Case Study Juxtaglomerular Filtrationr
In Case Study #2 we look at Rivka a young physically active college student who participated in strenuous activities on a hot day without planning for proper hydration.
In pronounced dehydration, hypotension can occur. How would this affect the glomerular filtration rate of the kidney? What actions by the juxtaglomerular apparatus would occur to restore GFR?
The glomerular filtration rate would decrease with a decline in blood pressure. The juxtaglomerular apparatus participates in renal autoregulation and, when activated, increases GFR. The process involves the release of renin from the juxtaglomerular cells found in the afferent arteriole. Renin enters the bloodstream and converts inactive angiotensinogen to angiotensin I. Angiotension-converting
enzyme (from the lungs) converts angiotension I to angiotensin II, a potent vasoconstrictor of the efferent arteriole that in turn increases GFR. Angiotensin II also encourages sodium reabsorption by the proximal convoluted tubule and stimulates aldosterone release by the adrenal glands.
What is the effect aldosterone has on the distal convoluted tubule? Why would the actions of aldosterone be useful to Rivka in her situation?
Aldosterone secretion causes sodium reabsorption and potassium secretion at the distal convoluted tubule. Aldosterone release by the adrenal cortex is stimulated by angiotensin II and would therefore be a component of water conservation in the dehydrated individual; when sodium is reabsorbed, an osmotic gradient is created and allows for the passive reabsorption of water.
What does a specific gravity test measure? If someone tested the specific gravity of Rivka’s urine, what might it indicate?
The specific gravity (or osmolality) urine test determines the concentration of solutes in a urine sample. It can therefore measure both hydration status of the patient and renal function. Rivka’s urine would be concentrated, and her specific gravity would be high (perhaps 1.030-1.040). This would reflect a decrease in hydration and water conservation by the kidneys.
In pronounced dehydration, hypotension can occur. How would this affect the glomerular filtration rate of the kidney? What actions by the juxtaglomerular apparatus would occur to restore GFR?
The glomerular filtration rate would decrease with a decline in blood pressure. The juxtaglomerular apparatus participates in renal autoregulation and, when activated, increases GFR. The process involves the release of renin from the juxtaglomerular cells found in the afferent arteriole. Renin enters the bloodstream and converts inactive angiotensinogen to angiotensin I. Angiotension-converting
enzyme (from the lungs) converts angiotension I to angiotensin II, a potent vasoconstrictor of the efferent arteriole that in turn increases GFR. Angiotensin II also encourages sodium reabsorption by the proximal convoluted tubule and stimulates aldosterone release by the adrenal glands.
What is the effect aldosterone has on the distal convoluted tubule? Why would the actions of aldosterone be useful to Rivka in her situation?
Aldosterone secretion causes sodium reabsorption and potassium secretion at the distal convoluted tubule. Aldosterone release by the adrenal cortex is stimulated by angiotensin II and would therefore be a component of water conservation in the dehydrated individual; when sodium is reabsorbed, an osmotic gradient is created and allows for the passive reabsorption of water.
What does a specific gravity test measure? If someone tested the specific gravity of Rivka’s urine, what might it indicate?
The specific gravity (or osmolality) urine test determines the concentration of solutes in a urine sample. It can therefore measure both hydration status of the patient and renal function. Rivka’s urine would be concentrated, and her specific gravity would be high (perhaps 1.030-1.040). This would reflect a decrease in hydration and water conservation by the kidneys.