Renal/Diuretics Flashcards
The functional unit of the kidney. Has four functionally distinct regions.
Nephron. Glomerulus, proximal convoluted tubule, loop of henle, distal convoluted tubule.
All nephrons seems oriented such that the upper portion of Henles loop is in renal cortex and lower end descends toward renal medulla.
Tubules into which nephrons pour their contents.
Collecting ducts. The final segment of the distal convoluted tubule plus the collecting duct into which it empties can be considered the distal nephron
Three basic functions of the kidney? Which of the three is the most affected by diuretics?
Cleansing of ECF, maintenance of ECF volume/composition; most affected by diuretics
Maintenance of acid-base balance
Excretion of metabolic wastes and foreign substances.
Effects of the kidney on ECF are the result of what three basic processes? Which are selective and which are not selective?
Filtration, reabsorption, active secretion. Filtration is non selective, and does not regulate the composition of uterine. Reabsorption and secretion and the primary determinantes of what urine contains.
Where does filtration occur? What size molecules are filtered?
At the glomerulus. Almost all small molecules present in plasma are filtered. Cells and large molecules such as lipids and proteins remain in the blood.
Most prevalent constituents of filtrate are Na and chloride ions. Bicarb and K+ jobs are also present in smaller amounts.
Filtration capacity of the kidney explained?
Each minute, kidney provides 125mL of filtrate, 180L qday. Can process all of the ECF every 100 mins. ECF is completely cleaned about 14 times per day.
Med that is a simple 6-carbon sugar that embodies the four properties of an ideal osmotic diuretic. What drug and what properties?
Mannitol (Osmitrol). Freely filtered at the glomerulus, undergoes minimal tubular reabsorption and minimal metabolism, is pharmacologically insert w/ no direct effects on cells.
What is mannitol’s mechanism of action?
IV admin, then filtered by glomerulus. Undergoes minimal reabsorption, so most of the filtered drug stays in the nephron, creating osmotic force that inhibits passive reabsorption of water. Urine flow increases.
Effects are directly related to concentration of mannitol intake filtrate: the more present, the greater the diuresis. Diuresis begins in 30-60 minutes and lasts for 6-8 hours. Most excreted in tact in the urine.
Under certain conditions, blood flow to kidney is decreased (hypovolemic shock, etc.) leading to reduction in filtrate volume. When filtrate volume is low, transport mechanisms of nephron area able to reabsorb almost all of the Na and Cl, causing reabsorption of water as well. Urine output ceases, then renal failure. How does mannitol help prevent this? Why do thiazides and loop diuretics not work as well for this?
Filtered mannitol isn’t absorbed, even when filtrate volume is small, so it remains in the system, drawing water with it. Preserves urine flow. Thiazides and loops suck for this cause when there’s low filtrate production, there is such an excess of reabsorptive capacity relative to amount of filtrate that they can’t make a sufficient blockade of reabsorbing to promote diuresis.
How does mannitol help with ICP caused by cerebral edema and intraocular pressure?
It’s presence in the blood vessels of the brain causes edematous fluid to go from brain to blood. No risk of increasing cerebral edema cause it can’t exit capillary beds of the brain.
Lowers IOP by rendering plasma hyperosmotic with respect to intraocular fluids. Draws ocular fluid into blood. Use of mannitol for IOP is for pts. that have not responded to more conventional treatment.
