Uro - Renal regulation Flashcards
How do you calculate osmolarity
Number of dissociated solute particles x concentration - expressed as Osm/L or mOsm/L
How does osmotic pressure correlate with number of solute particles
Increase in solute particle number increases osmotic pressure - NOT SIZE
What is osmosis
Passive movement of water from an area of low solute concentration to high solute concentration across a semi-permeable membrane until they reach an equilibrium
How much of the body weight does fluid make up
60%
What is the split of ICF and ECF
2/3 ICF, 1/3 ECF - separated by cell membrane
What is ECF split into
3/4 extravascular, 1/4 intravascular (Plasma) - separated by capillary
What is extravascular split into
95% interstitial fluid, 5% transcellular fluid e.g. peritoneal fluid
What constitutes unregulated water loss
Sweat
Faeces
Vomiting
Water evaporation from the skin or respiratory lining
What makes up regulated water loss
Water loss from urine
How does osmolarity normalise in positive water balance
- Excess water intake
- ECF hit first - volume increases
- Dilution effect = sodium conc decreases
- Osmolarity decreases
- Hyposmotic urine production
- Osmolarity normalises
How does osmolarity normalise in negative water balance
- Low water intake
- ECF hit first - volume decreases
- Sodium concentration increases
- Osmolarity increases
- Hyperosmotic urine production
- Osmolarity normalises
Where is water reabsorbed in the nephron
67% reabsorbed in the PCT
It is then passively reabsorbed in the thin descending loop of henle (15%)
Then, variable amounts are reabsorbed in the DCT and CD - none is reabsorbed in the ascending LoH
What do we need in order for water to be passively reabsorbed in the loop of Henle and Collecting Duct
We need a hyperosmotic medullary interstitium
By what process do we create a hyperosmotic medullary interstitium
Countercurrent multiplication
Describe countercurrent multiplication
Tubular fluid arrives in the DLOH at 300 (arbitrary mOsm/L), and moves through until it reaches the thick ALOH where sodium is actively reabsorbed. This means that the tubular osmolarity decreases but medullary osmolarity increases. Due to the increase in medullary osmolarity e.g. to 400, tubular fluid now arriving in the DLOH will lose water passively to equalise osmolarity. Therefore the new tubular osmolarity in the DLOH = 400 too. AS tubular fluid moves through the LoH, Na is still actively reabsorbed in the thick ALOH, therefore we get multiplication of the process and a gradient will eventually form.
The reason as to why the top of the intersitum (outer) is less hyperosmotic is because when water first arrives in the DLOH it will move into the top of the interstium therefore the outer inertsitium will by more hypo osmotic
What gradient does countercurrent mutliplaction create
1200 in the inner medulla
300 in the outer medulla
What else occurs in the medulla to aid with water reabsorption
Urea recycling
How does urea leave the collecting duct
It can leave the collecting duct via UT-A1 and then UT-A3 - AVP boosts these transporters to concentrate urine
What is the medulla conc of urea
600mmol/L
What are the 2 fates of urea having entered the medullary interstitum
It can either enter the DLOH via UT-A2 or it can enter the vasa recta via UT-B1 - this means that urea is recycled in the nephron to increase the osmolarity of the medulla
What is the effect of urea recycling
Urea excretion requires less water
Urine concentration occurs
Describe ADH
Short protein hormone produced in the magnoceullar neurones of the supraoptic and paraventricular nuclei of the hypothalamus, and then stored in the PPG. The main function is to promote water reabsorption in the CD and concentration urine
What stimulates ADH
Increase in plasma osmolarity Decrease in blood volume Decrease in blood pressure Nausea Nicotine Angiotensin II
What inhibits ADH
Decrease in plasma osmolarity Increase in blood pressure Increase in blood volume Atrial natriuretic peptide Ethanol
