Renal II Flashcards
Which of the following substances will and will not pass freely through glomerular filtration?
a) Water
b) Proteins
c) Fatty acids
d) Low-molecular weight substances
e) Calcium ions
f) Cells
a) Yes
b) No
c) No
d) Yes
e) 1/2 yes, 1/2 no (those bound to albumin)
f) No
What are the major forces responsible for glomerular filtration? What direction do they act in with regards to filtration?
Glomerular capillary blood pressure (PGC) - favours filtration
Fluid pressure in Bowman’s space (PBS) - opposes filtration
Osmotic force due to protein in plasma (piGC) - opposes filtration
What is PGC?
It is the pressure exerted by the blood flow on the glomerular capillary, favouring filtration of the blood into Bowman’s space.
What is PBS?
PBS is the fluid pressure in Bowman’s space, which pushes fluid back into the glomerular capillaries.
What is piGC?
It is the osmotic force created by the proteins in the plasma in the glomerular capillaries, pulling fluid back into the capillaries from Bowman’s space.
What is the formula for net glomerular filtration pressure? What is the typical value?
Net glomerular filtration pressure = PGC - PBS - piGC
Typical value: around 16
What is glomerular filtration rate?
GRF is the volume of fluid filtered from the glomeruli into Bowman’s space per unit time.
GFR is regulated by what three factors? Which is/are the most important?
- Net filtration pressure
- Membrane permeability
- Surface area available for filtration
Net filtration pressure is the biggest contributor.
The others, membrane permeability and surface area available for filtration, are not as significant in normal physiology. In pathological conditions, these get lower.
What is the standard GFR value?
180 L/day
How often does plasma get filtered at the glomeruli? Why?
Plasma is filtered 51 times a day, as most of it gets reabsorbed after it initially gets filtered.
Will the following conditions lead to an increase or decrease in GRF?
a) Constriction of afferent arteriole
b) Dilation of afferent arteriole
c) Constriction of efferent arteriole
d) Dilation of efferent arteriole
a) Decrease GFR
b) Increase GFR
c) Increase GFR
d) Decrease GFR
What is filtered load? What is the formula?
Filtered load is the total amount of any freely filtered substance per unit time.
Filtered load = GFR x plasma concentration of the substance
If filtered load > amount excreted in urine, […] has occurred.
net reabsorption
If filtered load < amount excreted in urine, […] has taken place
net secretion
The tubular lumen is lined by […] cells connected by […] junctions
The tubular lumen is lined by epithelial cells connected by tight junctions
What are the two routes by which reabsoption can occur? Explain the difference between them.
Paracellular: fluid passes through tight junctions between epithelial cells.
Transcellular: fluid passes through epithelial cell.
Compare the reabsorption rates for water, sodium, glucose, urea, and potassium.
Water: 99%
Sodium: 99.5%
Glucose: 100%
Urea: 44%
Potassium: 86.1%
How does the size of filtered loads compare to the amount of that substance in the body?
Filtered loads are enormous, generally greater than the amounts of the substance in the body. This is because most gets reabsorbed and then filtered again.
What determines the reabsorption percent for a given substance?
Its usefulness to the body. Reabsorption of waste products is relatively incomplete (e.g. urea), while reabsorption of important ions and water is relatively complete.
What types of substances have heavily regulated tubular reabsorption? Which don’t?
Not regulated: glucose, amino acids
Highly regulated: water, inorganic ions
What are the two mechanisms of reabsorption?
Diffusion and mediated transport
How does reabsorption by diffusion occur? Is this process usually paracellular, transcellular, or both?
Almost paracellular. Occurs across the tight junctions connecting the tubular epithelial cells, following the electrochemical gradient of the substance.
The reabsorption of urea in the proximal tubule occurs by what mechanism? Explain how.
It occurs via diffusion.
- Urea is freely filtered at the glomerulus
- In the proximal tubule, water reabsorption occurs
- Urea concentration in the tubular fluid becomes higher
- Urea diffuses into the interstitial fluid and peritubular capillaries.
How does reabsorption by mediate transport occur? Is this process usually paracellular, transcellular, or both?
Reabsorption by mediated transport occurs across tubular cells (transcellular epithelial transport).
Requires the participation of transport proteins in the plasma membrane of tubular cells. Usually coupled to the reabsorption of sodium.