Renal Regulation of acid-base

Question 1

Normal H+ concentration in body fluids

Answer 1

-low, 0.00004 mEq/L with a narrow change in margins
-must be tightly regulated for normal enzymatic activities

Question 2

Acids

Answer 2

-molecules that can release H+ in solution
Ex.carbonic acid

Question 3

Bases

Answer 3

-molecules that can accept H+ in solution
Ex.bicarbonate, proteins

Question 4

Acidosis

Answer 4

-a condition where the H+ concentration is higher than normal in body fluids

Question 5

Alkalosis

Answer 5

-condition when H+ concentration is lower than normal

Question 6

Acids and bases in extracellular fluid

Answer 6

-are weak acids and bases

Question 7

pH calculation

Answer 7

-pH of body fluids is directly determined by the concentration of H+
pH=-log [H+]

Question 8

Normal body pH

Answer 8

7.4
**our body can still function at pH range of 6.8-8 but other changes are life threatening

Question 9

pH of arterial blood vs venous blood/extracellular fluids

Answer 9

-arterial: 7.4
-venous/extracellular fluids: 7.35

Question 10

pH of intracellular fluid

Answer 10

6-7.4
-lower because inside of cells is metabolically active producing products and acids

Question 11

pH in urine

Answer 11

4.5-8
-dangerous lower than that and can cause damage

Question 12

Three defense mechanisms against changes in H+ concentration

Answer 12

1.acid-base buffer systems of body fluids (reacts within seconds)
2.Respiratory system (reacts within minutes)
3. kidneys (reacts within hours and days)

Question 13

Acid-base buffer system

Answer 13

-converts strong acids to weak acids, AND strong bases to weak bases

Question 14

How does acid-base buffer system work?

Answer 14

-An acid-base buffer system is composed of a weak acid and a salt. The salt provides basis for weak acid and when a stronger acid is added to the system, the H+ from strong acid binds to base of weaker acid and forms a weak acid
Acid Ex. HCl ionized to H+ and Cl-, H+ is removed by buffer
Base ex. NaOH ionized to Na+ and OH-, then hydroxyl reacts with weak acid and gives H2O and Na reacts to form salt

Question 15

Common buffer systems in the body

Answer 15

-bicarbonate buffer system
-phosphate buffer system
-proteins

Question 16

Bicarbonate buffer system

Answer 16

-includes carbonic acid (H2CO3) and bicarbonate salt (NaHCO3-)

1. carbonic acid=H2O + CO2; catalyzed by carbonic anhydrase
   >carbonic acid ionizes weakly so H+ is sequestered

2.NaHCO3- is most common form of bicarbonate salt in ECF
>NaHCO3- ionized to Na + HCO3-

3.Bicarbonate buffers acids
>HCO3- + H+ -> H2CO3 -> CO2 + H2O

4.Bicarbonate buffers bases
> HCO3- + H+ -> H2CO3 -> H2CO3 + NaOH -> H2O + NaHCO3

Question 17

Phosphate buffer system

Answer 17

-composed of H2PO4^- (acid) and HPO4^2- (base)

Question 18

Phosphate buffer system with acid

Answer 18

-salt provides base with acid resulting in NaH2PO4
> Na2HPO4 + HCl -> NaH2PO4 +NaCl
-salt providing base with base resulting in Na2HPO4 + H2O
> NaOH + NaH2PO4 -> Na2HPO4 + H2O

Question 19

Protein buffer system

Answer 19

-important cellular buffering molecules
-extracellular pH changes affect the intercellular pH, however adjustment mechanisms via moving H+ and HCO3- across the cell membrane are slow (hours_, so intracellular proteins play an important role for fast buffering of intracellular pH changes

Question 20

Respiratory regulation of acid-base

Answer 20

-system is based on CO2 exchange in the lungs.

Question 21

Ventilation increased or decreased- impact on pH

Answer 21

> Increased ventilation decreases extracellular CO2 and H+ concentrations= pH goes up
decreased ventilation increases extracellular CO2 and H+ concentration= pH goes down

Question 22

Ventilation doubled vs ventilation decreased 1/4- impact on pH

Answer 22

-doubling the ventilation leads to increased pH from 7.4-7.63
-reduced ventilation to ¼ of the normal reduces the pH to 6.95

Question 23

H+ concentration in body fluids-impact on ventilation

Answer 23

-increased H+ leads to increased ventilation
>due to feedback mechanism between H+ concentrations and resp rate
-decreased H+ leads to decreased ventilation as well but limited due to reduction of PO2 and stimulation of ventilation

Question 24

Respiratory system pH compensation efficiency

Answer 24

-effective for 50-75% compensation
-eg. If pH is dropped from 7.4 to 7.0, the respiratory system can bring it back to 7.2-7.3

Question 25

Alveolar ventilation changes

Answer 25

-at normal alveolar ventilation, not pH change of body fluids
-at increased ventilation, positive change in pH (alkalosis)
-at decreased ventilation, negative change in pH (acidosis)

Question 26

Renal regulation of acid-base balance

Answer 26

-body produces 80 mEq of nonvolatile acids per day (mainly from metabolism of proteins). These non-volatile acids are excreted by kidneys (in form of H+) because they cannot be removed by the lungs

Question 27

Renal acid-base adjustments

Answer 27

-HCO3- is filtered and if less is reabsorbed, the pH goes down
-Lots of H+ is secreted into the tubules and if more H+ is excreted than normal the pH goes up
>H+ is secreted for reabsorbing the HCO3- (almost all HCO3- that is filtered is absorbed)

Question 28

Acidosis and kidney regulation

Answer 28

-extracellular H concentration is high, so kidneys secrete more H+ and reabsorb more HCO3- and produce HCO3-

Question 29

Alkalosis and kidney regulation

Answer 29

-Extracellular H+ concentration is low, so kidneys secrete less H+ and reabsorb less HCO3-

Question 30

Distribution of reabsorption of HCO3- in renal tubules

Answer 30

*secretion of H+ and reabsorption of HCO3- by renal tubules

-reabsorption of HCO3- occurs in all segments of the nephron except the thin descending and ascending limbs of loop of Henle
>Proximal tubules: 80-90%
>Thick part of loop of Henle: 10%
>Distal tubules and collecting ducts: remaining percent

Question 31

Proximal tubules, thick segment of loop of Henle, early distal tubule: secretion of H and absorption of HCO3- mechanism

Answer 31

1.Kidney secretes H+ (from carbonic acid) which combines with HCO3- in tubular lumen to form H2CO3
2.bicarbonate is diffused from tubular lumen into tubular cells as CO2 + H2O from H2CO3
3.Transport across the basolateral membrane into peritubular capillaries by Na-HCO3- cotransport and Cl-HCO3- exchanger
4.Can reduce pH to 6.7 (no free H+ in the lumen)

Question 32

Late distal and collecting tubules: secretion of H+ and absorption of HCO3- mechanism

Answer 32

-H+ from carbonic acid is secreted by primary active mechanism (H+ transporting pumps)
>acidic tubular fluid can form here unlike the earlier segments because free H+ was removed by bicarbonate in earlier segments

-Cl-HCO3 exchanger on basolateral side allows for HCO3 reabsorption

-pH can be reduced to 4.5

Question 33

Excretion of acid with urine

Answer 33

-80mEq non-volatile acids produced daily
-urine pH of 4.5 means that 2667 L of urine must be excreted
-To do this must combine H+ with either phosphate or ammonia
>additional bicarbonate is produced which is important for maintaining extracellular HCO3- stores

Question 34

H+ combination with phosphate

Answer 34

-important buffer in tubular fluid because reabsorption is less than water so its concentration in the tubule increases

Question 35

H+ combination with ammonia

Answer 35

-buffering H+ with ammonia (NH3) or ammonium (NH4)
-under normal conditions, 50% of acid excreted and 50% of produced HCO3- is from this buffering system

Question 36

Where does NH3 or NH4 come from?

Answer 36

-comes from glutamine metabolism. Glutamine from metabolism of amino acids in liver
>glutamine enters the epithelial cells of renal tubules and is metabolized there and produced ammonium and bicarbonate
**mechanism is different in collecting tubules

Question 37

H+ combination with phosphate and ammonia in collecting tubules

Answer 37

-secreted H+ binds to ammonia in the tubule and forms the ammonium ion. The luminal membrane of cells is not permeable to ammonium, and ammonium is trapped in the tubule and excreted