Podcast
Questions and Answers
What effect does an increase in blood levels of ADH have on urine concentration?
What effect does an increase in blood levels of ADH have on urine concentration?
Which mechanism primarily contributes to the hyperosmolarity of the medullary interstitium?
Which mechanism primarily contributes to the hyperosmolarity of the medullary interstitium?
What is the expected osmolarity of urine produced under conditions of hypervolemia and hypotonicity?
What is the expected osmolarity of urine produced under conditions of hypervolemia and hypotonicity?
What type of diuresis occurs when large amounts of water are ingested?
What type of diuresis occurs when large amounts of water are ingested?
Signup and view all the answers
Which substance is commonly associated with osmotic diuresis?
Which substance is commonly associated with osmotic diuresis?
Signup and view all the answers
What is the primary function of the initial part of the distal convoluted tubules?
What is the primary function of the initial part of the distal convoluted tubules?
Signup and view all the answers
Which hormone primarily controls $Na^+$ reabsorption in the late part of the distal convoluted tubules?
Which hormone primarily controls $Na^+$ reabsorption in the late part of the distal convoluted tubules?
Signup and view all the answers
How does the distal convoluted tubules manage $H^+$ secretion?
How does the distal convoluted tubules manage $H^+$ secretion?
Signup and view all the answers
What percentage of the filtered water is typically reabsorbed in the distal convoluted tubules?
What percentage of the filtered water is typically reabsorbed in the distal convoluted tubules?
Signup and view all the answers
What is the effect of parathyroid hormone on $Ca^{++}$ reabsorption in the distal convoluted tubules?
What is the effect of parathyroid hormone on $Ca^{++}$ reabsorption in the distal convoluted tubules?
Signup and view all the answers
Which of the following is NOT a buffer system used for excess $H^+$ in the distal convoluted tubules?
Which of the following is NOT a buffer system used for excess $H^+$ in the distal convoluted tubules?
Signup and view all the answers
The fluid delivered from the distal convoluted tubules to the collecting ducts is characterized as:
The fluid delivered from the distal convoluted tubules to the collecting ducts is characterized as:
Signup and view all the answers
How is the majority of $H^+$ secreted in the initial part of the distal convoluted tubules?
How is the majority of $H^+$ secreted in the initial part of the distal convoluted tubules?
Signup and view all the answers
What mechanism is primarily responsible for K+ secretion in the distal convoluted tubules (DCTs)?
What mechanism is primarily responsible for K+ secretion in the distal convoluted tubules (DCTs)?
Signup and view all the answers
Which of the following factors can increase K+ secretion in the DCTs and cortical collecting ducts?
Which of the following factors can increase K+ secretion in the DCTs and cortical collecting ducts?
Signup and view all the answers
Where does the acidification of urine primarily occur?
Where does the acidification of urine primarily occur?
Signup and view all the answers
Which cells are primarily involved in primary active transport of H+ in the collecting ducts?
Which cells are primarily involved in primary active transport of H+ in the collecting ducts?
Signup and view all the answers
What is the effect of increasing extracellular K+ levels on K+ secretion?
What is the effect of increasing extracellular K+ levels on K+ secretion?
Signup and view all the answers
What is the initial source of H+ in renal tubular cells for urine acidification?
What is the initial source of H+ in renal tubular cells for urine acidification?
Signup and view all the answers
In which part of the nephron does Na+ reabsorption primarily occur through primary active transport?
In which part of the nephron does Na+ reabsorption primarily occur through primary active transport?
Signup and view all the answers
Which of the following describes the counter-transport mechanism for H+ secretion?
Which of the following describes the counter-transport mechanism for H+ secretion?
Signup and view all the answers
Where does urea reabsorption primarily occur in the renal tubules?
Where does urea reabsorption primarily occur in the renal tubules?
Signup and view all the answers
What is the primary mechanism by which water reabsorption occurs in the collecting ducts in the presence of ADH?
What is the primary mechanism by which water reabsorption occurs in the collecting ducts in the presence of ADH?
Signup and view all the answers
What percentage of filtered water is typically reabsorbed in the cortical collecting ducts?
What percentage of filtered water is typically reabsorbed in the cortical collecting ducts?
Signup and view all the answers
Which hormone primarily increases potassium secretion in the cortical collecting ducts?
Which hormone primarily increases potassium secretion in the cortical collecting ducts?
Signup and view all the answers
During which condition does urine concentration primarily occur?
During which condition does urine concentration primarily occur?
Signup and view all the answers
In which part of the collecting ducts does primary active transport mainly contribute to hydrogen ion secretion?
In which part of the collecting ducts does primary active transport mainly contribute to hydrogen ion secretion?
Signup and view all the answers
What is the fate of approximately 99.7% of the filtered water in the renal tubules?
What is the fate of approximately 99.7% of the filtered water in the renal tubules?
Signup and view all the answers
What process is primarily responsible for producing urine with an osmolarity of about 400 mOsm/liter?
What process is primarily responsible for producing urine with an osmolarity of about 400 mOsm/liter?
Signup and view all the answers
Study Notes
Distal Convoluted Tubules (DCTs)
- DCTs receive hypotonic fluid from the ascending limbs of the loops of Henle
- Functionally divided into 2 parts:
- Initial part:
- Has the same characteristics as the thick segment of the ascending limbs of the loop of Henle
- Impermeable to water and solutes (urea, Na+, Cl-) except for Na+ (reabsorbed by primary active transport. Cl- follows passively)
- Tubular fluid becomes more hypotonic (about 100 mOsm/liter), hence called the diluting segment
- Initial parts secrete H+ mainly by secondary active transport
- Late part:
- Performs reabsorption functions:
- Na+ reabsorption occurs by primary active transport, controlled by aldosterone, followed by passive reabsorption of Cl- and water
- Only about 5% filtered water is reabsorbed in DCTs due to poor permeability
- No urea reabsorption due to poor permeability
- Fluid delivered to collecting ducts is hypotonic
- Ca++ reabsorption occurs by primary active transport and is increased by parathyroid hormone
- Secretes H+ mainly by secondary active transport
- Intercalated cells begin appearing increasing in abundance. These cells secrete H+ independent of Na+ by primary active transport and via H-ATPase
- Performs reabsorption functions:
- Initial part:
- III Secretion of buffers for excess H+ in the DCTs
- Kidneys can excrete urine as low as pH 4.5 in acidosis or as high as 8 in alkalosis
- In acidosis, to prevent pH below 4.5, urine is buffered using bicarbonate (HCO3- and H+), phosphate and ammonia systems.
- Main buffering in the PCTs
- Remaining excess H+ in the tubular fluid is buffered by phosphate and ammonia in tubular fluid.
- Phosphate is a more powerful buffer in tubular fluid due to higher concentration.
Collecting Ducts (CDs)
-
CDs receive hypotonic fluid from DCTs
-
Divided into two parts (cortical and medullary)
-
Medullary Part:
- Reabsorption
- Na+ reabsorption occurs by primary active transport, increased by aldosterone in cortical parts only
- Followed by passive diffusion of Cl- and water, coupled with K+ secretion
- Urea reabsorption
- Occurs by passive diffusion in inner medullary parts only, mainly in presence of ADH
- Not reabsorbed in cortical parts or outer medulla due to impermeability.
- Water reabsorption in CDs
- Relatively impermeable to water in the absence of ADH
- In the presence of ADH, CDs become permeable to water.
- Aquaporins (AQP2 & AQP3) activate in presence of ADH
- Water reabsorption depends on blood ADH levels, and is also called facultative water reabsorption
- Cortical CDs receive hypotonic fluid
- About 10% of filtered water is passively reabsorbed, plus additional 4.7 % absorbed by medullary interstitium.
- Leads to isotonic tubular fluid at the end of the cortical CDs
- Medullary CDs absorb more water from hyperosmotic medullary interstitium leading to more concentrated urine, about 1000 mOsm/liter
- Reabsorption
-
Secretion:
- K+ secretion occurs only in cortical parts in exchange for Na+ reabsorption and is enhanced by increasing aldosterone.
- H+ secretion, takes place in both cortical and medullary parts. Cortical via both primary and secondary active transport. Medullary occurs primarily via primary active transport.
-
Summary of Water Reabsorption
- About 99.7% of filtered water is reabsorbed:
- 65% in PCTs
- 15% in descending limb of loop of Henle
- 5% in DCTs
- 10% in cortical CDs
- 4.7% in medullary CDs
- About 99.7% of filtered water is reabsorbed:
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Explore the structure and functions of the Distal Convoluted Tubules (DCTs) in the nephron. This quiz delves into the processes of sodium reabsorption, water permeability, and the differences in the initial and late segments of DCTs. Test your knowledge on how these functions impact kidney operations and fluid balance.
