9 Control of Plasma Osmolarity Flashcards
Between what range does urine osmolarity vary?
50-1200 mOsm/Kg
1200 (maximum possible)
What is the normal osmolarity of cells?
280-310 mOsm/Kg
Juxtamedullary nephrons make up 10-15% of the total nephrons in the kidneys. What is there function and how does their structure differ from the cortical nephron?
Responsible for making concentrated urine
How is the vertical concentration gradient in the kidney maintained?
Vasa recta and long loope of henle
Why are there no aquaporin channels in the ascending loop of henle?
Diluting action of filtrate
Removes solute without water
Increase osmolarity in interstitium
In which patients might there be a lack of vertical concentration gradient within the kidney?
Patients on prolonged loop diuretics
Transplant patients
At what point is the osmotic gradient within the loop of henle at its highest?
At deepest point of loop of henle
How is urea reabsorbed from the lumen of the tubule in the proximal convulted tubule?
Small changes in plasma concentration cause small hormonal changes. What happens as a result of these hormonal changes? Where does this hormonal regulation take place?
- Alter water uptake in kidney
- Stimulate thirst
Where?:
Late distal tubule
Collecting duct in nephron
Hormone= aldosterone
Outline the thirst response. (how is it sensed, where and how is it perceived?)
- Perceived:
- Peripherally eg drying of oral mucosa
- Sensed:
- Lateral pre-optic area of hypothalamus- responsive to raised plasma osmotic pressure/reduced ECF volume
Outline the thirst mechanism. (when is it active)
Thrist mechanism active when level of hyperosmotic dehydration surpasses protective capacity of kidneys
What is normal osmolarity in the body?
- 280-310 mOsm/kg
- 290 in interstitial fluid
- 291 in blood plasma due to plasma proteins ==> oncotic pressure
How do you alter plasma osmolarity?
What nephrons are responsible for concentrating urine and how do they do this?
- Juxta medullary long LOH generates gradient
- Vasa recta from efferent arteriole running paralell with Loop of Henle and blood running countercurrent maintains gradient
- Counter current multiplier system
What is the difference in transport between the ascending and descending limb?
When may you see this concentration gradient between the loop of henle and the medullary interstitium and what are the consequences of this?
- Newly transplanted kidney or long term loop diuretics as they block NKCC2 so no gradient can be established
- Lots of dilute urine made
How can urea be used to help reabsorb more water?
- Uptake in the PCT, 50% filtered is taken back
- Under ADH influence, urea reabsorbed from medullary CD
- Urea increases osmotic gradient in the interstitium so more water reabsorbed
- Urea then just taken back up into loop and cycles round
How do we supply blood to the medulla of the kidney without washing away the osmotic gradient needed to reabsorb water?
- Vasa recta with very slow flow
- No active transport just passive absorption through endothelial cells
- Flow opposite direction to tubular fluid flow
- Equilibriates at each level
How is a change in plasma osmolality detected in the body and what are the 2 pathways used to restore osmolarity?
- Osmoreceptors in hypothalamus in OVLT
- Cells in supraoptic nucleus containing baroreceptors sit close to OVLT so if low pressure means low volume and means high osmolarity so ADH secreted
- (organum vasculosum of the lamina terminalis)*
What is the plasma osmolarity feedback loop?
Always a little bit of ADH, never 0
How does the effectiveness of ADH change with changes in plasma volume?
Changes in B.P (plasma volume) have an effect on response to changes in osmolarity
What happens once you have corrected a high plasma osmolality by taking a large drink?
What is diabetes insipidus? What are the 2 types of diabetes insipidus?
What is SIADH and how can it cause issues with plasma osmolarity?
