Renal Acid-Base

Question 1

the normal range of blood pH in domestic mammals is __

Answer 1

7.35-7.45

Question 2

describe why carbon dioxide is a volatile acid

Answer 2

because it can be released from the body through respiration

• in the presence of carbonic anhydrase water and CO2 combine to make carbonic acid (H2CO3) which dissociates into H+ and bicarb (HCO3-)
• bicarb and H+ are taken to the lungs where the reaction works in reverse to form water and CO2 which is exhaled out of the body

Question 3

what is the source of fixed (non-volatile) acids in the body?

Answer 3

the breakdown of proteins and phospholipids generate fixed acids
- fixed acids cannot be released from the body

Question 4

describe how bicarbonate is resorbed from the proximal tubule and the role bicarbonate plays in pH regulation

Answer 4

• all bicarb filtered in the glomerulus is resorbed, mostly in the PCT
• if bicarb load is high, the tubular maximum is reached and excess bicarb is excreted into urine, lowering plasma pH
• because in a normal state, all bicarb is resorbed, it is not able to counteract increased levels of acid in the blood

Question 5

describe a buffer and how, without buffering, the kidneys would reach maximum level of excretion much earlier

Answer 5

buffer: any mechanism that resists changes in pH

the buffer tones down what would be free H+, so you can move more H+ out because its buffered and hidden in the buffer so its not out being an acid. this means it can moves a lot more hydrogen before the environment gets too acidic because the H+ are buffered and not acidic

Question 6

what role does phosphate play in buffering secreted hydrogen ions?

Answer 6

during states of acidosis, H+ is pumped into the renal tubule by ATPase pumps

• in order to prevent H+ from diffusing back into the cell, it must be trapped by being bound to another substance, phosphate binds most of this H+ so that it can be excreted in urine

Question 7

what role does ammonium play in acid secretion/absorption?

Answer 7

• in the proximal tubule, glutamine is metabolized into bicarb and ammonium
• ammonium is exchanged for sodium and goes into the interstitial space
• ammonium is recycled in the loop of henle during countercurrent mutliplication and creates a medullary gradient
• in the distal tubule and collecting duct, NH4+ secretion is increased in the face of acidosis

Question 8

paradoxical aciduria

Answer 8

acidotic urine in the face of metabolic alkalosis

• loss or sequestration of HCl occurs due to vomitting or LDA
• lack of H+ to exchange with sodium and reduced blood leads to increased Na+ delivered to distal tubule
• during alkalosis, K+ moves intracellularly when H+ moves out of the cell in attempt to counteract the basic pH
• because K+ is sequestered in cells, it cannot be exchanged for Na+ in the kidney so instead H+ is exchanged, leading to H+ excretion into urine to conserve water and Na+ retention