Homeostasis by the kidney- Acid-Base balance Flashcards
What are the 2 mechanism of dealing with the acid load in the body
Buffering
Elimination
What is used in mechanisms of buffering when dealing with acid load in the body
Bicarbonate in Extracellular Fluid (ECF)
HPO42- in Intracellular Fluid (ICF)
CO3 2- in Bones
How is the acid load in the body dealt with through elimination
Increased respiratory drive to increase CO2 excretion
Acute response
Increased hydrogen ion secretion by kidneys
Chronic sustained response
What is the acute response of the body to acid load
increased respiratory drive to increase CO2 excretion
What is the chronic sustained response to acid load
increased hydrogen ion secretion by the kidneys.
Homeostasis maintains the pH of the ECF between
7.35 - 7.45
plasma ph level below 7.35 is _____
acidosis
plasma levels rise above 7.45 is __
Alkalosis
Alterations outside these normal plasma pH range affects all body systems and result in
coma, cardiac failure and circulatory collapse
What does Henderson-Hasselbalch Equation explain in acid base balance?
Inverse relationship between pH and plasma concentration of CO2 i.e. when one goes up the other goes down and vice versa. So when pCO2 increases, e.g. in COPD, pH decreases (acidosis) as CO2 reacts with water to form carbonic a
What are the 2 main sources of acid generations in the body
carbolic (volatile) acids
Non-Carbolic (non-volatile) Acids
What are the sources of carbolic acids in the body
Generated from metabolism of carbohydrates and fats
Produced as CO2 and converted to H+ and HCO3-
Reconverted back to CO2 and eliminated by the lungs through loss of CO2
What the sources of non-carbolic (non-volatile) acids in the body
Generated from metabolism of sulphur containing amino acids
Buffered with HCO3- before eliminated by the kidneys through loss of H
What is the normal range of urine PH
4.6 - 8
What is the normal range of blood pCO2
4.7 - 6.0
What is the normal ranges of blood HCO3-
22 - 26 mmol/L
What are main sites of nephron where acid is excreted
proximal convoluted tubule and the intercalated cells of cortical collecting ducts
The kidney has limited acid secretions in form of
H+
______of filtered bicarbonate is reabsorbed back into systemic circulation
80-90%
How does the kidney excrete acid in the proximal convoluted tubule?
secrets H+ through the NaHE
NH3 + H+ –> NH4+ –> Glutamine –> alpha ketoglutarate –> 2HCO3
PH of the ultrafilterate falls from about 7.40 to ___ at the end of the proximal convoluted tubules
6.70
____ is the most prevalent filtered buffer in the distal nephron where urinary pH< 5.8 (pKa = 6.8)
HPO4-2
What is the name of the specialised cell lining the collecting duct
Intercalated cell type A
How is acid excreted in the cortical collecting duct?
Ammonium excretion both in the Proximal collecting ducts and direct diffusion of lipid soluble ammonia constitutes a major adaptive response to acid load
What is the effect of decrease in extracellular bicarbonate on the PH of the cell?
increases the gradient across basolateral membrane for bicarbonate diffusion out of the cell thereby lowering tubular cellular pH
What are the causes of metabolic acidosis
Loss of bicarbonate - Diarrhoea, Diuretic therapy
Ingestion of acid -Aspirin, Ethylene glycol, Methanol
Endogenous acid production - Lactic acidosis, ketoacidosis
Decrease acid excretion - Renal failure
Inadequate oxygen delivery resulting in anaerobic metabolism (lactic acid generation)
what are some examples of bicarbonate loss that can cause metabolic acidosis?
Diarrhoea, Diuretic therapy
what are some example of acid ingestion that can cause metabolic acidosis?
Aspirin, Ethylene glycol, Methanol
what are some example of endogenous acid production that can cause metabolic acidosis?
Lactic acidosis, Ketoacidosis
what is an example of decrease acid excretion that can cause metabolic acidosis?
renal failure
What is the main causes of metabolic alkalosis (increased HCO3 – concentration)?
Loss of acid
Loss of stomach acid (vomiting)
What is the main cause of respiratory acidosis
Chronic lung diseases- COPD, Pulmonary fibrosis
Causes Respiratory alkalosis (reduced CO2 concentration)
Hyperventilation- anxiety, pneumonia
Acute bronchial asthma
Case 1: A 28 year old diabetic lady is admitted with high blood sugars following a viral illness.
Arterial blood gas on admission:
PH 7.0 (7.35-7.45), PCO2 3.5 Kpa (4.7-6.0), Bicarbonate 18 mmol/L (22-26). what is the diagnosis
metabolic acidosis
Case 2: A 72 year old female is admitted with exacerbation of COPD.
Arterial blood gas on admission
PH 7.0 (7.35-7.45), PCO2 8.5 Kpa (4.7-6.0), Bicarbonate 32 mmol/L (22-26)
What is the diagnosis?
respiratory acidosis with compensation
Case 3: A 28 year with profuse vomiting for 2 days following a kebab meal.
Arterial blood gas on admission
PH 7.90 (7.35-7.45), PCO2 6.5 Kpa (4.7-6.0), Bicarbonate 32 mmol/L (22-26)
What is the likely diagnosis?
Metabolic alkalosis with compensation
Case 4: A 18 year anxious medical student is admitted with palpitations and light headedness a day before their final examination. He was tachypnoeic on admission with respiratory rate of 28/min.
Arterial blood gas on admission
PH 7.90 (7.35-7.45), PCO2 3.2 Kpa (4.7-6.0), Bicarbonate 20 mmol/L (22 -26).
What is the diagnosis
respiratory alkalosis with compensation
rise in plasma acid concentration results in the metabolic acidosis, what are the main compensatory mechanisms?
Hyperventilation
Renal hydrogen excretion
Buffering of acid in extracellular fluid, cells and bones
Rise in plasma bicarbonate concentration causes metabolic alkalosis, what are the main compensatory response to this?
hypoventilation
reduced bicarbonate reabsorption
elevated CO2 causes respiratory acidosis, what are the main compensatory response to this?
Increased renal hydrogen ion excretion
Increased buffering of carbon dioxide within haemoglobin
Loss of bicarbonate in urine
reduced CO2 causes respiratory alkalosis, what is the main compensatory response to this?
Increased renal bicarbonate excretion
In relation to cation shift during acid base imbalance, Metabolic acidosis is frequently associated with ______ and alkalosis is associated with
hyperkalaemia (high K+)
hypokalaemia (Low K+)
Treatment of acid-base imbalance
IV sodium bicarbonate 2.7% (especially useful if patient is volume deplete)
IV furosemide (especially useful if patient is passing urine and is volume replete)
Dialysis - if renal failure
what is the treatment of metabolic alkalosis
IV sodium/potassium chloride
What is the treatment of respiratory acidosis
Ventilation
What is the treatment of respiratory alkalosis?
Breathing into a paper bag (hyperventilating patients)
