lecture 16 (T3)- Tubular reabsorption and secretion Flashcards
what must happen for a substance to be reabsorbed (it must first be transported):
- across the tubular epithelial membranes into the renal interstitial fluid
- through the peritubular capillary membrane back into the blood
what is wanter transported form the lumen through the tubular cells into the interstitial by
both transcellular and paracellular routes by osmosis
what are attributes of aquaporin-1
widespread, including renal tubulesq
what are attributes of aquaporin-2
present in apical membranes of collecting tubule cells
controlled by ADH
what are attributes of aquaporin-3
present in basolateral membranes of collecting tubule cells
what establishes ionic gradients across nephron cell membranes
ATPases
what are attributes of ENaC channel
found in apical membrane of nephron cells
closed by drug amiloride
opened by a number of hormones
where are CFTR (chloride channels) and K+ channels sometimes found on some segments of nephrons
apical membranes
what are uniporters in cell membranes driven by
concentration gradient of substance concerned
what is an transport occurring through channels or uniporters and an example
facilitated transport
ie: glucose transport
what is transport directly coupled to an energy source
active transport
what is transport that is coupled indirectly to an energy source
secondary active transport
what are examples of primary active transporters
Na+K+ ATPase
H+ ATPase
H+K+ ATPase
Calcium ATPase
what does SGLT2 do
reabsorbs 90% of glucose in early proximal tubule
what does SGLT1 do
reabsorbs 10% of glucose in late proximal tubule
what substances are actively secreted into the renal tubules
creatinine
para-aminohippuric acid
what is transport maximum due to
saturation of a specific transport system
what is transport maximum
limit to the rate at which the salute can be transported
what is the transport max for glucose
375 mg/min
what is the filtered load for glucose
125 mg/min
what are some reasons that some passively reabsorbed substances do not have a transport max
rate of diffusion is determined by electrochemical gradient of the substance
permeability of the membrane for the substance
time that the fluid containing the substance remains within the tubule
what does the rate of transport depend on
the electrochemical gradient
time the substance is in the tubule (depends on tubular flow rate)
define solvent drag
osmotic movement of water can also carry some solutes
passive water reabsorption by osmosis is coupled mainly to sodium reabsorption
what are characteristics of the proximal tubule
highly metabolic (large number mitochondria) extensive brush border on luminal surfaces extensive intercellular and basal channels on interstitial surfaces
what does the proximal tubule reabsorb
all filtered glucose and amino acids
65% of filtered sodium, chloride, bicarbonate and potassium
what does the proximal tubule secrete
organic acids, bases and hydrogen ions into tubular lumen
what reabsorption occurs in first half of proximal tubule
reabsorption is via co-transport along with glucose, amino acids, and other solutes
what reabsorption occurs in second half of proximal tubule
reabsorption is mainly with chloride ions
what is most sodium entry in proximal tubule done by
via anti port with H+
what is the electoral gradient of sodium transport in proximal tubule
cytoplasm: -70 mV
tubular lumen: -3 mV
what is the concentration gradient for sodium transport in proximal tubule
luminal Na+ concentration= 140mOsm
cytoplasmic Na+ concentration= 30mOsm
why does H+ concentration in lumen of proximal tubule increase
due to anti port transport with Na+
what does H+ combine with in proximal tubule
luminal bicarbonate, forming carbonic acid
what splits carbonic acid into CO2 and water in the proximal tubule
carbonic anhydrase
how is H+ removed from cell in proximal tubule
anti port with Na+
H+ ATPase
what are attributes of thin descending segment of loop of henle
highly permeable to water and moderately permeable to most solutes (including urea and sodium)
reabsorbs about 20% of filtered water
is the thin ascending segment of the loop of henle permeable to water
NO!!!!
what does the Na+K+ ATPase pump in the basolateral membranes of the thick ascending segment do
drives reabsorption of K+ into cell against concentrating gradient
what does the sodium. potassium, chloride co-transporter do in the thick ascending segment
moves 1 sodium, 2 chloride and 1 potassium into the cell
what does the slight back leak of K+ into the lumen in the thick ascending segment of the loop of hence do
creates positive charge of +8mv
forces Mg++ and Ca++ to diffuse through tubular lumen through paracellular space into interstitial fluid
is the thick ascending loop of hence permeable to water
NOOOOOO
what is the site of action of powerful loop diuretics and what are they
thick ascending segment of loop of henle
furosemide, ethacrynic acid, bumetanide
what forms the macula densa
first portion of distal tubule
what is another name for the distal tubule
diluting segment
what are 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 (spironoactone, eplerenone, amiloride, triameterene)
what are examples of aldosterone antagonists
spironolactane and eplerenon
what are examples of Na+ channel blockers
amiloride and triamterene
what is the main thing that intercalated cells do
reabsorb K+ and bicarbonate from tubular lumen
secrete H+ into tubular lumen
what are intercalated cells mediated by
H+ ATPase transporter
what are attributes of medullary collecting duct
epithelial cells are cuboidal
permeability to water controlled by ADP
permeable to urea
capable of secreting H+ against a large concentration gradient
what is the source of aldosteron
adrenal cortex
what is the function of aldosterone
increases sodium reabsorption and stimulates potassium secretion
stimulates Na+K+ ATPase pump on basolateral side of cortical collecting tubule membrane
what is the site of action for aldosterone
principal cells of cortical collecting ducts
what is the stimulus for secretion of aldosterone
increased extracellular potassium
increased levels of angiotensin II
what is addisons diesase
absence of aldosterone
results in marked loss of sodium and accumulation of potassium
what is the diseased caused when there is 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 norma;
what are the effects of angiotensin II
stimulates aldosterone secretion
constricts efferent arterioles
directly stimulates sodium reabsorption in proximal tubules, loop of henle, distal tubules, and collecting tubules
what is the source of ADH
posterior pituitary
what is the function of ADH
increase 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( stimulating movement of aquaporin 2 proteins to lumen side of cell membranes)
what is the source of ANP
cardiac atrial cells in response to distension
what is the function of ANP
inhibits reabsorption of sodium and water
what is the function of parathyroid hormones
increases calcium reabsorption
what is renal clearance of a substance
volume of plasma that is completely cleared of the substance by the kidneys per unit time
what is the equation for renal clearance
Cs X Ps = Us X V
how much plasma flowing through the kidneys must be filtered to deliver the inulin that appears in the urin
125 ml of plasma
