9.6 Urine Flashcards
What are the ascending and descending limb of the loop of Henle permeable to?
Descending limb is permeable to water, water leaves and filtrate becomes concentrated inside the loop of Henle
Ascending limb is NOT permeable water, pumps out NaCl without allowing water to balance
What is the vasa recta? What is it’s function?
countercurrent exchange: vasa recta blood flow turns up and around the loops of henle, exchanging NaCl and water along with the established gradient
= maintain countercurrent
How does ADH work on the nephron?
More ADH-> more aquaporin channels in collecting duct-> more water retained
How do diuretics work?
prescribed for high blood pressure, block hormonal mechanisms, block medullary gradient formation, dilute, large volumes of urine excreted
What is tubular secretion?
selectively adding to the filtrate by removing molecules from the blood
Excess in blood, needs excretion: metabolic waste (creatinine, etc), plasma protein bound drugs, acid (H+) or base (HCO3-), ions (K+), urea
Where is K+ secreted? Why is this important?
is regulated to maintain electrical gradients, especially in the heart, and maintain Na/K pump activity in the kidneys
Secretion occurs in the DCT and Collecting Duct
Na/K Pump, moves K+ into tubules
K+ leaky channels in DCT and collecting duct lumen
Secretion stimulated by aldosterone
Where is H+ secreted? Why important?
H+ secretion is regulated in order to maintain acid/base balance
Normally causes urine to be acidic pH = 6
occurs in mainly in PCT and Collecting Duct
H+ ATPase pumps
H+/K+ ATPase pumps
Na+/H+ cotransporters; antiporters
Balanced with HCO3- formation and reabsorption to blood
What are sources of acid?
phosphoric acid: due to protein breakdown
lactic acid: due to anaerobic metabolism
ketone bodies: due to fatty acid metabolism (lack of glucose energy source)
CO2 production
What is the timeframe for respiratory vs urinary compensation to acid?
respiratory compensation within seconds
urinary compensation within hours to days
How are organic ions secreted? Consequences?
Two types of non-selective carriers for
organic anions
organic cations
Consequence of general anion/cation group carriers is that drugs compete for carriers during elimination, causes drug interactions
Two drugs taken that use the same carrier, will NOT be fully eliminated
What determines the plasma clearance rate of something?
GFR
Reabsorption rate
Secretion rate
Compare creatine, glucose, and H+ clearance to GFR
Creatinine- normal breakdown product, usually 100% cleared, so creatinine clearance rate is a good estimate of GFR
Vs Glucose- filtered, should be 100% reabsorbed: glucose < GFR, should be 0
Acid- filtered, actively removed, clearance rate should be much higher than GFR
How can creatinine clearance be used to estimate GFR?
fully filtered, not reabsorbed 100% produced creatinine should be found in urine (and very little in the blood)
simple way to estimate GFR
low creatinine clearance low GFR, impaired renal function, hypotension, heart failure, shock
high creatinine clearance high creatinine production ex: pregnancy, diabetes mellitus, high protein diet
What regulate Na+ reabsorption and secretion?
Renin-angiotensin-Aldosterone System (RAAS)
Increases Na+ reabsorption
Atrial and Brain Natriuretic Peptides: ANP & BNP
Decreases Na+ reabsorption
What regulates water reabsorption and secretion?
Osmotic Gradient & Vasopressin (ADH)
Increases H20 reabsorption, maintains blood volume
