Regulation Of Body Fluid Osmolality Lecture Flashcards
Is the renal medulla hypertonic, hypotonic, or isotonic?
Hypertonic
What is the maximum osmolality of the interstitium at the tip of the loop of Henle?
1200-1400 mOsmol/kg
What is the osmolality of the fluid leaving the loop of Henle and is it hypertonic, isotonic, or hypotonic?
100 mOsmol/kg H20
Hypotonic
What is the difference that the TAL maintains between the tubular fluid and the interstitium at any point along its length?
200 mOsmol/kg H20
What is the descending limb of the loop of Henle highly permeable to?
H20
What is the purpose of the vasa recta?
It supplies blood to the medulla and removes the water and solutes that are continuously added to the medullary interstitium
What occurs if there is increased blood flow in the vasa recta?
It decreases the salt and solute transport by nephron segments in the medulla reducing its ability to concentrate the urine, since it dissipates the medullary gradient
What areas are relatively impermeable to urea?
Thick ascending limb of the loop of Henle, the distal tubule, and the cortical collecting tubule
Where is ADH synthesized?
Supraoptic and Paraventricular Nuclei in the hypothalamus
From where is ADH secreted?
Posterior pituitary gland
What do principal cells reabsorb and secrete?
Reabsorbs Na+, Cl-, and H20
Secretes K+
What do intercalated cells reabsorb and secrete?
Reabsorb K+
Secretes H+
In the absence of ADH, are the principal cells permeable or impermeable to water?
IMpermeable
What is the mechanism of ADH on the principal cells?
Directs insertion of AQP-2 channels into the apical membrane allowing H20 permeability
What is the effect of aldosterone?
It is able to increase ENaC channels which increases the amount of sodium being reabsorbed from the tubular fluid in exchange for secretion of K+
What activates aldosterone?
High plasma K+ concentration or decrease in plasma Na+ concentration through the RAAS pathway
What is the effect of hypothalamic osmoreceptors when the plasma is hypoosmotic?
It “turns” ADH off which leads to dilution of the urine
What is the effect of Hypothalamic osmoreceptors when the plasma is hyperosmotic?
It “turns” ADH on and initiates the thirst response
Leading to concentrating urine and trying to get greater intake of fluids
What are the values for plasma osmolality in an adequately hydrated person?
275-295 mOsm
What are the values for a dehydrated person in plasma osmolality?
> 300 mOsm
What is the cause of central/neurogenic diabetes insipidus?
An ability to produce or release ADH from the posterior pituitary can be caused by head injuries, infections, or can be congenital
What is the treatment for central diabetes insipidus?
Desmopressin, a synthetic analog of ADH, which acts selectively on V2 receptors to increase water permeability in the late distal and collecting tubules
What can lead to nephrogenic diabetes insipidus?
Loop diuretics that inhibit electrolyte reabsorption in the loop of Henle
Lithium and tetracyclines can impair the ability of the distal nephron segments to respond to ADH
How do you distinguish between central and nephrogenic diabetes insipidus?
If you administer desmopressin and there is a response then it is central. If no response within 2 hours, then it is nephrogenic
What is SIADH?
An excessive release of ADH, which causes inappropriate and excessive water retention
What results due to SIADH/water retention?
Reduced plasma osmolality, dilutional hyponatremia, diminished aldosterone secretion, and elevated glomerular filtration rate
What are the sx associated with diabetes insipidus?
High UO, low levels of ADH, HYPERnatremia, dehydrated, lose too much fluid, excessive thirst
What are the sx for SIADH?
Low UO, high levels of ADH, HYPOnatremia, overhydrated, retain too much fluid, excessive thirst
What are the causes and characteristics of hyponatremia?
Causes: drugs, pain, nausea, decreased effective arterial volume, strenuous exercise
Traits: high urine osmolality (>300)
What are the causes and characteristics of hypernatremia?
Inadequate free water intake because of impaired access or impaired thirst
Traits: >600-800 urine osmolality
What are the four mechanisms that can cause polyuria?
- Increased intake of fluids with psychogenic causes
- Increased GFR with hyperthyroidism, fever, and hypermetabolic states
- Increased output of solutes as occurs in DM, hyperthyroidism, hyperparathyroidism, and use of diuretics
- Inability of the kidney to reabsorb water in the DCT due to drugs or renal failure
What is free water clearance?
The rate of free-water clearance represents the rate at which solute-free water is excreted by the kidneys
If + = h20 is excreted
If - = h20 is conserved
What is the ratio of urine osmolality and what does it indicate?
It is urine osmolality to plasma osmolality which determines the ability of the kidneys to concentrate or dilute urine
Uosm: Posm >1 indicates kidneys are able to concentrate urine
Uosm: Posm =1 urine is iso-osmotic with plasma
Uosm: Posm <1 indicates the kidneys are able to dilute urine
Where does ADH bind to?
It binds to the V2 receptor (a Gs GPCR) on the basolateral membrane of the collecting duct
