Phys 1 Flashcards
What is the role of the vasa recta?
- supplies blood to the medulla
- removes solute and water that is added to the medullary interstitium
- maintains medullary interstitial gradient flow
What causes “medullary washout”?
substantial increase in vasa recta blood flow dissipates the medullary gradient
*decreased blood flow decreases solute transport by the nephron in the medulla, which reduces ability to [urine]
What is the role of UT-A1 and UT-A3?
cause urea to leave the CD and go into the medullary intersititum
*some will diffuse into the thin LoH, and travels back to the CD (recycling)
What creates the medullary interstitial osmotic gradient?
- AQ channels and absence of tight junctions within the thin limb
- LoH/CD anatomy contributes to the countercurrent multiplication
What neurons synthesize ADH? Where are they found? What stimulates their activity?
- supraoptic and paraventricular nuclei
- hypothalamus
- increased osmolarity (their activity leads to release of ADH)
What response happens first: ADH or thirst?
ADH
What is the role of principal cells? intercalated cells?
- reabsorb Na+, Cl-, and H2O (virtually impermeable if no ADH); secrete K+
- reabsorb K+ and secrete H+ (aldosterone stimulated H+ ATPase)
What releases aldosterone?
adrenal cortex
*works to increase ENaC channels
Where do aquaporin channels get inserted?
apical membrane of principal cells
What are the two roles of the hypothalamic osmoreceptors?
- Turn on ADH
- Thirst
*applies with increased osm
What’s the difference between the cortical and the medullary CD’s permeability to H2O?
Cortical is always permeable, but the medullary permeability is determined by ADH
Diabetes Insipidus: Central Neurogenic
- inability to produce or release ADH from the posterior pituitary due to head trauma, infection, or congentical abnormality
- formation of large amounts of dilute urine
- water restriction can lead to severe dehydration
- treatment: desmopressin, which selectively acts on V2Rs to increase H2O permeability in the late distal and collecting tubules
Diabetes Insipidus: Nephrogenic
- inability of the kidneys to respond to ADH
- due to failure of the countercurrent mxn to form a hyperosmotic renal medullary interstitium or failure of the distal and collecting tubules/ducts to respond to ADH
- formation of large amounts of dilute urine, which can cause dehydration
What is a problem found with the drugs tetracyclines and lithium?
they can impair the ability of the distal nephron segments to respond to ADH
How can we clinically distinguish between central and nephrogenic?
administer desmopressin
SIADH
- excessive release of ADH
- major cause of low sodium levels
Diabetes Insipidus vs. SIADH
- Urinary Output
- ADH levels
- Hyper or hypo natremia?
- Hydration status
- Fluid Loss
- Thirst
- High vs. Low
- Low vs. High
- Hypernatremia vs. Hyponatremia
- Dehydrated vs. Overhydrated
- Lose vs. Retain
- Excessive thirst for both
Hyponatremia: urine osm with true volume depletion, effective circulating volume depletion, and volume depletion and SIADH?
> 300
Hypernatremia: urine osm with water depletion, water and volume depletion, and salt intoxication?
> 600-800
Polyuria: volume and causes
- > 2.5 L/day
2. DM, DI, excess caffeine or alcohol, kidney disease, diuretics, sickle cell anemia, excessive water intake
Oliguria: volume and causes
- 300-500 mL/day
2. dehydration, blood loss, diarrhea, cariogenic shock, kidney disease, enlarged prostate
Anuria: volume and causes
- <50 mL/day
2. kidney failure, obstruction, enlarged prostate
Four Mxns of Polyuria
- Increased intake
- Increased GFR
- Increased output of solutes
- Inability of the kidneys to reabsorb water from the DCT
Free water clearance (Ch2o)=
V - Cosm = V - ((Uosm x V) / Posm)
Uosm=urine osm
V=urine flow rate
Posm=plasma osmolarity
