Kidney Function IV, Regulation of osmolarity and blood volume

Question 1

Definition of myogenic response

Answer 1

Contraction of a blood vessel that occurs when intravascular pressure is elevated and conversely vasodilation that follows a reduction in pressure

Question 2

Definition of autoregulation

Answer 2

Intrinsic ability of an organ to maintain a constant blood flow despite changes in perfusion pressure

Question 3

How is volume regulated when there is water deprivation

Describe the pathway of water reabsorption

Answer 3

Increased osmolarity

Osmoreceptors near supraoptic and paraventricular nuclei stimulate ADH release from posterior pituitary

Osmoreceptors near lateral preoptic area stimulate thirst, causing you to drink more

More water uptake via CD

Osmolarity restored

Question 4

How is volume regulated when there is an excess of water

Describe the pathway for water excretion

Answer 4

Decreased osmolarity

Osmoreceptors near supraoptic and paraventricular nuclei suppress ADH release

Osmoreceptors near lateral preoptic area suppress thirst

Less water uptake via CD

Osmolarity restored

Question 5

Why is it important to control Na in plasma

Answer 5

Dictates BP, BV

Osmolarity must be maintained, even at the expense of volume

Question 6

What are the 3 ways of controlling the [Na] via GFR

• Extrinsic
• Intrinsic
• Hormones

Answer 6

Extrinsic

• Decreased BP detected by baroreceptors => activate SNS
• VC afferent arterioles/mesangial cells decrease SA => decreased GFR

Intrinsic
-Autoregulation of afferent arterioles via myogenic response
-Tubuloglomerular feedback via macula densa in JGA
(Increased NaClK triporter, NaKATPase activity => decreased renin => VD => increased GFR)

Hormones

• renin/Ang2/aldosterone => increased Na uptake
• ANP/dopamine => decreased Na uptake

Question 7

Describe the activation pathway of angiotensin

Answer 7

Angiotensinogen from liver
(renin from JGA)
Ang1
(ACE)
Ang2

Question 8

What are the 5 main effects of Ang2

Answer 8

PT Na reabsorption increases

• NaH
• NaKATPase

Aldosterone from zone glomerulosa
Act on principle cells, DCT
-ENaC
-ROMK
-NaKATPase channel synthesis increases
-If Na uptake increases, water follows

ADH release => increased water uptake

• DCT
• CD

VC of arterioles

Thirst generated from lateral paraoptic

Question 9

Describe the pathway of the volume sensor in the atria and ventricles

Answer 9

Heart stretched due to
-increased BV, BP

ANP/BNP release

Question 10

What are the 3 mechanisms that are affected by ANP/BNP

Answer 10

Principle cell
-ENaC inhibited => more Na excretion

Renin/ADH/aldosterone
-Release inhibited

NaKATPase in PT
-Synergistic with dopamine => Na uptake inhibited

Question 11

What are the effects of pressure natriuresis

Answer 11

Decreased BP via systemic VD => renal afferent arteriole VD => increased GFR => increased Na excretion