Control Of Plasma Osmolarity Flashcards
What are most body fluids osmolarity in comparison to cells, what’s the exception to this?
Isotonic to cells 280-310 mOsm/ Kg
Bar urine normally 500-700 mOsm/ Kg
Can be 50-1200
Which nephrons are responsible for making concentrated using? What percent of nephrons do they make up? What are the blood vessels nearest to them?
Juxtamedullary nephrons
10-15%
Vasa recta within peritubular capillaries runs parallel to long LOH
How do we generate a vertical conc grad in the kidney? What’s this functional organisation known as?
medullary counter current mechanism:
Juxtamedullary nephron - long LOH establishes
- vasa recta maintains osmotic gradient (runs countercurrent to filtrate)
- collecting duct (uses gradient + ADH produce urine varying concentrations)
- urea (effective osmole in urine bc no transporters in kidney bar aquaporins, recycled in PCT )
Describe the osmolarity as you move from the corticomedullary border to medullary interstitium.
More hypertonic
Corticomedullary border - isotonic to plasma 300mOsm/Kg
Medullary interstitium - hyperosmotic 1200mOsm/Kg at papilla
Describe the relative solubilities and movement of H20 and Na from the different limbs of LOH
Descending limb:
Highly permeable H20 due to open AQP-1 channels.
Not permeable to Na+ so remains inside and filtrate conc increases
Ascending limb:
Actively transports NaCl out into interstitium through NKCC2 thick part.
Passively NaCl diffuses out this part.
Impermeable to H2O.
Osmolarity decreases -> hyposmotic to plasma
What hypertonicity is the filtrate leaving the ascending limb to reach the DCT in comparison to plasma?
Hypotonic
Hyposmotic
How and where do loop diuretics work?
Block NaKCC channels on thick ascending limb so interstitium becomes isosmotic and lots of dilute urine produced
How do we recycle urea in the kidney?
half Urea reabsorbed from medullary collecting duct
Cortical collecting duct impermeable to urea so moves into interstitium -> travels back to proximal convoluted tubule and uptaken by aquaporins
Thick ascending limb LOH secretes urea
increases with ADH
What happens to the 50% of filtered urea not recycled?
It’s excreted
ADH decreases excretion
How does the vasa recta work to maintain conc grad of interstitium while also supplying nutrients and O2?
Low flow so moves very slowly counter-current to filtrate and equilibrates at each stratified level so as solutes enter descending VR, H2O enters ascending VR
What are some physiological adaptions to high plasma osmolarity and how do these get signalled?
Osmoreceptors in hypothalamus in OVLT sense changes in plasma osmolarity through fenestreated endothelium exposed directly to systemic circulation signal secondary responses -> increase conc of urine and make thirsty (primary efferent pathway is ADH secretion never zero)
How does ECF and blood pressure effect ADH secretion?
Lower ECV means set point for ADH secretion is at a lower osmolarity (so ADH more easily secreted and more H20 reabsorbed)
If pressure increases the set point is higher (to reduce ADH and therefore ECV)
volume is more important than osmolarity
What conditions cause too little ADH secretion?
- central diabetes insipidus - damage to hypothalamus/ pituitary gland (e.g. Brain injury, tumour, sarcoidosis, TB, aneurysm, encephalitis, meningitis) -> large quantities urine
- nephrogenic diabetes insipidus (congenital, kidney cells insensitive to ADH) -> lots of urine ✅ADH injections/ nasal spray
What causes too much ADH secretion?
Syndrome of inappropriate ADH secretion (SIADH) XS release from PP/ another source
-> dilutional hyponatraemia, plasma Na low and total body fluid increased
What is hedonistic appetite?
Salt appetite when too much H20 or lack Na - deficiency drives need
