Kidney IV

Question 1

Describe the Osmolarity regulation for Increased ECF osmolarity and Decreased

Answer 1

Normal osmolarity 290 mOsm/l

Water deprivation, solute ingestion, diarrhoea etc –> water excretion by kidney

Excessive fluid ingestion –> water retention by kidney / drink water

Question 2

Volume regulation of ECF

Answer 2

Volume of the ECF is determined by the total quantity of solute (mainly NaCl)
So regulation of ECF volume is all about Na+ balance

Average dietary salt intake 2.3g/day

Question 3

Why important a person maintains ECF osmolarity

Answer 3

bc if volume were to change dramatically in the ECF, this can have serious consequences in confined spaces

Normally osmolarity is maintained at expense of volume via ‘osmo-regulation’

Question 4

What’s the volume and solute composition of the human body

Answer 4

ECF consists of plasma (4L), Interstitial water (10L), intracellular water (28L)

Main osmotically active solute in ECF is Na+
Main osmotically active solute in ICF is K+
very small amounts of glucose found in both

Plasma volume important determinant of BP in veins, cardiac chambers and arteries

Question 5

How is Na+ content regulated by the kidney

Answer 5

By controlling:
i) GFR
iiI Na+ Reabsorption

Little evidence for regulatory ‘Na appetite’

Question 6

What happens when GFR is decreased

Extrinsic control of GFR

Answer 6

Autoregulation

Extrinsic control - maintains arterial BP by controlling GFR
Low BP… detected by Baroreceptors, cause activation of sympathtic NS (innervate AA)
-Vasoconstricts AA, decreases GFR so decreases hydrostatic pressure in GC
-Reduces SA of filtration barrier via mesangial cells, decreases GFR

Reduction in GFR will conserve Na+ and H2O and increase BV/P

Question 7

Describe the intrinsic control of GFR

Answer 7

Intrinsic control - protects renal capillaries from hypertensive damage and maintains a healthy GFR

Autoregulation within kidney

Can control AA constriction in 2 ways:

1) Myogenic response by the renal smooth muscle cells that surround arterioles (vasoconstriction in response to stretch)
2) Tubuloglomerular feedback b the JG apparatus (controls vasoconstriciton and renin release)

Question 8

Autoregulation-intrinsic mechanisms

Answer 8

Renal blood flow and GFR remain constant for arterial pressures b/w 90-200 mmHg.

Afferent arterioles constrict when BP is raised and dilate when BP is lowered, thus maintaining constant capillary pressure and glomerular blood flow.
Outcome - renal blood flow will also be maintained.

Purpose: to protect glomerular capillaries from hypertensive damage and maintain a healthy GFR. Also maintains a stable renal BF

Question 9

Based on the TG feedback mechanism, describe the multiple regulatory pathways controlling Na reabsorption

Answer 9

Sensors (affect renin or natriuretic peptide release)

Effector pathways