Urine Concentration and Dilution Mechanisms Flashcards
What do we need to concentrate Urine?
- ADH
2. Functioning Loop of Henle to establish concentration gradient
What is the process of ADH water reabsorption?
- Osmoreceptors in Hypothalamus detect high blood Osmolarity activating Thirst and ADH secretion
- ADH released into bloodstream from Posterior Pituitary
- ADH causes the Aquaporin Channels of the Collecting Duct to open
- Water is reabsorbed and blood Osmolarity decreases
Descending Limb of Loop of Henle:
- What is it called?
- What is it Permeable to?
- What is it Impermeable to?
- “Concentrating Segment”
- PERMEABLE to Water
- IMPERMEABLE to Solutes
Ascending Limb of Loop of Henle:
- What is it called?
- What is it Permeable to?
- What is it Impermeable to?
- “Diluting Segment”
- IMPERMEABLE to Water
- PERMEABLE to Solutes
What are the two types of Nephrons?
- Cortical Nephrons
2. Juxtamedullary Nephrons (long)
What solutes are reabsorbed in the Proximal Tubule?
- Na
- Water
- Glucose
- Bicarb (HCO3)
- K
- Cl
What solutes are reabsorbed in the Ascending Limb of the Loop of Henle?
“ClaNK”
- Na
- Cl
- K
What solutes are reabsorbed in the Distal Tubule?
- Na
- K
- Cl
- Ca
Osmolarity at the bottom of the Loop of Henle depends on…
HOW LONG THE LOOP OF HENLE IS
Longer Juxtamedullary Nephrons can get up to 1200 mOsm/L
What is the Osmolarity at the start of the Distal Tubule?
150 mOsm/L
What is the Osmolarity at the start of the Collecting Duct?
150 mOsm/L
How does the PRESENCE of ADH effect Urine concentration?
If the urine is more concentrated in the ECF than inside of the Collecting Duct, ADH creates HYPERTONIC URINE
Osmolarity goes up if water leaves
What is the highest Osmolarity that Urine can reach?
1200 mOsm/L if ECF is that high and ADH causes Aquaporin channels to open
How does the ABSENCE of ADH effect Urine concentration?
Water cannot escape so urine is labeled as HYPOTONIC
What is the main transporter on the Ascending Limb of the Loop of Henle?
Na/K/Cl Transporter
-pumps 1 Na, 1, K, and 2 Cl into ECF
What is unique about the Na/K/Cl Transporter?
“Tmax=200mOsm gradient”
The Transport Max of the Na/K/Cl Transporter is based on an Osmolarity difference of 200 mOsm
Describe the steps taken to establish the Concentration Gradient:
- Na/K/Cl Transporter is turned on and pumps solutes out until a difference of 200 mOsm is established everywhere between the Ascending Limb and the ECF (In Example: Asc Limb is 200 mOsm and ECF is 400 mOsm)
- Water channels on the Descending Limb open and water flows out to equilibrate the Descending Limb with the ECF (both ECF and Descending Limb are now 400 mOsm)
NOTE: At this point the Descending Limb is all 400 mOsm and the Ascending Limb is all 200 mOsm
- Fluid from the Proximal Tubule moves into the Descending Loop. Fluid from the Descending Loop moves into the Ascending Loop. Fluid from the Ascending Loop moves into the Proximal Tubule.
- Gradient is reestablished. Na/K/Cl Transporter establishes the 200 mOsm difference between Ascending Limb and ECF. Concentration at the bottom of the Loop of Henle gets higher.
- Fluid from the Proximal Tubule moves into the Descending Loop. Fluid from the Descending Loop moves into the Ascending Loop. Fluid from the Ascending Loop moves into the Proximal Tubule.
About 40% of the Solutes in the Medulla are
Urea
What solutes add to the Concentration gradient in the Medullary Loop of Henle?
- Urea
- Na
- Cl
- K
Where is the Vasa Recta found?
Medulla around the Juxtamedullary Loop of Henle
What is the purpose of the Vasa Recta?
Helps to preserve the Concentration gradient that was established by the Loop of Henle
What are the unique characteristics of the Vasa Recta?
- Low Medullar Blood Flow (increases exchange)
2. Countercurrent Exchangers (allow for exchange of solutes)
The Juxtamedullary Loop of Henle is called…
Countercurrent Multiplier System
Because it has opposing currents that allow for the gradient to exist
What is important about the shape and flow of the Vasa Recta?
The slow blood flow and countercurrent movement helps to maintain the concentration gradient established by the Loop of Henle without washing it away