test 7 respiratory and kidneys with [H+]

Question 1

Respiratory center with increase metabolic rate

Answer 1

• increase in metabolic rate => increase in [CO2] => [H+] increases => stimulates alveolar ventilation => Increased ventilation “blows off” CO2 => ECF PCO2
  falls
• quick response 1 to 3 minutes

Question 2

Negative feedback loop with respiratory center

Answer 2

• Chemoreceptors sense [H+]
  - Medulla oblongata
  - Aortic and carotid bodies
• Stimulate inspiratory area in the medulla oblongata
• Diaphragm contracts more forcefully and frequently

Question 3

How do kidneys affect acid base balance

Answer 3

• Control acid base balance by excreting either acidic or basic urine
• 3 mechanisms
  1. Secretion of H+
  2. Reabsorption of filtered HCO3-
  3. Production of new HCO3-

Question 4

how much Secretion of H+ and reabsorption of HCO3-

Answer 4

• All parts of tubule EXCEPT the thin limbs of loop of Henle
• HCO3- filtered continuously
  - 4320 mEq/day
  - 80% to 90% reabsorbed proximal tubule
  - For every bicarb reabsorbed one hydrogen secreted
• H+ secreted by tubular epithelial cells
  - 4320 mEq/day (to allow for HCO3-
  reabsorption)
  - 80 mEq/day nonvolatile acids produced by protein metabolism

Question 5

H+ secretion achieves HCO3- reabsorption

Answer 5

• Proximal tubule, thick ascending loop, & early distal tubule
• Secrete H+ by Na+/H+ counter transporter
• HCO3- movement across basolateral membrane
• Na+-HCO3- cotransport
• Cl–HCO3- exchange
- Accounts for 95% of bicarbonate reabsorption
• The quantity of H+ and HCO3- entering the tubules is almost equal
• They combine with each other to form CO2 and H2O
“titrate each other”
• Excess H+ is excreted in combination with other urinary buffers
• Phosphate
• Ammonia
- Basic mechanism of control is incomplete titration of H+ against HCO3- leaving one or the other to pass into the urine and be removed from the ECF

Question 6

Late distal and collecting tubules H+ secretion and HCO3- absorption

Answer 6

• Intercalated cells
• H+ secreted by primary active transport
• For each H+ secreted, a HCO3- is reabsorbed
• 5% of total H+ secreted
- Able to produce 900 fold increase in hydrogen ion concentration in the tubule – lowest pH in tubule of 4.5

Question 7

Regulation of tubular H+ secretion

Answer 7

• Stimuli for increasing H+
secretion during acidosis
1. An increase in PCO2 of ECF in respiratory acidosis
2. An increase in [H+] of ECF in respiratory or metabolic acidosis
• Tubular cells respond to alkalosis by decreasing H+
secretion

Question 8

Factors that decrease H+ secretion and HCO3- reabsorption

Answer 8

• decrease pCO2
• decrease H+ and increase HCO3-
• increase extracellular fluid volume
• decrease angiotensin II
  - Angiotensin II stimulates NaH exchanger
• decrease aldosterone
  - Aldosterone stimulated H+ secretion in intercalated cells
• Hyperkalemia
  - K+ moves out of the cell while H+ moves in (intracellular acidosis)
  - Increased intracellular H+ stimulates bicarb reabsorption and increases activity of Na+/H+ exchanger
  - Result: increased H+ secretion (metabolic alkalosis)