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58 Cards in this Set

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  • Back
Why is it important to keep balance of Na and water?
Critical for blod pressure blody volume and maintenance of life
Does the body salt or water content vary a lot?
No, stays ~constant despite the highly variable intake
How does the water output vary? NaCl output?
Water output: vary depending on intake :0.4 to 25L/day
NaCl output: vary depending on intakes; 0.05 to 25g/day
What is insensible loss?
How much does it contribute to the total output?
Loss of water from the skin and lungs (but not sweating)
->contributes to 900mL
What is the greatest loss of NaCl?
Through the urine (10 out of 10.5 total g)
Where is bood filtered?
In Bowman's space at the glomerulUS
What is the filtrate?
Cell free plasma
**Needs to be modified before becoming the final urine
What is absorption?
Solute or water movement from the tubule (urine) back to the blood
What is secretion?
Movement of solute from blood or the cel interior into the tubukle lumen (urine)
Are Na and water freely filtered? Where are they reabsorbed? How much is reabsorbed?
Yes, freely filtered from the glomerulus to the tubule
Reabsorbed in the nephron, 99%
Where is most of the sodium and water reabsorbed?
Proximal tubule: ~2/3
How much Na is reabsorbed in the TAL?
DCT: 4-5%
CD: ~3%
Is water reabsorbed in the TAL?
Is Na reabsorption an active or passive process?

Na isreabsobed in all tubular segments EXCEPT the descending limb of the loop of Henle
By which process is water reabsorbed? What is it dependent on?
Reabsorbed by Diffusion
Depends on Na reabsorption
Describe the tubule cell
One-cell thickness
Has one side facing the urine side, one side facing the blood side
On which side of the membrane does the active Na+/K+ ATPase pump sodium out of the cell? Why?
Pumps on the basolateral (blood side) of the membrane
Why? Keep intracellular concentration of Na low
What hapens on the apical (lumenal/urine side) of the membrane?
Na moves down its gradient from the tubular lumen into the tubular epithelial cells
What are the mechanisms of the Proximal tuble to move Na?
Na+-H+ antiporter
Na-glucose co-transporter
Na-aa cotransporter
What are the mechanisms of Na+ transport in the cortical collecting duct?
Diffusion via Na+ channel
-> can be btw cells or when no E is required (through a channel)
What are the 3 steps involved in Na reabsorption?
1) Active Na transport out of the cell -> blood
2) Na goes down its gradient from the urine into the cell
3) Water moves passively out of the cell into the intestitium -> towards the blood
What role does the proximal tubule play in reabsorption?
Reabsorbs the bulk of filtered small solutes
(most of the filtrate is good .: our bodies want it back)
About 60% of the filtere NaCl, K, Ca and water and more than 90% of the filtered HCO3 are reabsorbed
ALL glucose and aa are reabsorbed here
How are all the glucose and aa reabsorved in the proximal tubule?
Na-dependent co-transport
What doe the late proximal tubule have?
Na/H exhanger
Where does secretion of toxins and drugs occur in the PT?
At the terminal portion of the proximal tubule: elimination
What are the other sites of Na absorption? (other than proximal tubule)
TAL of loop: Na-K-2Cl cotransporter
DCT: Na/Cl cotransporter
Collecting duct: Na channel
What happen to the uriniary excretion of Na if:
Na intake inc?
Na intake dec?
Na intake inc: Na excretion in urine inc
Na intake dec: Na excretion in urine dec
What kind of solute is Na for the body?
The major extracellular solute
What happens if there are changes in the total body Na?
Changes in extracellular fluid volume in the interstitium and the vascular space
Is the [Na] in the plasma a good marker for total bodt Na?
P(Na) only reflects the relative relationship of total body Na and H2O
What senses total body Na?
Baroreceptors sens total body Na as volume-intravascular filling
Why doesn't plasma Na reflect the total amt of sodium in the body?
Can have a high total body Na and accompanying water (high extracellular fluid volume and plasma vlume) or low total Na and water (low volume state), with a steady Na concentration
What % of BW is:
Total body water?
Intracellular fluid?
Extracellular fluid?
Total: 60%
Intracell: 40%
Extracell: 20% -> 3/4 ISF, 1/4 plasma
What regulates Na excretion?
GFR (minor role)
Na reaborption (very important)
Is Na excreted at the tubules?
Describe GFR control of renal Na regulation.
Inc Na and H2O loss due to diarrhea
-> dec in plasma volume
-> dec venous P
-> dec venous return
-> dec atrial P
-> dec ventricular end-diastolic volume
-> dec stroke volume
-> dec cardiac output
-> dec arterial BP
.: Inc activity of renal sympathetic nerves (reflexes mediated by venous, atrial and arterial baroreceptors)
---> Get increased constriciton of renal afferent arterioles
.: dec net GF pressure.: DEC GFR
End result: DEC in Na and H2O excreted (retained to preserve blood volume)
How does reabsorption control renal regulation of Na?
Hormone: Aldosterone (steroid H secreted by th e adrenal cortex, zona glomerulosa)
What does aldosterone do?
Simulates reabsorption in the DCT and CCD
What happens if there is no aldosterone? High aldosterone?
No: ~2% of filtered load is excreted (=35 g of NaCl)
High: ~0% of filterd load is excreted (Na is totally reabsorbed)
Where does aldosterone actually act?
Cortical collecting duct cells
How does aldosterone increase Na+ reabsorption?
Inc upregulation of:
Na/K ATPase: increaes its activity
Na channel (helps Na enter the cell)
K channel
->also inc H+ secretion
Does aldoesterone increase glucose uptake?
Because aldosterone only works in the cortical collecting duct
->there is no Na+/glucose cotransporter in the CCD
What regulates aldosterone secretion?
Renin-angiotensin (AG) system
Describe the renin-angiotensin system.
Liver makes angiotensis (AG)
Renin convert AG --> AG I
ACE converts AG I --> AGII
AG II stimulates aldosterone secretion by the adrenal gland
What increases aldosterone secretion?
What does ANP do?
Decreases secretion of aldosterone from the adrenal gland
When does the TAL become the distal tubule?
When the tubule touches the originating glomerulus
At this point, the cell become tall and thin: Macula densa (transmits signals to the juxtaglomerula cells)
What do the macular densa cells do?
"taste" the fluid. if Na concentration is low: means the glomerular lood flow is low and informs the arteriole to releases renin
Which cells actually secrete renin?
Jusxtaglomerular cells
What do the juxtaglomerular cells respond to?
Tension of afferent fibres
Sympathetic activity
Signals from the macula densa
How does the extracellular fluid volume regulate renin secretion? (What does the initial changein volume do before the renin system?)
Dec plasma volume (causes 3 things):
1) Inc of activity in the renal sympathetic nerve
2) Decrease in arterial P (direct effect on tone of afferent fibers or less stretch)
3) Dec in GFR, causes dec in flow to macula densa, which dec NaCl deivery to macula densa
What do these 3 things do to the renin system?
In the renal juxtaglomerular cells:
Inc Renin secretion
Inc Plasma renin
Inc plasma AG II
Adrenal cortex: Inc aldosterone secretion
Inc plasma aldosterone
CCD/DCT: Inc Na reabsorption
.: DEC overall secretion of Na
Is water reabsorption a direct effect of aldosterone?
What is ANP?
Atrial natriuretic peptide
Peptide H secreted by cardiac atrail cells when they're stretched
When is ANPO secreted?
In a High Volume state
What does ANP do? How?
Inhibit sodium reabsorption by acting on the tubules
->INC GFR (opposite effect of aldosterone)
How does BP affect Na excretioln?
BP Increases Na excretion
Describe the action of ANP.
Inc in plasma volume
->Cardiac atria: Inc distension -> Inc ANP secretion
->inc plasma ANP (which can dec plasma aldosterone)
-> Tubules: dec Na+ reabsorption
->Arterioles: afferent dialation, efferent constriction: Inc GFR
End result: Inc sodium secretion