Chemistry Review for MLT ASCP or AMT – Flashcards

Bicarbonate/carbonic acid

Because of its high concentration in blood,

the bicarbonate/carbonic acid pair is the most

important buffer system in the blood.

This buffer system is also effective in the lungs and in the kidneys in helping to regulate body pH. The other buffers that also function to help maintain body pH are the phosphate, protein, and hemoglobin buffer systems. The acetate buffer system is not used by the body to regulate pH.

Storage form of glucose is glycogen

Glycogen is

found in a variety of animal tissues, particularly

in the liver, and provides the storage form for

carbohydrates in the body. When energy requirements warrant it, glycogen may be broken down to glucose by a series of phosphorylating and related enzymes.

The hexokinase method for quantifying glucose

uses two coupled enzymatic reactions.

In the first reaction, which is catalyzed by hexokinase, glucose is phosphorylated by adenosine triphosphate, forming glucose-6-phosphate and adenosine diphosphate.

In the second reaction, glucose-6-phosphate dehydrogenase (derived from yeast) catalyzes the oxidation of glucose-6-

phosphate and the reduction of nicotinamideadenine dinucleotide phosphate. The amount of reduced NADPH formed is proportional to the glucose concentration in the sample. Thus, the greater the absorbance reading of NADPH at 340 nm, the greater is the glucose concentration.

If bacterial G-6-PD is used, the cofactor is NAD+ with the production of NADH.

Acetyl-coenzyme A

Carbonic acid (H2CO3)

C

PO2 and pH will increase; PCO2 will decrease

When a blood specimen is drawn for gas

analysis, it is important to avoid exposure of the

specimen to air because of the differences in the partial pressures of carbon dioxide and oxygen in air and in blood. The PCO2 in blood is much greater than the PCO2 in air. Hence on exposure of blood to air, the total CO2 and the PCO2 both decrease, causing an increase in pH. Similarly, the PO2 of air is much greater than that of blood, thus, the blood PO2 increases on exposure to air.

PO2 decreases; PCO2 increases; pH decreases

Glycolysis and other oxidative metabolic processes will continue in vitro by red blood cells when a whole blood specimen is left standing at room temperature. Oxygen is consumed during these processes, resulting in a decrease in PO2 levels. A decrease of 3-12 mm Hg/hr at 37°C has been observed for blood specimens exhibiting normal pO2 ranges. This rate of decrease is accelerated with elevated PO2 levels. Additionally, carbon dioxide is produced as a result of continued metabolism. An increase in pCO2 levels of approximately 5 mm Hg/hr at 37°C has been demonstrated. The increased production of carbonic acid and lactic acid during glycolysis contributes to the decrease in blood pH.

chloride

The red blood cell membrane is permeable to

both bicarbonate and chloride ions. Chloride ions participate in buffering the blood by diffusing out of or into the red blood cells to compensate for the ionic change that occurs when bicarbonate enters or leaves the red blood cell. This is called the chloride shift.

Increased Na+/H+ exchange by the kidneys

Respiratory acidosis is a disturbance in acid base balance that is caused by the retention of

CO2 by the lungs.

This imbalance is associated with such conditions as bronchopneumonia, pulmonary

emphysema, pulmonary fibrosis, and

cardiac insufficiency.

Respiratory acidosis is characterized by a primary excess in physically dissolved CO2, which is quantified by measuring the blood PCO2 level.

The primary problem leading to an increase in the PCO2 level is hypoventilation. This retention of CO2 alters the normal 20:1 ratio of cHCO3/PCO2, causing a decrease in blood pH level.

In respiratory acidosis, because the initial defect is associated with the lungs, the kidneys respond as the major compensatory system. The production of ammonia, the exchange of Na+ for H+ with the excretion of H+, and the reabsorption of bicarbonate are all increased in the kidneys to compensate for the malfunction of the lungs. In cases where the defect is not within the respiratory center, the excess of pCO2 in the blood can actually have a stimulatory effect on the center, causing an increase in the respiration rate. Thus compensation can also occur through CO2 elimination by the lungs.

decreased

metabolic alkalosis

Base excess is a measure of the nonrespiratory

buffers of the blood. They are hemoglobin, serum protein, phosphate, and bicarbonate. Therefore, base excess reflects an abnormality in the buffer base concentration.

Bicarbonate has the greatest influence on base excess, which is an indicator of metabolic function. The normal range for base excess is ±2.5 mmol/L.

A quick estimation of base excess is to subtract the average "normal" reference bicarbonate level set by the laboratory from the measured bicarbonate level

(if laboratory reference bicarbonate = 25 and patient's bicarbonate = 30, then base excess = (30 — 25) = + 5; if patient's bicarbonate = 20, then base excess = (20 — 25) = —5).

As demonstrated, a positive base excess is associated with metabolic alkalosis, and a negative base excess is associated with

metabolic acidosis.