Renal - Lecture 4 Flashcards
What is osmolarity?
total solute concentration of a solution; measure of water concentration in that the higher the solution osmolarity, the lower the water concentration
What is hypoosmotic?
having total solute concentration less than that of normal extracellular fluid (300 mOsm)
What is isoosmotic?
having total solute concentration equal to that of normal extracellular fluid
What is hyperosmotic?
having total solute concentration greater than that of normal extracellular fluid
Water is ___ filtered.
freely
How much of water is reabsorbed?
99%
Where does the majority of water reabsorption occur?
in the proximal tubule
Where does the major hormonal control of reabsorption of water occur?
CD
What kind of process is water reabsorption?
passive
What is the direction of movement of water in the proximal tubule?
tubular lumen -> interstitial fluid
What happens to the osmolarity in the tubular lumen?
it decreases
What happens to osmolarity in the interstitial fluid?
it increases
Step 1 of water reabsorption:
Na is reabsorbed from the ___ ___ to the ___ ___ across the epithelial cells.
tubular lumen
interstitial fluid
Step 2 of water reabsorption:
The local osmolarity in the lumen ___, while the local osmolarity in the interstitium ___.
decreases
increases
Step 3 of water reabsorption:
This difference in osmolarity causes net diffusion of water from the ___ into the ___ ___.
via tubular cells’ plasma membranes via ___ ___.
lumen
interstitial fluid
tight junctions
Step 4 of water reabsorption:
From the interstitium, water, sodium, and everything else dissolved in the interstitial fluid move together by ___ ___ into ___ ___.
bulk flow
peritubular capillaries
When the water intake is small, the kidney reabsorbs ___ water.
more
What is the urine output when the kidney reabsorbs more water?
0.4 L
When water intake is large, the kidney reabsorbs ___ water.
less
What is the urine output when the kidney reabsorbs less water?
25 L
Where does the dynamic regulation of water reabsorption occur?
collecting duct
What are the 2 critical components of the dynamic regulation of water reabsorption?
- high osmolarity of the medullary interstitium
- permeability of CD to water (regulated by vasopressin)
The kidney has the ability to concentrate urine up to ___.
1400 mOsm/L
Urinary concentration takes place as ___ ___ flows through the ___ collecting ducts.
tubular fluid
medullary
What does urinary concentration depend on?
the hyperosmolarity of the interstitial fluid
In the presence of ___, water diffuses out of the ducts into the interstitial fluid in the medulla to be carried away.
vasopressin
The countercurrent multiplier system comes from the anatomical structure of the ___ ___ ___.
Loop of Henle
The medullary interstitial fluid becomes hyperosmotic through the function of ___ ___.
Henle’s loop
Is the ascending limb thick or thin?
thick
What kind of flow is found in the descending and ascending limb?
countercurrent
The proximal tubule cells reabsorb Na and water cells ___.
proportionally
What is the fluid that leaves the proximal tubule?
isoosmotic (300 mOsm)
The thick ascending limb is very active in the reabsorption of ___.
NaCl
The thick ascending limb is impermeable to ___.
water
Near the ascending limb, the interstitial fluid becomes a bit ___.
hyperosmotic
In the tubule of the ascending limb, it becomes ___.
hypoosmotic
The descending limb does not reabsorb ___.
NaCl
The descending limb is permeable to ___.
water
In the descending limb, water gets pulled ___, into the ___.
away, interstitium
The fluid in the descending limb becomes ___.
hyperosmotic
After the movement of fluid, the osmolarity pattern is:
hyperosmotic -> hypoosmotic
The interstitial osmolarity is identical to the ___ limb.
descending
What are vasa recta?
blood vessels in the medulla
What kind of structure are vasa recta?
hairpin-loop
What is the function of the vasa recta?
it minimizes excessive loss of solute from the interstitium
In addition to NaCl, ___ also contributes to medullary osmolarity.
urea
Water reabsorption depends on the water permeability of the ___.
tubules
What does the permeability of the epithelium depend on?
the tubular segment
The proximal tubule has a ___ permeability to water.
high
What does permeability largely depend on?
the presence of water channels in the plasma membrane (aquaporins)
Water permeability in the ___ and ___ is subject to physiological control.
CCD and MCD
What controls the water permeability in the CCD and MCD?
vasopressin
What kind of hormone is vasopressin?
anti-diuretic hormone
What is vasopressin produced by?
hypothalamic neurons
Where is vasopressin released from?
posterior lobe of the pituitary gland
What 2 receptors does vasopressin bind to?
GPCR V1 and V2
Where is GPCR V1 found?
smooth muscle
Where is GPCR V2 found?
kidney
What does vasopressin stimulate the insertion of in the luminal membrane of the collecting duct cells?
aquaporins
Where does vasopressin stimulate the insertion of aquaporins?
in the luminal membrane of the collecting duct
What does vasopressin increase?
water permeability
When vasopressin is present, collecting ducts become ___ to water —-> water ___
permeable
reabsorption
When vasopressin is not present, collecting ducts become ___ to water —-> water ___
impermeable
diuresis
What is diabetes insipidus caused by?
malfunction of the vasopressin system (vasopressin does NOT work)
What regulates the rate of water reabsorption from the tubules?
vasopressin
Vasopressin is a major regulator of water___.
excretion
What are the two mechanisms to regulate vasopressin secretion?
- Osmoreceptor control (most important)
- Baroreceptor control (less sensitive)
Excess H20 ingestion causes ___ in H20 excretion.
increase
What happens to body fluid osmolarity and firing by hypothalamic osmoreceptors when excess H20 is ingested?
they decrease
What happens to vasopressin secretion when excess H20 is ingested?
it decreases
What happens to tubular permeability to H20 and H20 reabsorption when excess H20 is ingested?
it decreases
What happens to venous, atrial and arterial pressures when plasma volume decreases?
it decreases
What happens to vasopressin secretion when venous, atrial and arterial pressures decrease?
they increase
What are the reflexes of the vasopressin secretion mediated by when venous, atrial and arterial pressures decrease?
cardiovascular baroreceptors
What happens to tubular permeability to H20 and H20 reabsorption when plasma vasopressin increases?
they increase
When plasma volume decreases, H20 excretion ___.
decreases
What causes us to feel thirsty?
the increase in plasma osmolarity
What senses an increase in plasma osmolarity and causes thirst?
osmoreceptors
___ in plasma volume can be sensed by ___ to increase thirst.
decrease, baroreceptors
What else can cause thirst?
dry mouth and throat
What can decrease thirst?
metering of water intake by GI tract
What does severe sweating cause a loss of?
hypoosmotic salt solution
Loss of hypoosmotic salt solution causes an ___ in plasma volume and ___ in plasma osmolarity during severe sweating.
decrease
increase
When plasma volume decreases, the GFR ___ and plasma aldosterone ___ during severe sweating.
decreases
increases
The decrease of GFR and increase in plasma aldosterone cause ___ in sodium excretion during severe sweating.
decrease
The increase in plasma osmolarity during severe sweating causes an ___ in plasma vasopressin.
increase
The increase in plasma vasopressin during severe sweating causes a ___ in H20 excretion.
decrease
