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

pH and Hydrogen ion concentration

The acidity or alkalanity of a solution depends on its hydrogen ion (H+) concentration. An increase in H+ leads to acidity; whereas a decrease in H+ ions leads to alkalanity. Despite the act that; acids are produced daily, the H+ concentration of body fluids is small (0.0004mEq/L) and maintained within a narrow range to ensure optimal cellular function. An acid solution has a pH <7 and alkaline solution pH > 7. Blood is slightly alkaline (7.35-7.45). If it drops below 7.35, the patient has acidosis, even though the blood may never become truly acidic. if the blood pH is greater than 7.45, the person has alkalosis

Acid-base mechanism

Normally the body has 3 main mechanisms to regulate the acid-base balance to maintain a pH between 7.35-7.45. These systems are the buffer systems, the respiratory system and the renal system. The regulatory mechanisms react at different speeds.Buffers react immediately. The respiratory system responds in minutes and reaches maximum effectiveness in hours. The renal system takes 2 or 3 days to respond maximally, but the kidneys can maintain balance indefinitely in patients with chronic imbalances

Buffer system

The buffer system is the fastest acting system and the primary-regulator of acid-base balance. Buffers act chemically to change strong acids into weaker acids or to bind acids to neutralize their effect. this minimizes the effect of acids on blood untill its excretion. The body buffers neutralizes acid load better than base excess. Buffers cannot maintain pH without proper functioning of respiratory and renal sytem

A buffer consists of a weakly ionized acid or a base and its salt. The buffers in the body include carbonic acid -bicarbonate, monohydrogen-dihydrogen phosphate, intracellular and plasma protein, and hemoglobin buffers. The cell can also act as a buffer by shifting hydrogen in and out of a cell. With an accumulation of H+ ions in ECF, the cells can accept H+ in exchange for another cation (for e.g: potassium ion)

The carbonic acid- bicarbonate(H2CO3/HCO3) buffer system neutralizes HCl acid in the following manner:

NaH2CO3 + HCl= NaCl +H2CO3

(strong base + strong acid) = salt + weak acid)

The phosphate buffer system is composed of sodium and other cations in combination with monohydrogn phopshate or dihydrogen phosphate. The intracellular buffer system acts in the same manner as bicarbonate buffer system. Bases neutralises strong acids forming sodium chloride and sodium biphosphate. Conversely, if a strong base such as NaOH, sodium dihydrogen phosphate neutralizs it into a weaker base (Na2HPO4) and H2O

Respiratory System

The lungs help maintain a normal pH by excreting CO2 and water, which are byproducts of cellular metabolism. When released into the circulation CO2 enters RBCs and combines with water to form H2CO3 . This H2CO3 dissociates into H+ and HCO3-. Hemoglobin buffers the free H+ and HCO3- and dissociates in the plasma. This process is reversed in the pulmonary capillaries, forming CO2 that is then excreted by the lungs

The amount of CO2 in the blood directly relates to carbonic acid concentration and subsequently to H+ concentration. With increased respirations, more carbondioxide is expelled and less remaind in the blood . This leads to less H+  and less carbonic acid in the blood. With decreased respirations,, more carbondioxide remains in the blood and thus more carbonic acid

The respiratory center in the medulla of the brainstem controls the rate of excretion of carbondioxide. If increased amount of H+ are present , the respiratory center stimulates an increased rate and depth of breathing (hyperventillation). If the center senses low H+ or CO2, respirations are inhibited(hypoventillation)

Renal system

Under normal conditions body depends on the kidneys to reabsorb and conserve all of the bicarbonate they filter and excrete a portion of the acid produced by cellular metabolism. The 3 mechanisms of acid elimination are

1. Secretion of free hydrogen ions into the renal tubules
2. Combination of H+ to NH3 to form ammonium (NH4+)
3. Excretion of weak acids

The kidneys normally excrete acidic urine with a pH of 6. As a compensatory mechanism, pH of urine varies between 4-8

Alterations in acid-base balance

Respiratory acidosis

It occurs whenever a patient hypoventilates, leads to retention of carbondioxide , resulting in accumulation of carbonic acid in the blood

Common Cause	pathophysiology	Lab findings
Respiratory acidosis COPD Barbiturate or sedative overdose Severe pneumonia Respiratory muscle weakness	carbondioxide retnetion from hypoventilation Compensatory mechanism is bicarbonate retention by kidneys	decreased plasma pH Increased partial pressure of carbondioxide HCO3- normal (uncompensated) increased bicarbonate(compensated) Sample ABG uncompensated pH 7.31 paCO2- 54 mm Hg HCO3- 25 mEq/L
Respiratory Alkalosis Hyperventilation (fear, anxiety, exercise, fever) Stimulated respiratory center Hypermechanical ventillation	Increased carbondioxide excretion from hyper ventillation Compensatory response is increased bicarbonate excretion by kidneys	Increased plasma pH Decreased partial pressure of carbondioxide Bicarbonate normal (uncompensated) Decreased bicarbonate (compensated ) Sample ABG uncompensated pH 7.52 paCo2- 27 mmHg HCo3- 24 mEq/L