6_HST110 Osmoregulation and Disorders of Water Balance 2017 Flashcards
What percentage of the total body weight is water in healthy adults?
60%
Positive water balance is when there is more (X) than (Y). Negative is the opposite
X = input Y = output
What percentage of TBW is extracellular, plasma, and arterial (effective), in order of decreasing quantities
Extracellular: 1/3
Plasma: 1/12
Arterial: 1/60
Plasma and interstitial Na+ concentration is (X) than inside the cell, where (Y) dominates
X = higher Y = K+
(X) determines the distribution of body water between the different fluid compartments. Water moves from low (Y) to high (Y)
X = Osmotic pressure Y = osmolality
(X) determine movement of water between plasma and interstitial compartments across a capillary wall.
X = Starling forces
Changes in plasma osmolality or plasma (X) reflect changes in water balance
X = [Na+]
(X) of all fluid compartments is essentially equal, so we can use plasma (X) to estimate (X) of the total body water
This is the parameter that is sensed and tightly regulated to maintain water balance
What is its normal range?
X = Osmolality
Normal range is 275-290 mOsm/kg
What is the expression for plasma osmolality (mOsm/kg)
P_osm ~ 2* Na+ (major component)
What is the human form of ADH?
Arginine Vasopressin (AVP)
ADH is produced by neuroendocrine cells in supraoptic and paraventricular nuclei of the (X). It is packaged in granules, transported down axons, and stored in nerve terminals located in the (Y). Acts on collecting ducts to regulate (Z)
X = hypothalamus Y = posterior pituitary Z = water reabsorption
The absence or presence of (X) is the major physiologic determinant of urinary water excretion or retention
X = ADH
What are the actions of ADH in the kidney (V2 receptors)
Increases permeability of the collecting ducts to water (AQP)
Increases permeability of the medullary collecting ducts to urea
Stimulates reabsorption of NaCl by the thick ascending limb, distal tubule, and collecting duct
What are the actions of ADH on the vasculature (V1 receptors)
Vasoconstriction
What are the 2 major stilmuli that regulates ADH release?
Plasma osmolality (Changes in plasma osmolality play the MOST important role in regulating ADH secretion)
Volume depletion
Osmolality is sensed by (X) in the anterior hypothalamus, which shrink or swell in response to changes in osmolality
X = osmoreceptors
Increase in Posm -> osmoreceptors shrink -> stimulates ADH secretion
opposite effect for decrease in Posm
Volume is sensed by baroreceptors
Carotid sinus, aortic arch, atria, afferent arteriole.
Over the physiologic range of effective circulating volume, ADH levels are determined almost entirely by plasma osmolality
However, volume depletion of (X) or greater significantly influences ADH levels (shifts ADH-osmolality curve to the left, resetting osmostat)
X = 10%
Name a few other stimuli for ADH release
Nausea Stress (pain, emotion, exercise) Drinking Acute hypoglycemia (>20% decrease) Drugs (Nicotine, Narcotics, Cyclophosphamide, Tricyclic antidepressants, Phenothiazine antipsychotic agents
Increase in plasma osmolality or decrease in volume stimulates (X). Osmotic threshold for triggering (X) is higher than that for ADH secretion (295 vs 285 mOsm/kg)
X = thirst
The differences between descending and ascending limbs of the (X) are essential to the process of concentrating or diluting the urine to conserve or remove water
X = LOH
Countercurrent Exchange occurs primarily in the juxtamedullary nephrons with (X) loops of Henle
X = long
What is the goal of the countercurrent exchange mechanism?
To establish a hyperosmotic medullary interstitium that will promote the reabsorption of water in the collecting duct