Topic 43 - Transport processes in the proximal tubule Flashcards
1
Q
Words to include
A
- Not permable for:
- Creatinine
- Urea
- HCO3-
- Proteins
- Reabsorption
- Actively to interstitium
- Passively to the peritubular capillaries
- Lumen
- ISF
- Sodium (Na+)
- Na+/K+-ATPase pump
- 3Na out/2K in
- Na+/K+-ATPase pump
- Hydrogen (H+)
- Na+ entry = H+ secretion
- Amiloride
- Carbonic anhydrase
- Bicarbonate (HCO3-)
- Impermable cells for HCO3-
- Indirect transport of HCO3-
- CO2 diffusing into cell
- H+
- HCO3-
- IC carbonic anhydrase
- Impermable cells for HCO3-
- Chloride (Cl-)
- Luminal membrane
- Chloride-acidic anion antiporter protein
- Cl- → cell
- Acidic anion → lumen
- Binds H+
- Free acid → diffuses back to cell
- Chloride-acidic anion antiporter protein
- Luminal membrane
- Water (H2O)
- Type 1:
- Increased peritubular oncotic pressure
- Paracellulary migrates
- Lumen → interstitium
- Type 2:
- Aquaphorin-1
- Type 1:
- Glucose, amino acids
- Secondary acitve symport
- Na+/K+-ATPase pump
- Glucose + Na+
- Amino acid + Na+
- Specific carrier
- Secondary acitve symport
- Urea
- Passively reabsorbed through cells
- Paracellular pathways
- Stays in interstitium
- Formation of osmotic layering
- Proteins
- Lume
- Back to tubular cells by pinocytosis
- From tubular cells as amino acids to interstitium
- Organic anions and cations
- Secretion
- Na+/K+-ATPase pump
- Secretion
2
Q
Topics to include in the essay
A
- Characteristic of the proximal tubule
- Sodium
- Hydrogen
- Bicarbonate ion
- Chloride
- Water
- Glucose & amino acids
- Urea
- Proteins
- Organic anions & cations
3
Q
Give the general characteristics of the transport processes in the proximal tubule
Give the substances transported in the proximal tubule
A
- High transport capacity
- No high gradient will be created
- 2/3 of water
- 95% of the filtered bicarbonate reabsorbed
- 70% of the filtrate is reabsorbed in the proximal tubule
- Hormonal regulation is not significant
- The wall of the tubule is not permeable for:
- Creatinine
- Urea
- HCO3-
- Proteins
- Reabsorption takes place in two phases:
- Actively to the intersitium
- Passively to the peritubular capillaries
- Substances transported in the proximal tubule:
- Sodium (Na+)
- Hydrogen (H+)
- Bicarbonate ion (HCO3-)
- Chloride (Cl-)
- Water (H2O)
- Glucose
- Amino acids
- Urea
- Proteins
- Organic cations & anions
4
Q
Transport of sodium in the proximal tubule
A
- Main motor: Na+/K+-ATPase pump
- 3 Na+ out / 2 K+ in
5
Q
Transport of hyrdogen in the proximal tubule
A
- Na+ entry = H+ secretion
- Inhibited by amilloride
6
Q
Transport of bicarbonate ion in the proximal tubule
A
- The cell is impermable for HCO3-
- Indirect HCO3- transport
- CO2 diffusing into the cell transforms into H+ and HCO3- with the help of IC carbonic anhydrase
7
Q
Transport of chloride in the proximal tubule
A
- The prerequisite for the transcellular chloride transport is the lower pH in the lumen than in the cell
- Then the chloride-acidic anion antiporter protein of the luminal membrane transports chloride to the cell, and acidic anion from the cell to the lumen
- In the lumen the acidic anion binds H+ and as free acid easily diffuses back to the cell
- Here it dissociated and another chloride transport can be carried out
8
Q
Transport of water in the proximal tubule
A
- Water can be transportet from the lume to the ISF in two different ways:
- Increased peritubular oncotic pressure makes the water paracellularly migrate from the lume → interstitium
- Facilitated by aquaporin-1, a special water channel
9
Q
Transport of glucose & amino acids in the proximal tubule
A
- Glucose and amino acids are 100% withdrawn from the proximal tubule together with Na+, via secondary active symport maintained by the Na+/K+-ATPase pump
- Glucose and amino acids have their own specific carriers
10
Q
Transport of urea in the proximal tubule
A
- Half of the urea are either:
- Passively resorbed through the cells
- Paracellular pathways
- Rest of the urea stays in the interstitium
- Contribues to the formation of osmotic layering in the kidney
11
Q
Transport of proteins in the proximal tubule
A
- Some proteins can get into the lumen
- The majority of these get back to the tubular cells by pinocytosis, then form here as amino acids to the interstitium
12
Q
Transport of organic anions & cations in the proximal tubule
A
- The removal of organic ions are not yet understood propperly
- The basis of the secretion is presence of normal Na+/K+-ATPase pump