Lecture 18: Tubular Reabsorption and Secretion Flashcards
For a substance to be reabsorbed it must be transported to where?
across the tubular epithelial membranes into the renal interstitial fluid
through the particular capillary membrane back into the blood
What channels is water transported through?
aquaporins
Where is aquaporin 1 located?
widespread, including renal tubules
Where is aquaporin 2 located?
present in apical membranes of collating tubule cells
controlled by ADH
Where is aquaporin 3 located?
present in basolateral membranes of collecting tubule cells
_______ establish ionic gradients across nephron cell membranes
ATPases
Describe ENaC channels
found in apical membrane of nephron cells
closed by drug amiloride
opened by number of hormones
Where are CTFR and K+ channels found?
apical membranes of some segments of nephron
What are some primary active transporters?
Na+ K+ ATPase
H+ATPase
H+K+ATPase
Calcium ATPase
Reabsorption of glucose or amino acids by renal tubule are example of ________ transport
secondary active
What substances are actively secreted into the renal tubules?
creatinine
para aminohippuric acid
What is the transport maximum?
limit to the rate at which the solute can be transported due to saturation of a specific transport system
Transport max for glucose=
375 mg/min
filtered load for glucose =
125 mg/min
GFR x plasma glucose =
125 ml/min x 1 mg/ml
What are some reasons why some passively reabsorbed substances do not have a transport maximum?
rate of diffusion is determined by electrochemical gradient of substance
permeability of the membrane for the substance
time that the fluid contacting the substance remains within the tubule
What does the rate of transport depend on?
electrochemical gradient
time the substance is in the tubule
What is passive water reabsorption coupled to?
sodium reabsorption
Describe the proximal tubule
- highly metabolic with large numbers of mitochondria
- extensive brush border on luminal surfaces
- extensive intercellular and basal channels on interstitial surfaces
What does the proximal tubule reabsorb?
65% of filtered sodium, chloride, bicarbonate, potassium
all filtered glucose and amino acids
What does the proximal tubule secrete?
organic acids, bases, and hydrogen ions into tubular lumen
In the first half of the proximal tubule, sodium reabsorption is via co transport with ______ ____ and _____
glucose, sodium, and other solutes
In the second half of the proximal tubule, reabsorption is mostly with _____
chloride ions
The thin descending segment of the loop of Henle is _____ permeable to water and _____ permeable to most solutes, including urea and sodium
highly; moderately
the thin descending segment of the loop of Henle reabsorbs about _____ percent of filtered water
20
The thin ascending loop of Henle is ______ to water
impermeable
Thick ascending loop of Henle is ______ to water
impermeable
The first portion of the distal tubule forms the ______
macula densa
Is the distal tubule permeable to water and urea?
no
Describe principal cells
reabsorb Na+ and water from tubular lumen
secrete K+ into tubular lumen
uses Na+K+ATPase pump
primary site of K+ sparing diuretics
Describe intercalated cells
reabsorb K+ from tubular lumen
secrete H+ into tubular lumen
Is the medullary collecting duct permeable to water and urea? what is controlled by?
yes; ADH
What is the source of aldosterone?
adrenal cortex
What is the function of aldosterone?
increases sodium reabsorption and stimulates potassium secretion
What is the site of action for aldosterone?
major site of action is on the principal cells of cordial collecting ducts
What is the stimulus for secretion for aldosterone?
increased extracellular potassium
increased levels of angiotensin II
What happens if there is an absence of aldosterone?
Addison’s disease
marked loss of sodium and accumulation of potassium
What happens in there is a hyper secretion of aldosterone?
Conn’s syndrome
What is the function of Angiotensin II?
increased sodium and water reabsorption
returns blood pressure and extracellular volume toward normal
What are the effects of angiotensin II?
stimulates aldosterone secretion
constricts efferent arterioles
directly stimulates sodium reabsorption in proximal tubules, loops of Henle, distal tubules, and collecting ducts
What is the source of ADH?
posterior pituitary
What is the function of ADH?
increases water reabsorption
What are the effects of ADH?
binds to V2 receptors in late distal tubules, collecting tubules, and collecting ducts
increases formation of cAMP
What is the source of atrial natriuretic peptide?
cardiac atrial cells in response to distention
What is the function of atrial natriuretic peptide?
inhibits reabsorption of sodium and water
What is the source of parathyroid hormone?
parathyroid glands
What is the function of parathyroid hormone?
increases calcium reabsorption
What is the renal clearance of a substance equal to?
volume of plasma that is completely cleared of the substance by the kidneys per unit time
