Kidneys and acid base Flashcards
Why does H+ conc of body fluids need to be constant?
Avoid detrimental changes in proteins, enzyme structure and cellular structure
What is the equation of removing H+ from the body by the lungs?
Describe acid secretion by the kidneys
free H+ conc in urine is very low
Most H+ secreted bound to filtered buffers e.g., phosphate or ammonia
Must absorb all filtered HCO3- as loss = same effect as adding H+ to plasma
What organs are involved in pH regulation?
lungs
liver
kidney
Describe bicarbonate reclamation in PCT cells
HCO3- is freely filtered into tubular lumen
H+ enters tubular lumen in via Na/H pump
HCO3- and H+ react => CO2 (under influence of carbonic anhydrase)
Resulting CO2 diffuses into PCT cells, dissociates in H+ and HCO3-
HCO3- is reabsorbed into the blood via Na3HCO3- co transporter
H+ returns to tubular lumen to react with more HCO3-
Describe acid secretion in PCT cells
Kidney has ability to excrete H+ as ammonium (NH4+)
New HCO3- generated in this process
What factors control bicarbonate reabsorption in the PCT?
luminal HCO3- conc
Luminal flow rate
Arterial pCO2
Angiotensin II
Describe acidification in the distal tubule
H+ secreted in cortical and medullary collecting tubules by active secretion
H+ combine with phosphate buffers => secreted
What factors cause increased H+ secretion and HCO3- reabsorption in the kidney?
Increased pCO2
Increased H+, decreased HCO3-
Decreased ECF volume
Increased angiotensin
Increased aldosterone
Hypokalaemia
What factors cause decreased H+ secretion and HCO3-reabsorption
Decreased pCO2
Decreased H+, increased HCO3-
Increased ECF volume
Decreased angiontensin
Decreased aldosterone
Hyperkalaemia
Describe the effect increased pCO2 has on hydrogen excretion in the kidney
Tubular cells respond to increased pCO2 of blood by increased rate of H+ secretion
What is the effect of decreased ECF volume on hydrogen excretion in the kidney?
Decreased ECF vol stimulates sodium reabsorption => increased H+ secretion and HCO3- reabsorption:
- increased angiotensin II levels stimulates activity of Na+/H+ exchanger
- increased aldosterone levels stimulates H+ secretion by the cortical collecting tubules
- can cause alkalosis due to excess H+ secretion and HCO3- reabsorption
How does plasma potassium effect hydrogen excretion in the kidney?
Hypokalemia stimulates H+ secretion in proximal tubule:
- decreased plasma K => increases H+ conc in renal tubular cells
- stimulates H+ secretion and HCO3- reabsorption
- => alkalosis
Hyperkalemia inhibits H+ secretion in proximal tubule:
- hyperkalemia decreases H+ secretion and HCO3- reabsorption => acidosis
what are the uses of arterial and venous blood gas measurement
Arterial:
- assessing respiratory status
- may not reflect changes in periphery
Venous:
- used in metabolic scenarios
- low pH and higher pCO2
- may not be accurate in low flow states
Fill in the table for changes in arterial pH
