Physiology of the Kidneys Flashcards
what is wilm’s tumor (nephroblastoma)
tumor of the kidney found in childhood that is associated w/ aniridia (lack of iris) and related ocular complications
-500 cases in the US annually
what waste products do the kidneys eliminate?
what else do the kidney eliminate
urea, uric acid, creatinine
-drugs and toxic compounds
how do the kidneys regulate osmotic pressure
what else do they regulate? how?
by excreting dilute or concentrated urine
- ions
- extracellular fluid by controlling Na and water excretion
how do the kidneys play a role in acid-base balance
synthesis and excretion of ammonia
how do the kidneys adjust blood prssure
by regulating Na excretion and producing renin
what do the kidneys produce
Vit D3 and erythropietin
what do the kidneys degrade
insulin and PTH (parathyroid hormone)
- insulin broken down by insulinase
- PTH increases Ca levels in the blood
what do kidneys synthesize to affect renal blood flow and Na excretion
prostaglandins and kallikreins
the total body water is _____% of body weight
plasma is ___% of body weight
60%
-mostly in intracellular compartment where there’s more K (40%)
-extracllular has more Na (20%)
4%
in body fluid composition, what are the major cations in electrolytes? major anion?
cations: Na, K, Ca, Mg
anions: Cl, HCO3 (bicarbonate), Po4 (phosphate), SO4 (sulfate)
what charge do proteins and organic acids have
what is the pH to organic acids
negatively charged
pH = 7.04
when is the ability for glucose to be reabsorbed compromised
glucose levels above 180mg%
-all glucose is reabsorbed under normal conditions
for urine formation, what is the total amount excreted equal to
total amt excreted=filtered-reabsorbed + secreted
for the renal clearance ratio, when does secretion occur and when does reabsorption occur
> 1=secretion
<1=reabsorption
what rate does inulin clearance equal
glomerular filtration rate
what is the glomerular filtration rate
the rate at which plasma is filtered by the glomeruli
why is it ideal to measure GFR by inulin (a fructose polymer)
- freely filterable by glomeruli
- not reabsorbed or secreted by tubules
- not synthesized, destroyed, or stored in kidneys
- nontoxic
- concentration in plasma and urine determined by simple analysis
what are the normal values of GFR
110-125 mL/min
what is the clearance ratio
Cx (x is compound of interest) / Cinulin
what are be used to clinically estimate GFR
endogenous creatinine clearance
what is creatinine derived from?
- levels in ____ are stable
- also secreted by ____ adds ____% to urniary values
creatine phosphate
- levels in plasma are stable
- also secreted by kidney: adds 20% to urinary values
there is an inverse relationship between GFR and…
why?
plasma creatinine concentration
-bc kidneys continuosly clear creatine from the plasma
what is it called when these substance are found in urine
- glucose
- protein
- amino acids
- blood cells
- ketones
- bilirubin
glycosuria -glucose threshold ~200mg% proteinuria -atkins diet aminoaciduria -seen in PKU hemouria ketonuria -seen in uncontrolled diabetes bilirubinuria -breakdown hemoglobin -seen in end stage liver disease/compromised liver function -newborns
a 70kg person contains how many L of total body water? how much intracallular fluid? extracell fluid? interstitial fluid? plasma?
70x0.6 = 42
intracellular: 42x0.4=28L
extracellular: 42x0.2=14L
interstitial fluid: 14x 3/4=10.5
plasma: 14x 1/4=3.5L
what is the rate of renal blood flow
- how much % of cardiac output does this produce
- how are cortex and medulla related
- 2L/min => 20% of cardiac output
- cortex>medulla
what is myogenic mechanism
-when blood flow it too high
increased pressure stretches vessels and opens cationic channels resulting in depolarization and calcium influx
-vessel diameter decreases and resistance increases
when does the tubuloglomerular feedback mechanism occur?
-what increases?
-what does ATP do?
what kind of secretion is reduced?
when blood flow is too high
increased pressure increases GFR
increases NaCl reabsorption and *ATP release from macula densa
-ATP broken down to release adenosine, which vasoconstricts
-renin secretion is reduced bc activation of renin would have opposite effect
what do sympathetic nerves do to renal blood flow
vasoconstrict and reduce flow
what is the glomeruar membrane shared btwn
endothelial cells and the visceral layer of bowman’s capsule
what kind of cells comprise the visceral layer of bowman’s capsule?
-what exist btwn these cells?
- podocytes-wrap their fingers around capillary
- filtration slits exist btwn the “feet” of the podocytes
in glomerular filtration, how does the fluid going from the capillaries get to bowman’s space
fluid going from capiallaries=>fenestrated endothelium=>glomerular BM=> podocyte feet=> bowman’s space
- what do the endothelial fenestrations of the glomerulus prevent?
- waht does the basal lamina of the glomerulus prevent?
- what does the slit membrane btwn btwn pedicels prevent?
- when proteins do pass through, what are they reabsorbed by
- filtration of blood cells but allows all components of blood plasma to pass through
- prevents filtration of larger proteins
- prevents filtration of medium-sized proteins
- anything negative will have a hard time getting through
- when proteins pass through, they’re later reabsorbed by the proximal CT
how many mmHg does net filtration pressure equal
what is the mmHg of the capillary hydrostatic pressure?
what is the pressure in bowman’s space?
what is the colloid osmotic presssure
(pressure generated from a highly concentrated sol’n)
10mmHg
55mmHg
15mmHg
30mmHg
what is the filtration fraction
%age of plasma flowing through kidneys that is filtered (~20%)
what does GFR depend on
- permeability and surface area of filtration barrier
- ultrafiltration pressure gradient
- capillary hydrostatic pressure (55mmHg)
- back pressure in bowman’s space (15mmHg)
- colloid osmostic pressure (30mmHg)
what does the proximal convoluted tubule reabsorb
all glucose and aa (under normal conditoins)
what is the driving force for the reabsorption of solutes and water?
- what come in and what come out
- where does it enter the cell?
- where is it pumped out by the Na/K ATPase?
- what follows
Na reabsorption
- Na/K ATPase: 2K in, 3Na out
- enters from the lumen
- leaves on the basolateral side
- where Na goes, water follows
Na has cotransport, what are they
Na/glucose
Na/amino acids
Na/Cl
what is the countertransport (antiport) used in the prox convoluted tubule
Na/H pump
- important for bicarbonate reabsorption
- carbonic anhydrase inhibitors block it (acetazolamide)=> reduces bicarbonate reabsorption
the tubular transport in the loop of henley creates a gradient such that extracellular fluid is…..
-what does this produce
hypertonic
-production of concentrated urine
in the descending limb of the loop of henle, what leaves and why
ONLY WATER leaves due to hypertonic interstitial fluid
-impermeable to NaCl
in the ascending limb of the loop of henle, what is it highly permeable to,
- what happens to water
- what does this create
- what cotransport is used and what is it driven by
- what can block this cotransport and what can this lead to
highly permeable to NaCl-pumps it into interstitium
- water does not follow
- creates high ionic interstitial gradient at bottom of loop
- Na 2Cl K cotransport driven by Na/K ATPase pump on interstitial side
- diuretic furosemide blocks Na 2Cl K cotransporter-can lead to hypokalemia (low potassium)
the distal convoluted tubule is impermeable to water unless…..
acted on by aldosterone and/or ADH
what cotransporter does the luminal membrane of the distal convoluted tubule contain?
- inhibited by what
- what kind of pump does it have on the intersititla side
- what goes inot the cell, what goes into the interstitium
- what is this fueled by
- what goes on the lumenal side
- what enhances this channel
Na Cl cotransporter
- inhibited by thiazine diuretics
- NaCa pump on intersitital/capillary side
- 3 Na into cell, 1 Ca into interstitium
- fueled by Na/K antiport
- passive Ca channel on lumenal side
- parathyroid hormone enhances this channel and increases Ca absorption
what does the cortical collecting duct regulate
-how
K
- secretes most of excreted K
- active uptake by Na/K ATPase followed by lumenal channel diffusion
what are the 2 types of cells in the collected duct
- principal cell
- K preferentiall goes down its gradient on the tubular luminal side bc the electrical gradient is smaller across the luminal surface than the other side - intercalated cell
- can lead to increased blood levels of K during conditions of acidosis
- have pumps which exchange H for K (H/K ATPase present in lumenal membrane)
what allows for the maintenance of the concentration gradient
vasa recta
what are the 2 countercurrent processes in the medulla?
what do they do
loops of henle: countercurrent multipliers -set up osmotic gradient vasa recta: countercurrent exchanges -maintain gradient -reduce dissipation of solute gradient
in countercurrent processes, how does fluid flow
fluid flows in opposite directions in adjacent structures
what do countercurrent multiplier system in loop of henle produce
a hyperosmotic renal medulla
waht does water do the in decending limb? ascending limb?
descending: only water leaves
ascending: no water leaves/salt is pumped out
=> hypertonic renal medulla
in the countercurrent exchange in the vasa recta, how does solute go in? out?
-what does it maintain
solute goes in one way (descending) and out the other (ascending)
-maintains the gradient being generated by the loop of henle
PCT reabsorbs 50% of urea, the DCT has as much urea as the amount filtered bc of…..
secretion
which limb and which duct are impermable to urea?
- what rises as water is reabsorbed
- what does this result in
ascending limb of the distal CT and outermedullary collecting ducts
- urea rises as water is reabsorbed
- results in high urea concentraion delivered to inner medulla
urea contributes to….
-it is _____ of the total osmolarit of the steym
hypertonic insterstitium
-1/2 of osmolarity of the system comes from urea
ADH doesnt just facilitate water flow, but also ___ flow
urea flow
what acts on cortical collecting ducts to make them water permeable
ADH (vasopressin)
inner medulla has facilitated ________ activated by ADH
- accounts for ____ of osmoalirty of inner medulla
- favors urea diffusion into _____
urea transporter
- 1/2
- interstitium
what forms when ADH levels are low
- attempts to maintain what
- what does ADH promote urea to do
dilute urine
- attempts to maintain the gradient
- ADH promotes urea flow out
what is formed when ADH levels are high
concentrated urine
- ADH => generation and insertion of aquaporins into collecting duct membrane
- water flows readily into hypertonic interstitum and is quickly collected into the vasa recta so the gradient isn’t disrupted
what is diabetes insipidus
excretion of large amounts of highly diluted urine (polyuria) that can’t be reduce when fluid intake is reduced
what are the 3 types of diabetes insipidus
- crainal
- low ADH release from post pitutary - nephrogenic
- collected ducts insensitive to AD
- problem in transcription or translation of the aquaporin gene - dipsogenic
- excessive thirst due to damage to thirst mechanism in hypothalamus
what cells produce atrial natriuretic factor? what do they sense? facilitates excretion of what? what follows this what does this decrease? what does this lead to?
atrial muscle cells
- sense volume expansion
- Na
- water follows
- decreases renin
- leads to natriuresis and diuresis
aldosterone release is triggered by what?
what is its action on the kidneys
high plasma (K) in the blood OR decreased blood volume -increases Na reabsorption and increases K secretion
what movement does insulin promote
K movement into cells
therefore reduces K in the blood
-K levels must be closesly watched corrected w/ DKA
how does the body compensate for alkalosis?
slowing down breathing
what does a loss of H cause in the blood?
what cna this cause
increases in HCO3
-causes metabolic alkalosis, hypochloremia and extracellular fluid volume contraction
which is harder for the body to deal w/, alkalosis or acidosis?
alkalosis bc in acidosis, at least the kidney can pump out H.
what kind of muscle does the bladder neck have
what innervates the body and neck
internal spincter (smooth muscle)
body (detrusor) and neck innervated by pelvic and hypogastric nerves
what is the external spincter innervated by
pudendal nerve
what mediates the contraction of detrusor and relaxation of the internal spincter in mictrition aka urination
parasympatheic nerves
sympathetic innervation not essention (mostly to blood vessels)
