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CHAPTER 42: SOLUTE REABSORPTION (Hormone regulate Na transport…
CHAPTER 42: SOLUTE REABSORPTION
Renal tubule reabsorbs filtered substance
100% glucose in proximal tubule
~99% h2o
~99% Na
Renal tubule function
Fractional excretion rate
% of filtered sub. excreted in urine
tubular reabsorption + secretion
Fractional reabsorption rate
Proximal tubule reabsorbs the bulk of filtered solutes
Transcellular pathway
across plasma membrane & discharged into interstitial fluid
carrier-mediated transport
Paracellular pathway
across zona occludens that communicate freely w IF
passive diffusion/solvent drag
IF into blood
Starling's forces
-proximity of peritubular capillary
plasma w high oncotic p. + low hydrostatic p. of peritubular cap. = favor fluid & solute uptake
Proximal tubule secretes organic ions
endogenous waste products & exogenous drugs/toxins → protein bound in plasma → poorly filtered by glomerulus
PT takes up & extrudes into tubule → carrier-mediated transport
endogenous: bile salts,oxalate, urate, creatinine, protaglandins, epinephrine, hippurates
drug & toxins: antibiotics, diuretics, analgesic morphine, paraquat
birds → uric acid at proximal portion of reptilian-type nephron
Distal tubule segments reabsorb salt & dilute tubule fluid
thick ascending lib of Loop of Henle & distal convulated tubule
reabsorb Na, K, Cl, Ca, Mg
NaK pump, NaCl co-transporter, Na channel, Cl channel
IMPERMEABLE to h2o
CD reabsorb NaCl & can secrete/reabsorb K into blood
principal cell → secrete K
intercalated cell → reabsorb K
NaK pump
Distal tubule & CD respond to systemic signals to alter secretions
aldosterone, angiotensin II, antidiuretic hormone, endothelin, atrial natriuretic peptide, parathyroid hormone, vitamin D3, calcitonin
homeostasis
Aldosterone
Na reabsorption
connecting segment cells, principal cell of CD → enhance water reabsorption
increased permeability of apical plasma membrane Na channel
stimulate NaK pump activity
K secretion
stimulate NaK pump
immediate: redistribution of K from extra → intracellular compartment
continued stimulation: renal K elimination
stimulated by:
systemic hypotension through renon-angiotensin system
hyperkalemia (elevated plasma K level)
Hormone regulate Na transport
Angiotensin II
stimulate aldosterone release
enhance Na reabsorption
act on proximal tubule, thick ascending limb, CD
Antidiuretic
ADH, vasopressin
released when dehydrated, hypotensive
enchance Na reabsorption
act on TAL, CD
Endothelin
peptide hormone produced by CD, TAL, endothelial cells
increase renal NaCl & h2o excretion
inhibit action of pumps/channels
Atrial Natriuretic Peptide
enhance Na excretion
act on distal tubule, CD
inhibit aldosterone release, vasopressin effect on CD
Ca is reabsorbed in distal nephron & connecting segments & regulated by
parathyroid hormone
stimulated by hypoclacemia
act on cortical TAL, DCT, connecting segments
increase plasma Ca level
calcitonin
reduce serum Ca by stimulate Ca deposition in bones
pharmacological dose: enhance Ca excretion
physiological dose: reduce Ca excretion
act on TAL, DCT
enchance Ca reabsorption
vitamin D3
converted into active form in PCT, stimulated by PTH
act on DCT, connecting segment
enhance Ca reabsorption