Lecture 2-Renal Physiology Flashcards
Production of urine begins with water and solute filtration from plasma flowing into the glomerulus via the ___ arteriole
Afferent
Function of the glomerulus—purpose is to form an ultrafiltrate of ___; blood enters via the ___ arteriole; it is the muscle tone of the ___ arteriole which plays a large role in flow through the glomerulus
Purpose is to form an ultrafiltrate of plasma; blood enters via the afferent arteriole; it is the muscle tone of the afferent arteriole which plays a large role in flow through the glomerulus
Once blood flows via the afferent arteriole, blood then goes through capillaries in ___ (the glomerulus)
Bowman’s capsule
The glomerular capillary membrane is similar to that of other capillaries, except that it has three (instead of the usual two) major layers: 1) the ___ of the capillary, 2) a ___ membrane, and 3) a layer of ___ cells (___cytes) surrounding the outer surface of the capillary basement membrane
1) the endothelium of the capillary, 2) a basement membrane, and 3) a layer of epithelial cells (podocytes) surrounding the outer surface of the capillary basement membrane
The cells of the glomerular capillary membrane are not continuous but have foot like processes (___) that encircle the outer surface of the capillaries; the footlike processes are separated by gaps called ___ through which the glomerular filtrate moves
Podocytes; gaps called slit pores through which the glomerular filtrate moves
Features of the glomerular filtration barrier—___ selective; basement membrane is ___ charged due to glycoproteins which compose it
Charge selective; basement membrane is negatively charged due to glycoproteins which compose it
Since the basement membrane is negatively charged, negatively charged proteins are thus ___ and are unable to pass through it
Repelled
The glomerular filtration barrier is ___ selective—molecules greater than ___-___ angstroms will not pass through
The glomerular filtration barrier is size selective—molecules greater than 50-100 angstroms will not pass through
The basement membrane effectively prevents filtration of ___, in part because of strong negative electrical charges associated with the proteoglycans
Prevents filtration of plasma proteins
___ is defined as total volume of blood per unit time (ml/min) which leaves the capillaries and enters Bowman’s space
Glomerular filtration rate
GFR is ~ ___ ml/min
120 ml/min
GFR is ~ ___ L/day
180 L/day
The two major determinants of filtration pressure are glomerular ___ pressure and glomerular ___ pressure
Glomerular filtration pressure and glomerular oncotic pressure
Glomerular capillary pressure = ___
PGC
Glomerular oncotic pressure = ___
Pgc
PGC is directly related to renal ___ pressure and is heavily influenced by ___ tone at points upstream (___) and downstream (___) from the glomerulus
PGC is directly related to renal artery pressure and is heavily influenced by arteriolar tone at points upstream (afferent) and downstream (efferent) from the glomerulus
Kf = ___ constant
Ultrafiltration constant
Ultrafiltration constant (Kf) is directly related to glomerular capillary ___ and glomerular surface ___
Glomerular capillary permeability and glomerular surface area
Renal blood flow is around ___% of cardiac output (~___ml/min)
20% of cardiac output (~1200 ml/min)
Of all organs, only the ___ gets a higher percentage of cardiac output than the kidneys
Liver
The vast majority of what is filtered from the kidneys is ___
Reabsorbed
Two capillary beds of renal circulation = ___ capillaries + ___ capillaries
Glomerular capillaries + peritubular capillaries
The glomerular and peritubular capillaries are arranged in ___ and are separated by ___ (afferent/efferent) arterioles
Arranged in series and are separated by efferent arterioles
___ (high/low) hydrostatic pressure in the glomerular capillaries (about 60 mm Hg) causes rapid fluid filtration, whereas a much ___ (lower/higher) hydrostatic pressure in the peritubular capillaries (about 13 mm Hg) permits rapid fluid reabsorption
High hydrostatic pressure in the glomerular capillaries; lower hydrostatic pressure in the peritubular capillaries
Filtration = ___ hydrostatic pressure in the ___ capillaries
High hydrostatic pressure in the glomerular capillaries (~60 mm Hg)
Reabsorption = ___ hydrostatic pressure in the ___ capillaries
Lower hydrostatic pressure in the peritubular capillaries (~13 mm Hg)
By adjusting the resistance of the afferent and efferent arterioles, the kidneys can regulate the hydrostatic pressure in both the glomerular and peritubular capillaries, thereby changing the rate of glomerular filtration, tubular reabsorption, or both in response to the body’s homeostatic demands—T/F?
True
Renal blood flow = ___ (afferent/efferent) arteriole enters glomerular capillaries, which exit ___ capsule and merge to form the ___ arteriole and ___ capillaries that nourish the tubules
Afferent arteriole enters glomerular capillaries, which exit Bowman’s capsule and merge to form the efferent arteriole and peritubular capillaries that nourish the tubules
The renal vasculature is unusual in having an arrangement of ___ capillary beds joined in ___ by arterioles
An arrangement of two capillary beds joined in series by arterioles
Blood supply to the entire tubular system comes from the glomerular ___ (afferent/efferent) arteriole, which branches into an extensive capillary network
Efferent
Some of these peritubular capillaries, the ___, descend deep into the medulla to parallel the loops of Henle; they then return in a cortical direction with the loops, join other peritubular capillaries, and empty into the cortical veins
Vasa recta
4 factors that determine GFR: 1) the ___ coefficient, 2) ___ pressure, 3) net ___ pressure, and 4) capillary ___ flow rate
1) the ultrafiltration coefficient
2) oncotic pressure
3) net hydraulic pressure
4) capillary plasma flow rate
This depends on capillary permeability and surface area available for filtration
Ultrafiltration coefficient
Since there should be no free protein in Bowman’s space, the net direction of this force should oppose filtration
Oncotic pressure
This drives fluid from capillaries into Bowman’s space
Net hydraulic pressure
Higher flow rate = greater filtration (and vice versa)
Capillary plasma flow rate
The production of urine begins with water and solute ___ from plasma flowing into the glomerulus via the ___ (afferent/efferent) arteriole
Water and solute filtration from plasma flowing into the glomerulus via the afferent arteriole
The ___ rate is a measure of glomerular function expressed as milliliters of plasma filtered per minute
Glomerular filtration rate (GFR)
The ___ constant (Kf) is directly related to glomerular capillary permeability and glomerular surface area
Ultrafiltration constant (Kf)
The two major determinants of filtration pressure are glomerular ___ pressure (PGC) and glomerular ___ pressure (pgc)
Glomerular capillary pressure (PGC) and glomerular oncotic pressure (pgc)
PGC (glomerular capillary pressure) is directly related to renal ___ pressure and is heavily influenced by ___ tone at points upstream (___) and downstream (___) from the glomerulus
PGC is directly related to renal artery pressure and is heavily influenced by arteriolar tone at points upstream (afferent) and downstream (efferent) from the glomerulus
Glomerular hydrostatic pressure is ~ ___ mm Hg
60 mm Hg, filtration pressure, fluid moving out of kidney
Glomerular colloid osmotic pressure is ~ ___ mm Hg
~ 32 mm Hg
Bowman’s capsule pressure is ~ ___ mm Hg
18 mm Hg
Net filtration pressure = ___ - ___ - ___
Net filtration pressure = glomerular hydrostatic pressure - Bowman’s capsule pressure - glomerular oncotic pressure
60 mm Hg - 18 mm Hg - 32 mm Hg = ~10 mm Hg —> net filtration pressure
The glomerular capillaries are relatively impermeable to ___, so the filtered fluid (called the glomerular filtrate) is essentially ___ free and devoid of cellular elements, including RBCs
Relatively impermeable to proteins, essentially protein free
How does the body get back filtered plasma?—as the plasma moves towards the end of the glomerular capillary, filtration slows because of a ___ (increase/decrease) in oncotic pressure (as fluid is removed, the protein concentration ___ (increases/decreases)
Filtration slows because of an increase in oncotic pressure (as fluid is removed, the protein concentration increases
How does the body get back filtered plasma?—capillary hydrostatic pressure ___ (increases/decreases) significantly at the level of the ___ (afferent/efferent) arteriole, resulting in maximal ___ (filtration/reabsorption) into the vasa recta and peritubular plexi
Capillary hydrostatic pressure decreases significantly at the level of the efferent arteriole, resulting in maximal reabsorption into the vasa recta and peritubular plexi
The glomerular capillary hydrostatic pressure has been estimated to be about ___ mm Hg under normal conditions
60
Changes in glomerular hydrostatic pressure serve as the primary means for physiological regulation of ___
GFR
Increases in glomerular hydrostatic pressure ___ (increase/decrease) the GFR, whereas decreases in the glomerular hydrostatic pressure ___ (increase/decrease) the GFR
Increase; decrease
Glomerular hydrostatic pressure is determined by three variables, each of which is under physiological control: 1) ___ pressure, 2) ___ arteriolar resistance, 3) ___ arteriolar resistance
1) arterial pressure
2) afferent arteriolar resistance
3) efferent arteriolar resistance
Increased arterial pressure tends to ___ (increase/decrease) glomerular hydrostatic pressure and therefore, ___ (increases/decreases) GFR
Increase glomerular hydrostatic pressure and therefore, increases GFR
Increased resistance of afferent arterioles ___ (increases/decreases) glomerular hydrostatic pressure and ___ (increases/decreases) GFR
Decreases glomerular hydrostatic pressure and decreases GFR
Dilation of the afferent arterioles ___ (increases/decreases) glomerular hydrostatic pressure and GFR
Increases glomerular hydrostatic pressure and GFR
This term reflects the kidney’s ability to regulate GFR over a range of conditions
Autoregulation
Over a range of systolic BP ___-___ mm Hg, GFR and RBF remain constant
80-200 mm Hg
2 mechanisms of GFR regulation: 1) constriction and dilation of ___ sphincters in the afferent and efferent arterioles; 2) increased Na delivery to the macula densa ___ (increases/decreases) GFR
1) constriction and dilation of precapillary sphincters in the afferent and efferent arterioles; 2) increased Na delivery to the macula densa decreases GFR
The ___ is a specialized group of epithelial cells in the distal tubules that comes in close contact with the afferent and efferent arterioles; these cells contain ___ apparatus, which are intracellular secretory organelles directed towards the arterioles
Macula densa; these cells contain Golgi apparatus
Decrease in sodium chloride concentration initiates a signal from the macula densa that has two effects: 1) it ___ (increases/decreases) resistance to blood flow in the afferent arterioles, which ___ (increases/decreases) glomerular hydrostatic pressure and helps return GFR toward normal, and 2) it ___ (increases/decreases) renin release from the juxtaglomerular cells of the afferent and efferent arterioles, which are the major storage sites for renin
1) It decreases resistance to blood flow in the afferent arterioles, which increases glomerular hydrostatic pressure and helps return GFR toward normal, and 2) it increases renin release…
Renin release from the juxtaglomerular cells of the afferent/efferent arterioles functions as an enzyme to increase the formation of ___, which is converted to ___; finally, the ___ constricts the efferent arterioles, thereby ___ (increasing/decreasing) glomerular hydrostatic pressure and helping return GFR toward normal
Renin increases formation of angiotensin I, which is converted to angiotensin II; finally, the angiotensin II constricts the efferent arterioles, thereby increasing glomerular hydrostatic pressure and helping return GFR toward normal
The ___ theory holds that an increase in arterial pressure causes the afferent arteriolar wall to stretch and then constrict (by reflex); likewise, a decrease in arterial pressure causes reflex afferent arteriolar dilation.
Myogenic reflex theory
This mechanism of renal blood flow autoregulation allows the composition of distal tubular fluid to influence glomerular function through actions involving the juxtaglomerular apparatus
Tubuloglomerular feedback
Tubuloglomerular feedback—when renal blood flow falls, the related decrease in GFR causes ___ (more/less) chloride delivery to the juxtaglomerular apparatus, which in turn induces afferent arteriole ___ (constriction/dilation); as a result, glomerular flow and pressure then ___ (increase/decrease), and GFR returns to previous levels
Less chloride delivery, afferent arteriole dilation; glomerular flow and pressure then increase
Tubuloglomerular feedback—chloride also acts as the feedback signal for control of efferent arteriolar tone; when GFR falls, declining chloride delivery to the juxtaglomerular apparatus triggers the release of ___, which ultimately causes the formation of ___; in response to ___, efferent arteriolar ___ (dilation/constriction) increases glomerular pressure, which increases glomerular filtration
Triggers the release of renin, which ultimately causes the formation of angiotensin II; in response to angiotensin II, efferent arteriolar constriction increases glomerular pressure, which increases glomerular filtration
Tubular ___ is quantitatively more important than tubular secretion in the formation of urine, but ___ plays an important role in determining the amounts of potassium and hydrogen ions and a few other substances that are excreted in the urine
Tubular reabsorption is more important than secretion in the formation of urine, but secretion plays an important role…
Most substances that must be cleared from the blood, especially the end products of metabolism such as urea, creatinine, uric acid, and urates, are poorly reabsorbed and are therefore excreted in large amounts in the urine—T/F?
True
Electrolytes, such as sodium ions, chloride ions, and bicarbonate ions, are highly reabsorbed, so only small amounts appear in the urine—T/F?
True
This is defined as the volume of plasma from which all of a given substance is removed per unit time in one pass through the kidney
Renal clearance
Renal clearance—if a substance is neither secreted nor reabsorbed then its clearance is equal to ___
GFR (i.e.: insulin)
Renal clearance—if a substance is completely reabsorbed, then clearance is ___
0 (i.e.: glucose under normal conditions)
Glomerular filtration, tubular reabsorption, and tubular secretion are all regulated according to the needs of the body—T/F?
True
When there is excess sodium in the body, the rate at which sodium is filtered usually ___ (increases/decreases), and a ___ (smaller/larger) fraction of the filtered sodium is reabsorbed, causing increased urinary excretion of sodium
The rate at which sodium is filtered usually increases, and a smaller fraction of the filtered sodium is reabsorbed, causing increased urinary excretion of sodium
If clearance > GFR, there must be net ___
Secretion
If clearance < GFR, there must be net ___
Reabsorption
If clearance = GFR, there is…
Neither net reabsorption or net secretion
Renal clearance of creatinine is used clinically to estimate ___
GFR
Creatinine is a normal component of ___, a byproduct of ___
Normal component of blood, a byproduct of skeletal muscle protein
As glomerular filtrate enters the renal tubules, it flows sequentially through the successive parts of the tubule—the ___ tubule, the loop of ___, the ___ tubule, the ___ tubule, and finally, the ___ duct—before it is excreted as urine.
The proximal tubule, loop of henle, distal tubule, collecting tubule, collecting duct
Urine that is formed and all the substances in the urine represent the sum of (3) basic renal processes: 1) glomerular ___, 2) tubular ___, 3) tubular ___
1) glomerular filtration
2) tubular reabsorption
3) tubular secretion
Normal renal function = ___% functioning nephrons; GFR ___ ml/min
100% functioning nephrons; GFR 125 ml/min
Reduced renal function = ___% functioning nephrons; GFR ___ ml/min
10-40% functioning nephrons; GFR 12-80 ml/min
Renal failure = ___% functioning nephrons; GFR ___ ml/min
< 10% functioning nephrons; GFR < 12 ml/min
(3) mechanisms of reabsorption and secretion:
1) active transport
2) passive transport
3) secondary active transport
This mechanism of reabsorption/secretion uses energy
Active transport
This mechanism of reabsorption/secretion has 2 kinds—simple and facilitated
Passive transport
This mechanism of reabsorption/secretion moves solute against a concentration gradient coupled to movement of another solute; uses energy indirectly
Active transport
Diffusion of lipid soluble agents or gases = ___ passive transport
Simple passive transport
Passive transport that uses a protein channel or carrier = ___ passive transport
Facilitated
Transport of water and solutes through cell membranes
Transcellular route
Transport of water and solutes through the spaces between cell junctions
Paracellular route
After absorption across the tubular epithelial cells into the interstitial fluid, water and solutes are transported through the peritubular capillary walls into the blood by ___ (bulk flow) that is mediated by hydrostatic and colloid osmotic forces
Ultrafiltration (bulk flow)
Transport that is coupled DIRECTLY to an energy source, such as the hydrolysis of ATP, is termed ___ active transport (i.e.: sodium transport)
Primary active transport
Transport that is coupled INDIRECTLY to an energy source, such as that due to an ion gradient, is referred to as ___ active transport (i.e.: reabsorption of glucose by the renal tubule)
Secondary active transport
Basic mechanism for active transport of sodium through the tubular epithelial cell involves a ___-___ ion ATPase carrier in the tubular cell’s ___ membrane
Na-K ion ATPase carrier in the tubular cell’s basolateral membrane
Active transport of sodium—the Na-K ion ATPase pump keeps sodium concentration ___ (high/low) in the tubular cells and ___ (high/low) in the lateral spaces outside the tubule
Keeps sodium concentration low in the tubular cells and high in the lateral spaces outside the tubule
Active transport of sodium—___ follows reabsorbed sodium by osmosis; thus, sodium reabsorption has a main effect on blood ___ and blood ___
Water follows reabsorbed sodium by osmosis; thus, sodium reabsorption has a main effect on blood volume and blood pressure
Active transport of sodium—___ promotes sodium retention by insertion of additional Na+ channels into the luminal membrane, and additional Na+/K+ ATPase into the basolateral membrane of the ___ and ___ tubules
Aldosterone promotes sodium retentions additional Na+/K+ ATPase into the basolateral membrane of the distal and collecting tubules
Secondary active transport utilizes ___ gradient
Na+ (sodium symport)
Secondary active transport is used for transporting what (4) things?—___ose, ___ acids, ___ns, ___ites
- Glucose
- Amino acids
- Ions
- Metabolites
Secondary active secretion into the tubules—mechanism of ___ reabsorption and Na+-___+ exchange in ___ tubule and ___ loop of henle
Mechanism of bicarbonate reabsorption and Na+-H+ exchange in proximal tubule and thick loop of henle
Some substances are secreted into the tubules by secondary active transport, which often involves counter-transport of the substance with sodium ions—T/F?
True
In counter-transport, the energy liberated from the downhill movement of one of the substances (i.e.: sodium ions) enables uphill movement of a second substance in the opposite direction—T/F?
True
Proximal convoluted tubule reabsorption—some parts of the tubule, especially the proximal tubule, reabsorb large molecules, such as ___, by ___
Reabsorb large molecules, such as proteins, by pinocytosis
Because pinocytosis requires energy, it is considered a form of ___ transport
Active transport
Active transport systems can be ___
Saturated
In renal tubules, reabsorption and secretion of substances (i.e.: glucose, amino acids) are coupled with the secondary active transport of ___
Sodium
The ___ is the limit due to saturation of the specific transport systems involved when the amount of solute delivered to the tubule (referred to as tubular load) exceeds the capacity of the carrier proteins and specific enzymes involved in the transport process
Transport maximum
Until the transport mechanism is saturated, the rate of secretion or absorption is proportional to the concentration of ___ and ___ of the carrier for the substrate
Concentration of substrate and affinity of the carrier for the substrate
Some substances that are ___ reabsorbed do not demonstrate a transport maximum because their rate of transport is determined by other factors
Passively reabsorbed
The rate of transport for substances that are passively reabsorbed is determined by other factors, such as: 1) the ___ gradient for diffusion of the substance across the membrane, 2) the ___ of the membrane for the substance, and 3) the ___ that the fluid containing the substance remains within the tubule
1) the electrochemical gradient, 2) the permeability of the membrane, and 3) the time that the fluid containing the substance remains within the tubule
Passive transportation—when solutes are transported out of the tubule by either primary or secondary active transport, their concentrations tend to ___ (increase/decrease) inside the tubule, while ___ (increasing/decreasing) in the renal interstitium; this phenomenon creates a concentration difference that causes ___ in the same direction that the solutes are transported, from the tubular lumen to the renal interstitium
Concentrations tend to decrease inside the tubule, while increasing in the renal interstitium; this phenomenon creates a concentration difference that causes osmosis of water in the same direction that the solutes are transported
Some parts of the renal tubule, especially the ___ tubule, are highly permeable to water, and water reabsorption occurs so rapidly that there is only a small concentration gradient for solutes across the tubular membrane
Especially the proximal tubule
Water follows solutes out of renal interstitium into renal tubules—T/F?
False! Water follows solutes out of renal tubules into renal interstitium
Steps for water and urea reabsorption—1) solutes like sodium are ___ (actively/passively) reabsorbed, increasing the osmolality of peritubular fluid and plasma; 2) water is reabsorbed by ___; 3) urea (permeating solute) is reabsorbed ___ (actively/passively)
1) Solutes like sodium are passively reabsorbed, increasing the osmolality of peritubular fluid and plasma; 2) water is reabsorbed by osmosis; 3) urea (permeating solute) is reabsorbed passively
Summary of tubular reabsorption and secretion—PCT reabsorbs ___% of glomerular filtrate and returns it to peritubular capillaries; much reabsorption by osmosis and cotransport mechanisms linked to active transport of ___
PCT reabsorbs 65% of glomerular filtrate; linked to active transport of sodium
Summary of tubular reabsorption and secretion—nephron loop reabsorbs another ___% of filtrate
25%
Summary of tubular reabsorption and secretion—DCT reabsorbs __+, ___-, and ___ under hormonal control, especially aldosterone and atrial natiuretic peptide (ANP)
DCT reabsorbs Na+, Cl-, and water under hormonal control
Summary of tubular reabsorption and secretion—the tubules also extract drugs, wastes, and some solutes from the blood and ___ them into the tubular fluid
Secrete
Summary of tubular reabsorption and secretion—___ convoluted tubule completes the process of determining the chemical composition of urine
Distal
Summary of tubular reabsorption and secretion—collecting duct conserves ___
Water
The nephron and its regions: ___ tubule, loop of ___, ___ convoluted tubule, ___ ducts
Proximal tubule, loop of henle, distal convoluted tubule, collecting ducts
Function of the proximal convoluted tubule: lower part of the Bowman’s capsule leads into PCT; it lies in the renal cortex; they reabsorb most of the useful substances of the filtrate—sodium ___%, water ___%, bicarbonate ___%, chloride ___%, glucose nearly ___%
Sodium 65%, water 65%, bicarbonate 90%, chloride 50%, glucose nearly 100%
~___% of filtrate is reabsorbed in PCT
~70%
PCT allows for active reabsorption of nutrients (___ose and ___ acids); ions (__+, ___+, ___-); small plasma ___; some ___ and ___ acid
Nutrients (glucose and amino acids); ions (K+, Na+, Cl-); small plasma proteins; some urea and uric acid
Proximal tubule functions as the main ___ area of the nephron
Re-absorptive
All reabsorption in the proximal tubule is ___-osmotic
Iso-osmotic
Proximal tubule has extensive ___ on luminal membrane; lots of intracellular channels for Na+, Cl-, and water reabsorption; basolateral membrane loaded with Na+/K+ ATPase
Extensive microvilli
Proximal tubule is the only region of the nephron where ___ is present on the luminal membrane
Carbonic anhydrase
Reabsorption in the PCT—2/3 of filtered Na and water reabsorbed (mostly through active transport of ___ at the basolateral membrane); all filtered amino acids and glucose are reabsorbed here via ___ with Na
Active transport of Na; co-transport with Na
Reabsorption in the PCT—preferential site of ___ reabsorption using carbonic anhydrase; vitamin ___ reabsorption also takes place here
PCT is the preferential site of HCO3- reabsorption; vitamin K reabsorption also takes place here
Secretion in the proximal tubule—organic acids and bases are secreted into tubular fluid from the proximal tubule (bile salts, oxalate, urate, catecholamines); proximal tubule is the site of ___ secretion, which is important in acid base function
Site of ammonia secretion
Fluid leaving the proximal tubule—osmolality is equal to ___
Plasma
Fluid leaving the proximal tubule—tubular flow is ___ GFR
1/3 GFR
Fluid leaving the proximal tubule—absence of ___ose, ___ein, or ___ acids
Glucose, protein, or amino acids
Fluid leaving the proximal tubule—increased ___- concentration compared to plasma—more ___ remains in tubular fluid to maintain electroneutrality because more ___ is reabsorbed
Increased Cl- concentration compared to plasma—more chloride remains in tubular fluid to maintain electroneutrality because more bicarb is reabsorbed
Three functional distinct segments of the loop of Henle:
- Descending thin segment
- Ascending thin segment
- Thick ascending segment (most important)
This segment is highly permeable to water and moderately permeable to most solutes; the function of this segment is to allow simple diffusion of substances through its walls; 20% of filtered water is reabsorbed in this segment
Descending thin segment
This segment is virtually impermeable to diffusion of water; has some reabsorptive capacity for ions such as calcium, bicarbonate, magnesium
Ascending thin segment
This segment is most important
Thick ascending segment
Thick ascending loop of Henle—paracellular and transcellular transport—The reabsorption of other solutes in the thick segment of the ascending loop of Henle is closely linked to the reabsorptive capability of the sodium-potassium ATPase pump, which maintains a ___ (low/high) intracellular sodium concentration; the low intracellular sodium concentration in turn provides a favorable gradient for movement of sodium from the tubular fluid into the cell
Low
In the thick ascending loop, movement of sodium across the luminal membrane is mediated primarily by a ___-sodium, ___-chloride, ___-potassium co-transporter; this co-transport protein carrier in the luminal membrane uses the potential energy released by the downhill diffusion of ___ into the cell to drive the reabsorption of ___ into the cell against a concentration gradient
1-sodium, 2-chloride, 1-potassium co-transporter; downhill diffusion of sodium into the cell to drive the reabsorption of potassium into the cell against a concentration gradient
The most important segment of the loop of Henle is the ___ limb—this is the “diluting segment of the nephron”
Thick ascending limb (TAL)
The key feature of the TAL is that it is impermeable to ___ while solute is pumped out of the tubular fluid
Water
The luminal membrane of the loop of Henle has a ___ Na ___ K ___ Cl transporter pump—this is the target site of ___ and the only nephron segment where Cl is actively transported
1 Na 1 K 2 Cl transporter pump—this is the target site of lasix
The TAL is important in ___ urine, as this active pumping helps create a ___tonic interstitium; in the meantime, the impermeability of the lumen to water creates a ___tonic dilute fluid in the tubules
TAL is important in concentrating urine, as this active pumping helps create a hypertonic interstitium; in the meantime, the impermeability of the lumen to water creates a hypotonic dilute fluid in the tubules
The intraluminal charge is ___ (positive/negative) in the TAL—this drives the reabsorption of Mg++ and Ca++
Positive
Distal tubule and cortical collecting tubule have similar reabsorptive characteristics as the thick segment of the ascending limb of the loop of Henle—T/F?
True
The distal tubule and cortical collecting tubule is permeable to water—T/F?
False—IMPERMEABLE to water
Distal tubule and cortical collecting tubule—tubular fluid becomes more ___ (dilute/concentrated) as solutes are reabsorbed
More dilute
Later distal tubule controls the degree of ___ or ___ of urine
Dilute or concentration
Later distal tubule—water permeability is controlled by the presence or absence of ___
ADH (vasopressin)
Later distal tubule—___ (high/low) levels of ADH make the tubular segment permeable to water
High levels
Later distal tubule—___ (presence/absence) of ADH makes the tubular cells virtually impermeable to water
Absence
The rate of reabsorption of sodium and potassium is controlled by ___
Aldosterone
Later distal tubule—secretion of hydrogen by hydrogen-ATPase against a large concentration gradient—___ to one
1,000
Hydrogen and potassium regulation—two distinct cell types perform these functions: ___ cells and ___ cells
Principal cells and intercalated cells
These cells reabsorb sodium and water from the lumen and secrete potassium into the lumen
Principal cells
These cells reabsorb bicarbonate and potassium ions and secrete hydrogen into the lumen (important for acid-base regulation by the kidneys)
Intercalated cells
___ collecting duct is the final site for processing the urine
Medullary collecting duct
Medullary collecting duct reabsorbs less than ___ percent of the filtered water and sodium; permeability to water is controlled by the level of ___
Less than 10 percent; permeability to water is controlled by the level of ADH
Medullary collecting duct is permeable to ___; reabsorption of this into the interstitial around the collecting duct increases the osmolality of the medulla and contributes to the ability to form concentrated urine
Urea
The medullary collecting duct is capable of secreting ___ ions against a large concentration gradient which is important for regulating ___ balance
Secreting hydrogen ions; important for regulating acid-base balance
