pH regulation and acid-base homeostatic are essential for normal physiology and biochemical processes. Acid-base balance refers to the mechanisms available in the body which maintains fluids close to neutral pH, ensuring the body functions correctly. Typically, hydrogen ions (H+) within the body are kept within the physiological reference range (40 +/- 0.05nmol/L), ensuring, a systemic acid-base balance and a regulated pH ~7.4. The homeostasis is primarily mediated by pH sensors located in the medulla oblongata within the brain and possibly the kidneys, connected via negative feedback loops to effectors in the renal and respiratory systems. Daily, the body produces 60mmol of surplus H+ from metabolic processes and produces 20,00mmol of CO2 from oxidative metabolism. To maintain the H+ homeostasis 3 main mechanism is required; buffer systems, renal mechanism and the respiratory mechanism. According to Palange (2007) in 110 consecutive patients, 56% of them showed a disturbance in the acid-base balance. However, the patients involved in the experiment were 68 +/- 8 years old, the control group is rather precise, which could affect the results and the validity. Increasing the range of the age group will consider more ages groups and will provide accurate results. ‘Children and elderly are more at risk of metabolic acidosis due to fluid and electrolyte imbalances’ Hamm (2015.)
Acid- base disorders.
Alterations to the pH, disturbing the acid-base balance can affect the homeostatic of the body, presenting a number of acid-base disorders. Research proves that the lower the pH equates to an increase in H+ concentration and acidosis of the blood and the higher the pH equates to a lower H+ concentration and alkalosis of the blood. There are two main types of disorders; metabolic a primary disorder linked to change in HCO3 and respiratory linked to change in PCO2 (Ahmed, Nessar (2010). Ayer (2015) agreed and stated, acidosis is defined as an arterial pH <7.35 and/or a low HCO3 concentration and alkalosis is defined by pH above 7.45 and/or a raised HCO3 concentration. Distributions in H+ concentration can be responsible for metabolic or respiratory disorders'. Therefore, a patient suffering from chronic lung disease has the decreased ability to breathe, consequential, creating problems with CO2 exchange increasing the PCO2 and may also result in an increase in carbonic acid, reducing the pH of the bloods. Acid-base imbalance can present itself in many forms and also a secondary illness. 'Patients can often experience a combination of 1 of the 4 disorders. Metabolic acidosis/alkalosis can occur separately or in combination with respiratory acidosis/alkalosis as a double acid-base disorder. A triple acid-base disorder is also possible; metabolic acidosis, metabolic alkalosis, respiratory acidosis or alkalosis. However, the combination of respiratory acidosis and alkalosis doesn't occur' Hamm (2015). Ayers (2015) and Hamm (2015) claim that metabolic acidosis is the most common among patients with insulin- dependent diabetes mellitus and chronic renal failure regardless of age. However, children and elderly are more at risk of metabolic acidosis due to fluid and electrolyte imbalances. Whereas, Farlex (2012) stated there is no known effect of age, ethnicity or gender-linked to acid-base imbalance. All 3 resources were academically correct and relevant, however, Ayer (2015) and Hamm (2015) are newer research presenting results with a higher validity rate rather than Farlex (2012). Clinical consequences to acid-base disorders. There are several clinical consequences to acid-base disorders; cardiovascular, metabolic and neurologic (Figure 2). As seen in figure 3 Lewis (2016) lists the main clinical consequences that may occur with the different acid-base disorders. Lewis (2016) disagrees with the main clinical consequences mentioned above. However, this could be due to research taking place at different years, or a matter of opinion. Buffer systems. Buffer systems, are usually the first mechanism to respond to disturbances to the pH. A substantial number of buffers come from bone and proteins, the physiologically most important one is the bicarbonate-carbonic acid buffer system which is coupled to the respiratory system. Ayers (2015) suggests that 'carbonic acid, a weak acid created from CO2 and H20, and bicarbonate its conjugate base is equilibrium with H+. HCO3- + H+ ? H2CO3- When H+ concentration increased, the concentration of bicarbonate will decrease, raising the CO2 gas as the acid is buffered'. Therefore, if there is an excess of acid or base the buffer will be able to release more base or acid to neutralise the pH. Agreeing with Ayers (2015) and expanding Batcheler (2013) explained that Carbonic acid breaks down to create H+ and bicarbonate. Once broken down the H+ then binds to haemoglobin and the bicarbonate passes back through the plasma. These findings are accurate, however, there is a possibility that a condition can affect the buffer system. 'Diabetic ketoacidosis is a serious condition that occurs when the body produces an excess of blood acids called ketones, this condition develops from the deficiency of insulin' Chandrasekara (2014). The excess acid will be too much for the buffer system alone to correct so may require additional medication. Respiratory mechanisms Respiratory mechanisms are the second fastest line of response, responding within minutes, estimated 6-12 hours for the mechanism to be fully effective. Alveolar ventilation usually removes ~15000mmols CO2 per day produced from normal oxidative metabolism, which maintains arterial PCO2 ~40mmHg. The respiratory mechanism acts as compensation when the CO2 level increase or decrease. 'Typically, with decrease or increase in CO2 production, the alveolar ventilation will respond, increasing or decreasing to maintain PCO2 and balancing the pH Hamm (2015). Ayer (2015) agreed with Hamm (2015) research and expanded; 'chemoreceptors cells located in the medulla oblongata are sensitive to pH and PCO2 levels, responding to alterations of pH in cerebral interstitial, which controls the alveolar ventilation'. As a result of this, a slight increase in plasma CO2, decreasing the pH, encourages stimulation of ventilation, rapidly returning PCO2 back too normal. 'Metabolic acidosis also increases ventilation, too lower PCO2, responding to the decrease in cerebral interstitial pH' Hamm (2015). Both references used were sourced from appropriate academic journals and both publishing within 10 years, however, the second reference provided more information and went into more detail. Renal mechanisms Renal mechanisms are the slowest line of response, 2-3days. Renal compensation is triggered via respiratory disorders. The kidneys support the buffer systems by; secreting or absorbing H+ or HC03, controlling the secretion of acids and bases and creating additional buffers. Both Ahmed (2010) and Weiner (2013) claimed 'the kidneys have two important roles in homeostasis; reabsorption of filtered bicarbonate and generation of new bicarbonate. The most common acid-base disturbance that occurs on a daily basis is excess acid from metabolism of proteins. The relationship between endogenous acid production and body mass happens due to protein metabolism being parallel to body mass, and endogenous protein metabolism leads to endogenous acid productions. The build-up of acid is buffered from intracellular and extracellular buffers, predominantly HCO3. Acid-base homeostasis over a period of time requires new production of alkali buffers, to replace those consumed by the daily acid excretion process'. Bicarbonate recovery and regeneration HCO3 is easily filtered via the glomerulus into the tubular lumen, the lumen walls are impermeable to HCO3, preventing it passing back through. Nevertheless, the reabsorption of the filtrated bicarbonate is mandatory, or consequentially the level of HCO3 within the body would rapidly decrease and severely destroy the buffering capacity. H+ are exchanged with sodium when secreted into the lumen, maintaining a neutral charge. H2CO3 is the product of H+ and filtered HCO3 combined within the tubular lumen. The H2CO3 detaches to form CO2 and H20, catalyzed by carbonic anhydrase. As the CO2 concentration rises, CO2 diffuses along the concentration gradient travelling into the renal tubular cells. Then it combines with H20 forming HCO3, allowing it to diffuse back into the ECF and returning to the buffer stock. This cycle repeats due to the formed H+ actively secreted into the tubular lumen in exchange for sodium. ~90% of filtered HCO3 is absorbed in the proximal tubule, the rest is absorbed into the distal tubules and collecting ducts, Ahmed (2010). This mechanism prevents the loss of HCO3. Hamm (2015) agreed with Ahmed (2010) and described bicarbonate regenerate as the same process as bicarbonate recovery, although there is a clear loss of H+ during the process. Conclusion The purpose of this report was to discuss the possible acid-base balance disturbances that can occur and the mechanisms that rectify the changes. The disorders were a result of a change in the body's pH balance, triggering the mechanism. The 4 main disorders discussed were; metabolic acidosis, metabolic alkalosis, respiratory acidosis and respiratory alkalosis. Buffer systems, renal mechanism and respiratory mechanisms all worked together or aside each other to correct the pH balance. On the other hand, a mechanism may not always be successful returning the pH back to ~7.4, meaning medication is required. For example, a common agent used to treat metabolic alkalosis is Diuretics, Acetazolamide (Diamox). The agent inhibits carbonic anhydrase, the enzyme catalyzes the hydration of CO2 and dehydration of carbonic acid. As a result of this, the Inhibition will reduce the reabsorption of NaHCO3 in the proximal tubule, leading too natriuretic, bicarbonate, diuresis, and a reduced serum bicarbonate level, Thomas (2017). Therefore, there are many different routes to correcting an acid-base balance disorder.