Renal 2 Flashcards
What is filtered by glomerular filtration? What isn’t?
Filtered: Water and low molecular weight substances
Not: Cells, proteins (albumin, globulins) and protein-bound substances
Why is it worrying if blood or albumin is found in the urine?
This means RBCs or proteins made their way through glomerular filtration when they are not supposed to
What are the 3 forces involved in glomerular filtration?
Glomerular capillary blood pressure: Pushed from the blood towards bowman’s space
Fluid pressure in bowman’s space: Pushes towards the blood
Osmotic force due to protein in plasma: pulls towards the blood
What is the formula for net glomerular filtration pressure?
Net GF pressure = Pgc - Pbs - πgc
PGC: glomerular capillary, PBS: bowman’s space, πGC: osmotic by proteins in GC
What is the definition of glomerular filtration rate? (GFR)
The volume of fluid filtered from the glomeruli into Bowman’S space per unit time (mL/min)
What can GFR be regulated by? (3)
Net filtration pressure (can change)
Membrane permeability (should not be changing)
Surface area available for filtration (should not be changing)
How can net filtration pressure be changed to regulate GFR?
The Afferent of Efferent vessel can be dilated or constricted to change the pressure at the glomerulus
What happens to the glomerular filtration rate if the Afferent vessel is constricted?
The GFR will decrease
What happens to the glomerular filtration rate if the Efferent vessel is constricted?
GFR will increase
What happens to the glomerular filtration rate if the Efferent vessel is dilated?
GFR will decrease
What happens to the glomerular filtration rate if the Afferent vessel is dilated?
GFR will increase
What is the definition of filtered load?
The total amount of any freely filtered substance
What is the formula for filtered load?
Filtered load = GFR x Plasma concentration of sbstance
How can filtered load be interpreted?
If the filtered load is greater than what can be found in the urine (excreted), there was a net absorption
If the filtered load is smaller than what can be found in the urine (excreted), there was net secretion
Reabsorption is the movement of substances from the __________ to the ________
tubular lumen
peritubular capillary
What are the two types of reabsorption? What is the difference?
Paracellular: substances pass through the interstitial fluid to be reabsorbed
Transcellular: substances pass through the tubular epithelial cells to be reabsorbed
What are 4 important facts about tubular reabsorption?
HINTS:
1. Amounts
2. Waste products
3. Useful components
4. Regulation
- Filtered loads are enormous, usually more than the amount of substance in the body
- Reabsorption of waste products is usually relatively incomplete (urea)
- Reabsorption of useful components is relatively complete
- Reabsorption of some substances are not regulated, while others are tightly regulated
What are the two mechanisms of reabsorption?
Diffusion and mediated transport
Across what do the two reabsorption mechanisms occur?
Diffusion: across the tight junctions (paracellular)
Mediated transport: across tubular cells (transcellular)
Explain how urea is reabsorbed by diffusion.
- Urea is freely filtered at glomerulus
- Proximal tubule reabsorbs water
- Urea concentration increases
- Urea diffuses into the interstitial fluid towards the capillaries
As an example of mediated transport, what are the steps of glucose or amino acid reabsorption?
- A Na/K ATPase pump makes a gradient for Na to enter the tubular epithelial cell (K in, Na out)
- Na is brought in
- Glucose / amino acids are co-transported into the cell with the Na, making a secondary gradient
- The secondary gradient pushes glucose and amino acids towards the capillaries
What is the transport maximum? What is an example of transport maximum being reached?
Tm: Membrane transport protein becomes saturated and the tubules can not reabsorb the substance any more
Ex: In uncontrolled diabetes mellitus, there is too much glucose to be reabsorbed by the transporters, resulting in glucosuria (with proper insulin levels, there isn’t too much insulin and the transporters are not overwhelmed)
What are the mechanisms responsible for secretion into the tubules?
Diffusion and mediated transport
What are the most important substances secreted by the tubules, and what is this secretion usually coupled with?
Hydrogen and potassium
Usually coupled with sodium reabsorption
How is reabsorption/ secretion divided throughout the tubules? (general)
Proximal tubule: Reabs. or most water and solutes, secretion for various solutes BUT NOT K
Henle’s loop: Reabs. large quantities of major ions but not water
DCT/ CD: Fine-tuning and homeostatic controls of excretion
What is the definition of clearance?
The volume of plasma from which the substance is completely removed by the kidneys
What is the formula for clearance?
C = Mass of substance excreted per unit time / Plasma concentration of a substance
Explain how inulin clearance can serve as a GFR indicator.
It is filtered at the glomerulus but not reabsorbed or secreted, so the volume of plasma cleared of inulin (C) is equal to the volume of plasma filtered (GFR)
How is creatinine an indicator of GFR?
It is filtered at the glomerulus but not reabsorbed and only slightly secreted, meaning the volume of plasma cleared is equal to the volume of plasma filtered
If you are given
Urine volume (V)
Urine concentration of creatinine (Ucr)
Plasma concentration of creatinine (Pcr)
How can you calculate creatinine clearance?
Clearance = UcrV/Pcr
What is the interpretation of clearance?
If the clearance of a substance is greater than the GFR, there was secretion at the tubules
If the clearance of a substance if less than the GFR, there was a reabsorption at the tubules
