Module 4: Section 5

Question 1

what does tubular secretion involve?

Answer 1

the movement of substances from peritubular capillaries to the tubule lumen

Question 2

what are the most important substances that undergo tubular secretion?

Answer 2

• H+
• K+
• organic ions and cations

Question 3

what can H+ be secreted by?

Answer 3

proximal, distal and collecting tubules

Question 4

what is the extent to which H+ is secreted dependent on?

Answer 4

acidity of plasma

Question 5

what does H+ secretion play a key role in?

Answer 5

regulation of acid-base balance

Question 6

what do K+ ions undergo?

Answer 6

both tubular reabsorption and secretion

Question 7

how. is potassium filtered by glomerulus?

Answer 7

freely

Question 8

how is K+ reabsorbed by proximal tubule?

Answer 8

actively

Question 9

what is K+ secretion in distal and collecting tubules dependent on?

Answer 9

Na+K+ ATPase pump

Question 10

what does a rise in plasma K+ cause a release of?

Answer 10

aldosterone from the adrenal cortex

Question 11

what will stimulate abnormal K+ secretion to the extent that K+ depletion occurs?

Answer 11

• decreased plasma Na+
• decreased ECF volume or decrease in arteriole BP

Question 12

what are the two types of secretory carriers that the proximal tubule contains?

Answer 12

one for organic anions and one for organic cations

Question 13

what are the three reasons that the organic ion secretory systems are important?

Answer 13

1. increase excretion
2. excrete poorly soluble organic ions
3. removal of foreign compounds

Question 14

organic ion secretory systems: increase excretion

Answer 14

• actively adds more organic ions to tubular fluid therefore increase excretion
• important for blood-borne chemical messengers to reduce or limit their biological activity
  – eg, norepinephrine , histamine, prostaglandins

Question 15

organic ion secretory systems: excrete poorly soluble organic ions

Answer 15

• most organic ions are not very soluble
• this will further remove the small, unbound organic ions
  – causes more “unloading” of organic ion from carrier molecule
• organic ions highly bound to its carrier can be excreted

Question 16

organic ion secretory systems: removal of foreign compounds

Answer 16

• eg, drugs, food additives, pesticides, environmental pollutants
• kidneys will remove then regularly but there is no regulatory mechanisms to increase removal if needed