Chapter 27 GFR and RBF Flashcards
How is the filtration fraction calculated?
Filtration fraction = GFR/renal plasma flow
Which of the following are ways that help regulate the substances filitered through the glomerular capillaries?
A. Endothelial fenestrations lined with positively charged endothelial cell proteins
B. Negatively charged proteoglycans in the basement membrane
C. Acceptance of negatively charged molecules not postively charged molecules of similar size
D. Slit pores of the epithelium, between podocytes, accept negatively charged solutes. c56
D. B
The basemement membrane surrounds the endothelium and has large spacs that water and small solutes can filter through, EXCEPT plasma proteins. The NEGATIVE CHARGED proteoglycans in the BM keep them out! Positive charged molecules are favored, over negative, of the same size, are filtered. The fenestrations of the endothelium and slit pores in the epithelium are made of fixed negatively charged proteins.
Describe the phenomenon of minimal change nephropathy.
This occurs early in renal damage, where the basement membrane loses its negative charge and allows negatively charged solutes through. Allowing for proteinuria.
The GFR is calculated by Kf x Net Filtration Pressure. Net filtration pressure is composed of the sum of the osmotic and hydrostatic forces across the glomerular capillary. What are forces favoring and forces opposing filtration?
Forces favoring filtration:
- Glomerular hydrostatic pressure
- Bowman’s osmotic pressure
Forces opposing filtration:
- Glomerular osmotic pressure
- Bowman’s hydrostatic pressure
Which is the primary means of physiologic regulation of GFR?
A. Increased Bowman’s capsule hydrostatic pressure
B. Increased glomerular capillary colloid osmotic pressure
C. Increased glomerulary capillary hydrostatic pressure
D. Increased glomerulary capillary filtration coefficient
C. Increased glomerular capillary hydrostatic pressure is the primary means of regulating GFR.
In general, changes in glomerular capillary hydrostatic pressure is what drives the regulation of GFR.
The filtration coefficient is different for each tissue type. What are ways Kf increases or decreases GFR?
An increased Kf would increase GFR and vice versa. Certain disease lower Kf by reducing surface area of filtration (reduction of glomerular capillaries) or by reduction of hydraulic conductivity (thickening of capillary membrane).
Give a cause for an increase in the hydrostatic pressure of the Bowman’s capsule and how would it change GFR?
Increasing Bowman’s capsule hydrostatic pressure will decrease GFR. This can occur with obstruction of the urinary tract, causing a back flow of fluid and increased pressure Bowman’s pressure. i.e. urolithiasis prevents outflow and ultimately can cause hydronephrosis.
Which of the following situations serves to decrease GFR?
A. Increased RBF
B. Decreased filtration fraction
C. Decreased glomerular hydrostatic pressure
D. Increasing arterial plasma colloid osmotic pressure
D. Increasing arterial plasma colloid osmotic pressure
The increase in arterial plasma colloid osmotic pressure increases glomerular capillary colloid osmotic pressure.
Remember, filtration fraction = GFR/RBF. If GFR increases or RBF decreases, filtration fraction increases! An increase in GFR or a decrease in RBF causes an increase in the filtration fraction. In turn, this causes an increase in the glomerular osmotic pressure, due to the increased amounts of plasma proteins left in the glomerulary capillaries. The osmotic pull decreases the GFR.
Describe how increasing the efferent arteriole resistance can increase and ultimately decrease GFR.
Initially, when efferent arteriole constricts, glomerular hydrostatic pressure increases. As long as the resistance does not decrease RBF, then GFR is slightly increased. Once RBF is decreased, this increases filtration fraction and the glomerular colloid osmotic pressure increases. Thus, GFR decreases due to the protein pull of fluid in the glomerular capillary.
In regards to physiologic control of glomerular filtration, which of the following cause a decrease in GFR?
A. Epinephrine, norepinephrine and endothelin
B. Norepinephrine, epinephrine, prostaglandins
C. Endothelin, nitric oxide, bradykinins
D. Parasympathetic nervous system activation
A. Epinephrine, norepinephrine and endothelin
These hormones and peptide cause vasoconstriction. Norepi and epi are released from adrenal medulla and blood levels tend to be parallel to activity of the sympathetic nervous system (SNS). The SNS is a vasoconstrictor as well, and is strong during severe, acute disturbances. Eg. during a defense reaction, brain ischemia or severe hemorrhage. Parasympathetic control of renal vasculature does not exist.
Endothelin is a peptide released during damage of enothelial cells and is a powerful vasoconstrictor.
Prostaglandins and bradykinins do not play a larre role in regulating renal blood flow, but do cause vasodilation and increased RBF and GFR. Can also dampen vasoconstricting effects of the sympathetic nervous system and angiotensin II.
Nitric oxide is released by vascular endothelium and decreases renal vascular resistance.
