Term
| Approximately what percent of the filtered solute and solvent are typically reabsorbed by the nephron? |
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Definition
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Term
| Define: positive sodium balance; negative sodium balance. What are the net effects? |
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Definition
1) sodium intake exceeds excretion; stimulate thirst and ingestion and retention of additional water
2) sodium excretion exceeds intake; water is excreted to maintain the sodium concentration |
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Term
| What percent of the filtered sodium is reabsorbed in the proximal tubule? water? What is responsible for creating the primary driving force for Na reabsorption? |
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Definition
1) 67%
2) 67% *iso-osmotic*
3) low intracellular Na concentration due to Na/K ATPase |
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Term
| What are the major routes that sodium uses to re-enter across the early proximal tubule luminal membrane? late PCT? |
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Definition
1) Na/H antiport; cotransport with sugars and amino acids
2) Na/H antiport (transcellular); Cl-induced transepithelial potential difference (paracellular) |
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Term
| How is the Na/H antiporter in the PCT involved in HCO3 reabsorption? |
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Definition
1) Na is switched in the lumen for H
2) Increased luminal H causes shift of HCO3 to H2O and CO2 via activity of carbonic anhydrase
3) CO2 diffuses into cell where it is recombined w/ H2O to form HCO3 and H+
4) HCO3 is transported by Cl/HCO3 and Na/HCO3 transporters
5) H+ is returned to lumen |
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Term
| What is the major mechanism of Na reabsorption in the early part of the PCT? Late part? JUST THE MAJOR ONES |
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Definition
1) sugars and AA - cotransport
2) Cl - paracellular |
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Term
| What percent of the sodium is reabsorbed in the loop of henle? water? which portion is each reabsorbed in? |
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Definition
1) 25%; thin ascending limb; thick ascending limb (Na/K/2Cl)
2) 25%; thin descending limb |
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Term
| What is the action of furosemide on the thick ascending limb of the loop of henle? |
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Definition
| 1) Na/K/2Cl inhibitor (loop diuretic) - decreases Na and H2O reabsorption; increases paracellular uptake of cations |
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Term
| What percent of filtered Na is reabsorbed in the distal tubule and collecting duct? What is the major mechanism? |
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Definition
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Term
| What are the actions of the two major types of cells in the distal tubule and collecting duct? |
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Definition
1) absorb Na; water reabsorption
2) acid secretion |
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Term
| Describe Liddle's syndrome |
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Definition
1) increased channel activity
2) increased Na reabsorption
3) increased BP |
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Term
| Define: effective circulating volume (ECV). What are the factors that determine this valu? |
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Definition
1) theoretical quantity defined as the fluid in the vascular space that effectively perfuses the tissues
2) depends on: volume; pressure; cardiac output; ECF volume; sodium balance |
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Term
| What are the major sensors of ECV? Where are they located? What do they sense? What is the major action? |
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Definition
1) low pressure (venous sensors); cardiac atria/pulmonary vessels; decreased ECV; inc. SNA and ADH
2) High pressure (arterial) sensors; carotid sinus, aortic arch; increased pressure; dec. SNA and ADH
3) JGA; inc/dec pressue; dec/inc. renin |
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Term
| Describe the effect of renal sympathetic nerve activity on sodium and water handling. |
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Definition
1) activated in response to dec. ECV
2) greater constriction of afferent compared to efferent (dec. GFR)
3) stim renin secretion |
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Term
| What is the effect of the renin-angiotensin-aldosterone system on sodium and water handling |
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Definition
1) renin secretion from JGA due to dec. perfusion/SNA/dec luminal Cl
2) activation of angiotensinogen -> AI -> AII
3) inc. systemic BP, selective constriction of efferent arteriole
4) inc. aldosterone, ADH secretion
5) inc. thirst
6) aldosterone -> principal cells inc sodium reabsorption |
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Term
| What is the effect of ANP on sodium handling? |
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Definition
1) inc. due to ECV
2) dilates the afferent and constricts the efferent arteriole
3) reduces renin, aldosterone, ADH secretion
4) inhibits sodium reabsorption by principal cells
*reduce sodium reabsorption and antagonize RAAS* |
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Term
| What is the response to volume depletion? |
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Definition
1) dec ECV
2) inc SNA ->inc. renin -> inc. AII -> inc reabsorption and aldosterone, ADH secretion -> thirst
3) dec. ANP
4) NET EFFECT: inc. sodium and water reabsorption, inc. blood pressure, increase water intake, all to restore ECV |
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Term
| Describe the body's response to volume overload |
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Definition
1) inc. cardiac filling P, cardiac output, blood pressure, and perfusion pressure
2) suppress SNA and RAAS; inc. ANP -> dec. renin, aldosterone, ADH
3) pressure natriuresis -> inc. P_gc, GFR, dec transit time, dec absorption time |
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Term
| Describe glomerulotubular balance (G-T) |
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Definition
- prevents large changes in Na excretion due to changes in GFR
- refers to change in NaCl and water reabsorption that occurs in the proximal tubule in response to changes in glomerular filtration rate at constant renal plasma flow
- as GFR increases, capillary oncotic pressure increases, drawing more fluid back into the capillaries |
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