Renal Physiology Flashcards
Positive Balance
input > output
Negative Balance
input < output
Functional unit of kidney
nephron
2 parts of nephron
Glomerulus + Tubule
3 filtration layers of glomerulus
Endothelial cells (fenestrated)
Basement membrane (protein mesh)
Podocytes (filtration slits w/ foot processes)
5 segments of nephron (in order)
Proximal Tubule
Loop of Henle
Distal Tubule
Collecting Tubule
Collecting Duct
Afferent Arteriole –>
Glomerular Capillaries
Efferent Arteriole –>
Peri-tubular capillaries
Glomerulus function
filtration
drives fluid into Bowman’s Capsule
Glomerulus has a high (negative/positive) charge to repel ______ from being filtered.
negative
proteins
Primary site of reabsorption
proximal tubule
Proximal Tubule functions
reabsorption + secretion
Parts of Loop of Henle + Functions
Thin Descending: water reabsorption
Thick Ascending: solute reabsorption
Function of Distal/Collecting Tubule
regulate reabsorption/secretion
What is juxtaglomerular apparatus?
part of distal tubule that communicates with glomerulus to regulate blood flow / filtration
Macula Densa function
sense change in Na+ filtration –> contact JG cells
Juxtaglomerular cells
vascular smooth muscle cells that release Renin (stimulated by macula densa)
Renin function
increases arterial pressure for more filtration into Bowman’s Capsule
4 Components of Nephron Function
glomerular filtration
tubular reabsorption
tubular secretion
urine excretion
3 primary functions of glomerular filtration
- maintain normal body fluid comp
- rapid excretion waste
- huge mag of blood filtration (60x per day)
What two factors influence rate of filtration
physical properties
pressure differences
What is the main physiological regulator of filtration?
Capillary Hydrostatic Pressure
Force that drive fluid from glomerular capillaries –> capsule
capillary hydrostatic pressure
2 Forces that are driving fluid from capsule –> glomerular capillaries
capsule hydrostatic pressure
capillary osmotic pressure (plasma proteins)
Definition of GFR (glomerular filtration rate)
volume plasma filtered per unit time
GFR equation
GFR = Kf x NFP
What two factors determine GFR?
Kf (filtration coefficient)
NFP (net filtration pressure)
What determines Kf (filtration coefficient)?
permeability + surface area
What determines NFP (net filtration pressure)?
pressure differences between capillaries + capsule
Glomerular capillaries have a (higher/lower) permeability, surface area, and pressure differences than systemic capillaries.
higher
Resistance in glomerular capillaries is (greater/less) than systemic capillaries.
greater
Physiologically, if the afferent arteriole constricts, that will (increase/decrease) GFR.
decrease
Physiologically, if the efferent arteriole constricts, that will (increase/decrease) GFR.
increase
What 4 diseased states alter GFR?
hemorrhage
heart failure/hypovolemic shock
diabetes mellitus
urinary obstruction
How does the body alter GFR during hemorrhage?
constricts afferent + efferent arteriole = reduce GFR & retain blood volume
How does the body alter GFR during Heart failure?
decreased CO –> decreased renal blood flow/pressure –> decreased GFR
How is GFR altered during Diabetes Mellitus?
BM thickens –> lose permeability (Kf down) = decreased GFR
How is GFR altered during urinary obstruction?
increased urinary pressure –> increased hydrostatic pressure = decrease GFR
Function of Reabsorption
move water/solute from tubule –> peritubular capillaries
Function of Secretion
move substances from peritubular capillaries –> tubule
Paracellular pathway
movement through tight junctions between cells
Transcellular pathway
movement through cells (luminal/apical –> basolateral)
Simple Diffusion
across electrical/chemical gradient
Facilitated Diffusion
across gradient + transport protein
Primary Active Transport
uses ATP directly (against gradient)
Secondary Active Transport
downhill movement of one solute drive uphill movement of another
Simple Diffusion example
chloride
Facilitated Diffusion example
urea
Primary Active Transport example
Na/K ATPase
Secondary Active Transport example
Na+/glucose tranporter
Secondary Active Transport example
Na+/glucose transporter
Speed of movement of carrier-mediated transport controlled by (3):
specificity (how specific carrier is to substance)
competition (between substrates)
saturation (how bound transporters are)
Transport Maximum (Tm)
maximum amount of solute in system where all transporters are bound
(“maxed out”)
Afferent arterioles constricting causes (increase/decrease) renal blood flow & (increase/decrease) GFR.
decrease flow
decrease GFR
Efferent arterioles constricting causes (increase/decrease) renal blood flow & (increase/decrease) GFR.
decrease flow
increase GFR
Afferent + Efferent arterioles constrict (during hemorrhage) causes:
decrease in renal blood flow + decrease GFR = conserve blood volume
Pressure in the glomerular capillaries is (higher/lower) than systemic capillaries to allow for _____.
higher
filtration
Pressure in the peritubular capillaries is (higher/lower) than systemic capillaries to allow for _____.
lower
reabsorption
(Autoregulation/Tubuloglomerular Feedback) is at the level of the individual nephron, while (autoregulation/tubuloglomerular feedback) effects vascular supply to all nephrons.
tubuloglomerular feedback
autoregulation
What is renal autoregulation?
global regulation of blood flow
affects vascular supply to all nephrons
responds to changes in arterial pressure
What is the mechanism of renal autoregulation?
increase in pressure –> afferent arteriole constricts = decreased GFR + renal blood flow
What is the mechanism for tubuloglomerular feedback?
decrease pressure –> increase GFR (back to normal)
^release Renin + Angiotensin II locally which constricts efferent arteriole
3 factors cause Renin secretion
-decreased tubular Na+
-changes in arteriolar pressure
-SNS
NE release stimulates B-adrenergic receptors on JG cells which releases ______ via (indirect/direct) mechanism of controlling GFR/blood flow.
Renin
direct
NE release stimulates ______ on tubular cells to increase _____ reabsorption in the proximal tubule. This is a (direct/indirect) mechanism in controlling renal blood flow/GFR.
Na/K ATPase
Na+
indirect
Another way SNS controls renal blood flow/GFR: SNS innervates afferent + efferent arterioles. NE release stimulates ___ receptors which constricts arterioles and (increases/decreases) blood flow/GFR.
a-adrenergic
decreases
What 3 things does Angiotensin-II stimulate?
- vasoconstriction
- aldosterone production
- ADH production
What do ADH + Aldosterone do?
help maintain blood volume (by increasing reabsorption of Na+ & H2O)
Sodium reabsorption transport mechanism
primary active transport
Chloride reabsorption transport mechanism
passive + active transport
H2O reabsorption transport mechanism
passive transport
___ + ___ reabsorption is coupled to ___. reabsorption.
Chloride + H2O
Sodium
Where is sodium reabsorbed in the tubule?
proximal tubule (majority)
ascending loop (1/4)
distal/collecting tubule (regulation)
Na+/K+ ATPase is on the (apical/basolateral) membrane.
basolateral
Order of reabsorption (by location)
tubular lumen –> tubular cells –> interstitial fluid –> peritubular capillaries
Movement of solutes from the ISF –> peritubular capillaries is primarily by:
passive / bulk flow
Na+ transport on apical membrane - proximal tubule (3 types)
Co-transport w/ organic substances
Counter-transport w/ H+ ions
Paracellular diffusion (passive)
What 2 specific transporters are used to transport Na+ across apical membrane by co-transport w/ organic substances?
Na+/glucose transporter (2nd active)
Na+/amino acid transporter (2nd active)
What specific transporter does Na+ use as counter-transport w/ H+ ions in the proximal tubule?
Na+/H+ exchanger (2nd active)
What 3 types of transport does Na+ use in Loop of Henle?
Co-transport w/ K+ & Cl- ions
Counter-transport w/ H+ ions
Paracellular diffusion (passive)
What specific transporter does Na+ use (co-transport w/ K+ & Cl- ions) in Loop of Henle?
NKCC (Na/K/Cl co-transporter)
What counter-transport does Na+ use in the Loop of Henle?
Na+/H+ exchanger
What two modes of transport does Na+ use in the Distal/Collecting Tubule?
Co-transport w/ Cl- ions
Na+ specific ion channels
What specific co-transporter w/ Cl- ions does Na+ use for transport in distal/collecting tubule?
NCC (Na, Cl co-transporter)
What specific transporter does Na+ use in the distal/collecting tubule that is a Na+ specific ion channel?
ENAC (epithelial sodium channel)
3 inhibitors that are drugs used to target sodium transporters
SGLT inhibitors (Na/glu transporter)
NHE inhibitors (Na/H+ exchanger)
NKCC inhibitors (Na/K/Cl co-transporter)
What disease does SGLT inhibitors treat?
diabetes / hyperglycemia
How do SGLT inhibitors treat diabetes/hyperglycemia?
allow to excrete more glucose
What disease do NHE inhibitors treat?
hypertension
How do NHE inhibitors treat hypertension?
vasodilate vasculature & protect kidney
What drug is an NKCC inhibitor?
Furosemide (a diuretic)
How does NKCC inhibitor (furosemide) work?
blocks reabsorption of Na+ which blocks reabsorption of water –> excrete more
Two diuretics that work further down in the tubule (less effective potentially)
NCC inhibitors
ENAC inhibitors
How is Cl- reabsorbed in the proximal tubule?
passive, paracellular flow
Na+ reabsorption causes negative charge in lumen –> Cl- wants to leave!
How is Cl- reabsorbed in the Loop of Henle?
Co-transported (NKCC) - secondary active
How is Cl- reabsorbed in the distal tubule?
co-transported with Na+
NCC (secondary active)
Which part of the tubule has low permeability to H2O? (no water is reabsorbed)
ascending loop of henle
Which two parts of the tubule does water permeability vary?
cortical part of distal tubule
collecting tubule/duct
What two ways is water reabsorbed across the tubular epithelium?
simple diffusion (paracellular)
facilitated diffusion (transcellular w/ aquaporins!!!)
What are aquaporins?
water-selective channels
allow for rapid movement of water from tubule –> ISF
Aquaporins are present on the (apical/basolateral) membrane.
TRICK QUESTION! Both!
How does water move from the tubule to ISF?
Na+ reabsorption causes concentration gradient in (more in ISF) so water moves from tubule –> ISF (via aquaporins + simple diffusion)
What is the primary driver of H2O from ISF –> peritubular capillaries?
capillary osmotic pressure (more proteins so sucks water in)
Match osmolality of fluid to location in tubule: proximal tubule | bottom loop of henle | distal/collecting tubule
Proximal Tubule: isosmotic (1:1 H2O/solute moving)
Loop: hyperosmotic (concentrated - water has been reabsorbed)
Distal/Collecting: hypoosmotic (dilute b/c solutes reabsorbed)
Loop of Henle mechanisms of urine concentration/dilution by location (thin descending | thin ascending | thick ascending)
Thin descending: high water / low solute permeability
Thin ascending: just moving fluid
Thick ascending: low water / high solute permeability
What is meant by Counter-Current Flow?
parts of Loop of Henle work in coordination
Na+ reabsorption (thick ascending) –> water reabsorption (thin descending) b/c concentration gradient
At the end of the Loop of Henle, urine is (concentrated/dilute) and volume of water is (high/low).
dilute
low
Where does ADH have its effect in the tubule?
distal tubule/collecting duct
What does ADH do (antidiuretic hormone)?
increases water reabsorption in the distal/collecting tubule
stimulates aquaporins to move to apical membrane
Low ADH –> (high/low) water reabsorption –> (dilute/concentrated) and (lower/higher) volume urine.
low
dilute
higher
High ADH –> (high/low) water reabsorption –> (dilute/concentrated) and (lower/higher) volume urine.
high
concentrated
lower
What is Na+ balance regulated by? (2)
GFR
amount Na+ reabsorbed
What are 2 challenges to Na+ homeostasis?
changes in GFR
changes in Na+ intake
3 ways kidney compensates for changes in GFR
- autoregulation (whole kidney)
- tubuloglomerular feedback (local)
- glomerulotubular balance
Explain glomerulotubular balance
amount of Na+ filtered is matched with amount of Na+ reabsorbed (so reduces Na+ loss if filtration increases)
Where does feedback of glomerulotubular balance occur?
proximal tubule
What is aldosterone? What is it produced by?
mineralocorticoid (steroid)
produced by adrenal glands
Where does aldosterone have its effect?
late distal tubule/collecting duct
Function of aldosterone
increases Na+ reabsorption (and therefore K+ secretion)
(T/F) Aldosterone controls whether or not all sodium in the body is secreted/absorbed.
False: only controls 2-3%
max aldosterone = NO Na+ excreted
min aldosterone = 2-3% filtered Na+ is excreted, rest reabsorbed
Which two Na+ transport mechanisms does aldosterone increase synthesis of to increase reabsorption?
Na/K ATPase (basolateral)
ENAC (apical)
4 factors that stimulate aldosterone secretion
decreased plasma Na+
increased K+
increase plasma ACTH
large increases in Angiotensin II (hemorrhage)
How does aldosterone contribute to the response to hemorrhage?
increase Na+ reabsorption –>
increase H2O reabsorption = conserve blood volume
What is ADH? What secretes it?
peptide hormone that increases water reabsorption in late distal tubule/collecting duct
secreted by pituitary
What 3 things regulate ADH secretion?
- Baroreceptors
- Osmoreceptors
- Angiotensin II
Baroreceptors sense changes in _____ and (activate/inhibit) ADH secretion.
blood volume
inhibit
Osmoreceptors sense changes in ____ and (activate/inhibit) ADH secretion.
osmolality/concentration
stimulate
High elevations in Angiotensin II (hemorrhage) can directly (stimulate/inhibit) ADH secretion.
stimulate
How does ADH increase water reabsorption in the late distal tubule/collecting duct?
ADH binds to receptor –> Gs signaling activates Protein Kinase A = aquaporins move to apical membrane
Water diuresis (urine volume + concentration)
high volume urine
hypoosmotic (dilute)
Osmotic diuresis (urine volume + concentration)
high volume urine
isosmotic (not dilute)
Causes of water diuresis
increased water intake, drugs, disease/inury
Causes of osmotic diuresis
disease, drugs (mannitol)
(Diabetes Mellitus/Diabetes Inspidus) can cause water diuresis.
Diabetes Insipidus
(Diabetes Mellitus/Diabetes Insipidus) can cause osmotic diuresis.
Diabetes Mellitus
How does increased water intake cause water diuresis?
increased blood volume / decreased osmolarity –> decreased ADH = decreased water reabsorption
What kind of drugs have a central effect on ADH?
glucocorticoids
What kind of drugs have a nephrotoxic effect on the kidney (ADH not effective)?
antifungal agent (amphotericin B)
Which drug blocks NKCC for clinical treatment?
furosemide
Which drug blocks NCC for clinical treatment?
hydrochlorothiazide
Which drug blocks ENAC channels and are K+ sparing?
amiloride
Which drug is an aldosterone antagonist and K+ sparing?
spironolactone
What are the 2 types of diabetes insipidus?
Central
Nephrogenic
In (central/nephrogenic) diabetes insipidus, ADH production is normal but not effective.
nephrogenic
In (central/nephrogenic) diabetes insipidus, ADH secretion is reduced.
Central
Who does Diabetes Mellitus induce osmotic diuresis?
increased glucose –> increased urine osmolality = water retained in tubule
How does mannitol induce osmotic diuresis?
shifts small amount of water in the wrong place (treat glaucoma, head injury)
Clearance
amount of plasma cleared of a substance over time
Excretion
amount of substance coming out in urine
What substance does clearance = GFR?
inulin
no reabsorption, no secretion
What substance is when clearance is LESS than GFR?
Na+
some reabsorbed, none secreted
What substance is clearance = 0?
glucose
everything is reabsorbed
What substance does clearance = renal blood flow?
PAH
not reabsorbed, is secreted so 100% is excreted
What substance uses clearance to determine GFR? (and therefore kidney function)
inulin
Not reabsorbed | Secreted =
clearance > GFR
Not reabsorbed | Not secreted =
clearance = GFR
Partially reabsorbed | Not secreted =
clearance < GFR
Fully reabsorbed | Not secreted
clearance «_space;GFR (clearance = 0)
Name 2 exogenous substances that can used to measure GFR (and therefore renal function)?
Inulin
Iohexol
Inulin
standard agent for GFR measurement
sugar in wheat, injected, takes a while for excretion
Needs electrochemical equipment
Iohexol
iodinated contrast agent, fast clearance, nephrotoxic
cannot give repeatedly
uses CT scanning
What two endogenous substances are used to measure GFR (and therefore kidney function)?
creatinine
SDMA
Creatinine
easily measured, not injected
slightly overestimates GFR
SDMA
amino acid, sensitive to early kidney dysfunction
Need IDEXX equipment
____ & ____ are two essential nutrients that need to be (reabsorbed/secreted).
glucose
amino acids
reabsorbed
Urea is (reabsorbed/secreted).
TRICK QUESTION: both!
Glucose & Amino acids are completely reabsorbed in the ______ via _____ transport and coupled to _____ reabsorption.
proximal tubule
secondary active
Na+
Explain why/how glucose + amino acids use secondary active transport for reabsorption.
downhill movement of Na+ is used to move them uphill against their concentration gradient
need Na+ reabsorption to move
What are the 2 Na/glu transporters on the apical membrane of the proximal tubule? Which is majority?
SGLT1 & SGLT2 (majority)
Match SGLTs with:
specificity (high/low)
competition (high/low)
efficiency (high/low)
high specificity (only bind glucose)
low competition (no substrate comp)
highly efficient (high Tm)
Tm (</>) glucose filtered.
> (much greater, none excreted)
Match Amino Acid Transporters with:
specificity (high/low)
competition (high/low)
efficiency (high/low)
low specificity (multiple AAs)
high competition (multi substrates comp)
low efficiency (less than glucose)
Tm (</>) filtered amino acids.
> (greater but lower than glucose)
What process is the small amount of protein filtered reabsorbed by?
endocytosis
What type of transport does protein get reabsorbed through?
primary active transport
What is urea?
nitrogen waste product made by protein metabolism
The amount of urea excreted depends on (aldosterone/ADH/angiotensin).
ADH
What type of transport does urea use for reabsorption?
passive transport (w/ urea transporters)
Urea is coupled to _____.
water (and therefore sodium)
What substance is recirculated to help increase hyperosmotic medulla for increased urine concentration/water conservation?
urea
ADH (increases/decreases) urea transporters –> (increased/decreased) reabsorption –> (increased/decreased) excretion.
increased
increased
decreased
Increased urine flow –> (increased/decreased) urea concentration gradient –> (increased/decreased) reabsorption –> (increased/decreased) urea excretion.
decreased
decreased
increased
Azotemia
increase in blood urea nitrogen (BUN) with or without increase in blood creatinine
3 types of azotemia
pre-renal
renal
post-renal
Explain pre-renal azotemia
decreased blood flow to kidneys (dehydration) –> increased BUN
Explain renal azotemia
decreased functional nephrons –> increased BUN (from toxin)
Explain post-renal azotemia
urinary blockage (urolithiasis) –> increased BUN
Organic ions are (reabsorbed/secreted).
secreted
Where are organic ions secreted?
proximal tubule
What type of transport is used for organic ion secretion?
active transport
Two types of organic ions
cations
anions
List 2 types of cations (organic ion type)
neurotransmitters
histamine
Match to organic ion transporter properties:
specificity (high/low)
competition (high/low)
efficiency (high/low)
low specificity
high competition
inefficient (low Tm - easily excreted)
(T/F) The ratio of K+ filtration to reabsorption = 1:1
True
What type of transport does K+ reabsorption use in the proximal tubule?
passive/paracellular transport
What type of transport does K+ reabsorption use in the Loop of Henle?
secondary active transport
(via NKCC using energy from Na/K ATPase)
What kind of transport does K+ reabsorption use in the distal/collecting tubule?
primary active transport
(via H+/K+ ATPase)
Where is K+ reabsorbed?
proximal tubule (most)
thick ascending loop (some)
distal/collecting tubule (little)
Where is K+ secreted?
ONLY in distal tubule / collecting duct
How is K+ secreted?
K+ specific channels (ROMK) on apical membrane
Where is K+ balance primarily regulated?
distal tubule/collecting duct
What 4 factors influence K+ secretion?
- Na/K ATPase activity
- Concentration gradient
- Electrical gradient
- Permeability of apical membrane to K+
How does Na/K ATPase activity influence K+ secretion?
up ATPase activity = up K+ secretion
How does electrical gradient influence K+ secretion?
more Na+ reabsorbed = increased K+ secretion
How does concentration gradient influence K+ secretion?
more K+ gradient = increased K+ secretion
How does permeability of apical membrane influence K+ secretion?
more K+ channels (ROMK) = increased K+ secretion
(T/F) K+ reabsorption increases when K+ intake decreases.
False
reabsorption rate constant & not influenced by changes in K+ intake
What is the only way to change K+ excretion?
regulation of K+ secretion in the distal/collecting tubule
How does K+ secretion increase in the distal/collecting tubule directly?
stimulates Na+/K+ ATPase on basolateral membrane
How does K+ secretion increase in the distal/collecting tubule indirectly?
stimulates aldosterone release –> K+ secretion, Na+ reabsorption
What substance is the primary controller of K+ secretion (and therefore K+ excretion)?
aldosterone
What are the effects of increased plasma K concentration on aldosterone
increased aldosterone secretion
2 mechanisms by which aldosterone increases K+ secretion in response to K+ intake
increase synthesis of Na/K on ATPase (basolateral)
increase ROMK expression (apical)
4 ways the two above mechs increase K+ secretion by aldosterone
- increase Na/K ATPase activity
- Increase concentration gradient
- increase electrical gradient
- increase apical permeability
Without aldosterone, there would be a huge (increase/decrease) in K+.
increase
Aldosterone secretion = increased __ reabsorption and increased __ secretion.
Na+
K+
If Na+ load increases, what happens to K+?
increased K+ secretion/excretion
What two ways goes Na+ handling impact K+ excretion?
increased Na+ load
increased Na+ flow
If Na+ flow increases, what happens to K+?
if less Na+ reabsorbed, less H2O is reabsorbed = K+ concentration diluted in distal/collecting tubule = increased K+ secretion
What do diuretic drugs do to Na+? K+?
Na: increase load + flow
K: increase secretion, decrease reabsorption
Which drug inhibits NKCC (in loop of henle)
Furosemide
Which drug inhibits NCC (early distal tubule)?
Thiazides
Two causes of diuresis
disease (diabetes mellitus)
diuretic drugs
How does alkalosis influence K+ secretion?
increases secretion (body tries to retain K+ to keep positive charge but increases K+ gradient)
What important renal enzyme stops functioning outside of physiological pH levels?
Na/K ATPase
3 examples of intracellular fluid buffers in blood
hemoglobin (primary)
organic phosphates
proteins
3 examples of extracellular fluid buffers in blood
bicarbonate (primary)
phosphate
proteins
How do the lungs control the HCO3-CO2 buffer system?
PCO2
increase resp in acidosis to decrease CO2
decrease resp in alkalosis to increase CO2
What do the kidneys do to control HCO3-CO2 buffer system?
increase HCO3 in acidosis
decrease HCO3 in alkalosis
What 2 mechanisms does the kidney use to increase HCO3- when the body is in acidosis?
- increase reabsorption of HCO3
- add “new” HCO3 in
Increase HCO3 = (increase/decrease) pH
increase
Increase PCO2 = (increase/decrease) pH
decrease
Metabolic/kidney compensation during acid-base disorders is (fast/slow) while Respiratory/lung compensation is (fast/slow)
slow
fast
Where are the majority of H+ ions secreted?
proximal tubule
What transport process + transporter are used for H+ transport across the apical membrane?
Na/H+ exchanger (secondary active)
HCO3 reabsorption is coupled to H+ secretion (directly/indirectly)
indirectly
do not reabsorb the same HCO3- ion that was filtered
Explain excretion of titratable acid
H+ is excreted as an acid (by combining = urine is acidified
Explain excretion of ammonia
H+ combines with ammonia (NH3) + chloride = excreted as a salt