Regulation of Ion and Water Balance Flashcards
After filtration, tubular fluid is subject to ___ and ___. These processes involve the transport of substances across the tubular epithelial cells in a ___.
reabsorption; secretion; nephron
___ transport moves molecules through tubular cells. ___ transport moves molecules between tubular cells.
Transcellular; Paracellular
Define passive transport, osmosis, facilitated diffusion, and active transport.
passive - does not require metabolic energy
osmosis - diffusion of water, solvent drag results from solutes being carried by water in paracellular transport
facilitated diffusion - requires a specific membrane protein (such as ion channels or transport proteins)
active - against gradient; coupled to ATP.
The rate of water diffusion can be regulated by ___.
aquaporins
A ___ moves single solute along gradient. A ___ moves molecules in the same direction. A. ___ moves molecules in the opposite direction.
uniporter; symporter; antiporter
How are vesicles transported?
endocytosis or exocytosis. These processes are energy dependent
T/F. Sodium can be reabsorbed in all but one segment of a nephron.
True, it is not reabsorbed in the thin descending limb.
How much sodium is reabsorbed in each segment of the nephron?
proximal tubule - 65-67% thin ascending limb - 7% thick ascending limb - 20% distal tubule - 8% of original remains; 5% reabsorbed collecting duct - 2-3%
In the proximal tubule, ___ and ___ ___ are reabsorbed with Na+ using a ___.
glucose; amino acids; symporter
What happens on the basal side of the proximal tubule to keep the intracellular Na+ low?
active transport
How does water move through the proximal tubule to keep the osmolarity of the tubular fluid constant?
via paracellular transport
In the proximal tubule, Na+ reabsorption also occurs in conjunction with ___ reabsorption using a ___/___ antiporter.
bicarbonate; Na+/H+
Explain how bicarbonate reabsorption occurs.
Reabsorption is not direct…H+ secretion = HCO3- reabsorption
CA reaction produces H+ and HCO3- in the tubule cell → HCO3- is transported into the blood → H+ transported into tubular fluid where it recombines with a filtered HCO3-
The proximal tubule also has transporters for organic ___ and ___. These transporters have ___ specificity and can be ___.
cations; anions; low; saturated
Many drugs are organic ionic compounds. They are commonly bound to plasma proteins so they are not filtered at the glomerulus, must be secreted in order for them to be excreted by the urine
Summarize what has happened by the end of the proximal tubule.
- 2/3 of Na+, Cl- and water reabsorbed; small proteins too (by endocytosis)
- K+ and divalent (Ca2+) cations reabsorbed by solvent drag
- all amino acids and glucose reabsorbed
- bicarbonate reabsorbed due to activity of Na+/H+ transporter
- secretion of organic ions (drugs)
In the loop of Henle, ___% of filtered NaCl and ___% of water is reabsorbed.
25; 15
T/F. The descending thin limb is impermeable to water but permeable to salt.
False, the descending thin limb is impermeable to SALT (fluid become HYPERtonic due to increase of salt) but permeable to WATER (due to presence of aquaporins).
T/F. The ascending thin limb is impermeable to water but permeable to salt.
True, reabsorption is passive
T/F. In the ascending thick limb, fluid is concentrated.
False, it is diulted
Where is the Na+/K+/2Cl- symporter and Na/K+ ATPase located in the ascending thick limb?
Na+/K+/2Cl- symporter - apical membrane
Na/K+ ATPase - basolateral membrane
T/F. Paracellular transport of monovalents and divalents is due to solvent drag.
False, Paracellular transport of monovalents and divalents is NOT due to solvent drag.
The tubular fluid becomes positive when Cl- reabsorbed so cations diffuse along an electrical gradient
Fluid leaving the loop is ___, but the renal countercurrent mechanism has established an osmotic gradient required for formation of ___ urine.
hyposmotic; hyperosmotic
When ADH is present/high (antidiuresis), what happens to the water in the collecting duct? What happens when it is absent/low (diuresis)?
present - water is reabsorbed to produce concentrated urine (up to 1200 mOsm/kg H2O)
absent - there is no water reabsorption in the collecting duct so the urine is hyposmotic / very dilute (50 mOsm/kg H2O).
The peritubular capillaries are permeable to ___ and ___ so plasma osmolarity changes as the capillaries follow the loop, but the osmolarity of the blood leaving the kidney (to veins) is ___.
NaCl; water; normal
In the distal tubule, the initial segment reabsorbs ~ ___% of filtered NaCl via a ___/___ symporter in ___ membrane and ___/___ ATPase in the ___ membrane.
8; Na+/Cl-; apical; Na+/K+; basolateral
reabsorption of K+, H+ and water is variable and sodium reabsorption in the latter half of the distal tubule and the collecting duct is similar
What are the two cell types in the collecting duct and late distal tubule?
- prinicpal cells
2. intercalated cells
Principal cells have ___ ___ channels that reabsorb Na+ and secrete K+. How do these channels affect the cell?
epithelial sodium channels (ENaC)
- Na+ reabsorption drives paracellular Cl- reabsorption
- K+ secreted due to Na/K ATPase activity in basal membrane
___ cells are involved in acid-base balance and can also reabsorb K+.
Intercalated
A positive or negative shift in water balance shifts extracellular volume away from ___ (normal volume). ___ and ___ responses to this shift help to re-establish this volume.
euvolemia; hormonal; neuronal
Where are vasopressin or antidiuretic hormone (ADH) released from? Why is it released?
the posterior pituitary gland
its release is stimulated by changes in osmolality of body fluids. It responds to osmolality above a set point of 275-290 mOsm/kg H2O.
its release is also stimulated by changes in blood volume / pressure.
Low pressure baroreceptors in the ___ ___ and large ___ vessels respond to a ___ in blood volume.
left atrium; pulmonary; decrease
High pressure baroreceptors in ___ ___ and ___ ___ respond to a ___ in blood pressure.
aortic arch; carotid sinus; decrease
How does ADH increase the permeability of the late distal tubule and the collecting duct to water?
by increasing aquaporins into the apical membrane (basolateral membrane is freely permeable to water)
In addition to water, what else does ADH increase the permeability of?
urea in the medullary collecting duct
T/F. The renin-angiotensin-aldosterone system stimulates events that increase reabsorption of sodium and water.
True.
Under what conditions is renin released?
- a drop in perfusion pressure
- decreased NaCl delivery to macula densa
- sympathetic input to juxtaglomerular cells
What converts angiotensinogen to angiotensin I? What converts angiotensin I into II?
renin
angiotensin converting enzyme (ACE)
What is the function of angiotensin II?
- vasoconstriction of arterioles to increase BP
- stimulate release of ADH - acts in brain and stimulates sense of thirst
- increase sympathetic activity to increase BP
- stimulate aldosterone secretion (can also be done by increasing K+ plasma)
Aldosterone from the ___ ___ acts to increase ___ reabsorption in the distal tubule and collecting duct by increasing ___ protein synthesis and ___ secretion.
adrenal cortex; NaCl; transport; K+
transport protein synthesis → more Na+/K+ ATPase and ENaC in distal tubule to ↑ Na+ reabsorption
___ peptides are hormones secreted when the heart dilates (during volume expansion).
Natriuretic
Where does atrial and brain natriuretic peptides come from? What effect do they have in the kidney?
atrial - atria
brain - ventricles
- vasodilation of afferent arterioles by ↑ GFR to ↑ tubular fluid
- vasoconstriction of efferent arterioles causes fluid to be filtered at high rates in the glomerulus
- inhibition of renin (and aldosterone) leads to NO absorption of Na+
The net effect is to increase the excretion of NaCl and water
What is the effect of volume expansion at various areas of the nephron on Na+ reabsorption?
in proximal tubule - euvolemia (67%) / expansion (50% - decreased reabsorption since moving faster)
in thick ascending limb - 25% vs 30% - more hyposmotic
in distal tubule - 4% vs. 12%
in collecting duct - 3% vs. 2%
urine has 1% vs. 6% therefore more Na+ excreted and H20 under expansive conditions.
Why is potassium regulation so important?
K+ is a major determinant of membrane resting potential. Therefore, it can affect electrically excitable cells (-70 to -90 RMP in most cells)
___ will depolarize Vm. ___ will hyperpolarize Vm.
Hyperkalemia cause the cell to become extra excitable due to the ↑ extracellular K+. This is common in ESRD patients
Hypokalemia will inhibit activity due to ↓ extracellular K+. This is tied to vomiting, diarrhea, and use of some diuretics
changes in K can cause cardiac arrhythmias
How is potassium regulated?
ingested K+ is fast shifted into cells - mediated by insuline, epi and aldosterone
Kidneys typically excrete 90-95% of ingested K+
T/F. In the glomerulus, K+ is freely filtered and in the proximal tubule, about 67% of filtered K+ is reabsorbed.
True, it is reabsorbed by paracellular transport/solvent drag
How is potassium reabsorbed in the thick ascending limb?
Na+/K+/Cl- symporter and paracellular transport (non-solvent drag)
In the late distal tubule or collecting duct, K+ is secreted by ___ cells depending on ___ activity, ___ gradient and/or ___ K+ permeability.
principal; ATPase; K+; apical
In the late distable tubule or collecting duct, K+ is reabsorbed by ___ cells when it is depleted.
intercalated
↑ plasma [K+} stimulates ___ release and ___ increases Na+/K+ ATPase in ___ cells.
aldosterone; aldosterone; principal
↑ flow rate of tubular fluid increase K+ ___. Local responses to bending of ___. This increase ↑ Na+ in collecting duct, which ↑ ___ reabsorption and favors ↑ ___ secretion.
secretion; cillia; Na+; K+
T/F. Reabsorption in the proximal tubule and thick ascending limb changes very little relative to plasma concentrations of potassium.
True.
T/F. The distal tubule and cortical collecting duct will reabsorb potassium when plasma concentrations are low.
True.
T/F. If plasma K+ is high, secretion increases in distal tubule and cortical collecting duct.
True.
