22 Questions
What is the term for the ability of the kidneys to maintain a constant GFR despite changes in arterial pressure?
Renal autoregulation
What is the mechanism by which the renal tubules increase their reabsorption rate when GFR rises?
Glomerulotubular balance
What is the term for the response of small arterioles to increased wall tension or wall stretch?
Myogenic mechanism
What is the purpose of the myogenic mechanism in the renal circulation?
To prevent excessive increases in renal blood flow and GFR
What is the term for the increase in urine production in response to increased arterial pressure?
Pressure diuresis
What is the composition of the glomerular filtrate?
Fluid with a similar composition to plasma, except for low molecular-weight substances
Why are certain low molecular-weight substances not filtered in the glomerular filtrate?
Because they are bound to plasma proteins
What is the purpose of the contraction of vascular smooth muscle in the myogenic mechanism?
To prevent excessive stretch of the vessel
What is the primary function of autoregulation in the kidneys?
To maintain constant renal blood flow and GFR over a range of arterial pressures
What is the main effect of a big activation of the renal sympathetic nerves on renal blood flow and GFR?
Decreases renal blood flow and GFR
What is the role of endothelin in the kidneys?
It contributes to renal vasoconstriction and decreased GFR
What is the effect of angiotensin II on renal blood flow and GFR?
Decreases renal blood flow and GFR
What is the primary function of vasodilators like nitric oxide and prostaglandins in the kidneys?
To dilate the afferent arterioles and increase GFR
What percentage of the kidney's blood flow goes to the renal cortex?
95%
What is the effect of vasoconstriction hormones like NA and epinephrine on renal blood flow and GFR?
Decreases renal blood flow and GFR under extreme conditions
What is the main mechanism by which the kidneys control renal blood flow and GFR?
Autoregulation
What is the effect of angiotensin II on the efferent arterioles?
Increases vasoconstriction
Which autacoid is responsible for basal level production of vasodilation in the kidneys?
Endothelial-derived nitric oxide
What is the effect of inhibiting nitric oxide formation on renal vascular resistance?
Increases renal vascular resistance
What is the effect of prostaglandins on renal blood flow and GFR in illness?
Increases renal blood flow and GFR
What is the purpose of autoregulation in the kidneys?
To control renal excretion of water and solutes
What is the effect of bradykinin on renal blood flow?
Increases renal blood flow
Study Notes
Renal Blood Flow and Glomerular Filtration Rate (GFR)
- Renal blood flow and GFR remain relatively constant despite changes in arterial pressure due to autoregulation.
- GFR barely changes by 10% due to autoregulation and additional adaptive mechanisms in the renal tubules.
Autoregulation of Renal Circulation
- Renal auto regulation prevents large changes in GFR.
- Additional adaptive mechanisms in the renal tubules, called glomerulotubular balance, increase reabsorption rate when GFR rises.
Pressure Diuresis and Natriuresis
- Changes in arterial pressure have significant effects on renal excretion of water and sodium, known as pressure diuresis or pressure natriuresis.
- This is crucial in regulating body fluid volumes and arterial pressure.
Myogenic Mechanism of Renal Circulation
- Myogenic mechanism is the ability of blood vessels to resist stretching during increased arterial pressure.
- It prevents excessive increases in renal blood flow and GFR when arterial pressure increases, protecting the kidney from hypertension-induced injury.
Glomerular Filtrate
- Urine formation begins with filtration of fluid through glomerular capillaries into Bowman's capsule.
- Glomerular filtrate has almost no protein or cells, with concentrations similar to plasma, except for a few low molecular-weight substances.
Renal Blood Flow Control
- The kidneys have effective mechanisms for maintaining renal blood flow and GFR relatively constant over an arterial pressure range of 80-170 mm Hg.
- Renal cortex receives more than 95% of the kidney's blood flow, with only 2% of blood flow in the renal medulla.
- The GFR is determined by many variables, including glomerular hydrostatic pressure and glomerular capillary colloid osmotic pressure.
Sympathetic Nervous System Control
- All blood vessels of the kidneys are innervated by sympathetic nerve fibers.
- A big activation of the renal sympathetic nerves constricts the renal arterioles and decreases renal blood flow and GFR.
Hormonal and Autacoids Control of Renal Circulation
- Vasoconstriction hormones (NA and epinephrine) only cause reductions in GFR and renal blood flow under extreme conditions, such as severe hemorrhage.
- Endothelin, a peptide released by damaged vascular endothelial cells of the kidneys, contributes to homeostasis and renal vasoconstriction.
- Angiotensin II is formed in the kidneys and in the systemic circulation, and there are receptors in all blood vessels of the kidneys, except the afferent arterioles.
- Prostaglandins (PGE2 and PGI2) and bradykinin cause vasodilation and increased renal blood flow and GFR.
- Endothelial-derived nitric oxide, an autacoid, decreases renal vascular resistance and maintains vasodilation of the kidneys.
This quiz covers the regulation of glomerular filtration rate (GFR) and its maintenance despite changes in arterial pressure, including renal auto-regulation and glomerulotubular balance.
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