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Renal Physiology > Urine Concentration and Dilution Mechanisms > Flashcards

Urine Concentration and Dilution Mechanisms Flashcards

1
Q

What do we need to concentrate Urine?

A
  1. ADH

2. Functioning Loop of Henle to establish concentration gradient

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2
Q

What is the process of ADH water reabsorption?

A
  1. Osmoreceptors in Hypothalamus detect high blood Osmolarity activating Thirst and ADH secretion
  2. ADH released into bloodstream from Posterior Pituitary
  3. ADH causes the Aquaporin Channels of the Collecting Duct to open
  4. Water is reabsorbed and blood Osmolarity decreases
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3
Q

Descending Limb of Loop of Henle:

  1. What is it called?
  2. What is it Permeable to?
  3. What is it Impermeable to?
A
  1. “Concentrating Segment”
  2. PERMEABLE to Water
  3. IMPERMEABLE to Solutes
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4
Q

Ascending Limb of Loop of Henle:

  1. What is it called?
  2. What is it Permeable to?
  3. What is it Impermeable to?
A
  1. “Diluting Segment”
  2. IMPERMEABLE to Water
  3. PERMEABLE to Solutes
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5
Q

What are the two types of Nephrons?

A
  1. Cortical Nephrons

2. Juxtamedullary Nephrons (long)

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6
Q

What solutes are reabsorbed in the Proximal Tubule?

A
  1. Na
  2. Water
  3. Glucose
  4. Bicarb (HCO3)
  5. K
  6. Cl
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7
Q

What solutes are reabsorbed in the Ascending Limb of the Loop of Henle?

A

“ClaNK”

  1. Na
  2. Cl
  3. K
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8
Q

What solutes are reabsorbed in the Distal Tubule?

A
  1. Na
  2. K
  3. Cl
  4. Ca
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9
Q

Osmolarity at the bottom of the Loop of Henle depends on…

A

HOW LONG THE LOOP OF HENLE IS

Longer Juxtamedullary Nephrons can get up to 1200 mOsm/L

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10
Q

What is the Osmolarity at the start of the Distal Tubule?

A

150 mOsm/L

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11
Q

What is the Osmolarity at the start of the Collecting Duct?

A

150 mOsm/L

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12
Q

How does the PRESENCE of ADH effect Urine concentration?

A

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

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13
Q

What is the highest Osmolarity that Urine can reach?

A

1200 mOsm/L if ECF is that high and ADH causes Aquaporin channels to open

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14
Q

How does the ABSENCE of ADH effect Urine concentration?

A

Water cannot escape so urine is labeled as HYPOTONIC

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15
Q

What is the main transporter on the Ascending Limb of the Loop of Henle?

A

Na/K/Cl Transporter

-pumps 1 Na, 1, K, and 2 Cl into ECF

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16
Q

What is unique about the Na/K/Cl Transporter?

A

“Tmax=200mOsm gradient”

The Transport Max of the Na/K/Cl Transporter is based on an Osmolarity difference of 200 mOsm

17
Q

Describe the steps taken to establish the Concentration Gradient:

A
  1. 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)
  2. 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

  1. 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.
  2. 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.
  3. 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.
18
Q

About 40% of the Solutes in the Medulla are

A

Urea

19
Q

What solutes add to the Concentration gradient in the Medullary Loop of Henle?

A
  1. Urea
  2. Na
  3. Cl
  4. K
20
Q

Where is the Vasa Recta found?

A

Medulla around the Juxtamedullary Loop of Henle

21
Q

What is the purpose of the Vasa Recta?

A

Helps to preserve the Concentration gradient that was established by the Loop of Henle

22
Q

What are the unique characteristics of the Vasa Recta?

A
  1. Low Medullar Blood Flow (increases exchange)

2. Countercurrent Exchangers (allow for exchange of solutes)

23
Q

The Juxtamedullary Loop of Henle is called…

A

Countercurrent Multiplier System

Because it has opposing currents that allow for the gradient to exist

24
Q

What is important about the shape and flow of the Vasa Recta?

A

The slow blood flow and countercurrent movement helps to maintain the concentration gradient established by the Loop of Henle without washing it away

25
Q

What factors contribute to the concentration of Urine?

A
  1. ADH Presence (Aquaporin activator)
  2. Osmotic Gradient
  3. Urea recycling
  4. Vasa Recta
26
Q

What happens if Osmolarity rises?

A
  1. Dehydration
  2. Plasma Osmolarity Increases
  3. Osmole Receptors in Hypothalamus are triggered and ADH is released
  4. ADH opens Aquaporin Channels of the Collecting Duct
  5. Water Reabsorption Increases
  6. More concentrated Urine
  7. Plasma Osmolarity goes back to normal

Renal Physiology (7 decks)

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