Transport In Mammals - Session 4

As we have studied, carbon dioxide is transported from the tissues to the lungs for exhalation. In red blood cells, carbonic anhydrase helps regulate the transport of carbon dioxide from the tissues to the lungs for exhalation. As carbon dioxide is produced in the tissues, it diffuses into the red blood cells. Inside the red blood cells, carbonic anhydrase converts carbon dioxide into bicarbonate ions and protons.

This process of converting carbon dioxide into bicarbonate ions helps maintain the pH of the blood. It facilitates the transport of carbon dioxide. In the lungs, where carbon dioxide needs to be eliminated, the carbonic anhydrase catalyzes the reverse reaction. It converts bicarbonate ions and protons again into carbon dioxide. The carbon dioxide is then exhaled out of the body.

The chloride shift is a physiological process that occurs in red blood cells to maintain the equilibrium of ions. It assists in the transport of carbon dioxide in the bloodstream. This process is essential for regulating blood pH and ensuring efficient oxygen and carbon dioxide transport. Shown here, is a detailed explanation of the chloride shift.

As tissues undergo metabolic activities, they produce carbon dioxide as a waste product. Carbon dioxide is generated in the cells as a result of cellular respiration. The carbon dioxide needs to be converted into a soluble form that can be carried in the bloodstream. This conversion primarily occurs in red blood cells.

Carbon dioxide diffuses from the tissues into red blood cells. Inside the red blood cell, an enzyme called carbonic anhydrase catalyzes the conversion of carbon dioxide and water into carbonic acid. Carbonic acid then rapidly dissociates into bicarbonate ions and protons. The formation of bicarbonate ions generates a surplus of negative charges within the red blood cell. This can create an electrochemical imbalance if not compensated.

To prevent the intracellular buildup of negative charges, the red blood cells use the chloride shift. This is where the chloride ions are exchanged for bicarbonate ions. The chloride ions are transported into the red blood cells from the plasma, mainly via an antiporter. Antiporter is a protein that exchanges one ion for another. The bicarbonate ions are diffused into the plasma. This exchange helps maintain the electrochemical equilibrium within the cell.

Blood plasma is the yellowish fluid component of blood in which blood cells are suspended. It makes up about fifty five percent of the total blood volume. It is composed mainly of water along with various dissolved substances, including electrolytes, hormones, waste products, and proteins. Some important proteins found in blood plasma include albumin, globulins, and fibrinogen.

Blood plasma plays a crucial role in transporting nutrients, hormones, and waste products throughout the body. It maintains blood pressure. It also serves as a medium for various physiological processes. Blood plasma contains antibodies and clotting factors, which are vital for the immune response and blood coagulation.

The oxygen dissociation curve is a graphical representation of the relationship between the partial pressure of oxygen and the oxygen saturation. The oxygen saturation represents the percentage of hemoglobin molecules that are bound to oxygen. Partial pressure of oxygen is a measure of the concentration of oxygen in the blood. It is the pressure exerted by oxygen molecules in a gas mixture. It is used to determine how much oxygen is available to bind to hemoglobin.

The oxygen dissociation curve is also called oxyhemoglobin curve. This curve is essential in understanding how hemoglobin binds to and releases oxygen in response to changes in oxygen pressure. The oxygen dissociation curve is typically sigmoidal. This means that there are distinct regions of the curve where small changes in partial pressure of oxygen result in significant changes in oxygen saturation.

Hemoglobin has high affinity for oxygen in the lungs. This is because partial pressure of oxygen is high in the lungs. The flat upper portion of the curve represents the efficient loading of oxygen in the lungs. Steep middle portion represents the efficient unloading of oxygen in the tissues where it is needed.

At low partial pressure levels, hemoglobin has a low affinity for oxygen. This means that it readily releases oxygen, ensuring that oxygen is delivered to the cells that need it. In the flat lower portion of the curve, the oxygen saturation remains relatively constant although significant drops in the partial pressure can occur.

The oxygen dissociation curve can shift to the left-side or right-side under different conditions. A left-shift in the oxygen dissociation curve implies that the hemoglobin has a higher affinity for oxygen. A rise in the pH, or a more alkaline environment, shifts the curve to the left. This condition makes hemoglobin more likely to bind to oxygen. A decrease in temperature also shifts the curve to the left.

A right-shift in the oxygen dissociation curve indicates that hemoglobin has a lower affinity for oxygen. A decrease in the pH, or a more acidic environment, such as during exercise shifts the curve to the right. This condition makes hemoglobin more likely to release oxygen to the tissues where it is needed.

An increase in the concentration of carbon dioxide in the blood, as seen during exercise, shifts the curve to the right. Higher carbon dioxide levels result in lower blood pH. Low levels of pH decreases the affinity of hemoglobin for oxygen. A rise in temperature also shifts the curve to the right.