Tubular Reabsorption and Secretion Flashcards
Water is transported from the lumen through the tubular cells into the interstitium via both______ and ______ routes by osmosis
transcellular, paracellular
Water is transported by way of
specific water channels (aquaporins (AQP))
Aquaporin ___ is widespread, including renal tubules
1
Aquaporin ____ is present in apical membranes of collecting tubule cells. and is controlled by ADH
Aquaporin 2
Aquaporin 2 is present in
apical membrane of collecting tubule cells
Aquaporin 2 is controlled by
ADH
Aquaporin ___ is present in basolateral membranes of collecting tubule cells
3
______ establish ionic gradients across nephron cell membranes
ATPases
_____ drive reabsorption or secretion of many other solutes
Gradients
What are the two types of secondary active transporters in the nephron
Sympoter (cotransport)
Antiport (countertransporter)
after a gradient is established solutes are transported by way of _____ in the nephron cell membranes
secondary active transport
ENaC channel is foud
in apical membrane of nephron cells
ENaC channel is closed by drug
Amiloride
ENaC channel is opened by
a number of hormones
CFTR (chloride) channels and K+ channels are found
in apical membranes of some segments of a nephron
Are uniporters found on nephron cell membranes
yes
Uniporters of the nephron cell membrane are driven by
concentration gradient of substance concerned
Transport directly coupled to an energy source is what type of
active transport
Transport occurring through channels or uniporters is
- Facilitated transport
- ex. Glucose transport
Transport that is coupled to an energy source (i.e. ion gradient)
Secondary active transport
Examples of primary active transport
- Na+K+ ATPase
- H+ ATPase
- H+K+ ATPase
- Calcium ATPase
Reabsorption of glucose or amino acids by renal tubule are examples of
secondary active transport
Sodium-glucose co-transporters are located on
brush border of proximal tubule cells
What are the two sodium-glucose co-transporters on brush border of proximal tubule cells
- SGLT2
- SGLT1
SGLT2 reabsorbs _____ of glucose in early proximal tubule
90%
SGLT1 reabsorbs ___% of glucose in late proximal tubule
10%
SGLT2 reabsords 90% of glucose in
early proximal tubule
SGLT1 reabsorbs 10% of glucose in
late proximal tubule
Substances that are actively secreted into the renal tubules
Creatinine
Para-Aminohippuric acid
The limit to the rate at which the solute can be transported (transport maximum) is 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
Reasons that some passively reabsorbed substances do not have a transport maximum
- 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
Rate of transport depends on
-The electrochemical gradient
- Time the substance is in the tubule
- depends on tubular flow rate
Solvent drag
- passive water reabsorption by osmosis is coupled mainly to sodium reabsorption
- Osmotic movement of water can also carry some solutes=solvent drag
What is the GFR (in liters/day) in average adult human
125 liters/day
Almost 90 percent of glucose reabsorption occurs in the early proximal tubule. by means of
secondary active transport via a sodium/ glucose cotransporter
The proximal tubule is highly ______ with large numbers of
Metabolic, mitochondria
Characteristics of the proximal tuble
- highly metabolic with large numbers of mitochondria
- extensive brush borders on luminal surfaces
- extensive intercellular and basal channels on interstitial surfaces
The proximal tubule reabsorbs
- 65 % of filtered sodium, chloride, bicarbonate and potassium
- Reabsorbs all filtered glucose and amino acids
The proximal convoluted tubule adds what into the lumen tubular fluid
H+, organic acids, bases
As we go through the proximal convoluted tubule the ratio of tubular fluid/plasma concentration of sodium does what
it stays the same (about 1.0)
As we go through the proximal tubule the tubular fluid/plasma concentration of creatinine and urea does what
increases
The proximal tubule secretes what into the tubular lumen
organic acids
bases
hydrogen ions
in the first half of the proximal tubule sodium reabsorption is via
co-transport along with glucose, amino acids, and other solutes
In the second half of the proximal tubule sodium reabsorption is mainly due to
reabsorption with chloride ions
Sodium transport in the proximal tubule
- most sodium entry is via antiport with H+
- Na+ is pumped out of cell via Na+K+ ATPase pump
- Electrical gradient
- Cytoplasm= -70mV
- Tubular lumen= -3 mV
- Concentration gradient
- Luminal Na+ concentration=14-mOsm
- Cytoplasmic Na+ concentration= 30 mOsm
What is the proximal tubule luminal Na+ concentration
140mOsm
What is the proximal tubule cytoplasmic Na+ concentration
30 mOsm
hyrogen and bicarbonarte ions in the proximal tubule
- H+ increases in lumen due to antiport transport with Na+
- H+ combines with luminal bicarbonate
- Forms carbonic acid
- Carbonic anhydrase in lumen splits carbonic acid into carbon dioxide and water
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
Carbon dioxide and water in the proximal tubule
- Carbon dioxide and water combine to form carbonic acid
- Carbon acid dissociates to form bicarbonate ion and H+
- Bicarbonate ion diffuses out of cell into interstitial space
- H+ removed form Cell via
- antiproton with Na+
- H+ ATPase
The thin descending segment of the loop of Henle
- Highly permeable to water and moderately permeable to most solutes, including urea and sodium
- Reabsorbs about 20% of filtered water
The thin ascending segment of the loop of Henle
impermeable to water
Thick ascending segment in loop of henle
- Na+ K+ ATPase pump in basolateral membranes
- Drives reabsorption of K+ into cell against concentration gradient
- Sodium, Potassium, Chloride co-transporter
- Moves 1-Sodium, 2-Chloride, 1 potassium into cell
- Slight back lead of K+ into lumen
- Creates positive charge of +8mv
- Forces Mg++ and Ca++ to diffuse through tubular lumen through paracellular space into interstitial fluid
- impermeable to water
- Site of action of powerful “loop” diuretics
- Furosemide
- Ethacrynic acid
- Bumetanide
Powerful diuretics that work on thick ascending segment of the loop of Henle
- Furosemide
- Ethacrynic acid
- Bumetanide
Source of Aldosterone
Adrenal cortex
Function of Aldosterone
- increases sodium reabsorption and stimulates potassium secretion
- stimulates Na+K+ATPase pump on basolateral side of cortical collecting tubule membrane
Aldosterone site of action
- Major site of action is on the principle cells of cortical collecting ducts
Stimulus for secretion of Aldosterone
- Increased extracellular potassium
- Increased levels of Angiotensin II
Absence of Aldosterone causes
- Addison’s disease
- Results in marked loss of sodium and accumulation of potassium
Hypersecretion of Aldosterone is caused from
Conn’s syndrome
Function of Angiotensin II
- Increased sodium and water reabsorption
- Returns blood pressure and extracellular volume toward normal
Effects of Angiotensin II
- Stimulates Aldosterone secretion
- Constricts efferent arterioles
- Directly stimulates sodium reabsorption in proximal tubules, loops of Henle, distal tubules, and collecting tubules
source of ADH
posterior pituitary
Function of ADH
Increases water reabsorption
Effects of ADH
- Binds to V2 receptors in late distal tubules, collecting tubules, and collecting ducts
- increases formation of cAMP
- Stimulates movement of aquaporin-2 proteins to luminal side of cell membrane (form cluster)
The source of atrial natriuretic peptide
-Cardiac atrial cells in response to distension
Function of Atrial natriuretic peptide
Inhibits reabsorption of sodium and water
Source of Parathyroid hormone
Parathyroid glands
Function of parathyroid hormone
Increases calcium reabsorption
