Tubular Secretion & Excretion

Question 1

what is the 4th step of urine production?

Answer 1

tubular secretion

Question 2

where does tubular secretion occur?

Answer 2

late DCT and cortical region of collecting duct

Question 3

what is the osmolarity of the late DCT and collecting duct?

Answer 3

300 mmol

Question 4

what 5 substances are secreted from peritubular capillaries into the filtrate?

Answer 4

H+ ions
ammonium ions
phosphate ions (buffer system)
drugs
toxins

Question 5

by the end of the DCT, 99% of ____ are reabsorbed

Answer 5

water & dissolved solutes

Question 6

what is reabsorption of water and dissolved solutes determined by?

Answer 6

combined action of aldosterone and ADH (vasopressin)

Question 7

where does aldosterone act?

Answer 7

principal cells

Question 8

describe the mechanism of action of aldosterone

Answer 8

• binds to nucleus
  -> increases transcription of Na/K ATP pumps
  -> increases Na reabsorption -> increases [Na] in blood, decreasing in urine
  -> increases K secretion -> decreases [K] in blood, increasing in urine

Question 9

what is the other role of aldosterone?

Answer 9

increases bicarbonate buffer system in intercalated cells which increases H+ secretion and HCO3 reabsorption

Question 10

what effect does aldosterone have on pH of the blood and urine?

Answer 10

decreased urine pH
increased blood pH

Question 11

where does ADH act?

Answer 11

principal cells

Question 12

where is ADH made?

Answer 12

supraoptic nuclei of hypothalamus

Question 13

what stimulates production of ADH?

Answer 13

increased Na concentration in blood

Question 14

where is ADH released from?

Answer 14

posterior pituitary

Question 15

where does ADH bind?

Answer 15

anti-luminal surface of cell

Question 16

what is the mechanism of action of ADH?

Answer 16

• by intercellular signaling, increases transcription of aquaporins which are inserted into membrane
• aquaporins allow reabsorption of water in DCT and collecting duct

Question 17

what effect does ADH have on sodium concentration in the urine and blood?

Answer 17

decreases in blood (diluted)
increased in urine (less water)

Question 18

what is the final step of urine production?

Answer 18

excretion

Question 19

where does excretion occur?

Answer 19

collecting duct

Question 20

what is the collecting duct permeable to?

Answer 20

water with ADH only

Question 21

when does the filtrate become urine?

Answer 21

once in the renal pelvis

Question 22

there is no reabsorption of ____

Answer 22

creatinine

Question 23

when ADH is present, the collecting duct holds the most ____ filtrate

Answer 23

concentrated (water reabsorbed)

Question 24

without ADH, the collecting duct holds the most ____ filtrate

Answer 24

diluted (water remains)

Question 25

the collecting duct is also permeable to small amounts of ____

Answer 25

urea

Question 26

what is the osmolarity at the end of the collecting duct?

Answer 26

1200

Question 27

what is the equation for excretion?

Answer 27

filtration - reabsorption (filtered load) - transport max

Question 28

what would a diuretic that inhibits the action of aldosterone do to potassium secretion by the cortical collecting tubule?

Answer 28

decrease

Question 29

in normal kidneys, what is the osmolarity of renal tubular fluid that flows through the early DCT in the region of the macula densa?

Answer 29

usually hypotonic compared to plasma

Question 30

what changes to the following would be expected in a patient with diabetes insipidus due to lack of ADH secretion?
- plasma osmolarity []
- plasma [Na]
- plasma renin
- urine volume

Answer 30

all would increase

Question 31

when the dietary intake of K+ increases, body K+ balance is maintained by an increase in K+ excretion primarily by…

Answer 31

increased K+ secretion by later DCT and collecting tubule

Question 32

what are the 2 mechanisms by which inhibition of aldosterone causes hyperkalemia?

Answer 32

1. shifts K+ out of cells into ECF
2. decreases cortical collecting tubular secretion of K+

Question 33

what changes would occur to the following with an adrenal tumor that causes excess aldosterone secretion:
- plasma [K+]
- plasma pH
- renin secretion
- BP

Answer 33

• decrease plasma K+
• increase plasma pH
• decrease renin secretion
• increase BP

Question 34

what effect would excessive ADH secretion have on plasma sodium concentration?

Answer 34

decrease (hyponatremia)

Question 35

in a patient with severe central diabetes insipidus caused by lack of ADH secretion, which part of the tubule would have the lowest tubular fluid osmolarity?

Answer 35

late DCT and collecting duct

Question 36

how do intracellular and interstitial body fluids compare in terms of total osmolarity?

Answer 36

same total osmolarity

Question 37

what is the most likely diagnosis:
- severe polyuria (0.5 L urine/hr)
- polydipsia (drinking 2-3 cups water /hr)
- no glucose in urine
- [Na] = 160mEq/L
- urine osmol = 80mOsm/L

Answer 37

diabetes insipidus (can’t reabsorb water)

Question 37

with a high potassium diet, which part of the nephron would secrete the most potassium?

Answer 37

collecting tubules

Question 38

what changes to the collecting duct would you expect when dehydrated for 24 hours?

Answer 38

increased water permeability

Question 39

what would the osmolarity of fluid in the early distal tubule be in a dehydrated person with normal kidneys and increased ADH levels?

Answer 39

less than 300mOsm/L

Question 40

what changes to ADH, renin, angiotensin II, and aldosterone would you expect in a severely dehydrated person?

Answer 40

release of ADH & renin stimulates formation of angiotensin II and aldosterone secretion

Question 41

at which renal tubular sites would the concentration of creatinine be expected to be highest in a normally hydrated person?

Answer 41

collecting duct