M3 L2 Flashcards
(157 cards)
1
Q
Purpose of kidney function?
A
1) Maintain water balance
2) maintain osmolarity of body fluids (keeps cell from enlarging/shrinking)
3) Regulate conc of ECM fluids
4) maintain plasma volume
5) maintain acid-base balance
6) Excreting end products of metabolism
7) Excreting foreign compounds
8) Producing renin
9) Producing erythropoietin
10) Converting vitamin D into active form
2
Q
What is the renal cortex? What does it contain
A
The outer part of the kidney. It contains blood vessels and most parts of the nephrons, like glomeruli and tubules. It’s where blood filtration begins.
3
Q
What is the renal medulla? What contain
A
The inner part of the kidney. It contains cone-shaped renal pyramids and helps concentrate urine by reabsorbing water.
4
Q
What are renal pyramids?
A
Cone-shaped structures in the renal medulla that contain tubules and ducts, which carry urine toward the renal pelvis.
5
Q
What is a nephron?
A
The basic filtering unit of the kidney. It filters blood, removes waste, and forms urine.
Each kidney has about a million.
6
Q
What are cortical nephrons?
A
Nephrons mainly found in the renal cortex. They have short loops of Henle and handle most everyday blood filtering.
7
Q
What are juxtamedullary nephrons?
A
Nephrons near the border of the cortex and medulla. They have long loops of Henle that go deep into the medulla and help concentrate urine.
8
Q
What is the glomerulus?
* where located/what do?
A
A bundle of capillaries inside each nephron where blood filtration starts.
Located in the cortex, it pushes fluid and small molecules into the nephron -
9
Q
What happens to the filtered fluid from the glomerulus?
A
It enters Bowman’s capsule, then flows through the nephron where the body reabsorbs what it needs and forms urine from the rest.
10
Q
What is Bowman’s capsule?
A
A cup-like structure that surrounds the glomerulus. It collects the fluid filtered from the blood and sends it into the nephron.
11
Q
What is the role of Bowman’s capsule?
A
It receives the filtrate from the glomerulus and sends it into the proximal tubule for further processing.
12
Q
What happens in the proximal tubule?
A
Reabsorption of most nutrients, water, and salts (e.g., glucose, amino acids, Na⁺). Also some waste is secreted into it.
13
Q
What happens in the distal tubule?
A
Fine-tuning of salt and pH balance. Controlled by hormones like aldosterone.
14
Q
What is the collecting duct?
A
The final part of the nephron where more water can be reabsorbed (especially if ADH is present). It carries urine to the renal pelvis.
15
Q
What hormones act on the collecting duct?
A
Mainly ADH (antidiuretic hormone), which tells it to reabsorb more water when you’re dehydrated.
16
Q
diff between cortical and juxtamedullary nephron?
A
cortical has a shorter loop of henle which only extends into the outer region of the renal medulla
bc juxtamedullary is longer and extends deeper into the inner medulla, it can reabsorb and conserve water better
17
Q
what do the kidneys form?
A
urine
18
Q
What is the Loop of Henle?
A
A U-shaped part of the nephron that dips into the kidney’s medulla. It reabsorbs water and salts to help concentrate urine and save water.
19
Q
What are the two main parts of the Loop of Henle?
A
Descending limb – water leaves; salt stays.
Ascending limb – salt leaves; water stays.
20
Q
What happens in the descending limb of the Loop of Henle?
A
Water is reabsorbed (leaves the tubule), making the fluid more concentrated. It’s permeable to water, but not to salt.
21
Q
What happens in the ascending limb of the Loop of Henle?
A
Salt (Na⁺, Cl⁻) is reabsorbed, but water stays. It’s permeable to salt, but not to water. The fluid becomes more dilute.
22
Q
Why is the Loop of Henle important?
A
It helps the kidney concentrate urine and conserve water, especially during dehydration.
23
Q
What vessel carries blood into the glomerulus?
A
Afferent arteriole
24
Q
What vessel carries blood away from the glomerulus?
A
efferent arteriole
25
What are peritubular capillaries in the vascular component?
Capillaries that surround the nephron tubules and are involved in reabsorption and secretion.
26
What is the glomerulus?
A tuft of capillaries that filters blood to form a protein-free plasma.
27
What does Bowman’s capsule do?
Collects the glomerular filtrate.
28
What is the function of the Loop of Henle?
Creates a salt gradient in the medulla to help concentrate urine.
29
What happens in the descending limb of the Loop of Henle?
Water is reabsorbed (permeable to water).
30
What happens in the ascending limb of the Loop of Henle?
Salts (Na⁺, Cl⁻) are reabsorbed (impermeable to water).
31
What does the distal convoluted tubule (DCT) do?
Controls Na⁺, K⁺, H⁺ levels and pH; reabsorption and secretion regulated by hormones.
32
What is the juxtaglomerular apparatus?
A structure that helps regulate blood pressure and filtrate rate using renin and sodium sensing.
33
which nephron is more abundant?
(cortical vs juxtamedullary)
cortical nephrons are 80% and juztamedullar are 20%
34
What are the cortical nephrons unable to do bc their loop of henle is short?
produce concentrated urine
35
Vascular Flow:
What is the first step of vascular flow in the kidney?
Blood enters through the renal artery.
36
Vascular Flow:
After the renal artery, where does blood flow next?
Into the interlobular arteries.
37
Vascular Flow:
What follows the interlobular arteries in vascular flow?
Blood flows into the afferent arterioles
38
Vascular Flow:
What is the role of the afferent arteriole?
tiny arteries that bring blood to the glomerulus for filtration.
39
Vascular Flow:
After the glomerulus filters blood, where does the blood flow?
Into the efferent arteriole where it carries blood away from the glomerulus
40
Vascular Flow:
What happens after the efferent arteriole?
Blood flows into the peritubular capillaries which help reabsorb useful substances from the filtrate back into the blood.
41
Vascular Flow:
After the peritubular capillaries, where does the blood go?
Into the interlobular vein.
42
Vascular Flow:
What is the last step of vascular flow inside the kidney?
Blood leaves through the renal vein and returns to general circulation.
43
Tubular Flow:
Where does tubular flow start?
Filtrate goes from the glomerulus to Bowmans capsule (filtrate is collected here)
44
What is filtrate
he fluid that is filtered out of the blood by the kidneys during the first step of urine formation.
45
Tubular Flow:
After Bowman’s capsule, where does the filtrate flow?
Into the proximal convoluted where many useful substances (like glucose and salts) are reabsorbed back into the blood.tubule.
46
Tubular Flow:
What comes after the proximal convoluted tubule?
The filtrate moves into the loop of Henle.
47
Tubular Flow:
After the loop of Henle, where does the filtrate flow?
Into the distal convoluted tubule.
* Further adjusts the filtrate by selective reabsorption and secretion.
48
Tubular Flow:
After the distal convoluted tubule, what is the next step?
Filtrate flows into the collecting tubule (or collecting duct).
* Collects filtrate from many nephrons, concentrates it further
49
Tubular Flow:
After the collecting tubule, where does the fluid go?
Into the renal pelvis.
50
Tubular Flow:
What is the final step of tubular flow?
Urine moves from the renal pelvis into the ureter.
51
whats the renal pelvis
It collects urine coming from the collecting tubules (collecting ducts) of the kidney.
52
whats the ureter
A tube that carries urine from the kidney to the bladder.
53
What is tubular reabsorption?
This is the process where the kidney takes back useful substances from the filtrate into the blood.
* from tubular lumen into peritubular capillaries
54
What is tubular secretion?
This is the process where the kidney adds extra unwanted substances from the blood into the filtrate.
* from peritubular capillaries into the tubular lumen
55
whats glomerular filtration
The process by which blood is filtered in the kidney’s glomerulus, where water and small molecules are pushed from blood into Bowman’s capsule, forming filtrate.
* from the glomerulus into Bowmans capsule
56
Full vascular flow:
Renal artery → interlobular arteries → afferent arterioles → glomerulus → efferent arteriole → peritubular capillaries → interlobular vein → renal vein
57
Full tubular flow:
Glomerulus → Bowmanʼs capsule → proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting tubule → renal pelvis → ureter
58
How does arterial blood pressure affect glomerular filtration?
Increasing BP in arteries → increase blood pushed into afferent arterioles & through glomerulus → increase BP of glomerular capillaries → increase net filtration pressure → increase glomerular filtration rate (GFR)
59
What happens when the afferent arteriole vasodilates?
(afferent is the one bringing blood to glomerulus)
More blood flows into the glomerulus, increasing pressure and raising glomerular filtration rate (bc there's more blood to filter)
60
What happens when the afferent arteriole vasoconstricts?
(afferent is the one bringing blood to glomerulus)
Less blood enters the glomerulus, lowering pressure and decreasing glomerular filtration rate.
* less filtration bc there just isn't that much blood
61
How does efferent arteriole vasoconstriction affect filtration?
(efferent carries blood away from glomerulus)
It causes blood to back up in the glomerulus, increasing pressure and filtration rate.
* filtration inc bc more pressure to push fluid out
62
What is the effect of efferent arteriole vasodilation?
(efferent carries blood away from glomerulus)
It lowers pressure in the glomerulus and decreases filtration rate (bc there is less press to push it out).
63
What does it mean to inc filtration
Increasing filtration means the kidneys are filtering more fluid and solutes (like salts, waste, water) from the blood into the filtrate.
64
Whats GFR
Glomerular Filtration Rate
measures the volume of filtrate formed in all the kidney’s glomeruli each minute.
65
What is tubular reabsorption?
The process where the kidney tubules take back useful substances (like water, glucose, and salts) from the filtrate into the blood.
66
What is the purpose of tubular reabsorption?
To retain essential substances and prevent unnecessary loss of water, glucose, and electrolytes in the urine.
67
What is transepithelial transport?
the movement of substances across the epithelial cells that line the kidney tubules — from the tubular fluid (filtrate) into the blood or vice versa.
68
What is the first step of transepithelial transport during reabsorption?
The substance leaves the tubular fluid by crossing the luminal membrane (apical side) of the tubular cell.
69
: After entering the tubular cell, what happens next?
The substance passes through the cytosol of the tubular cell from one side to the other.
70
After moving through the cytosol, what membrane does the substance cross?
It crosses the basolateral membrane of the tubular cell to exit into the interstitial fluid.
71
How does this cycle get started? And then what happens (vague)?
Blood flows into the glomerulus through the afferent arteriole.
Filtration occurs: water and small solutes (Na⁺, glucose, urea, etc.) are pushed into Bowman's capsule.
Next the fluid flows through the nephron and stops at diff tubules
72
What substances are filtered into the nephron at the glomerulus?
Water (H₂O)
NaCl
HCO₃⁻
H⁺
Urea
Glucose
Amino acids
Some drugs
73
First stop: What is reabsorbed back into the bloodstream in the proximal tubule?
Via active transport:
* Na+
* glucose & amino acids
* K+
Via passive transport:
* Cl, H2O, HCO3
74
First stop: What is secreted at the Proximal Convoluted Tubule?
Via active transport:
* H⁺
* NH₃ (ammonia)
* drugs
75
Second stop (loop of henle): What happens in the thin descending limb?
H2O is reabsorbed via passive facilitated diffusion
76
Third stop (loop of henle): What happens in the thin ascending limb?
Thin: NaCl is reabsorbed passively
77
Third stop (loop of henle): What happens in the thick ascending limbs?
Thick: NaCl is reabsorbed using ATP
78
Fourth stop: What is reabsorbed at the distal convoluted tubule
Via active transport:
* Na+
* Aldosterone
* HCO3
Via passive transport:
* H2O
* Vasopressin (ADH)
79
Fourth stop: What is secreted at the distal convoluted tubule
Via active transport:
* K+
* H+
80
What hormone acts in the distal convoluted tubule?
* what do
Aldosterone → increases Na⁺ reabsorption and K⁺ secretion by acting on principal cells
* it binds to aldosterone receptors and controls how much sodium it can absorb
* More Na+ leak channels on apical
membrane & Na+/K+pumps on basolateral membrane
○ Water passively follows
81
What happens in the distal convoluted tubule without aldosterone?
more sodium in urine - salt loss (hyponatremia?)
82
Fifth stop: What is reabsorbed at the collecting duct?
Via Active transport:
* NaCl
Via passive transport:
* Urea
* H2O
83
Fifth stop: What hormone acts on the convoluted tubule and what does it do?
Aldosterone → promotes sodium reabsorption
84
Arrows:
* What does the arrow leaving gold tube mean?
* what does arrow entering tube mean?
* it is being reabsorbed back into bloodstream (so it was valuable)
* it is being secreted (going to pee out)
85
What is reabsorption?
moving something out of the nephron (tubular fluid) and back into the bloodstream (via peritubular capillaries).
86
What does vasopressin do?
* how do?
* overall effect?
Vasopressin increases water reabsorption in both DCT and collecting duct, but primarily in the collecting duct.
* It does this by increasing water channel (aquaporin-2) insertion into the cell membranes, allowing water to move from the urine back into the blood.
* This helps the body conserve water and maintain proper hydration.
87
Why does the thin ascending limb reabsorb NaCl passively, while the thick ascending limb uses active transport?
The thin ascending limb has low energy and relies on passive diffusion of NaCl down its gradient. The thick ascending limb has many mitochondria and uses active transport to pump NaCl against its gradient, creating the medullary osmotic gradient needed for urine concentration.
88
What does the apical membrane face? What does the basolateral membrane face?
Apical: The lumen (inside of a tubule, like kidney or intestine).
Basolateral: The interstitial fluid (near blood vessels).
89
What type of channels and transport are typically found on the apical membrane?
Passive transport - Na⁺ channels (e.g., ENaC) that allow Na⁺ to enter the cell from the lumen. (going down its gradient)
90
What key transporter is on the basolateral membrane?
Na⁺/K⁺ ATPase, which pumps Na⁺ out of the cell and K⁺ into the cell using ATP (active transport)
91
What is an example of passive transport on the basolateral membrane?
K⁺ leak channels — K⁺ moves down its gradient out of the cell.
92
What is renin?
* what released by?
Renin is an enzyme that is involved in blood pressure regulation and fluid balance.
It is released by the kidneys
93
What triggers renin release from the kidney?
Low NaCl, low ECF volume, or low arterial blood pressure.
94
What is the first step in the RAAS (Renin-Angiotensin-Aldosterone System) pathway after renin is released?
Renin converts angiotensinogen (in the bloodstream) into angiotensin I.
95
What is angiotensin converted to and by what enzyme (released by what)?
Converted to angiotensin II, In the lungs, by angiotensin-converting enzyme (ACE).
96
What are the major actions of angiotensin II?
* Causes vasoconstriction (raises BP quickly)
* Stimulates thirst (which inc fluid intake)
* Stimulates aldosterone release from the adrenal cortex
97
What does aldosterone do in the kidneys? (and then those affects)
Increases Na⁺ reabsorption by kidney tubules, which causes Cl⁻ and water to follow passively and be conserved.
Na+ and Cl osmotically hold more H2O in the ECF which raises ECF volume and blood pressure.
98
What hormone increases water reabsorption in the kidneys during low BP?
Vasopressin (ADH)
99
How does vasopressin help restore blood pressure?
It increases H₂O reabsorption in kidney tubules, which raises ECF volume and BP.
100
What are the long-term compensatory responses to low BP?
Aldosterone → Na⁺ and water retention
Vasopressin → water retention
Restores ECF volume and BP
101
What are the short-term compensatory responses to low BP in this system?
Vasoconstriction via angiotensin II
Increased thirst → more water intake
102
Why is increasing water reabsorption in the kidneys helpful?
It prevents water loss in urine → restores ECF volume → raises blood pressure
103
What are Natriuretic peptides
Hormones (ANP, BNP) released by the heart in response to stretch; promote natriuresis (Na⁺ excretion), vasodilation, and lower BP.
104
What are the two natiretic peptides released by the heart in response to a detected stretch (that indicates inc BP)
ANP (Atrial Natriuretic Peptide) – from atria
BNP (Brain Natriuretic Peptide) – mostly from ventricles
105
What triggers the release of natriuretic peptides (ANP, BNP)?
↑ NaCl, ↑ ECF volume, or ↑ Arterial BP or stretches atria/ventricles
106
What are the main effects of natriuretic peptides?
* Inhibit Na⁺ reabsorption by kidney tubules
* Suppress renin system (which is salt conserving)
* Vasodilate afferent arterioles (which inc filtration of Na+)
* Suppress sympathetic activity (to calm)
All work to ↓ BP and ↓ blood volume
107
How do natriuretic peptides affect kidney function?
↓ Na⁺ reabsorption which leads to ↑ Na⁺ excretion
Water follows Na⁺ (osmosis - low conc to high) → ↑ H₂O excretion in urine
this ↑ GFR via afferent arteriole vasodilation → more filtration
108
How do natriuretic peptides affect the RAAS
reduced Renin release → ↓ aldosterone → ↓ Na⁺ retention
109
How do natriuretic peptides affect the SNS?
Sympathetic activity → ↓ cardiac output and TPR
110
What is GFR and how is it affected by natriuretic peptides?
GFR = rate of blood filtration in glomeruli; increased by afferent arteriole vasodilation from natriuretic peptides.
111
Why is inhibiting sodium reabsorption important?
It increases Na⁺ excretion in the urine, which draws water out by osmosis → lowers ECF volume and BP.
112
How does inhibiting smooth muscle contraction in afferent arterioles affect filtration?
Causes vasodilation → ↑ GFR (more blood filtered) → ↑ Na⁺ and water excretion
113
What are 3 other ways to control BP besides natriuretic peptides?
Vasodilation/vasoconstriction
Beta blockers (↓ HR)
Vasopressin secretion (↑ water reabsorption)
114
What is this diagram showing?
* goal?
Showing water reabsorption in the proximal tubule of the nephron (in the kidney).
The goal of the nephron here is to reabsorb water from the filtrate (in the lumen) and move it back into the blood (peritubular capillary).
115
What is the main driving force for water reabsorption in the proximal tubule of the nephron?
When sodium is reabsorbed it creates an osmotic gradient. then water follows Na⁺ passively via osmosis through AQP-1 channels and tight junctions.
116
Through which two mechanisms does water enter proximal tubular cells from the lumen (apical side)?
AQP-1 water channels on the apical membrane.
Paracellular route via tight junctions (claudins).
117
What are AQP-1 (Aquaporin-1) channels?
Protein channel that passively allows water to move across the membrane.
118
What are Tight Junctions (e.g., Claudins)
Structures between cells that can allow selective paracellular water movement.
119
what is the Peritubular Capillary
Blood vessel surrounding the nephron that reabsorbs substances like water.
120
What happens after water enters the proximal tubular cell? (via what forces?)
Water exits the cell into the interstitial fluid via basolateral AQP-1 channels, then moves into the peritubular capillary driven by low hydrostatic and high oncotic pressure.
121
What is the role of Na⁺/K⁺ ATPase in water reabsorption?
It actively pumps Na⁺ out of the cell into the interstitial fluid, lowering intracellular Na⁺ and drawing Na⁺ (and water) in from the lumen.
122
What role do claudins play in water movement?
They form selective tight junctions that allow paracellular (between cells) water reabsorption.
123
What is this diagram showing?
This is the process of sodium (Na⁺) reabsorption in the proximal tubule of the nephron in the kidney.
124
Explain the flow of how sodium reabsorption in the proximal tubule
1) Passive Na⁺ entry from lumen into cell (via channels or cotransporters).
2) Active Na⁺ pumping out of cell into interstitial fluid via Na⁺/K⁺ ATPase (on basolateral membrane).
3) Passive diffusion of Na⁺ from interstitial fluid into peritubular capillary.
125
How does sodium exit the proximal tubule cell after entering from the lumen?
Through active transport via Na⁺/K⁺ ATPase on the basolateral membrane, moving Na⁺ into the interstitial fluid.
126
How is K⁺ handled during sodium reabsorption in the proximal tubule?
K⁺ is pumped into the cell by the Na⁺/K⁺ ATPase, then leaks back out through K⁺ channels to maintain balance.
127
What is Urea
the chief nitrogenous end product of the metabolic breakdown of proteins.
128
Why does the concentration of Urea inc after filtration?
Because Na+ is actively reabsorbed and then water will passively follow. Urea is left behind alone so it is more concentrated
129
How do the glomerulus and Bowmans capsule work together?
Glomerulus- Filters blood
Bowman’s capsule - Collects the filtered fluid (filtrate)
130
What is happening here?
ex:
This substance is not reabsorbed (back to bloodstream) or secreted (back to nephron for filtration round 2) - it is filtered which means it goes straight to the urine and is excreted.
ex: inulin
131
What is happening here?
ex:
The substance is not secreted, but it is filtered and then complete reabsorbed into the bloodstream
ex: glucose
132
What is happening here?
ex:
The substance is not secreted, it is only filtered and then partially reabsorbed. the other part is excreted.
ex: urea
133
What is happening here?
ex:
The substance is filtered and secreted but it is not reabsorbed. So it goes back into the nephron for a second round.
134
What happens if you block the Na⁺/K⁺ ATPase pump?
Na⁺ builds up inside the cell, reducing the Na⁺ gradient, which impairs K⁺ secretion into the lumen and can lead to K⁺ buildup in the bloodstream.
135
What does aldosterone do to filtrate concentration
Increase Na+ channels on apical
membrane & Na+/K+ pumps on basolateral membrane → increase sodium reabsorption
136
What does vasopressin do to filtrate concentration
Increase aquaporin (AQP-1) channels →
increases water reabsorption
137
What kind of receptor is the vasopressin receptor? and explain what happens
G protein coupled receptor
Binding of vasopressin receptor (aka ADH) → activates G-Protein Coupling → increases cAMP → activates PKA → inserts aquaporin-2 (AQP2) water channels into the apical membrane.
Result in more water reabsorbed, filtrate becomes more concentrated.
138
Where does H2O get reabsorbed when vasopressin is present?
Descending limb, distal tubule, and collecting duct.
139
what are loop diuretics for and what do they do?
used to treat hypertension.
These drugs inhibit the reabsorption of Na+ and Cl– ions by acting on the thick ascending limb of the loop of Henle
140
How do loop diuretics work?
They inhibit the Na⁺/K⁺/2Cl⁻ cotransporter (NKCC2) which normally reabsorbs Na⁺, K⁺, and Cl⁻ from the filtrate back into the medulla.
* Less salt reabsorbed → less solute in the medulla
* Medulla becomes less hyperosmotic (less concentrated)
* Water has no reason to leave filtrate (osmotic gradient is weaker)
* More water stays in the tubule → ends up in the urine
more pee
141
Does glomerular filtration need ATP?
no it is passive
142
What region of the nephron is under hormonal control?
The remainder of the Na+ absorption occurs in the distal nephron. This process is regulated by hormones such as aldosterone and antidiuretic hormone (ADH), and also by the osmolality of the plasma.
143
What causes uremic toxicity and what does it lead to?
Caused by the retention of waste products in the blood; leads to bleeding (platelet issue), CNS effects, and sensory/motor abnormalities
144
What digestive symptoms are caused by uremic toxicity?
Nausea, vomiting, diarrhea, and ulcers due to toxic effects on the digestive system.
145
What is metabolic acidosis? what does it affect
Inability to excrete H⁺ leads to buildup of acid in the body
* altered enzyme
* depression of CNS
146
What causes potassium retention in kidney failure? what lead to?
Inadequate tubular secretion of K⁺
* altered cardiac things
147
What causes sodium imbalances in kidney failure?
* what can lead to
Inability of the kidneys to regulate Na⁺ excretion based on intake.
Elevated BP, generalized edema, congestive heart failure.
if low Na+ - hypotension/shock
148
What causes phosphate and calcium imbalances in kidney failure?
* what lead to
Impaired reabsorption of these electrolytes
* hardened bones
149
What causes loss of plasma proteins in kidney failure?
* what lead to
Increased "leakiness" of the glomerular membrane.
* edema
150
What causes inability to vary urine concentration?
Impaired countercurrent system in the nephron.
151
What causes depression of the immune system in kidney failure?
*what lead to
Toxic levels of waste and acids.
* Increased susceptibility to infections.
152
What is pseudohypoaldosteronism (PHA)?
disorders involving renal tubular unresponsiveness or resistance to aldosterone, leading to electrolyte imbalance (hyperalkemia)
153
What is Type 1 Pseudohypoaldosteronism (PHA)?
salt wasting due to target organ unresponsiveness to mineralocorticoids like aldosterone.
* present in neonatal period
154
What causes renal type 1 PHA?
Autosomal dominant mutations in the mineralocorticoid receptor (MR) gene.
155
What is the effect of the MR gene mutation in renal PHA?
Aldosterone cannot bind to its receptor, leading to ineffective sodium reabsorption and potassium/H⁺ secretion.
156
What causes the systemic form of Type 1 PHA?
Autosomal recessive mutations in the epithelial sodium channel (ENaC).
157
