lecture 16 (T3)- Tubular reabsorption and secretion Flashcards by Anna Woods

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

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what is wanter transported form the lumen through the tubular cells into the interstitial by

both transcellular and paracellular routes by osmosis

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what are attributes of aquaporin-1

widespread, including renal tubulesq

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what are attributes of aquaporin-2

present in apical membranes of collecting tubule cells

controlled by ADH

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what are attributes of aquaporin-3

present in basolateral membranes of collecting tubule cells

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what establishes ionic gradients across nephron cell membranes

ATPases

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what are attributes of ENaC channel

found in apical membrane of nephron cells
closed by drug amiloride
opened by a number of hormones

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where are CFTR (chloride channels) and K+ channels sometimes found on some segments of nephrons

apical membranes

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what are uniporters in cell membranes driven by

concentration gradient of substance concerned

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what is an transport occurring through channels or uniporters and an example

facilitated transport

ie: glucose transport

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what is transport directly coupled to an energy source

active transport

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what is transport that is coupled indirectly to an energy source

secondary active transport

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what are examples of primary active transporters

Na+K+ ATPase
H+ ATPase
H+K+ ATPase
Calcium ATPase

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what does SGLT2 do

reabsorbs 90% of glucose in early proximal tubule

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what does SGLT1 do

reabsorbs 10% of glucose in late proximal tubule

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what substances are actively secreted into the renal tubules

creatinine

para-aminohippuric acid

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what is transport maximum due to

saturation of a specific transport system

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what is transport maximum

limit to the rate at which the salute can be transported

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what is the transport max for glucose

375 mg/min

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what is the filtered load for glucose

125 mg/min

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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

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what does the rate of transport depend on

the electrochemical gradient

time the substance is in the tubule (depends on tubular flow rate)

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define solvent drag

osmotic movement of water can also carry some solutes

passive water reabsorption by osmosis is coupled mainly to sodium reabsorption

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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

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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