54 Acid base homeostasis Flashcards
This portion of the nephron secretes H+ and reabsorbs bicarbonate?
The proximal tubule
T/F. 60 % of filtered bicarbonate reabsorbed in the PT. The rest is reabsorbed in the ascending loop of henle or the collecting duct
False. ~85% is reabsorbed in the PT. The rest is reabsorbed in the ascending loop of henle or the collecting duct.
Note: The amount that is reabsorbed varies depending on whether acidosis or alkalosis is occurring
T/F. For each bicarbonate that is reabsorbed in the PT, one H+ is secreted. However, the H+ does not contribute to the pH of the urine
True
What are the locations of carbonic anhydrase in the kidneys?
In the tubular cells and on the membrane brush border
T/F. In the presence of a Carbonic anhydrase inhibitor, you cannot reabsorb bicarbonate, leading to increased excretion (pH of blood will decrease)
True
T/F. After all bicarbonate has been reabsorbed, the remaining H+ in the lumen will contribute to the pH of the filtrate.
True
H+ is secreted into the lumen. This H+ then combines w/ a phosphate buffer and is excreted as a titratable acid (w/ phosphate buffer)
Titratable acid (method of managing urine pH)
This is the major adaptation to acidosis (acid load). Acidosis promotes enzymatic glutamine breakdown into bicarbonate and ammonia. Bicarbonate reabsorption helps control acidosis. Ammonia is transported into the lumen (antiporter), where it acts as a base and helps manage the pH
Ammonia (method of managing urine pH)
T/F. The kidney synthesizes glutamate. It then activates enzymatic breakdown of glutamate, which is degraded into bicarbonate and ammonia. The ammonia is transported into the tubular lumen where it neutralizes the pH of the urine
False. The kidney synthesizes glutamine. It then activates enzymatic breakdown of glutamine, which is degraded into bicarbonate and ammonia. The ammonia is transported into the tubular lumen where it neutralizes the pH of the urine
These cells reabsorb Na+ and secrete K+
Principal cells
These cells control H+ and HCO3- secretion or reabsorption
Intercalated cells
These cells secrete H+ ions into the tubular lumen. Occurs by V-ATPase H+ secretion and K+/H+ antiporter (both are active transport). H+ is provided by the carbonic anhydrase reaction. Bicarbonate created in this process is reabsorbed and contributes to the stabilization of blood pH
Alpha-intercalated cells
These cells secrete bicarbonate in the DT and collecting ducts
Beta-intercalated cells
Which type of intercalated cells are increased during acidosis?
Alpha. B/c this transports H+ into the filtrate while reabsorbing bicarbonate that can contribute to pH neutralization
Which type of intercalated cells are increased during alkalosis?
Beta. B/c these cells increase excretion of bicarbonate
T/F. The RAAS also influences the H+ concentration. Ang II promotes Na+ reabsorption in the PT. It does this by promoting the Na+/H+ antiporter expression.
True
This hormone promotes H+ ion secretion by promoting H+/K+ antiporter (bicarbonate is then reabsorbed).
Aldosterone
Excessive stimulation of the RAAS is associated w/ ___
Alkalosis
What is the normal blood pH?
7.4
Normal bicarbonate concentrations are ___
Normal CO2 levels are ___
bicarbonate: 24 mEq/L
CO2: 40 mmHg
T/F. The kidney is able to regulate bicarbonate and H+ by: reabsorbing and generating bicarbonate and secreting H+
True
A primary disturbance that has its origins in CO2 mismanagement
Respiratory disturbance
A primary disturbance that has its origins in bicarbonate (or metabolic ion) mismanagement
Metabolic disturbance
Increase H+ secretion, increase bicarbonate reabsorption, and produce new bicarbonate (a product of increased H+ secretion)
Renal compensation for acidosis
decrease H+ secretion, decrease bicarbonate reabsorption, increased excretion of bicarbonate in urine (increase filter load past the reabsorptive capacity)
Renal compensation for alkalosis
T/F. Alkalosis usually presents w/ hyperkalemia
False. Alkalosis usually presents w/ hypokalemia (low ICF potassium levels)
T/F. Acidosis usually presents w/ hyperkalemia
True
This hormone stimulates the Na+/H+ exchanger. This increases the capacity of the kidney to reabsorb bicarbonate (H+ combines with bicarbonate in the tubular lumen, which is then converted into water and CO2 by carbonic anhydrase… CO2 then diffuses into the tubule cells, which convert it back into bicarbonate and reabsorb it)
Angiotensin II
The difference b/t measurable and non-measurable cations in the blood. Na+, Cl-, and bicarbonate are the only measure anions/cations of the blood
Anion gap
Occurs when Cl levels have increased to compensate for the low bicarbonate levels. This presents as a normal anion gap in a patient that is known to have metabolic acidosis
Hyperchloremic metabolic acidosis
Occurs when the unmeasured anions are increased. Caused by lactic acidosis, ketoacidosis, and alcoholism
Increased anion gap (normochloremic)
What is the primary adaptive response of the kidney to sustained acidosis?
Ammoniagenesis (production of ammonia, which can buffer the excreted H+)
Optimal recovery from a severe metabolic acidosis (or alkalosis) is most dependent on what?
The rate of H+ renal excretion
