Acid-Base Regulation

Question 1

T/F: Hydrogen concentration in the body is kept very high compared to other ions.

Answer 1

FALSE - very low and tightly regulated

Question 2

Acidosis

Answer 2

pH BELOW 7.4

Question 3

Alkalosis

Answer 3

pH ABOVE 7.4

Question 4

3 systems that defend against changes in H+ concentration

Answer 4

1) Acid-base buffering system of fluids
2) Respiratory conter
3) The kidneys

Question 5

Acid-Base buffering system of fluids

Answer 5

• FIRST line of defense
• reacts within SECONDS
• do NOT eliminate H+, but keep them tied up until they can be eliminated
  1) bicarbonate buffering system
  2) phosphate buffering system
  3) proteins

Question 6

Respiratory Centers

Answer 6

• SECOND line of defense
• reacts within MINUTES
• control of extracellular CO2 by the lungs
• increase in ventilation -> eliminates CO2 -> reduces H+

*emphysema can cause respiratory acidosis!

Question 7

The kidneys (H+ regulation)

Answer 7

• THIRD line of defense
• reacts within HOURS to DAYS
• most powerful
• work by excreting acidic or basic urine

Question 8

3 ways the kidneys regulate extracellular H+

Answer 8

1) secretion of H+
2) reabsorption of filtered HCO3 (bicarbonate)
3) production of new HCO3

Question 9

T/F: Hydrogen ion secretion and HCO3 occure in the thin ascending and thin descending limb of the loop of Henle.

Answer 9

FALSE!!! - all other parts of the tubule EXCEPT these

Question 10

Where does most HCO3 reabsorption occur?

Answer 10

Proximal tubule (~80-90%)

-other 10% in the THICK ascending portion of the loop of Henle

Question 11

T/F: For each HCO3 absorbed, a H+ is secreted.

Answer 11

TRUE

Question 12

How is 95% of bicarbonate absorbed?

Answer 12

by coupling H+ with Na+ into call at the luminal cell

Question 13

Where is H+ secreted by SECONDARY ACTIVE TRANSPORT?

Answer 13

• proximal tubule
• THICK segment of ascending limb
• early DISTAL tubule

Question 14

H+ and secondary active transport explained

Answer 14

• Co2 is formed in the cell or diffuses into the cell
• CARBONIC ANHYDRASE combines with water to form H2CO3 (dissociates into HCO3 and H)
• when Na+ moves into cell, creates a gradient that allows H+ to move from cell to TUBULAR LUMEN
• HCO3 moves into blood through the basolateral membrane using a downhill gradient

Question 15

Other ways H+ is secreted and HCO3 is reabsorbed

Answer 15

• rxn of HCO3 with H+ form H2CO3 (CO2 and water, CO2 moves across tubular membrane)
• HCO3 is “TITRATED” against H+ in the tubules
• PRIMARY active transport in the INTERCALATED CELLS of the:
  1) late distal tubule
  2) collecting tubules

Question 16

2 main buffers to combine with H+ for excretion

Answer 16

1) phosphate

2) ammonia

Question 17

What happens to the tubular secretion of H+ during ALKALOSIS?

Answer 17

decreases; H+ is then too low for complete HCO3 reabsorption

Question 18

What happens to the tubular secretion of H+ during ACIDOSIS?

Answer 18

increases; increased reabsorption of HCO3

Question 19

What are the primary reasons for stimulation of H+ secretion by the renal tubules?

Answer 19

• an increase in pCO2 of the ECF in RESPIRATORY ACIDOSIS

- an increase in H+ concentration of the ECF in RESPIRATORY ACIDOSIS or METABOLIC ACIDOSIS

Question 20

Factors the INCREASE H+ secretion and HCO3 reabsorption

Answer 20

• INC pCO2
• INC H+, DEC HCO3
• DEC extracellular volume
• INC angiotensin II
• INC aldosterone
• hypokalemia

Question 21

Factors that DECREASE H+ secretion and HCO3 reabsorption

Answer 21

• DEC pCO2
• DEC H+, INC HCO3
• INC extracellular volume
• DEC angiotensin II
• DEC aldosterone
• hyperkalemia

Question 22

Respiratory acidosis

Answer 22

increase in pCO2

Question 23

Metabolic acidosis

Answer 23

fall in HCO3

Question 24

Gluconeogenesis

Answer 24

• occurs during periods of prolonged fasting
• similar process as occurs in liver
• only ~60% of AAs available in the body are convertable
• kidney primarily uses:
  1) lactate
  2) glutamine
  3) glycerol