what happens when arterial [H+] increases from non-respiratory sources?
respiratory centre in the brain stem is stimulated
- increase pulmonary ventilation
- removes CO2 so less H2CO3 and HCO3-
what happens when arterial [H+] decreases?
decreased pulmonary ventilation
- slower, shallow breathing decreasing exhalation of CO2 so more H2CO3 and HCO3-
what is respiratory system considered?
second line of defence
- since slower than chemical buffer systems
3 ways the kidneys help control the pH of ECF
1) excretion of H+
2) excretion/reabsorption of HCO3-
3) secretion of ammonia
what is almost all H+ secreted by urine from?
from tubular secretion from proximal, distal and collecting tubules
renal secretion: what does secretion of H+ start with?
CO2
Renal secretion: how does CO2 enter tubular cells?
- from plasma, tubular fluid or metabolically produced within tubular cells
what does CO2 and H20 under the influence of intracellular carbonic anhydrase form?
H2CO3 which dissociates into H+ and HCO3-
what transports H+ into tubular fluid?
an energy dependent carrier on the luminal membrane
what is the secretion of H+ directly related to?
acid-base status of the ECF
- no neural or hormonal control
Pathway 1 involved in regulating H+ secretion
increase in plasma [H+] -> increased H+ secretion -> increased H+ excretion -> decreased plasma [H+]
Pathway 2 involved in regulating H+ secretion
increased plasma [CO2] -> increased HCO3- conservation -> decreased HCO3- excretion -> increased plasma [HCO3-]
how is renal HCO3- reabsorbed?
- HCO3- in tubular fluid combines w/ H to form H2CO3
– the H2CO3 breaks down into CO2 and H2O (both cross luminal membrane) - once inside tubular cell, carbonic anhydrase converts CO2 + H2O-> H2CO3
– it freely dissociates into HCO3- and H+ - HCO3- can pass basolateral membrane
– leaves H+ in cell
what happens to the filtered HCO3-
reabsorbed
what does it mean that tubular cells are able to produce new HCO3-
the H+ that is excreted is coupled with the addition of HCO3- to plasma
how is new HCO3- added to plasma?
- CO2 from plasma and tubular cell metabolism, and hydroxyl radical from dissociation of H2O is converted HCO3- within tubular cells
- then transported across basolateral membrane -> plasma
- H+ is released from dissociation of water
- H+ is then secreted into tubular lumen
- H+ combines with urinary buffers (basic phosphate)
- then excreted from body
what would happen in the absence of urinary buffer systems?
only allow for secretion of 1% of all daily H+ generated
urinary buffers
- can remove the free H+ from tubular fluid so it doesn’t contribute to tubular acidity
- 2 types
– phosphate and ammonia
is there a mechanism to increase the amount of basic phosphate added to tubular fluid?
no, it has a limited buffering capacity
when do tubular cells secrete ammonia into tubular fluid?
under acidic conditions when the phosphate buffer system is overwhelmed
what happens to ammonia in tubular fluid?
reacts w/ H+
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Module 4: Section 136
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Module 4: Section 228
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Module 4: Section 330
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Module 4: Section 454
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Module 4: Section 516
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Module 4: Section 637
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Module 5: Section 115
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Module 5: Section 223
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Module 5: Section 321
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Module 5: Section 427
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Module 6: Section 146
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Module 6: Section 229
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Module 6: Section 351
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Module 6: Section 450
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Module 6: Section 534
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Module 6: Section 629
