Water Balance Flashcards
Water impermeable section of the nephron
In the ascending limb of the loop of henle and the early distal tubule.
ADH in water reabsorption
Uncouples the water and solute handling by the renal system to change concentration and urine flow.
Overall effect of low ADH
Hypoosmotic urine
High flow, low osmolality
Occurs when EFV is high
Overall effect of high ADH
Hyperosmotic urine
Low flow, high osmolality
Occurs when EFV is low
In ADH changes, total solute excretion is _______
Constant!
ADH origin as a peptide hormone
Synthesised in hypothalamus, released from posterior lobe of the pituitary gland based on osmoreceptors int he hypothalamus and peripheral baroreceptors
Stimulation of ADH secretion
Increase in plasma osmolarity but decrease in blood volume.
ADH effect on nephrons
Modulates permeability in distal tubule and collectiong duct to change volume and concentration of urine
ADH mechanism to change water permeability in nephron epithelial cells
ADH -> V2 receptor -> cAMP -> PKA - > AQP2-P
Causes aquaporins to be synthesis and trafficked in membranes along microtubules to apical membrane.
Corticopapillary osmotic gradient in interstitial fluid
Osmolarity increases towards the the medullary end (becomes
Rules in generating the CPO gradient (3)
- NaCl is reabsorbed without water in the ascending limb (decreases urine osmolarity)
- Osmolarity in the descending limb is the same as in the IF, always.
- Flow of isoosmotic fluid from the proximal tubule.
Urine dilution under low ADH
Distal tubule/Collecting duct, low water permeability, salt reabsorbed without water.
High volume, dilute.
Urine under high ADH (antidiuresis)
Increased water permeability in distal tubule and collecting duct, solutes remain transported the same, increased osmolarity decreased volume.
Urea recycling
Reabsorption increases interstitial fluid osmolarity, contributing to increase in corticopapillary osmotic gradient
ADH on Urea regulation
ADH stimulates high urea permeability via the UT1 facilitated transporter
Vasa recta countercurrent exchange
U-shaped blood vessel, easily permeable to water and solutes. Blood concentration changes to match the gradient, and free flow means very little excess solutes are washed away by the blood
Diabetes insipidus
Failure of ADH regulation, permanently off.
Constant high volumes of urine
Dehydration thirst.
Central vs nephrogenic diabetes insipidus
Central - failure to secrete from the pituitary, genetic mutations, head injury.
Nephrogenic - nephron don’t respond, mutations in V2 receptor of AQP2 channels.
