Lecture 27: Urinary 3: Urine Formation Counter-Current System Flashcards
How the kidney regulate water balance?
-Dilutes or concentrates urine in accordance with hydration state
-If deprived of water, lower urine volume, much higher osmolality
-If “water loaded” excrete larger volumes of urine with low osmolality
How is concentration and dilution or urine done?
-Water movement occurs by osmosis through pores
-Dilution/concentration depends on osmolarity of interstitial and tubular fluids in the kidney
-If osmolarity in interstitial issue was constant in the kidney –>urine could not be formed at a higher osmolarity
-Handling of ions, urea and water creates increasing osmolarity from the medulla to the pelvis in the kidney
-This enables urine to be secreted at a higher osmolarity than plasma
What are the 3 components of idk cause he didn’t say on the slide :/
Hypertonic medullary interstitium: allows concentrated urine
Dilution of the tubule fluid in the thick ascending limb and the distal convoluted tubule: allows diluted urine (open door for water to go back in)
Variability in water permeability of collecting duct in response to vasopressin (antidiuretic hormone, ADH)
What is the counter-current multiplier?
-Loop of henle has two parallel limbs that run in opposite directions
-Descending (cortex –> medulla)
-Ascending (medulla –>cortex)
-Epithelial cells in the ascending limb
-Actively pump Na+, accompanies by secondary active transport of K+ and Cl-
-Apical membrane is impermeable to water
-Epithelial cells in the descending limb
-No active pumps, highly permeable to water
What happens with water in distal tubules and collecting ducts?
-When tubular fluid passes through the distal tubules and collecting ducts
-Goes from cortex to medulla= Increase in interstitial osmolarity
-Water will be allowed to exit the duct through the epithelial cells only if ADH is present (if no-little ADH water will be let go in urine)
-ADH stimulate the formation of aquaporins on the apical membrane of epithelial cells
-When ADH decreases: number of aquaporins decrease water is NOT reabsorbed
How is ADH regulated?
-ADH produced in hypothalamus, stored in posterior pituitary
-Hypothalamic osmoreceptors sense plasma osmotic pressure (release by reflex)
-Increase osmolality (or loss of water/too concentrated) trigger increase stimulus for ADH release
-Increase ADH release acts (via cAMP/protein kinase) to insert water channels (aquqporins) in distal tubules and collecting ducts
-Hypothalamic osmoreceptors also send excitatory signals to thirst centres in the hypothalamus
