Question

Compare the buffer, renal, cell polarity, and respiratory compensations for alkalosis and acidosis.Diagram the cells in the area of the Nephron where these occur.

Answer 1

1) Buffer system:- Buffers are the solutions which resist change in pH by addition of small amounts of acid or bases. any substance that can reversibly bind hydrogen ions can be labelled as a buffer. Buffers can neither remove hydrogen ions from the body nor add them to it. They can only keep hydrogen ions in a temporarily suspended form. The hydrogen ions have to be ultimately eliminated by the kidney.

Buffer​- + H+ ------> H-Buffer.

When hydrogen Ion concentration increases for whatever reason the reaction is driven to the right and more hydrogen ions combine with the buffer to form H-Buffer. With this mechanism, Hydrogen ion concentration doesn't increase as much as it would have otherwise.

Three major buffer systems are: Bicarbonate buffer (most important), Phosphate buffer, Protein Buffer.

Bicarbonate buffer:::: NaHCO3 and H2CO3 is the pridominent buffer system in extracellular fluid. Bicarbonate is regulated by the kidneys (metabolic component) whereas the acid part carbonic acid is regulated by respiratory control.

2) Respiratory regulation of pH

The respiratory response to the alter the plasma pH is very swift compared to the slow but steady response of the kidneys.

The rate of respiration and therefore the rate of removal of carbon dioxide is under the control of chemoreceptors in the respiratory centre located in the medulla of the brainstem and the receptors in the carotid and aortic bodies. Any decline in blood pH stimulates ventilation and this reflex hyperventilation removes carbon dioxide and lowers arterial pCO2 and hence by mass action reduces hydrogen ion concentration.

Role of hemoglobin:: hemoglobin serves as a strong buffer in the deoxygenated state and its buffering capacity increases during the flow of blood through the capillary beds as oxygen is lost to the tissues. Hemoglobin buffers hydrogen ions at the peripheral tissues and helps in the transport of carbon dioxide as bicarbonate with minimum possible change in pH. This process is called isohydric transport.

Generation of bicarbonate by RBCs

The CO2 gets converted into bicarbonate in erythrocytes. This bicarbonate is is diffused out and chloride ion enter into the cell to maintain electrical neutrality. This is called chloride shift.

The respiratory system responds to any change in pH very rapidly. But it is very short lived because hyperventilation cannot proceed for long.

3) Renal regulation of pH

The addition of a bicarbonate to the plasma lowers the plasma hydrogen ion concentration just as if hydrogen ion had been removed from the plasma. Similarly, the excretion of bicarbonate in the urine enhances the plasma hydrogen ion concentration just as if hydrogen ion had been added to the plasma. Basic mechanisms are following. These all occurs in Proximal Convoluted tubules.

• Reabsorption of bicarbonate

• Addition of new bicarbonate

• Excretion of ammonium ions

Disorder	Primary abnormality	Predicted compensation
Metabolic acidosis	decreased plasma HCO3	pCO2 fall by hyperventilation
Metabolic alkalosis	increased plasma HCO3	rise in pCO2 by hypoventilation
Respiratory acidosis	increased PCO2	rise in plasma HCO3 by renal reabsorption of HCO3
Respiratory alkalosis	decreased pCO2	fall in plasma HCO3 by lowered renal conservation of HCO3