Nephron Physiology

Question 1

What substance is secreted into the lumen of the early proximal convoluted tubule of the kidney and acts as a buffer for hydrogen (H+) ions?


Answer 1

Ammonia (NH3)


Question 2

What substances are largely reabsorbed in the early proximal convoluted tubule?


Answer 2

All glucose and amino acids and most bicarbonate, sodium, chloride, potassium, phosphate, and water


Question 3

The reabsorption of glucose, amino acids, HCO3-, Na+, Cl-, PO43-, and H2O in the proximal tubule is ____ (isotonic/hypotonic/hypertonic).


Answer 3

Isotonic


Question 4

In a study, radiolabeled angiotensin II (AT II) is found in high concentrations in the early proximal convoluted tubules (PCTs). Why?


Answer 4

AT II stimulates Na+/H+ ion exchange, increasing sodium, water, and bicarbonate reabsorption and permitting contraction alkalosis


Question 5

A hiker high up on a mountain is delirious. What mechanism makes acetazolamide a treatment? Will his urine be acidic or alkalotic?


Answer 5

It is useful in altitude sickness because it blocks the uptake of bicarbonate via inhibition of carbonic anhydrase; urine will be alkalotic


Question 6

In the thin descending loop of Henle, ____ (H2O/Na+) is ____ (actively/passively) reabsorbed via medullary ____ (hyper-/iso-/hypotonicity).


Answer 6

Water; passively; hypertonicity (medulla is hypertonic and impermeable to Na+)


Question 7

In the loop of Henle, the thin part is ____ (impermeable/permeable) to water; the thick part is ____ (impermeable/permeable) to water.


Answer 7

Permeable; impermeable


Question 8

Which segment of the kidney nephron do the hormones aldosterone and antidiuretic hormone (vasopressin) act on?


Answer 8

The collecting tubules


Question 9

What type of cell in the collecting tubule of a nephron is responsible for sodium/potassium exchange and the reabsorption of water?


Answer 9

The principal cell


Question 10

A patient taking lithium loses aquaporin-linked receptor function in renal principal cells. Which hormone normally binds to these receptors?


Answer 10

Antidiuretic hormone (ADH) normally binds to V2 receptors on principal cells


Question 11

Early PCT fluid tonicity is measured in a patient. He is healthy and not taking medication. Is the fluid hypertonic, isotonic, or hypotonic?


Answer 11

Isotonic


Question 12

In the loop of Henle, the thin part makes urine ____ (hyper-/iso-/hypotonic), and the thick part makes it ____ (hyper-/iso-/hypotonic).


Answer 12

Hypertonic; hypotonic (diluted)


Question 13

The early distal convoluted tubule ____ (concentrates/dilutes) urine, causing it to be ____ (hypertonic/isotonic/hypotonic).


Answer 13

Dilutes; hypotonic


Question 14

In what action does antidiuretic hormone (ADH) activity at V2 receptors result?


Answer 14

Insertion of aquaporin water channels on the luminal side of the collecting tubules, resulting in increased water reabsorption


Question 15

What hormone inhibits the sodium/phosphate cotransporter in the early PCT?


Answer 15

Parathyroid hormone (to increase phosphate excretion)


Question 16

What indirectly induces the paracellular absorption of magnesium and calcium at the thick ascending loop of Henle?


Answer 16

Positive lumen potential generated by potassium backleak


Question 17

What is aldosterone’s main action at the collecting tubules?


Answer 17

Acts on mineralocorticoid receptors and inserts sodium channels, thereby reabsorbing sodium and secreting potassium and hydrogen


Question 18

What percentage of nephron lumen sodium is reabsorbed in the early PCT? The thick ascending tubule? The early DCT? The collecting tubule?


Answer 18

65%–80%; 10%–20%; 5%–10%; 3%–5%


Question 19

How does the influence of aldosterone affect principal cells?


Answer 19

Increased apical K+ conductance, increased Na+/K+ pump activity, and increased ENaC channels, leading to lumen negativity and K+ loss


Question 20

How does the influence of aldosterone affect α-intercalated cells?


Answer 20

Increased H+ ATPase activity, leading to increased HCO3-/Cl- exchanger activity


Question 21

A patient ingests a toxin that interferes with protein synthesis. Will the kidneys be able to utilize aldosterone effectively?


Answer 21

No—aldosterone binding acts by increasing mRNA production and protein synthesis, so such a toxin would interfere with its function


Question 22

What is the effect of PTH on the early DCT?


Answer 22

Increases activity of the sodium/calcium exchanger between the blood and the DCT cells, thereby promoting calcium uptake from the lumen


Question 23

In terms of ion processing, what is the main function of α-intercalated cells?


Answer 23

They secrete H+ into the urine (and take up K+ from it), promoting HCO3- release into the blood (in exchange for Cl-)


Question 24

In terms of ion processing, what is the main function of β-intercalated cells?


Answer 24

β-intercalated cells secrete HCO3- into the urine (and take up Cl- from it), promoting H+ release into the blood


Question 25

In the early DCT, which ion diffuses from the urine into the blood as a result of transporter activity?


Answer 25

Chloride


Question 26

In the thick ascending tubule of Henle, which two ions diffuse from the urine into the blood down their electrochemical gradient?


Answer 26

Chloride and potassium


Question 27

In the collecting tubule, which ion diffuses from the urine into the blood passively?


Answer 27

Chloride


Question 28

Which three ions are actively taken up by the thick ascending loop of Henle?


Answer 28

Sodium, potassium, and chloride