Lecture 7 - Regulation of Renal Hemodynamics Flashcards
Does the process of glomerular filtration utilize O2?
NOPE
Why does the kidney use O2?
Active reabsorption
Does the blood flow to the kidney exceed its O2 needs?
BY FAR
What is the relationship between higher renal blood flow and O2 consumption?
Higher blood flow => higher GFR => higher rate of active reabsorption => higher O2 consumption
Equation for flow rate through an organ?
Q = ΔP/R
ΔP = pressure differential through the capillary bed
Resistance in the kidney?
- Afferent arteriole = RA
- Efferent arteriole = RE
RT = RA + RE
How does pressure vary through the efferent arteriole?
Decreases
Describe hydrostatic and oncotic pressures in the peritubular capillaries. What does this facilitate?
Higher oncotic pressure than hydrostatic because of the filtration of plasma through the glomerulus => facilitates reabsorption
How is RPF affected by increasing mean renal arterial pressure? What is this called? What does this mean for GFR?
Relatively constant (very slight increase) from 80 to 180 mmHg and increases outside of that range => MYOGENIC (AUTO)REGULATION: renal arterioles constrict reflexively in response to increased pressure to increase resistance
Same for GFR
Why are there limits to the kidney autoregulation of blood flow?
- Past 180 mmHg: renal arteriole is maximally vasoconstricted
- Before 80 mmHg: renal arteriole is maximally vasodilated
Describe autoregulation of blood flow. Purpose?
Increase in transmural pressure of the arteriole/capillary sphincter => stretched smooth muscle => depolarization of smooth muscle => contraction => decreased vessel diameter (or opposite mechanism with hyperpolarization)
Purpose: ability to normalize flow in the face of fluctuating transmural pressure to keep local flow relatively constant
Effect of afferent arteriole vasoconstriction on glomerular hydrostatic pressure?
Decreases it
Effect of efferent arteriole vasoconstriction on glomerular hydrostatic pressure?
Increases it
Effect of efferent arteriole vasodilation on glomerular hydrostatic pressure?
Decreases it
Effect of afferent arteriole vasodilation on glomerular hydrostatic pressure?
Increases it
Constriction of afferent arteriole:
- Effect on renal plasma flow?
- Effect on GFR?
- Effect on filtration fraction (GFR/RPF)?
- Oncotic pressure in peritubular capillary compared to normal?
- Decrease
- Decrease
- No change
- No change
Dilation of afferent arteriole:
- Effect on renal plasma flow?
- Effect on GFR?
- Effect on filtration fraction (GFR/RPF)?
- Oncotic pressure in peritubular capillary compared to normal?
- Increase
- Increase
- No change
- No change
Constriction of efferent arteriole:
- Effect on renal plasma flow?
- Effect on GFR?
- Effect on filtration fraction (GFR/RPF)?
- Oncotic pressure in peritubular capillary compared to normal?
- Decrease
- Increase
- BIG increase
- Increase
Dilation of efferent arteriole:
- Effect on renal plasma flow?
- Effect on GFR?
- Effect on filtration fraction (GFR/RPF)?
- Oncotic pressure in peritubular capillary compared to normal?
- Increase
- Decrease
- BIG decrease
- Decrease
Dilation of afferent arteriole + constriction of efferent arteriole:
- Effect on renal plasma flow?
- Effect on GFR?
- Effect on filtration fraction (GFR/RPF)?
- Oncotic pressure in peritubular capillary compared to normal?
- No change
- BIG increase
- BIG increase
- BIG increase
What endogenous hormone will dilate the afferent arteriole and constrict the efferent arteriole?
ANP
Do the vasomotor effects of ANP extend beyond the renal arteries?
NOPE
Effects of angiotensin II on renal blood flow?
Filtration fraction in particular? Explain how it works in detail.
Decrease in blood volume => kidney secretes renin => renin converts angiotensinogen (from liver) to angiotensin I => ACE (from lungs endothelium and every other endothelial cell) converts angiotensin I to II =>
- Angiotensin II first constricts the afferent arteriole, which decreases RPF and GFR
- Angiotensin II then constricts the efferent arteriole, which increases GFR slightly (not back to its normal value though), and further decreases RPF + decrease GFR further accentuated by the effect of angiotensin II on the size of the filtration slits leading to decreased filtration surface area
- Overall, there is a large decrease in RPF and a slight decrease in GFR leading to an INCREASE in filtration fraction
=> increases GFR/RPF => increases peritubular oncotic pressure => increased BP and intravascular volume
What does the oncotic pressure in the peritubular capillaries depend on?
GFR/RPF