Question

As PCO2 of the blood decreases, what happens to the urine H+ concentration as kidneys compensate for this change? (increase, decrease, or no change

Explain what the kidneys are doing that makes the H+ concentration change in this manner, and how this change acts as a compensation to the decreasing PCO2.

As PCO2 of the blood decreases, what happens to the urine HCO3- concentration?

Explain what the kidneys are doing that makes the HCO3- concentration change in this manner, and how this change acts as a compensation to the decreasing PCO2.

Give an example of the kind of physiological change that would CAUSE a decrease in [H+] DIRECTLY (without causing a change in PCO2 first).

What would such a condition be called?
Give an example of the kind of physiological change that would CAUSE an increase in [H+] DIRECTLY (without causing a change in PCO2 first).

What would such a condition be called?

If the root cause of the H+ concentration changes is an abnormality of the kidneys, how might the respiratory system respond to:

a. an increasing H+ concentration.

b. a decrease in H+ concentration.

Answer 1

1) decreases

• Respiration depends on sensitivity of respiratory control mechanisms , to change in blood pCO2 and pH.
• CO2 , which is mildly acidic ,  is waste from cells. which is excreted into blood along with other waste products
• Blood carries CO2 to lungs where it is exhaled.
• As CO2 accumulates in the blood , due to decreased PCO2 , the pH of blood decreases.
• The brain control this by increasing the speed of breathing.
• In the kidney, CO2 acted upon by carbonic anhydrase combines with water to form, H2CO3. Which dissociates into HCO3- and H+.
• he H+ ions secretion in the tubules increases. Also in the collecting duct, H+ ion secretion continues until the pH of the tubular fluid fall
• The excess H+ , in the urine is carried by two buffer system- phosphate buffer and ammonium buffer system.
• Which help in the excretion of excess H+ ions.

2)

• To carry excess H+ in the urine, 2 buffer systems are available in tubular fluid. They are:-
• 1)Phosphate buffer- It consist of mixture of HPO4- and H2PO4-. Both become concentrated in tubular fluid..
• Because of poor absorption and removal of water from tubular fluid.
• 2) Ammonium buffer system- It consists of NH3 and NH4+.
• Epithelial cells of PCT synthesis NH3, The secreted Nh3 combine with H+ to form NH4+
• This will decrease Nh3 concentration.
• Thus causes more diffusion of NH3
• If H+ was transported in combination with Cl-, the pH oof the tube will fall. HoweverNH3 combine with H and Cl to form NH4Cl - which is a weak acid and pH is not altered.

3) with decrease in PCO2 the urine concentration of HCO3 will increase to comensate the acidity by the kidney so as to enabling the expellsion of HCO3 ions

4)

• If H+ is added with HCO3, resulting in the formation of H2CO3. which can be removed by expiration of carbondioxide.
• But there is decrease in HCO3 during this process.
• In kidney tubules, H+ ions is secreted in a tubular fluid and one HCO3 is formed which moves into plasma  
• At high pH , H+ secretion in the tubules reduced and vice versa.
• At high K+ concentration inside cells, causes increased intracellular pH and decreased H+ secretion in the urine.
• H+ secreted in urine binds with HPO4 and ammonia.
• Thus , the regulation of H+ ion concentration by increasing or decreasing HCO3 ion, concentration in boduy fluidis done by series of reactions , such as: H+ ion secretion, Na ion reabsorption and HCO3 ion ecretion into urine.

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