Acid-base balance Flashcards

Question

What happens when H+ is secreted into the tubular fluid?

Answer 1

Combines with urinary buffers: | phosphate or ammonia

Answer 2

Alkalosis | Type B intercalated cells

Answer 3

Through synthesis and excretion of ammonium ions Ammoniagenesis occurs mainly in the PCT - generated ammonium secreted and HCO3- allow to re-enter the bloodstream Produced through metabolism of glutamine Glutamine → glutamic acid (glutaminase) Glutamic acid → α-ketoglutarate (glutamate dehydrogenase) Each step yields a molecule of NH4+ and HCO3- HCO3- leaves basolaterally NH4+ leaves cell, substituting for H+ in the Na+/H+ antiporter Much of the secreted NH4+ from the PCT is reabsorbed in the TALH, substituting for K+ in NKCC2 (as well as the +ve transepithelial voltage means that there is paracellular absorption of NH4+) The NH4+ reabsorbed by the TALH accumulates in the medullary interstitium. From there it is secrered into the tubular fluid by the collecting duct NH3 which diffuses into the collecting duct through Rh glycoproteins from medullary interstitium becomes trapped as it is protonated in the acidic tubular fluid (increased diffusion trapping as pH falls luminally). This leads to the excretion of the NH4+. Important as should the NH4+ instead be reabsorbed, it is neutralised to produce urea (consuming HCO3-) in the process, meaning it doesn’t result in the net excretion of acid

Answer 4

the intake and output of all substances that can affect [H+]

Answer 5

Stewart model based upon three ‘independent’ variables that determine pH: the strong ion difference (SID), the total weak acids ([ATot]) and pCO2

Answer 6

hose that fully dissociate in plasma, including sodium, potassium, and chloride, thus the SID can be calculated by subtracting the sum of all the strong anions from the sum of all the strong cations: SID ≈ [Na+] + [K+] – [Cl-]

Answer 7

Because SID is dependent on plasma electrolyte concentration, it is largely controlled by the kidneys, and under normal physiological conditions is approximately equal to 40mEq/L

Answer 8

[ATot] is the concentration of weak acid, composed in the plasma mainly of albumin and phosphate It can therefore be defined as the total protein in the blood and as such, the liver and haematopoietic system are crucial in its control

Answer 9

Davenport diagrams

Answer 10

Respiratory deviations are compensated for by renal mechanisms, whereby plasma [HCO3-] is either increased or decreased (in acidosis or alkalosis respectively), which helps to return plasma pH to normal Comparatively, the compensatory response for metabolic deviations is mediated by alterations in the rate of ventilation, thereby increasing or reducing pCO2 to bring about a change in plasma pH of the opposite nature

Answer 11

Low [HCO3-]

Answer 12

``` 1- Hyperkalaemia 2 - Intense exercise 3 - Diarrhoea → loss of HCO3- 4- Diabetic ketoacidosis 5 - Renal tubular acidosis → where the kidney fails to either reabsorb or regenerate HCO3- ```

Answer 13

Respiratory compensation | Characteristic Kussmaul breathing n DKA -hyperventilation

Answer 14

- sodium bicarbonate

Answer 15

Characterised by high pCO2 and a compensatory high [HCO3-]

Answer 16

- Reduced ventilation (e.g. kyphoscoliosis) - Opoid analgesics or damage to respiratory centre - COPD or asthma

Answer 17

mechanical ventilation, however it may be possible to treat the cause of the disturbance – for example the administration of salbutamol (a β2-agonist, hence bronchodilator) to asthmatics.

Answer 18

Upregulation of ammonia genesis (increasing formation of NH3 buffer) Increased expression of apical H+/K+ ATPase in type A intercalated cels in order to increase H+ secretion and thus increase HCO3- reabsorption

Answer 19

Elevated [HCO3-]

Answer 20

- vomiting (loss of HCl) - hyperaldosteroism or Conns (upregulation of Na+/K+ ATPase, ENac, increase Na+ reabsorption and K= excretion → hypokalaemia → H+ secreted in order to attempt to take up K+) - diuretics

Answer 21

Respiratory Central chemoreceptors detect increased pH and cause a decreased ventilatory drive → hypoventilation This raises levels of pCO2 in the body, which is used to form the carbonic acid intermediate, thus decreasing pH This hypoventilation however may cause hypoxia, which would stimulate the peripheral chemoRs to increase ventilatory drive, nullifying any effects of the alkalaemia on ventilatory drive This is thought to account for the variability in patients’ pCO2 levels in respiratory alkalosis This is important clinically as patients presenting with hypoxaemia and hypercapnia may be incorrectly diagnosed with respiratory failure, with the underlying respiratory alkalosis going undetected

Answer 22

oral ammonium chloride

Answer 23

hyperventilation – can occur due to anxiety (in which there is increased respiratory drive) or ascent to high altitude, as hypoxia stimulates peripheral chemoRs which increase ventilatory drive as a result This causes more CO2 to be “blown off”, decreasing [H+] of the plasma

Answer 24

Long-term compensation can occur in the kidneys through the activation of B-type intercalated cells, which have the reverse orientation to type A intercalated cells, and so secrete HCO3- and retina H+, causing elevated levels of [HCO3-]

Answer 25

carbonic anhydrase inhibitors (e.g. acetazolamide), are often used in the treatment of altitude sickness. These inhibit the uptake of HCO3- in the kidney, thereby helping to correct alkalosis.