Jill Renal Intro 1 Flashcards
urine formation involves which processes? (2)
- Filtration
2. reabsorption of electrolytes and nutrients
high pressure capillary filtration system located between 2 arterioles
glomerulus
high pressure in the glomerulus allows for…
face of fluid and solutes out of blood into glomerular space along bed’s entire length
bowman’s space
fluid filled space in bowman capsule
glomerular filtrate
portion of blood filtered into capsule space
large molecules don’t cross the glomerular wall (therefore no proteins)
similar composition to plasma
average daily GFR
125 mL of filtrate
regulated by afferent and efferent arterioles
effect of constriction of AFFERENT arteriole
pressure and GFR
not as much going in so…
DECREASED glomerular pressure and DECREASED GFR
effect of constriction of EFFERENT arteriole
pressure and GFR
can’t get out!
INCREASED glomerular pressure
INCREASED GFR
peritubular capillaries
originate from efferent arteriole and are low-pressure vessels
adapted for reabsorption
surround tubules and allow for reabsorption in the lumen
tubular transport can result in
reabsorption from fluid into capillaries OR secretion into tubular fluid from blood
Active reabsorption
Na, K, Cl, Ca, PO4
urate, glucose, amino acids
passive reabsorption
water and urea
secreted by kidneys
H+, K+, and urate ions
transport maximum
max amount of substance that can be reabsorbed per unit of time
depends upon the number of carrier proteins available for transport
renal threshold
palm level at which substance appears in urine
site of the most reabsorptive and secretory processes
proximal tubule
proximal tubule
complete reabsorption of
glucose, amino acids, lactate, water soluble vitamins
electrolytes partially reabsorbed in the proximal tubule
Na, K, Cl, bicarbonate
proximal tubule and water reabsorption
movement of sodium out of the tubular lumen
concentration gradient for water causes rapid movement out of the lumen
where are exogenous organic compounds excreted?
proximal tubule
i.e. penicillin, ASA, morphine
typically bound to plasma proteins and not filtered freely unless bound
loop of henle function
controlling concentration of urine
est. high concentration of osmotically active particles in renal parenchyma surrounding medullary collecting tubules where antidiuretic hormone exerts effects
taken as a whole, the loop of henle always reabsorbs
more sodium and chloride than water
drugs that work on thick ascending loop of Henle
site of action of loop diuretics
inhibit Na/K/Cl transporters
body is unable to reabsorb Na, so therefore unable to absorb water
thin descending limb of henle
highly permeable to water
moderately permeable to urea, Na, other ions
where does osmolality of filtrate reach highest point
elbow of loop of henle
ascending limb of loop
impermeable to water
solutes are reabsorbed but water can’t follow therefore filtrate becomes more and more diluted
thick loop of henle
20-25% filtered Na, K, Cl are reabsorbed
development of transmembrane potential that favors passive reabsorption of Ca, Mg
distal convoluted tubule
only about 5% of Na, Cl left to be reabsorbed
Calcium ions are actively reabsorbed in
what drugs act on the distal convoluted tubule
thiazide diuretics
inhibit Na/Cl reabsorption
NOT as much reabsorption occurs here, so TZDs are weak drugs
late distal tubule
site where aldosterone exerts its action
major site of regulation of K excretion
vasa recta
found in the medulla of the kidney
blood vessels that work to concentrate urine
ADH
secreted by posterior pituitary
aquaporin channels to open renal tubule
free water to be reabsorbed from urine therefore increasing osmolality
ADH and low ECV
kidney senses decreased CO and signals release
3rd spacing, HF, nephrotic disease
renal blood flow
20-25% of cardiac output
needed to ensure sufficient GFR for removal of waste products
regulation to keep blood flow and GFR constant
renal blood flow neuronal control
affarent and efferent arterioles innervated by sympathetic NS
sensitive to vasoactive hormones
during period of strong sympathetic stimulation… (urine output)
urine output can fall
due to constriction of afferent arteriole (decrease in renal flow)
vasoconstrictors that work on kidney flow
angiotensin II, ADH, endothelians
endothelians
peptides released from damaged endothelial cells and may play role in decreasing blood flow following acute renal failure
vasodilators
dopamine, nitric oxide, prostaglandins
NO
produced by vascular endothelium
PREVENTS vasoconstriction of renal blood vessels to allowing normal excretion of sodium and water
prostaglandins
mediators of cell function, local production and action
protect kidney against vasoconstriction effects of sympathetic stimulation and angiotensin II
NSAIDs
inhibit prostaglandin synthesis
may cause a reduction of renal flow and GFR (therefore AKI)
auto regulation of renal flow function
maintain renal flow consistent with needs of renal cells
allow for precise regulation of solute and water excretion
resistance to blood flow must be varied in proportion to arterial pressure
autoregulator mechanisms
- direct effect on smooth muscle
2. juxtaglomerular complex
direct effect on smooth muscle
causes blood vessels to relax when there is increased BP and constrict when w/ decreased systemic pressure
work opposite the systemic BP
juxtaglomerular complex
found in distal tubule (macula densa cells w/renin)
measures arterial and glomerular pressures and Na concentration and directly releases renin to raise stretch and increase GFR
what happens if urine moves thru too quickly?
less time for sodium reabsorption and higher concentration delivered to distal tubule in urine
this is the result of macula densa cells
effect of high protein and glucose levels on GFR
cause decreased sodium delivery to distal tubule
increase GFR by same mechanisms
as renal function declines…
increase in serum levels of substances such as urea, Cr, PO4, K
this can be measured with blood tests
renal clearance
volume of plasma that is completely cleared ea. minute of any substance that finds its way to urine
renal clearance is determined by
ability of glomeruli to filter substance and capacity of renal tubules to reabsorb or secrete it
ea. substance has its own clearance rate
aldosterone present and sodium
all sodium in distal tubular fluid is reabsorbed and urine is essentially sodium free
aldosterone absent and sodium
no sodium is reabsorbed from distal tubule
aldosterone and potassium
potassium is reabsorbed from and secreted into tubular fluid under influence of aldosterone
only about 70 mEq sent to distal tubule, but more is consumed (excess K must be eliminated)
ANP
hormone synthesized in atrial muscle cells in response to stretch
increases sodium and water excretion by kidney
effects of ANP
- vasodilation of afferent and constriction of efferent arterioles = INCREASED GFR
- inhibition of aldosterone = sodium reabsorption from collecting tubules
- inhibition of ADH thereby increasing excretion of water by kidney
kidney and pH
regulate body pH by conserving bicarbonate and eliminating H ions
only site for H ion removal
buffers of urine
- bicarbonate
- HPo4
- ammonia
bicarbonate
combines with H+ to reform into water and CO2
CO2 is then reabsorbed by tubular cells and bicarb is regenerated
the kidney tries to keep the CO2 low, so that the reaction favors hydrogen elimination
bicarbonate reaction
CO 2 + H2O –> H2CO3 –> H + HCO3
ammonia
formed by deamination of glutamine
can be accelerated and will increase if H+ concentrations have been elevated for 1-2 days
how is uric acid produceD?
product of purine metabolism (A/G of DNA)
hyperuricemia
elevations in levels of uric acid
causes gout, kidney stones
uric acid elimination
freely filtered and is reabsorbed and secreted into proximal tubules
typically more is reabsorbed so that uric acid is eliminated from filtrate
controlled to maintain a constant plasma level
how much urea does an adult produce a day?
25-30 g.day
rises with high protein diet is consumed, excessive tissue breakdown, GI bleed
GI bleed and uric acid
blood is broken down to form ammonia
ammonia is absorbed into portal circulation and converted by liver
normal BUN
8-25mg/dL
during dehydration, BUN levels
INCREASE
decreased blood volume and FGR
drugs eliminated by kidney
only drugs NOT bound to plasma proteins are filtered and able to be eliminated
endocrine functions of kidney
- control of BP via RAAS
- calcium metabolism/vitamin D
- erythropoietin and RBC
erythropoietin
regulates RBC production in bone marrow
synthesis is stimulated by hypoxia
CKD pos are often anemic bc kidneys can’t produce this hormone
vitamin D function
increases Ca absorption from GI
regulate calcium deposition into bone
stimulates renal calcium absorption
activation of vitamin D
either cholecalciferol (skin) or synthetic (ergocalciferol) must have 2 hydroxylations to form 1-25 Dihydroxi….
if CKD, unable to transform vitamin D to active form
