renal lecture 4 water

Question 1

What is the defintion of osmolarity?
What does it mean when the solution osmolarity is high?

Answer 1

-Osmolarity: total solute concentration of a solution
-measure of water concentration in that the higher the
solution osmolarity, the lower the water concentration

Question 2

What is hypoosmotic vs isoosmotic?

Answer 2

-Hypoosmotic: having total solute concentration less
than that of normal extracellular fluid (300 mOsm)
-Isoosmotic: having total solute concentration equal to
that of normal extracellular flui

Question 3

What does hyperosomtic mean?
How is urine the only regulable output

Answer 3

Hyperosmotic: having total solute concentration
greater than that of normal extracellular fluid
-it responds to an input of how much you eat or drink

Question 4

How much water is reabsorbed?
Where is the majority of water reabsorption?
-Where is the major hormonal control reabsorbed?

Answer 4

-Water is freely filtered but ~99% is reabsorbed
* The majority of water reabsorption (~2/3) occurs in the proximal tubule.
* But the major hormonal control of reabsorption occurs in the CD.

Question 5

What does water reabsorption depend on?
What does a high osmolarity in interstial fluid mean?
What happens in tubular lumen to osmolarity when Na+ gets reabsorbed?

Answer 5

-depends on Na reabsorption (proximal tubules)
-low water tone
-tubular osmolarity decreases since it loses solutes (high water conc.)

Question 6

Where is water reabsorbed when in the proximal tubule?
What happens to osmolarity in the lumen vs the intersitium?
What does this difference between lumen and intersitium cause, via what parts?

Answer 6

1.Na is reabsorbed from the tubular lumen to the interstitial fluid across the epithelial cells.
2. The local osmolarity in the lumen decreases, while the local osmolarity in the interstitium increases.
3. This difference in osmolarity causes net diffusion of water from the lumen into the interstitial fluid.
via tubular cells’ plasma membranes
via tight junction

Question 7

Where is water, sodium, etc dissolved in?
what method do they move by, and where do they move to?

Answer 7

From the interstitium, water, sodium, and everything else dissolved in the interstitial fluid move together by bulk flow into peritubular capillaries

Question 8

What does the kidney do when the water intake is small vs when it it large?

Answer 8

The body has to maintain water balance.
* When the water intake is small, the kidney reabsorbs more water (e.g. urine output 0.4 L per day).
* When the water intake is large, the kidney reabsorbs less water (e.g. urine output 25 L per day)

Question 9

Where does dynamic regulation of water balance occur?
What are the 2 crtical components of this part of the kidney?
What does vasopressin regulate?

Answer 9

-This dynamic regulation takes place in CD and there are two critical components:
1. High osmolarity of the medullary interstitium.
2. Permeability of CD to water (regulated by vasopressin)
vasopressin regulates water permeability

Question 10

How much can the kidney concentrate urine by?
Where does urinary concentration take place?

Answer 10

• The kidney has the ability to concentrate urine up to 1400 mOsm/L.
• Urinary concentration takes place as tubular fluid flows through the medullary collecting ducts.

Question 11

What does urinary concentration depend on?
What happens in the presence of vasopressin, where does water diffuse out/go into?

Answer 11

-Urinary concentration depends on the hyperosmolarity of the
interstitial fluid.
In the presence of vasopressin, water diffuses out of the ducts into the interstitial fluid in the medulla to be carried away

Question 12

How does the medullary interstial fluid become hyperosmotic?
What does a countercurrent involve?

Answer 12

-through function of Henle’s loop
-it involves the descending and ascending limb running in opposite directions

Question 13

What happens in the first step of the countercurrent multiplier what are the osmolarities of each side?
What are the characterisitcs of the distal side at this osmolarity?

Answer 13

proximal side is isoosmotic
-distal side is hypoosmotic
-it can actively absorb NaCL and it is impermeble to water

Question 14

What happens in the 2nd step of the countercurrent multiplier system when the descending limb becomes hyperosmostic?

Answer 14

-it does not reabsorb NaCL and it is permeable to water
-water starts to flow out

Question 15

What happens to counter current multiplier during the move?

Answer 15

-there is movement goinng out the proxima direction and going out the distal direction?

Question 16

What happns to the countercurrent multiplier after the move?

Answer 16

-one 300 mosm/L moves down from the proximal side
-one 200 m/osm moves out the distal side
-everything gets shifted over

Question 17

What happens at the end of the movement after the second move?

Answer 17

Question 18

how is the flow rate of the countercurrent multiplier system limited?
What happens as you go up ascending loop?

Answer 18

-limited based on length of the loop of henle
-decreasing osmolarity as you go up

Question 19

What is the vasa recta?
What is its structure and what does this minimize?
What also contributes to medullary hyperosmolarity?

Answer 19

-Vasa recta:blood vessels in the medulla
-Its hairpin-loop structure, minimizes excessive loss of solute from the interstitium
-in addition to NaCl, urea also contributes

Question 20

What does water reabsorption depend on?
What does permeability of the epithelium depend on, whats and example?

Answer 20

-depends on the water permeability of
the tubules
-Permeability of the epithelium depends on the tubular segment.
e.g. proximal tubule: high permeability to water

Question 21

What tyoe of channels does permeability depend on?
What is water permeability in the CCD and the MCD (medullar collecting duct) subject to, what is the key control?

Answer 21

-Permeability largely depends on the presence of water channels (termed aquaporins) in the plasma membrane.
-Water permeability (regulated by the amount of aquaporins in the plasma membrane) in the CCD and MCD is subject to physiological control and vasopressin is the key hormone in this control.

Question 22

What section of kidney is impermeable to water?
What sectino of kidney is under hormonal control of vasopressin?

Answer 22

-ascending thick limb loop of henle
-CCD and the MCD

Question 23

What is vasopressin also known as?
What is vasopressin produced and released from?

Answer 23

Peptide hormone, also called anti-diuretic hormone (ADH)
Produced by a group of hypothalamic neurons, Released from the posterior lobe of the pituitary gland

Question 24

What is vasopressin coupled with?
What does vasopressin stimulate the insertion of?

Answer 24

-Couples to GPCR V1 (smooth muscle) and V2 (kidney)
-Vasopressin stimulates the insertion of aquaporins in the luminal membrane of the collecting duct cells and increases the water permeability

Question 25

What happens to the collecting ducts when vasopressin is present?
What happens to collecting ducts when vasopressin is not present?
What is diabetes insipidus caused by?

Answer 25

-they become permeable to water, leading to water reabsorption
-CD become impermeable to water, water diuresis
-Diabetes insipidus (DI) is caused by malfunction of the vasopressin system (vasopressin does NOT work)

Question 26

How does CCD get affected with vasopressin present, in terms of pressure?

Answer 26

-they become isoosmotic

Question 27

How does CCD get affected without vasopressin in terms of pressure

Answer 27

-it has a very low osmolarity

Question 28

What regulates rate of water excretion?
What hormone regulates this rate?

Answer 28

Water excretion is mainly regulated by the rate of water
reabsorption from the tubules.
-Vasopressin regulates this rate. Hence, vasopressin is a major regulator of water excretion

Question 29

What are the 2 mechanisms of control that regulate vasopressin?

Answer 29

1. Osmoreceptor control (most important)
2. Baroreceptor control (less sensitive)

Question 30

How do osmoreceptor control vasopressin secretion, what is injested and what happens if no vasopressin?
What happens to osmolarity, osmoreceptor firing, vasopressin,etc in this control?

Answer 30

-excess of H2O is ingested
-is no vasopressin kidney cannot absorb water

Question 31

How do baroreceptors control vasopressin secretion when the plasma volume get decreased?
What happens to pressure in blood vessels, vasopressin secretion, permeability, etc?

Answer 31

venous, atrial, arterial pressure decreases
-increase in vasopressin secretion and in plasma vasopressin
-increas ein permeability to water, causing increased reabsorption, decreasing amount of H2O excreted

Question 32

What are the 4 factors that cause thirst?

Answer 32

-decrease plasma volume
-increase plasma osmolarity
-dry mouth/throat
-metering of water intake by GI tract

Question 33

What occurs to the body during severe sweating?
-to the plasma volume, gfr, aldosterone and sodium excretion?
What happens to plasma osmolarity, vasopressin and water excretion?

Answer 33