Section 3 Flashcards
(35 cards)
What role does the respiratory system play in acid-base balance, and how does it achieve this?
The respiratory system plays an important role in acid-base balance by altering pulmonary ventilation to increase or decrease the removal of CO2. (CO2 leads to H+ generation)
How do changes in arterial [H+] affect the respiratory system?
Unbuffered Solution: When arterial [H+] increases from non-respiratory sources, the respiratory center in the brain stem is stimulated to increase pulmonary ventilation, leading to increased gas exchange and the removal of excess CO2.
The removal of CO2 means there is less H2CO3 and thus less HCO3- and H+
Why is the respiratory system critically important for maintaining [H+], in comparison to the kidneys?
The respiratory system removes 100 times as much H+ derived from carbonic acid than the kidneys, making it critically important for maintaining [H+].
Why is the respiratory system considered the second line of defense in pH regulation?
The respiratory system is considered the second line of defense because it is slower than chemical buffer systems and less efficient. Without chemical buffers, the respiratory buffer system can only return the pH to about 50% of the way towards its normal level.
What is the role of the kidneys in acid-base balance?
The kidneys play a crucial role in acid-base balance by removing excess H+ from the body fluids, particularly those produced by sulfuric, phosphoric, and lactic acid, as well as some extra H+ produced by carbonic acid.
How do the kidneys help to control the pH of extracellular fluid? (3 ways)
Excretion of H+: The kidneys excrete excess H+ from the body fluids.
Excretion/Reabsorption of HCO3-: The kidneys regulate the levels of bicarbonate (HCO3-) by either excreting or reabsorbing it as needed to maintain pH balance.
Secretion of Ammonia: The kidneys secrete ammonia, which helps in buffering excess H+ ions.
Why are the kidneys important in removing H+ from metabolic sources?
While the respiratory system can help remove some H+, it is not effective enough to eliminate all excess H+ from metabolic sources. The kidneys play a crucial role in removing H+ produced by metabolic processes such as the breakdown of sulfuric, phosphoric, and lactic acid.
Where does almost all of the H+ excreted in the urine come from?
Almost all of the H+ excreted in the urine comes from tubular secretion in the proximal, distal, and collecting tubules of the kidney.
Describe the process of secretion (3 steps).
- The secretion of H+ all begins with CO2. CO2 enters the tubular cells either from the plasma, the tubular fluid, or metabolically produced within the tubular cells.
- Within the cells, CO2 and H2O, under the influence of intracellular carbonic anhydrase, form H2CO3, which dissociates into H+ and HCO3-.
- An energy dependent carrier on the luminal membrane will then transport H+ into the tubular fluid
How is the secretion of H+ regulated in the kidneys? Hormonal or neural?
The secretion of H+ in the kidneys is directly related to the acid-base status of the extracellular fluid (ECF), with no neural or hormonal control involved.
T or F: Secretion of H+ is under neural/hormonal control.
FALSE, it is directly related to the acid-base state of the ECF, with no neural or hormonal control involved.
What happens to the rate of H+ secretion when the [H+] in the peritubular capillaries is greater than normal?
When the [H+] passing through the peritubular capillaries is greater than normal, the tubular cells increase the secretion of H+.
Vice versa is also applicable
How does the rate of H+ secretion change with variations in plasma [H+]?
Increased plasma [H+]: Tubular cells increase the secretion of H+.
Decreased plasma [H+]: Tubular cells decrease the secretion of H+.
What effect does plasma [CO2] have on the rate of H+ secretion?
Increased plasma [CO2]: More H+ is secreted.
Decreased plasma [CO2]: Less H+ is secreted.
Why is the renal regulation of [HCO3-] important for acid-base balance?
The renal regulation of [HCO3-] is crucial for acid-base balance as the kidneys regulate plasma [HCO3-] through two ways:
- through reabsorption of HCO3- back into the plasma
- addition of “new” HCO3- to the plasma
T or F: HCO3- is freely filterable.
True
T or F: the luminal membranes of the tubules are permeable to HCO3-
False, the luminal membranes are impermeable to HCO3- , so its reabsorption is indirect.
How does renal HCO3- reabsorption occur? (3 steps)
- HCO3- in the tubular fluid combines with secreted H+ to form H2CO3. H2CO3 then breaks down into CO2 and H2O, both of which can cross the luminal membranes.
- Inside a tubular cell, carbonic anhydrase converts the CO2 and H2O back into H2CO3, which then freely dissociates into HCO3- and H+.
- HCO3- can cross the basolateral membrane, leaving the cell, and H+ is again secreted. A greater amount of H+ is secreted than HCO3- filtered. This means all of the filtered HCO3- is normally reabsorbed, as H+ is available to combine with it to form highly absorbable CO2
Why is HCO3- reabsorption considered indirect?
HCO3- reabsorption is considered indirect because although HCO3- is freely filterable, the luminal membranes are impermeable to it, so its reabsorption involves conversion to CO2, which can then cross the luminal membranes.
How does renal HCO3- reabsorption contribute to acid-base balance?
Renal HCO3- reabsorption ensures that all of the filtered HCO3- is normally reabsorbed, maintaining plasma [HCO3-] levels and contributing to acid-base balance by ensuring the availability of bicarbonate ions in the blood.
What is meant by the addition of “new” HCO3- to the plasma in the kidneys?
The addition of “new” HCO3- to the plasma refers to the process in which H+ that is excreted by the kidneys is coupled with the addition of new HCO3- to the plasma, rather than being coupled with HCO3- reabsorption.
How is “new” HCO3- added to the plasma in the kidneys?
- Formation of HCO3-: CO2 from the plasma and tubular cell metabolism, along with hydroxyl radicals from the dissociation of H2O, are converted into HCO3- within the tubular cells.
- Transport into Plasma: HCO3- is then transported across the basolateral membrane into the plasma.
What happens to H+ during the process of adding “new” HCO3- to the plasma?
H+ is released from the dissociation of water and then secreted into the tubular lumen, where it combines with urinary buffers, usually basic phosphate, and is ultimately excreted from the body.
How does the addition of “new” HCO3- contribute to acid-base balance?
The addition of “new” HCO3- to the plasma increases the plasma [HCO3-] levels, helping to maintain acid-base balance in the body by providing additional bicarbonate ions for buffering excess H+.
