Glossary of 5.2 - Distal tubule and collecting ducts
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- What is the osmolarity of the filtrate that enters the DCT from the ascending loop of Henle?
- It is hyposmolar to plasma
- Name three of the four functions of the DCT and the collecting ducts.
- 1.ADH-dependent water reabsorption
2.aldo-dependent NaCl reabsorption
3.aldo-independent NaCl reabsorption
4.aldo-dependent K+ secretion
- What channel is used to move Na+ from the lumen to the cell in the distal tubule? How is the channel activated?
- How is Na+ moved from the cell to the interstitium in the distal tubule?
- Na+/K+ ATPase
- In the distal tubule, Na+ moves down its gradient from the lumen into the cell. How is the charge balanced?
- Passive diffusion of K+ from the cell to the lumen.
- Describe the structure of the ENaC. What binding sites does it feature?
- *multi-subunit channel
*apical sites bind amiloride which blocks the channel
*gates on the cytoplasmic side are responsive to aldosterone
- What are 2 mechanisms used by the alpha cells of the distal tubule to secrete H+?
- 1.H+/K+ ATPase
2.specific primary transporter (H+ ATPase)
- When CO2 enters an epithelial cell of the distal tubule it combines with water and forms H+ and HCO3-. What happens to the bicarbonate ion?
- It is moved to the interstitium via a HCO3-/Cl- ATPase antiporter.
- How do alpha cells of the distal tubule help the body cope with respiratory acidosis?
- The activity of K+/H+ ATPase and other H+ transporters is increased to increase the secretion of H+.
- What is the minimal urinary pH that can be attained?
- What are the beta cells of the distal tubule? What transporters do they feature? During what condition are these cells most active?
- *HCO3- secreting cells
*HCO3-/Cl- ATPase moves HCO3- into the lumen
*H+ ATPase moves H+ into the interstitium
- The osmolarity of the filtrate in the medullary collecting duct can vary widely - what causes this? What is the range of osmolarity of this filtrate?
- *the presence of ADH
*80mOsm/L (no ADH) to 300mOsm/L (max ADH)
- What are two ADH-dependent functions of the medullary collecting duct?
- 1.ADH-dependent activation of AQP-2 for reabsorption of water
2.ADH-dependent expression of UT-1 for urea reabsorption
- How does ADH affect the reabsorption of Na+ in the medullary collecting duct?
- It doesn't - ADH mediates only the reabsorption of water, independent of Na+.
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