
PART III: Test the Potential BuffersImportant: Click on the single-cursor mode icon for the rest of this experiment. Solutions to test: Saline, Phosphate Buffered Saline (PBS), 5% Bovine Serum Albumin (BSA) in PBS, 10X sheep blood plasma in PBS, 10X sheep whole blood in PBS For each solution to be tested:
Lab Clean UpWhen the buffer part of lab is complete, please remove small labels from beakers and place in the trash. Rise the beakers several times with water and return them to their original locations to dry. Please leave the electrode in the same condition is was found: place electrode back in its small beaker with lid on (please make sure buffer solution is in the container because the electrodes must not dry out), and place the electrode storage bottle upright inside a larger beaker. Blood glucose testingWhen buffer work in lab has completed, TAs will offer students the opportunity to participate in a blood glucose test. Students will record their last meal and blood glucose value on the lab report; however, this part of the lab is volunteer only, since students must draw blood. TAs may offer one point extra credit for participation in this activity. Students who decide to participate must sign the consent form at the TA podium. Please cite: Haen Whitmer, K.M. (2021). A Mixed Course-Based Research Approach to Human Physiology. Ames, IA: Iowa State University Digital Press. https://iastate.pressbooks.pub/curehumanphysiology/ What are blood buffers give examples?Human blood contains a buffer of carbonic acid (H2CO3) and bicarbonate anion (HCO3-) in order to maintain blood pH between 7.35 and 7.45, as a value higher than 7.8 or lower than 6.8 can lead to death. In this buffer, hydronium and bicarbonate anion are in equilibrium with carbonic acid.
What are the 3 blood buffers?The body's chemical buffer system consists of three individual buffers: the carbonate/carbonic acid buffer, the phosphate buffer and the buffering of plasma proteins.
Which of the following is the blood buffer system?The pH of blood is maintained at ~ 7.4 by the carbonic acid – bicarbonate ion buffering system.
What is the most common buffer in blood?The Carbonic Acid-Bicarbonate buffer system is the most important buffer for maintaining the pH homeostasis of blood. In this system, gaseous metabolic waste carbon dioxide reacts with water to form carbonic acid, which quickly dissociates into a hydrogen ion and bicarbonate (see below).
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