Week 1 - Renal Function: Salt + Water Regulation

Lots of diagrams, hard to make into cards

What does Angiotensin II do?

Increases Na+ transport in the nephron

What does Nitric oxide do?

Inhibits Na+ uptake in the nephron

What does Aldosterone do?

• Increases the opening of existing Na+ channels (and increases number of)

• Increase Na reabsorption

• Increases water reabsorption

• Increases K+Na+ ATPase

In DCT and CD

What does ADH do?

Increases Na+ reabsorption in LOH (DL), DCT, & CD

What stimulates ADH?

Volume depletion (Na+), dehydration, hypotensive

What does Atrial Natriuretic Peptide do?

• Inhibits ADH & Aldosterone

• Decreases Na channels

• Decreases Na & water reabsorption

• Decreases blood pressure

What stimulates Atrial Natriuretic Peptide?

Responds to increases blood pressure

What does Hyperkalemia do?

Stimulates Aldosterone which

• increases K+ secretion/excretion via Na/K pump

• increases number of apical K channels

How is Phosphate reabsorption regulated?

PO4- is reabsorbed via Na-coupled transporters

• Fibroblast growth factor 23 is stimulated by high PO4- and it decreases expression & activity of co-transporter

• PTH also decreases co-transporter abundance & uptake

What regulates Ca2+ reabsorption?

High Ca2+ triggers a few receptors:

• Calcitonin (mechanism unknown)

• Basolateral calcium sensing receptor decreases reabsorption

Low Ca2+ triggers PTH which triggers:

• increases Ca channels & paracellular transport & transcellular transport

• increases Calcitriol which increases apical Ca channels & basolateral Ca ATPase & Na/Ca exchanger

What determines water movement?

Osmosis

Which section of the nephron has the highest osmolarity?

The descending limb and the very bottom of the Loop of Henle

Which section of the nephron has the lowest osmolarity?

The DCT and certain sections of the CD (but can change to very good)

Despite osmolarity, which section of the nephron reabsorbs the most water?

The PCT reabsorbs 60% of filtered water

How does heavy drinking (water) effect salt/water regulation?

Increase ECF/Plasma volume. Extra plasma volume overcomes autoregulation, inc GFR. Decreased peritubular capillary plasma oncotic pressure reduces tubular reabsorption and causes greater onward filtrate flow (potential urine)

How does dehydrated effect salt/water regulation?

Smaller plasma volume/pressure and decr GFR. Incr oncotic pressure from peritubular capillaries incr tubular reabsorption and less potential urine flow

How does hypovolemia effect salt/water regulation?

Low arterial BP activates SNS and stimulates ADH and thirst. Incr JGApp and renin secretion which over-rides autoregulation to cut GFR to preserve plasma volume. RAAS also incr Na reabsorption which w/ ADH incr final urine specific gravity

How does hypervolemia effect salt/water regulation?

SNS low tone and low JGA and renin activity. High blood volume, detected by baroreceptors in right atrium of heart-secretion of ANP - Aldosterone inhibited. Na wasted into urine. ADH inhibition - final urine low specific gravity