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44 Cards in this Set

  • Front
  • Back
How much water does the average healthy dog drink? How much urine is produced in 24 hours?
100 ml/kg.

Produces less than 50 ml/kg of body weight of urine per 24 hours.
When dehydrated, how much can a dog concentrate its urine? How about if it drinks too much?
7-8 times that of plasma when dehydrated.

Can excrete water that is 1/3 as concentrated as plasma when excessively drinking.
The high oncotic pressure and low hydrostatic pressure of the peritubular capllaries ____ (favors/decreases) the movement of reabsorbed water and solute from the interstitial fluid.
Favors!
Why is there little change in the osmolality of tubular fluid between the Bowman's space and the beginning of the thin limb of the Loop of Henle?
Because water is reabsorbed with the solute.
How can the kidney concentrate urine? How can it dilute it?
Concentration: Generate a hypertonic medullary interstitium which permits formation of concentrated urine.

Dilute: Dilute tubule fluid in the thick ascending limb of the loop of Henle and DCT which permits dilution of urine.

Varying the permeability of the collecting duct to water in response to ADH can dilute or concentrate urine.
What are two factors that are responsible for the hypertonicity of the medullary interstitium?
The reabsorption of osmotically active substances by tubules in the medulla.

Removal of water from the interstitium by the vasa recta.
Tell me about juxtamedullary nephrons.
They have the long loops of Henle that extend deep into the inner medulla (superficial nephrons have loops of Henle that are only in the outer medulla).

They are responsible for the kidney's ability to concentrate urine.
Collecting ducts in the inner medulla (IMCD) reabsorb NaCl, but more importantly, reabsorb ___.
Urea.

ADH release enhances reabsorption of this by the IMCD in order to concentrate the urine.
How can water be removed from the tubular fluid to concentrate the urine?
Must be removed passively, following an osmotic gradient, so kidneys must be able to generate a hyperosmotic gradient.

The loops of Henle produce the gradient by acting as a countercurrent multiplier. (The loops are parallel and juxtaposed, so that tubular fluid flows in opposite directions).
How does countercurrent flow work?
Incoming fluid equilibrates with exiting fluid at every level in the gradient, allowing an energy efficient conservation of solute in the region.

Osmolality of the interstitium increases deeper in the medulla. (the tips are about 4 times the osmolality of plasma)
What happens if osmolality in the medullary interstitium is upset?
Urine cannot be maximally concentrated.
Where can water be removed from the medullary interstitium without depleting hypertonicity?
In the vasa recta capillaries.

(They are permeable to both water and salt.)
How does blood flow in the vasa recta affecte the countercurrent exchange?
Lower blood flow = less depletion of solute.
If blood flow affects renal urine concentration, why does it still occur?
Needs to have nutrient blood flow to tissues.

The water needs to be moved away from the areas of reabsorption to prevent swelling.
Fluid entering the descending thin limb of Henle's loop from the proximal tubule is ____.
Isosmotic.
The concentrated urine has an osmolality of 1200 mOsm/kg H2O and contains high concentrations of ____ and other nonreabosrbed solutes.
urea.
What are the diluting segments of the nephron?
The TALH (Thick ascending limb of the Loop of Henle) and DCT (Distal convoluted tubule)

They reabsorb solute but not water to dilute the urine.
The dilue urine has an osmolality of 50 mOsm/kg H2O and contains ___ concentrations of NaCl and urea.
LOW.

(It's dilute!)
If ADH is not present, will the urine be more dilute or concentrated?
Dilute!

(Because less water is being reabsorbed).
If ADH is present, will the urine be more dilute or concentrated?
Concentrated!

(More water is reabsorbed)
Does ADH alter the excretion of solute?
NO.
Where is ADH synthesized?
By the neuroendocrine cells within the supraoptic and paraventricular nuclei of the hypothalamus.
What are the two primary physiological regulators of ADH secretion?
Plasma osmolality.

Blood volume and pressure.
Of the primary physiological regulators of ADH (plasma osmolality and blood vlolume/pressure), which plays the most important role in regulating ADH secretion?
Changes in plasma osmolality.
How much does blood volume or pressure need to decrease before ADH secretion is stimulated?
5-10%.
What are the three primary actions of ADH on the kidney?
Increase permeability of collecting ducts to water.

Increase permeability of medullary portion of collecting duct to urea.

Stimulates NaCl reabsorption by the Thick Ascending Loop of Henle (TALH)
What usually coincides with an increased in ADH?
An increase in thirst.
What are some organic osmolytes accumulated in the inner medulla to adapt to interstitial hyperosmolality?
Sorbitol.

Betaine.

Inositol.

Glycerophosphorylchloride.
What is ECV??
Effective Circulating Volume.

It relates to the adequacy of tissue perfusion and is the volume that maintains normal perfusion pressure and determines renal Na+ excretion.
What do Renal Sympathetic Nerves (Inc activity, dec NaCl excretion) also do?
Decrease glomerular filtration rate.

Increase renin secretion.

Increase proximal tubule, TALH, distal tubule and collecting duct NaCl reabsorption.
What does the Renin-Angiotensin-Aldosterone pathway (INC secretion, DEC NaCl excretion) also do?
Increase AnII levels to stimulate proximal tubule NaCl reabsorption.

Increase aldosterone levels to stimulate TALH and collecting duct NaCl reabsorption

Increase ADH secretion.
What does Atrial Natriuretic Peptide (INNC secretion, INC NaCl excretion) also do?
Increase glomerular filtration rate.

Increase renin secretion.

Decrease aldosterone secretion.

Decrease NaCl and water reabsorption by the collecting dut.

Decrease ADH secretion and inhibition of ADH actions on the collecting duct.
What does ADH (INC secretion, DEC H2O excretion) also do?
Increase H2O absorption by the collecting duct.
What is ANP? Where is it produced? What does it do?
ANP = Atrial Natriuretic Peptide.

Produced by Atrial Myocytes.

Relaxes vascular smooth muscle and promotes NaCl and water excretion by the kidney.

Generally, ANP opposes the actions of the Renin-An II-ADS system.
Where are the bubbles lodged in a diver with a ruptured lung for the following: a) air embolism, b) subcutaneous emphysema, c) mediastinal emphysema, d) pneumothorax ?
a) brain b)under the skin of the neck and shoulders, c) center of chest cavity surrounding heart, d) between lungs and the walls of the chest cavity
During euvolemia (normal ECV/extracellular volume), how is Na+ handled in the kidneys?
Na+ reabsorption by PT, Loop of Henle and DT is regulated so a constant portion of the filtered Na+ is delivered to the CD.

Reabsorption of Na+ by the CD is regulated so that the amount of Na+ excreted in the urine matches the amount ingested in the diet.
How is Na+ delivery in the collecting ducts kept constant?
Autoregulation of GFR.

Glomerulotubular balance. (Na+ reabsorption by the PT is adjusted to parallel changes in GFR).
What is the filtered load of Sodium?
FIltered load = GFR x [Na+]
What are two mechanisms that control G-T (Glomerulotubular) balance?
Starling forces between the PTC and lateral intercellular spaces.

Filtered load of glucose and amino acids.
What do volume sensors that send signals to the CNS in order to control Na+ excretion with ECV ultimately do?
Decrease activity of the renal sympathetic nerves.

Cause release of ANP from atrial myocytes.

Inhibit ADH secretion by the posterior pituitary.

Decrease renin secretion, and thus An II and ADS secretion.
What three general responses occur with an increase in ECV?
GFR increases.

Reabsorption of Na+ decreases in the PT.

Na+ reabsorption decreases in the CD.
True or False:

The nephron's response to ECV expansion involves all components of the nepphon.
True!
How is Na+ excretion controlled when ECV is decreased?
Increases activity of the renal sympathetic nerves.

Inhibits release of ANP by atrial myocytes.

Stimulates ADH secretion by the posterior pituitary.

Increases renin secretion, and thus An II and ADS secretion.
What three general responses occur with a decrease in ECV?
GFR decreases

Reabsorption of Na+ increases in the PT.

Na+ reabsorption in the CD increases.