Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
22 Cards in this Set
- Front
- Back
|
What is osmolarity?
|
The number of osmoles in 1 L of water
|
|
|
How does osmolarity affect water flow?
What is the average plasma osmolarity? |
Increased difference in osmolarity between fluid compartments means there is more osmotic pull of water toward greater osmolar (concentration)
Kidneys maintain osmolarity of plasma at ~300 mOsm |
|
|
What is the purpose of countercurrent mechanisms?
What are the two types? |
To establish and maintain osmotic gradient from the renal cortex through the medulla & to allow kidneys to vary urine concentration
Countercurrent Multiplication & Countercurrent Exchange |
|
|
What is countercurrent multiplication?
|
the process by which a progressively increasing osmotic gradient is formed in the Interstitial Fluid of the Renal Medulla as a result of countercurrent flow
|
|
|
What is countercurrent flow?
|
-Establishes the osmotic gradients in the Renal Medulla
-In the Descending Limb it caries tubular fluid deep into the medulla -In the Ascending Limb it caries tubular fluid in the opposite direction |
|
|
What ions primarily forms the medullary osmotic gradient?
What substance secondarily forms the medullary osmotic gradient? |
Primarily by Na+ and Cl- movement out of the Loop of Henle
Secondarily by Urea recycling |
|
|
What nephron classification is involved in countercurrent mechanisms?
|
The juxtamedulliary nephron
|
|
|
Upon what is a nephron’s ability to concentrate the filtrate dependent upon?
How is each important? |
Magnitude of single effect: The bigger the gradient is = the more movement of substance there is
Length of Vertical Gradient: the deeper the Descending Tubule goes into the Medulla = the greater the concentration gradient multiplier Relative permeability solute & water in ascending & descending limbs: Some areas only permeable to solute, others are only permeable to water Rate of fluid flow in system: High flow rate in the tubules = less solute reabsorbed = less water reabsorbed Low flow rate in the tubules = more solute reabsorbed = more water reabsorbed |
|
|
How is the countercurrent system applied to the human kidney?
|
1. fluid entering loop of Henle (33% of filtrate) is 300 mOsm/l.
2. Descending limb 3. Ascending limb relatively impermeable to water 4. fluid entering distal tubule is hyposmotic |
|
|
What is involved in each part of the countercurrent system?
|
-Fluid entering the Loop of Henle (33% of filtrate) is 300 mOsm/l
-Descending Limb= Water reabsorbed (due to high interstitial osmolarity), Minor passive Na+ & Cl- secretion--> concentrates the tubular fluid because it is primarily loosing solvent (water) By hairpin turn, tubular fluid osmolarity is 1200 - 1400 mOsm/l -Ascending limb relatively impermeable to water= Primary region responsible for the creation of the concentration gradient in the medulla ~Thin - passive NaCl absorption ~Thick limb - active reabsorption by Na+,K+, 2Cl- symporter--> this dilutes the tubular fluid because it is loosing solute -fluid entering distal tubule is hyposmotic= Less concentrated than the interstitial fluid |
|
|
How does the ascending limb contribute to the medullary concentration gradient?
How does this lead to water reabsorption in the descending limb? |
Ascending limb is relatively impermeable to water so it concentrates the gradient
Water is reabsorbed in the Descending Limb because of the high interstitial osmolarity |
|
|
What happens to the osmolarity of the filtrate fluid in the descending and ascending limbs as it moves through the loop? Why?
|
-it starts off at 300 mOsm/l when it enters the Loop of Henle -----> in the Descending Limb it is 1200-1400 mOsm/l -----> then in the Ascending Limb it gets back to about 300 mOms/l
-In the Descending Limb water leaves the fluid making it more concentrated BUT in the Ascending Limb salt leaves and makes the fluid less concentrated again |
|
|
How would fast fluid flow affect absorption of water and NaCl?
How would this affect medullary concentration gradient? |
There would be less absorption of water and NaCl and the concentration gradient would be less dilute
|
|
|
What is the countercurrent exchanger, what does it do ?
|
The process by which solutes and water are passively exchanged between the blood of the vasa recta and interstitial fluid of the real medulla as a result of counter flow
Provides oxygen and nutrients to the medullary cells & preserves the medullary gradient |
|
|
How does the countercurrent exchanger work?
|
Water enters the ascending vasa recta either from descending vasa recta or reabsorbed from nephron loop and collecting duct = the volume of blood at end of vasa recta being greater than at beginning
|
|
|
How would increase/decrease in vasa recta blood flow affect medullary osmotic gradient and urine volume formation?
|
As medullary blood flow increases, medullary osmotic gradient decreases = less water reabsorbed from the tubules = more urine formation
|
|
|
Where does urea come from
|
it is a byproduct of protein metabolism
It is both reabsorbed and secreted in the nephron |
|
|
How does the nephron process urea?
|
in the nephron helps contribute to medullary osmotic gradient (~40 %)
|
|
|
What is urea recycling how does it work and why is it important to medullary osmotic gradient?
|
In deep medullary region urea moves from the collecting duct --> the interstitial fluid of medulla --> it is secreted back into the ascending thin limb = increased osmolarity in medulla (from movement of urea through medullary interstitial fluid)-----> ADH produces water reabsorption in the collecting duct = increased urea concentration in the tubular fluid deep in the medullary region of the collecting duct = more urea moving from the tubule --> the interstitial fluid
|
|
|
What enhances urea recycling
|
increased by ADH which creates further water reabsorption
|
|
|
How is urine finally concentrated or diluted
What hormone does it depend on? What increases/decreases the release of the hormome? What is the effect cascade of increase or decrease in amount of said hormone? |
ADH in the Collecting Duct (if ADH is there= water is absorbed= concentrated urine; if ADH is not there= water is not absorbed= dilute urine)
Higher fluid intake means decreased plasma osmolarity leading to less ADH secretion (and vice versa) -- (Decreases water reabsorption in the collecting duct = more urine volume (more dilute) = less blood volume = increase in blood osmolarity) |
|
|
What are diuretics?
List some examples and what they do? |
Chemicals that enhance urinary output
-ADH inhibitors, e.g., alcohol -Na+ reabsorption inhibitors e.g., caffeine, drugs for hypertension or edema -Loop diuretics inhibit medullary gradient formation -Osmotic diuretics= substance not reabsorbed so water remains in urine, e.g., high glucose of diabetic patient |
