Decreased GFR, Anuria, Polyuria Flashcards
what is the pressure in the glomerular capillaries like compared to other capillaries?
higher hydrostatic pressure
is the efferent or afferent arteriole of wider diameter?
afferent arteriole
what pressure increases in the efferent arteriole?
oncotic pressure
what is the bowmans capsular oncotic pressure?
zero normally
net filtration pressure=
difference between glomerular hydrostatic pressure and opposing forces (plasma oncotic pressure and pressure in bowmans capsule)
hydrostatic pressure in the capillaries and renal blood flow are under physiological regulation. what happens to capillary pressure, renal blood flow, and glomerular filtration rate if the afferent arteriole is constricted?
all three are decreased
what happens to capillary pressure, renal blood flow, and glomerular filtration rate if the efferent arteriole is constricted?
capillary pressure increases
renal blood flow decreases
glomerular filtration rate increases
what are decreases in glomerular filtration rate often due to?
tubular problems
less often glomerular disease
what structure is responsible for tubuloglomerular feedback?
macula densa
how is the glomerular filtration rate held relatively constant?
intrinsic autoregulatory mechanisms
extrinsic hormonal and neural mechanisms
what can the sympathetic nervous system do to regulate glomerular filtration rate?
sympathetic nerves can constrict afferent arteriole: decreases GFR
can stimulate renin secretion which helps to restore GFR
what normalizes glomerular filtration rate in the face of sympathetic nervous system response?
angiotensin II
what physiologic changes trigger vasoconstriction of afferent arterioles and thus a decrease in glomerular filtration rate?
increased blood pressure
increased flow rate
increased NaCl in distal tubule
what substances increase glomerular filtration rate?
angiotensin II
atrial natriuretic peptide
nitric oxide
prostaglandins E2 and I2
what are some substances that decrease glomerular filtration rate via vasoconstriction?
norepinephrine
epinephrine
endothelin
what things control renin secretion?
macula densa and tubuloglomerular feedback
sympathetic nervous system
afferent arteriolar pressure
what are some key components of a normal renal tubular cell?
microvilli increase surface area for transporters
tight junctions help to control transport
Na/K ATPase in basal membrane establishes Na gradient
hemidesmosomes attach cells to basement membrane
what are some cytoskeleton alterations in acute kidney injury?
ischemia and toxins cause decrease ATP: actin cannot polymerize into filaments
loss of apical microvilli and brush border
loss of tight junctions
what does loss of tight junctions in a renal tubular cell lead to?
fluid moving from lumen into interstitial space: backleak leads to decreased urine output
loss of polarity can result in Na/K ATPase moving from basal membrane to apical membrane. what will be the result?
increase sodium in filtrate, leading to vasoconstriction of afferent arteriole
macula densa
why we see a plummet in GFR with AKI
loss of tight junctions allows redistributions of membrane proteins and ___________________ diffuses to apical membrane
Na/K ATPase
what can decreased ATP production lead to?
cellular obstruction of tubules
what does decreased Na/K ATPase activity lead to?
Na remains in cells
cell swells as water follows
what does an increase in intracellular calcium do?
activates proteases and phospholipases
further cell damage
what does increased intracellular calcium lead to?
cells slough and form cellular casts
do some nephrotoxins cause tubular obstruction through crystal formation?
yes
what toxin causes calcium oxalate monohydrate crystals?
ethylene glycol
what is one thing ethylene glycol is in?
antifreeze
what are some oxalate containing plants?
pigweed
halogeton
sour grass/shamrock
sorrel/rhubarb
what does melamine/cyanuric acid cause?
intratubular crystals causing obstructive injury
what is the difference in appearance of calcium oxalate monohydrate and calcium oxalate dihydrate crystals?
monohydrate: picket-fence, pointed ends
dihydrate: square, flat pyramids or crossed squared
what do sulfonamides cause?
tubular obstruction
crystals bind to plasma membrane proteins
do crystals cause irritation to the bladder?
no
what can large numbers of crystals do?
predispose to stone formation
does the presence of crystals indicate presence of a stone?
no
what do casts indicate?
renal damage
what does a cast form in response to?
increased protein or electrolytes
what is a hyaline cast?
tamm-horsfall mucoprotein alone
what usually causes hyaline casts?
proteinuria
can casts plug tubules?
yes
what are microscopic lesions of acute tubular injury usually?
subtle
what microscopic lesions can you see with acute tubular injury?
loss of brush border
vacuolated cells
dilated tubules
release cytoplasmic blebs into tubular lumen
cells detach from basement membrane
edematous interstitium
does the clinical syndrome correspond with histopathologic findings?
no
why does tubular stress trigger a decrease in glomerular filtration rate to reduce workload?
preservation of oxygen tension in medullary area
up-regulation of tubular cellular survival factors
what would happen without tubuloglomerular feedback with tubular stress?
catastrophic loss of sodium and circulating volume
what happens occasionally with severe toxicity?
acute tubular necrosis
what can reduce the length or size of the capillary bed and therefore decrease glomerular filtration rate?
loss of nephrons
decreased glomerular permeability
what can loss of nephrons be caused by?
neoplasia
inflammation
fibrosis
what are histologic findings like with chronic renal disease?
more dramatic than with AKI
what can happen in chronic glomerular disease that decreases the glomerular ultrafiltration coefficient?
changes in glomerular wall
possible decreases in endothelial cell fenestrations
possible capillary constriction/collapse
why do we often see a much less severe drop in GFR in animals with CRD than in those with AKI?
AKI affects all of the glomeruli or large swaths: no time for compensation
CRD affects individually, so neighbors can help
why do animals with chronic renal disease often present with polyuria and polydipsia? as opposed to acute kidney injury which presents with anuria/oliguria
loss of urine concentrating ability
what are reported values of glomerular filtration rate in healthy dogs?
1.56 to 2.96 mL/min/kg
what does the loop of henle do?
uses Na and Cl to create a hypertonic medullary interstitium
_____________ is greater in the inner medullar than in the outer
osmolarity
what is the thin descending limb permeable to?
water
essentially impermeable to small solutes such as NaCl and urea
what is the thin ascending limb permeable to?
NaCl
impermeable to water
where is urea reabsorbed?
proximal convoluted tubule
distal convoluted tubule
collecting duct
what is the effect of the loop of henle?
hypertonic interstitium
progressively more hypertonic as you go deeper into medulla
filtrate entering distal tubule is hypotonic
what maintains the gradient?
vasa recta
how does antidiuretic hormone work?
inserts aquaporins into collecting ducts and water passively moves out of filtrate
what does angiotensin II lead to?
increased aldosterone which increases blood volume and vasoconstriction of systemic arterioles
how can the sympathetic nervous system override autoregulation?
constrict afferent arteriole
stimulate renin secretion which helps to restore GFR
angiotensin II preferentially constricts ______________ arterioles more than ______________ arterioles
efferent
afferent
what do increased blood pressure, flow rate, or NaCl in the distal tubule trigger?
vasoconstriction of afferent arterioles
what hormones lead to increased GFR?
angiotensin II
atrial natriuretic peptide
nitric oxide
prostaglandins E2 and I2
does increased or decreased pressure in the afferent arteriole lead to increased renin production?
decreased
gorging on halogeton can cause _______________________ in sheep and horses
renal problems
what do cattle and pigs get from ingesting pigweed?
nephrotoxin, oxalates, and nitrates
acute nephrosis and heart failure
what does tamm-horsfall mucoprotein normally do?
protects tubular cells and contributes to permeability barrier
what does tubular stress trigger?
decrease in GFR to reduce workload: preserves oxygen tension in medullary area (relative hypoxia) and up-regulates tubular cellular survival factors
what will decrease the filtration coefficient?
loss of nephrons
decreased glomerular permeability
what can cause loss of nephrons?
neoplasia
inflammation
fibrosis
how does the filtration coefficient decrease with chronic glomerular disease?
changes in glomerular wall
possible decreased in endothelial cell fenestrations
possible capillary constriction/collapse
what does aldosterone regulate?
Na retention
what contributes to the polydipsia/polyuria with CRD?
increased solute load per functional nephron
altered function of countercurrent mechanism
impaired renal responsiveness to ADH
