Renal - 18 Flashcards
which is true about water reabsorption from the filtrate
facultative water reabsorption is in large part by adh
why do we make dilute urine
if there is too much water or too few ions in the body, dilute urine mist be made to concentrate blood
-6L of water in less than 3 hours = fatal water intoxication (blood too dilute)
-to concentrate the blood, urine made bust be more dilute in ions than the blood (urine must be less than 300mOsm/L)
Creating Dilute Urine (short loop?)
-start by making filtrate
-in the PCT solutes are reabsorbed and water follows them out of the tubule (300)
(gets saltier towards middle of kidney)
-filtrate enters descending LOH - loss of water makes the filtrate more concentration and the osmolarity goes up (500)
-bottom of loop =900mmosml
-filtrate moves back up ascending limb (550)
-filtrate enters thick ascending limb of LOH -where pump out salt and water cant follow (symporters), so filtrate loses solute and osmolarity goes down
-filtrate flows to the distal convoluted tubule and loses more solute (but not water) so osmolarity falls further
-enters collecting duct (sometimes water permeable or impermeable)
-this case filtrate enter permeable collecting ducts (only in presence of ADH) so a bit more solute is pumped out until most dilute urine in formed
Ions pumped out but not water
-the osmotic gradient is set up primarily by ascending limb of lop of henle pumping out ions but not water
-the descending limb loses water but not ions so much water is removed by descending limb of LOH
Creating Concentrated Urine
-if there is too little water or too many ions in body, urine must be made to reastiblich ionic balance
-the urine must be more concentration in ions than the blood –> more than 300mosml
-we can make urine that is about 1200mosml or about 4x more concentrated than blood
Long Loop Creating Concentrated urine
-make filtrate around 300mosml
-in the PCT, solutes are reabsorbed and water follows them out the tubule
-as it goes down descending loop, water leaves and filtrate gets increasingly concentrated (1200 at bottom)
-filtrate enters LOH and equilibrates - the loss of water make filtrate more concentrated and osmolarity goes up
-filtrate enters the thick ascending limb of LOH and solutes are pumped out by symporters but water cannot follow. the filtrate loses solute and the osmolarity goes down
-in distal convoluted tubule filtrate loses more solute (but not water) so osmolarity falls further (300)
-collecting duct is now water permeable (presence of ADH) to water flows out to match high osmolarity of surrounding interstitial fluid
-back at 1200 at base of medulla
Facts about concentrating urine
-the longer the loop of henle, the grater the time for the ascending limb to pump out solutes
-diuretics (water pills) such as furosemide (LASIX) work by inhibiting Na/K/CL pumps in the ascending loop of henle
Hormonal Regulation of Tubular Reabsorption
-hormone pathways that alter the rate of water reabsorption (Na/Cl/K) and thus regulates blood pressure and fluid balance
-ADH
-Renin-Angiotensin 2- Aldosterone System
How are Collecting Ducts Selectively Permeable to Water
concentrated urine = ADH leads to fusion of aquaporin 2 to the basolateral membrane of the collecting ducts
ADH -antidiuretic hormone (vasopressin)
-produced in hypothalamus and released from posterior pituitary (alongside oxytocin)
-adh is released when high osmolarity is plasma and interstitial fluid is detected by osmorecptors in hypothalamus
-adh leave in blood and leads to synthesis of water pores (aquaporin 2) in collecting ducts and nephrons
-this means water can easily leaved tubular fluid and can dilute blood and bring osmolarity down to normal
-adh increases activity of Na/K/Cl symporter
Angiotensin 2 and Blood Pressure
-decrease in blood pressure
-juxtaglomerular apparatus causes release of renin
-renin to angiotensin 1
-ace to angiotensin 2
-angiotensin 2 causes constriction of arterials and an increase in blood pressure
Angiotensin 2 and Aldosterone USE SLIDES
-decrease in blood pressure
-juxtaglomerular apparatus causes release of renin
-renin to angiotensin 1
-ace to angiotensin 2
-angiotensin 2 causes constriction of afferent arteriole
-thay causes decrease in glomerular filtration rate
-also increases sodium reabsorption by Na/H+ anti porters
-angiotensin 2 causes aldosterone release (check effects)
-increase in blood volume
Which of the following facilitates water loss from filtrate in the descending limb of the LOH
symporters in the thick lib of the ascending LOH
Evaluating Kidney Function
-urinalysis (volume, physical, chemical, and microscopic levels)
-blood test (levels of waster products)
Blood Tests for Kidney Function
-blood urea nitrogen (BUN)
measures urea nitrogen that is produced from protein breakdown
BUN will increase in blood
-the more filtrate you make, the more urea
-plasma creatinine
waster product from breakdown of phosphate of skeletal muscle
-normal in exercise but high levels can indicate poor kidney function
