Week 6: Renal Function

general functions of the renal system

• removes substances from plasma

• water balance

• electrolyte regulation

• pH

• hormone regulation

___________ = outer, ____________ = inner

cortex, medulla

bilateral ureters

thick-walled canals that connect the kidneys to the bladder

around ___________ nephrons are found in each kidney

1 million

5 basic parts of the nephron

1. glomerulus

2. proximal convoluted tubule

3. loop of henle

4. distal convoluted tubule

5. collecting duct

which part of the nephron is described?

• capillary tuft surrounded by expanded end of renal tubule

glomerulus

which parts of the nephron are described?

• located in cortex

proximal convoluted tubule and distal convoluted tubule

which part of the nephron is described?

• comprising descending and ascending limbs

loop of henle

which part of the nephron is described?

• formed by 2 or more distal convoluted tubules as they pass through the cortex and medulla

collecting duct

the glomerulus separates the ________________, which lacks high molecular weight molecules

ultrafiltrate

what is the average total urine volume?

0.4-2.0 L daily

what are factors that increase facilitate filtration?

• unusually high pressure in glomerular capillaries

• semipermeable glomerular basement membrane

how much blood do the kidneys receive?

1200 - 1500 mL

how much glomerular filtrate (protein-free, cell-free) is produced by the kidneys?

125-130 mL

____________________ rate = volume of blood filtered per minute

glomerular filtration

proximal convoluted tubule function

• reabsorption — water, electrolytes, glucose, amino acids

• secretion — metabolism products

loop of henle function

reabsorption of water, sodium, and chloride

distal convoluted tubule function

• reabsorption & secretion

• electrolyte and pH balance through hormonal control (ADH and aldosterone)

  • Na+, K+, H+ exchange

collecting duct function

final site for concentrating/diluting urine through the reabsorption of water, sodium, chloride, and urea

what is excreted by the kidneys?

metabolic wastes (non-protein nitrogen), water, and electrolytes

aldosterone increases the reabsorption of ______

Na+

aldosterone increases the secretion of ______

K+ and H+

aldosterone is regulated by what system?

renin-angiotensin

what stimulates the release of aldosterone?

decreased plasma Na+ and decreased blood flow

ADH _____________ water reabsorption

increases

why does chronic renal failure cause anemia?

the kidneys control erythropoietin → RBC production

the ____________________ system regulates blood pressure and aldosterone secretion

renin-angiotensin

what hormones do the kidneys synthesize?

1. renin

2. erythropoietin

3. 1,25-dihydroxy vitamin D

4. prostaglandins

function of 1,25-dihydroxy vitamin D

active form of vit D that determines phosphate and calcium balance → bone calcification

function of prostaglandins

• increases renal blood flow, sodium and water excretion, and renin release

• opposes renal vasoconstriction

what are some kinds of renal diseases (general) that can occur?

• glomerular disease

• tubular disease

• UTIs

• renal calculi (kidney stones)

• renal failure

what disease is described?

• large and inflamed glomeruli with a decreased capillary lumen

• rapid onset of hematuria and proteinuria

acute glomerulonephritis

what disease is described?

• glomerular scarring and eventual loss of functioning nephrons

• gradual development of uremia may be 1st sign

chronic glomerulonephritis

what disease is described?

• associated with massive proteinuria, hypoalbuminemia, edema, hyperlipidemia, and lipiduria

nephrotic syndrome

what disease is described?

• decreased excretion/reabsorption of certain substances or reduced concentrating capability

• renal tubular acidosis

tubular disease

what disease is described?

• infection in either kidneys or urinary bladder

• obstruction in upper or lower tract

UTI

what disease is described?

• formed by combination of various crystallized substances

renal calculi

what disease is described?

• acute = sudden, sharp decline in function

• chronic = gradual decline over time

• renal hypertension caused by decreased perfusion to kidney

renal failure

therapy for acute renal failure

dialysis → removal of waste from blood by external, synthetic membrane

therapy for end-stage renal disease

dialysis and transplantation

clearance is the rate at which ______________ and urea are removed from blood into urine

creatinine

creatinine

endogenous metabolic product synthesized at a constant rate and cleared only by glomerular filtration

creatinine clearance rate

standard lab method used to measure GFR

estimated glomerular filtration rate

• used to predict GFR based on serum creatinine, age, body size, gender, and race

• does NOT require urine collection

clearance measurements

• urea

• cystatin C

• creatinine

urea does not provide full ______________ assessment, and is no longer widely used

clearance

___________ is a LMW protein produced by nucleated cells, and its levels remain stable if kidney function is normal

cystatin C

_____________ has less within-subject variation, making it more helpful in monitoring an individual

creatinine

what are NPNs?

non-protein nitrogens → urea, creatinine, uric acid, amino acids, nucleic acid wastes

what is azotemia?

condition where high levels of nitrogen-containing waste products (urea and creatinine) build up in the blood

what type of azotemia is described?

• increased urea

• normal creatinine

pre-renal

what can cause pre-renal azotemia?

• decreased renal blood flow — CHF, shock, low blood volume

• increased protein catabolism — diet, fever, upper GI bleeds

• dehydration

urea moves with ___________

water

decreased water excretion → ____________ urea excretion

decreased

what type of azotemia is described?

• increased urea

• increased creatinine and uric acid

renal

what can cause renal azotemia?

decreased renal function (glomerular and/or tubular disease)

what can cause post-renal azotemia?

• urinary obstruction

  • nephrolithiasis (kidney stone)

  • prostate hypertrophy

  • severe infection

  • tumors

what are the various BUN (blood urea nitrogen) methods?

• coupled enzyme

• indicator dye

• conductimetric

urease catalyzes the following: urea → _______ + HCO3-

NH4+

coupled enzyme reaction for BUN method

• glutamate dehydrogenase

• NADH → NAD+

• rate of disappearance of NADH is measured

an pH indicator dye is used with __________

ammonia

BUN method interferences

ammonia contamination

specimen for BUN

• serum

• plasma

• pre-diluted urine

• no anticoagulants can be used that inactivate urease

what anticoagulants should be avoided that inactivate urease when analyzing BUN?

Na fluoride, Na citrate

what is the reference range for BUN?

6-23 mg/dL

plasma creatinine has a constant level proportional to ______________

muscle mass

plasma creatinine should receive a ___________ check, and it varies <10% daily

delta

reference range of plasma creatinine

0.6-1.1 mg/dL

increased creatinine indicates ___________ insufficiency

renal

the creatinine produced is relatively equal to…

the creatinine filtered and excreted

creatinine clearance ____________ linearly as renal function decreases

decreases

which test can monitor/detect renal failure or nephrotoxicity?

creatinine clearance test

which test is more accurate for GFR in elderly or children?

cystatin c clearance test

specimen for creatinine clearance test

24 hour urine + serum drawn at midpoint

what is measured for the creatinine clearance test?

• urine total volume

• serum creatinine

• urine creatinine

interferences in creatinine clearance test

incomplete urine collection

what is the formula for corrected creatinine clearance (mL/min)?

(Cu/Cs) * (TV/min) * (1.73/surface area)

how many minutes in 24 hours?

1440

reference range for corrected creatinine clearance

• male = 97-137 mL/min

• female = 88-128 mL/min

what are these drugs examples of?

• aminoglycosides — gentamicin, tobramycin, amikacin, kanamycin

• cyclosporine, salicylates

nephrotoxic drugs

specimen collected for creatinine methods

• serum

• plasma

• pre-diluted urine

what are the various methods for creatinine?

• jaffe reaction (colorimetric)

• kinetic jaffe reaction

• enzymatic

what is the jaffe reaction?

creatinine + alkaline picrate → red-orange

creatinine method interferences

• falsely increased

  • hemolysis

  • ketones, glucose, protein, ascorbic acid

• falsely decreased

  • icterus

kinetic jaffe reaction

measures the reaction rate of the jaffe reaction, and is more specific

only __________ interfere with the kinetic jaffe reaction

ketones

enzymatic creatinine methods

• creatininase

• creatine hydrolase

the ____________ method has a greater specificity over Jaffe

enzymatic

uric acid is a ___________ metabolism end product

purine

the _________ converts purines → uric acid

liver

normal renal uric acid excretion

• glomerulus filters

• proximal tubule reabsorbs most

• distal tubule secretes

reference range for uric acid

• male = 4.0-8.5 mg/dL

• female = 2.7-7.3 mg/dL

what does hyperuricemia cause?

gout

how does gout form?

urates precipitate in joint fluid

who is most commonly affected by gout?

males 30-50

causes of gout

• primary = increased purine production

• secondary = alcohol and drugs, and increased dietary intake

hyperuricemia can result from increased _________________, which occurs in chemotherapy (esp. leukemia)

cell breakdown

hyperuricemia can be caused by ________ renal disease, where uric acid excretion is decreased

chronic

fanconi syndrome

hypouricemia caused by defective tubular reabsorption

uric acid method

• coupled enzyme

• uric acid + O2 → allantoin + CO2 + H2O2

• H2O2 + red. chromogen → ox. chromogen + H2O

• ox. chromogen = colored