18 Questions
What is the consequence of H+ moving into the interstitial space when the plasma is too acidic?
Decreased secretion of K+
Why are the organic ion secretory systems in the proximal tubule important?
To excrete poorly soluble organic ions
What is the main function of actively adding more organic ions to the tubular fluid?
To reduce biological activity of chemical messengers
What happens to poorly soluble organic ions that are bound to carrier proteins in the plasma?
They remain in circulation
Which statement best describes the role of organic ion secretory systems in the proximal tubule?
They help reduce biological activity of certain chemicals
Why is actively adding more organic ions to the tubular fluid important?
To reduce or limit biological activity of chemical messengers
Which substance is often used as an example to calculate plasma clearance and estimate glomerular filtration rate?
Inulin
What is the primary reason why inulin is difficult to use and not commonly used clinically?
Inulin must be continually injected to maintain a steady plasma concentration
Which substance is typically used clinically to determine glomerular filtration rate due to its relatively steady plasma concentration?
Creatine
What is the estimated plasma clearance rate for inulin based on the provided calculation?
$125$ ml/min
What is the main role of inulin in estimating glomerular filtration rate?
To assess renal function by measuring the volume of plasma cleared per minute
Why is creatine preferred over inulin for clinical use in determining glomerular filtration rate?
Creatine does not require continuous injection to maintain a stable plasma concentration
What is the primary responsibility of the proximal tubule in the nephron?
Reabsorption of filtered water and solutes
How are organic ions highly bound to carrier proteins excreted?
Through tubular secretion
What does the removal of foreign compounds from the body primarily involve?
Routine removal by the kidneys
Which nephron portion determines the final amounts of H2O, Na+, K+, and H+ that will be eliminated by the body?
Collecting duct
In what manner are organic ions highly bound to carrier proteins removed from the body?
Unloading through tubular secretion
Which renal process is responsible for transferring much of the filtered water and needed solutes back into the blood?
Regulated reabsorption in the proximal tubule
Study Notes
Substances that are Filtered, Not Reabsorbed
- Inulin is an exogenous carbohydrate found in onions and garlic, freely filtered, but neither reabsorbed nor secreted.
- Inulin's plasma clearance is used to estimate glomerular filtration rate.
- Clearance rate for inulin = (30 mg/ml urine x 1.25 ml urine/min) / 0.3 mg/ml plasma = 125 ml/min.
Substances that are Filtered and Reabsorbed
- The proximal tubule is responsible for most of the reabsorption of filtered water and needed solutes back into the blood in an unregulated fashion.
- The distal and collecting tubules determine the final amounts of H2O, Na+, K+, and H+ that will be eliminated by the body through processes that are subject to control.
Substances that are Filtered and Secreted, Not Reabsorbed
- The proximal tubule contains two types of secretory carriers, one for organic anions and another for organic cations.
- These organic ion secretory systems are important for:
- Increasing Excretion: Actively adding more organic ions to the tubular fluid, increasing the amount of the organic ion excreted.
- Excreting Poorly Soluble Organic Ions: Many organic ions are not very soluble and circulate within the plasma bound to carrier proteins.
- Removing Foreign Compounds: The kidneys remove foreign organic ions, such as food additives, drugs, pesticides, and environmental pollutants, but there are no regulatory mechanisms to increase their removal if necessary.
Transport Across the Proximal and Distal Nephron
- When the plasma is too acidic, H+ move into the interstitial space and are transported into the epithelial cell, leading to less K+ secretion and potentially high levels of K+.
- The proximal tubule transfers much of the filtered water and needed solutes back into the blood in an unregulated fashion.
- The distal and collecting tubules determine the final amounts of H2O, Na+, K+, and H+ that will be eliminated by the body through processes that are subject to control.
Explore the process of renal tubular secretion, including the removal of small, unbound fractions of organic ions and excretion of highly bound organic ions. Learn how foreign organic ions are also eliminated from the body, including food additives, drugs, pesticides, and pollutants.
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