L6: Control of ECF Part I

Question 1

Na responds primarily to changes in _____. Describe how this works (including primary effector).

Answer 1

Blood VOLUME

• Na regulation affected by changes in BP
• Primary effector: RAAS
• RAAS activity increases when BP decreases

Question 2

Water regulation is responsive to changes in _____. What is the primary effector?

Answer 2

OSMOLARITY and volume of ECF

-Primary effector: ADH

Question 3

Describe how aldosterone works to regulate NaCl and water reabsorption.

Answer 3

• Stimulates Na reabsorption in LDT and CD + K secretion

- Aldosterone levels increase if there is an increase in [ATII] or plasma [K]

Question 4

What does Aldosterone bind to upon entering a principal cell? Describe what this complex upregulates (5).

Answer 4

Binds to intracellular mineralocorticoid receptor (MR)

Aldo-MR complex upregulates:

• Apical ENaCs
• Apical K channels
• Na/K ATPase
• Mitochondrial metabolism
• H-ATPase

Question 5

What diuretic antagonizes aldosterone?

Answer 5

Spironolactone (WEAK diuretic)

Question 6

What transporter does ATII stimulate?

Answer 6

NHE in the proximal nephron (Na/H exchange)

Question 7

What is the overall effect of ATII?

Answer 7

Increases salt retention and elevates arterial BP

• Powerful vasoconstrictor
• Stimulates release of aldosterone
• Stimulates NHE
• Stimulates dipsogen

Question 8

ATII ______ RBF due to its effects on the efferent arteriole.

Answer 8

Reduces

Question 9

Describe ATII’s effect on GFR depending on concentration.

Answer 9

Low conc: Vasoconstricts efferent arterioles; GFR maintained or increased

High conc: Vasoconstricts afferent arterioles; Kf reduced, greatly reduces RBF, GFR decreased

Question 10

What protective effect does ATII have on RBF?

Answer 10

Stimulates production of PGE2 and PGI2 (vasodilate afferent and efferent arterioles)

Question 11

What controls ATII levels?

Answer 11

Renin release (JGA)

Question 12

What are the 3 components of renin release by the JGA?

Answer 12

1. Intrarenal baroreceptors: G cells of afferent arteriole stretched; renin release inversely related to pressure in afferent arterioles
2. Macula densa: Senses flow to distal tubule (GFR); renin release inversely related to GFR
3. Renal sympathetic nerves: Stimulation of RSN increases renin release via stimulation of Beta receptors

Question 13

Describe the RAAS.

Answer 13

Angiotensinogen > RENIN > Angiotensin I > ACE > Angiotensin II

Question 14

When is ANP released?

Answer 14

Released from atria when pressures are HIGH

Question 15

What does ANP do to GFR and filtered load?

Answer 15

Increases GFR (dilates afferent and constricts efferent arterioles)
Increases filtered load of NaCl

Question 16

How does ANP DECREASE NaCl reabsorption by the CD?

Answer 16

Directly inhibits secretion of renin and aldosterone
Directly inhibits Na uptake by medullary CD

*ANP trying to lower pressures

Question 17

What is the most important hormone for regulating water balance?

Answer 17

ADH

*has little effect on NaCl excretion

Question 18

When is ADH secreted by the pituitary?

Answer 18

When plasma osmolality increases (becomes concentrated) or when plasma volume decreases

Question 19

How does ADH get told to be released in regards to osmolarity?

Answer 19

Hypothalamic osmoreceptors are very sensitive to small changes is [plasma]osm (1%)

Question 20

How does ADH get told to be released in regards to blood volume?

Answer 20

Hypovolemia stimualtes ADH secretion via arterial and left atrial baroreceptors

Question 21

What are 3 important functions of ADH?

Answer 21

Increase permeability of the CD to water
Increase NKCC2 in the LOH (to increase medullary gradient)
Increase permeability of inner medullary CD to urea

Question 22

Equation for osmolar clearance

Answer 22

Cosm = (Uosm)(V)/Posm

*ml/min of blood plasma cleared of a given substance

Question 23

What does a reduced Cosm indicated (<1)? Name 3 circumstances that can cause this.

Answer 23

Positive osmolar balance: gaining osmoles, progression towards edema
-Caused by: Decreased GFR, increased aldosterone (keeps Na in body), or disease that decreases ability of kidney to eliminate solute

*reduced Cosm means you have reduced amount of clearance of solutes, so solutes remain in body which causes you to retain water

Question 24

What does an increased Cosm indicated (>2)? Name 3 circumstances that can cause this.

Answer 24

Dumping osmolytes, leads to loss of ECF

-Caused by: Diuretics, reduced aldosterone, or disease that reduces the ability of kidney to reabsorb normally