Renal Water Electrolytes Flashcards
important functions of the kidneys
- urine formation
- fluid and electrolyte balance
- regulation of acid-base balance
- excretion of waste products of protein metabolism
- excretion of drugs and toxins
- secretion of hormones
macroscopic anatomy of kidneys
- paired, bean-shaped organs located retroperitoneally on either side of the spinal column
- enclosed by fibrous capsule of connective tissue
- outer region: cortex
- inner region: medulla
- connected to urinary bladder through bilateral ureters
microscopic anatomy of kidneys
made up of a million nephrons (functional units of the kidney)
fractional distribution of water in average individuals
- average water content of human body varies between 40-75% of total body weight
- intracellular fluid accounts for two-thirds of total body water
- extracellular fluid accounts for one-third of total body water
five basic parts of a nephron
- glomerulus
- proximal convoluted tubule
- loop of henle
- distal convoluted tubule
- collecting duct
three basic renal processes
- glomerular filtration
- tubular reabsorption
- tubular secretion
factors that facilitate glomerular filtration
- unusually high pressure in glomerular capillaries
- semipermeable glomerular basement membrane
what does the semipermeable glomerular basement membrane allow to pass through?
- allows water, electrolytes, small dissolved solutes, amino acids, low-molecular weight proteins, urea, creatinine to pass through and enter the proximal convoluted tubule
- albumin, many plasma proteins, cellular elements, protein-bound substances are too large to be filtered
- basement membrane is negatively charged, repelling negatively charged molecules like proteins
what and how much does the glomerulus filter out?
- kidneys receive 1200-1500 mL of blood per minute
- glomerulus filters out 125-130 mL of glomerular filtrate (protein-free, cell-free fluid)
functions of the proximal convoluted tubule
- to return the bulk of each valuable substance back to the blood circulation through tubular reabsorption
- to secrete products of kidney tubular cell metabolism
tubular reabsorption
process by which renal tubule substances filtered by the glomerulus are reabsorbed as filtrate passes through tubules
what happens when the concentration of the filtered substance exceeds the capacity of the transport system/renal threshold?
substance is excreted in urine
what does the renal threshold help assess?
tubular function and nonrenal disease states
tubular secretion
passage of substances from peritubular capillaries into tubular filtrate which serves two functions
- eliminating waste products not filtered by the glomerulus
- regulating acid-base balance in the body through secretion of hydrogen ions excreted by kidneys
loop of henle
the u-shaped portion of a renal tubule lying between the proximal and distal convoluted portions
function of loop of henle
- maintains the hyperosmolality that develops in the medulla
- reabsorbs water, sodium, chloride
countercurrent flow
the downward flow in the descending limb and the upward flow in the ascending limb
how does the urine become hypo-osmolal when it leaves the loop of henle?
water leaves in the descending loop and sodium and chloride leave in the ascending loop to maintain a high osmolality within the kidney medulla and creates the osmotic gradient
countercurrent multiplier system
an active process occurring in the loops of henle in the kidney which is responsible for the production of concentrated urine in the collecting ducts of the nephrons
function of distal convoluted tubule
to effect small adjustments to achieve electrolyte and acid-base homeostasis under the hormonal control of both aldosterone and arginine vasopressin (AVP)
arginine vasopressin (AVP)
- peptide hormone secreted by the posterior pituitary
- responds to increased blood osmolality and decreased blood volume
- synthesized in hypothalamus, secreted by posterior pituitary and circulated to kidneys
what does vasopressin stimulate?
makes walls of distal collecting tubules permeable to water for water reabsorption, resulting in a more concentrated urine and decreased plasma osmolality
aldosterone
- hormone produced by the adrenal cortex under the influence of the renin-angiotensin mechanism
- secreted when there is decreased blood flow or blood pressure in the afferent renal arteriole
what does aldosterone stimulate?
sodium reabsorption in the distal tubules and potassium and hydrogen ion secretions
what is reabsorbed in the collecting ducts?
water, sodium, chloride, urea
what is the role of urea in the collecting ducts?
diffuses down the collecting ducts concentration gradient out of the tubule and into the medulla interstitium, increasing its osmolality
what hormones act on the collecting ducts to control reabsorption of water and sodium?
vasopressin and aldsoterone
nonprotein nitrogen compoundns
waste products formed in the body as a result of the degradative metabolism of nucleic acids, amino acids, proteins
what are the three principle nonprotein nitrogen compounds/
urea, creatinine, uric acid
urea
- makes up majority of waste excreted as a result of the oxidative catabolism of protein
- synthesized in the liver
- converted from ammonia
- kidney is only significant route of excretion of urea
- 40-60% reabsorbed by collecting ducts to contribute to high osmolality in medulla
creatinine
- waste product of muscle creatine spontaneously dehydrating
- levels represent a function of muscle mass and remain the same unless muscle mass or renal function changes
- not reabsorbed normally unless high concentration
uric acid
- primary waste product of purine metabolism
- undergoes complex cycle of reabsorption and secretion as it courses through the nephron
- has clinical significance in development of urolithiasis (formation of calculi) and gout
what major system regulates water intake?
thirst
what happens in state of dehydration to the body’s water balance?
renal tubules reabsorb water at their maximal rate, resulting in production of a small amount of maximally concentrated urine
what happens in states of water excess to the body’s water balance?
tubules reabsorb water at a minimal rate, resulting in excretion of a large volume of extremely dilute urine
sodium
- primary extracellular cation
- excreted principally through the kidneys
- major mechanism for controlling sodium balance is renin-angiotensin-aldosterone hormonal system
- freely filtered by glomerulus and actively reabsorbed throughout nephron
- reference range: 136-145 mmol/L
potassium
- main intracellular cation
- controlled by aldosterone to be excreted by the distal convoluted tubule and collecting ducts
- regulates neuromuscular excitability, heart contraction, hydrogen concentration
- competes with hydrogen ions in exchange with sodium
- freely filtered by glomerulus and actively reabsorbed mostly by proximal tubules
- reference range: 3.5-5.1 mmol/L
chloride
- principal extracellular anion
- involved in maintenance of extracellular fluid balance with sodium
- shifts after movement of sodium or bicarbonates
- readily filtered by glomerulus and passively reabsorbed as counterion when sodium is reabsorbed by proximal convoluted tubule
- reference range: 98-107 mmol/L
phosphate
- occurs in higher concentrations in the intracellular than in the extracellular fluid environments
- homeostatic balance is chiefly determined by proximal tubular reabsorption under the control of parathyroid hormone
- affinity of hemoglobin for oxygen
calcium
- second most predominant intracellular cation
- most important inorganic messenger
- parathyroid hormone and calcitonin-controlled regulation of calcium absorption form gut and bone stores is more important than renal secretion or reabsorption
- reabsorbed in proximal tubule, most in loop of henle
magnesium
- major intracellular cation
- important enzymatic cofactor
- ionized fraction is easily filtered by glomerulus and reabsorbed in tubules by influence of parathyroid hormone
glomerular filtration rate (GFR)
a measurement of renal function involving flow rate and filtration capacity over urine; the rate or urine formation as plasma passes through the glomeruli of the kidneys
estimated glomerular filtration rate (eGFR)
equation used to predict glomerular filtration rate based on serum creatinine, age, body, size, and gender without the need of a urine creatinine
glomerular diseases
- acute glomerulonephritis
- chronic glomerulonephritis
- nephrotic syndrome
acute glomerulonephritis
- pathologic lesions
- hematuria and proteinuria (usually albumin)
- rbc casts
- decreased GFR, anemia, elevated blood urea nitrogen (BUN) and serum creatinine, oliguria, sodium and water retention
- often related to recent infection with group a strep
chronic glomuerlonephritis
- can lead to glomerular scarring and eventual loss of functioning nephrons, lengthy inflammation
- minor decreases in renal function and slight proteinuria and hematuria
- gradual development of uremia
nephrotic syndrome
- massive proteinuria and resultant hypoalbuminemia
- decreased plasma oncotic pressure
- hyperlipidemia and lipiduria
tubular diseases
- distal renal tubular acidosis
- proximal renal tubular acidosis
- interstitial nephritis
distal renal tubular acidosis
- renal tubules are unable to to keep up the pH gradient between blood and tubular fluid
- affects acid-base balance
- low serum values for phosphorous and uric acid and by glucose and amino acids in the urine
- may be some proteinuria
proximal renal tubular acidosis
- decreases bicarbonate reabsorption resulting in hyperchloremic acidosis
- affects acid-base balance
- low serum values for phosphorous and uric acid and by glucose and amino acids in the urine
- may be some proteinuria
interstitial nephritis
- acute or chronic inflammation of the tubules and surrounding interstitium
- could be result of radiation toxicity, renal transplant rejection, viral-fungal-bacterial infections, reaction to medication
- decreases in GFR, urinary concentrating ability, metabolic acid excretion, inappropriate control of sodium balance
renal obstructions
- caused by either raised intratubular pressure until nephrons necrose and chronic renal failure ensues or predispose urinary tract to repeated infections
- upper tract blockages characterized by constricting lesion below a dilated collecting duct
- lower tract blockages characterized by residual urine in bladder after cessation of urination
- useful laboratory tests include urinalysis, urine culture, blood urea nitrogen (BUN), serum creatinine, complete blood count
acute kidney injury
- sudden, sharp decline in renal function as a result of an acute toxic or hypoxic insult to the kidneys
- initiated by hemolytic transfusion reactions, myoglobinuria due to rhabdomyolysis, heavy metal/solvent poisonings, antifreeze ingestion, analgesic and aminoglycoside toxicities
- increased BUN and serum creatinine values
prerenal acute kidney injury
- defect in blood supply before it reaches kidney
- causes are cardiovascular system failure and consequent hypovolemia
intrinsic acute kidney injury
- defect in kidney
- causes are acute tubular necrosis, vascular obstructions/inflammation, glomerulonephritis
postrenal acute kidney injury
- defect in urinary tract after it exits the kidney
- caused by acute renal failure due to lower urinary tract obstruction or rupture of urinary bladder
chronic kidney disease
gradual decline in renal function over time with presence of kidney damage or decreased kidney function
stages of chronic renal failure
(1) kidney damage with normal or increased GFR
(2) kidney damage with normal or decreased GFR
(3A) moderately decreased GFR
(3B) moderate to severe decreased GFR
(4) severely decreased GFR
(5) kidney failure
(5D) end-stage renal disease; patients undergoing chronic dialysis
(5T) end-stage renal disease; patients with kidney transplant
ammonia
- formed in the renal tubules when glutamine is deaminated by glutaminase
- reacts with secreted hydrogen ions to form ammonium ions which are excreted into urine
albuminuria
- presence of albumin in urine
- important in management of patients with diabetes mellitus who are at risk of developing nephropathy
myoglobin
- a heme protein found only in skeletal and cardiac muscle in humans; can reversibly bind oxygen similar to hemoglobin but is unable to release oxygen except under vey low oxygen tension
- in rhabdomyolysis, myoglobin release from skeletal muscle can overload proximal tubule and cause acute renal failure
beta-2 microglobulin
- polypeptide that is one of the major histocompatibility markers on cell surfaces
- easily filtered by glomerulus and reabsorbed by proximal tubules to be catabolized
- elevated levels in serum indicate increased cellular turnover like in myeloproliferative and lymphoproliferative disorders, inflammation, renal failure
- used clinically to asses renal tubular function in renal transplant patients with elevated levels indicating organ rejections
cystatin c
- cysteine protease inhibitor found in bloodstream in elevated concentrations in patients with impaired kidney function
- rise more quickly than creatinine levels in acute kidney injury
electrolytes
ions with an electrical charge
- cations: electrolytes with positive charge
- anions: electrolytes with negative charge
what processes are electrolytes an essential component in?
- volume and osmotic regulation
- myocardial rhythm and contractility
- cofactors in enzyme activation
- regulation of adenosine triphosphatase ion pumps
- acid-base balance
- neuromuscular excitability
- production and use of atp from glucose
osmolality
colligative property of solution; how much of a solute is dissolved in a solvent
what is the clinical significance of osmolality?
- parameter to which hypothalamus responds
- associated with osmotic activity in plasma, regulation of blood volume
renin
- initial component of renin-angiotensin-aldosterone system, produced by juxtaglomerular cells of renal medulla when extracellular fluid volume or blood pressure decreases
- catalyzes synthesis of angiotensin by cleavage of circulating plasma precursor angiotensinogen
general causes of hyponatremia
- increased sodium loss
- increased water retention
- water imbalance
causes of increased sodium loss (hyponatremia)
- hypoadrenalism
- potassium deficiency
- diuretic use
- ketonuria
- salt-losing nephropathy
- prolonged vomiting or diarrhea
- severe burns
causes of increased water retention (hyponatremia)
- renal failure
- nephrotic syndrome
- hepatic cirrhosis
- congestive heart failure
causes of water imbalance (hyponatremia)
- excess water intake
- syndrome of inappropriate antidiuretic hormone
- pseudohyponatremia
general causes of hypernatremia
- excess water loss
- decreased water intake
- increased intake or retention
causes of excess water loss (hypernatremia)
- diabetes insipidus
- renal tubular disorder
- prolonged diarrhea
- profuse sweating
- severe burns
causes of decreased water intake (hypernatremia)
- older persons
- infants
- mental impairment
causes of increased intake or retention (hypernatremia)
- hyperaldosteronism
- sodium bicarbonate excess
- dialysis fluid excess
general causes of hypokalemia (hypernatremia)
- gastrointestinal loss
- renal loss
- cellular shift
- hydration
causes of gastrointestinal loss (hypernatremia)
- vomiting
- diarrhea
- gastric suction
- malabsorption
- cancer therapy
- large doses of laxatives
causes of renal loss (hypernatremia)
- diuretics
- nephritis
- renal tubular acidosis
- hyperaldosteronism
- cushing’s
- hypomagnesemia
- acute leukemia
cause of cellular shift (hypernatremia)
- alkalosis
- insulin overdose
general causes of hyperkalemia
- decreased renal excretion
- cellular shift
- increased intake
- artifactual
causes of decreased renal excretion (hyperkalemia)
- acute or chronic renal failure
- hypoaldosteronism
- addison’s
- diuretics
causes of cellular shift (hyperkalemia)
- acidosis
- muscle/cellular injury
- chemotherapy
- leukemia
- hemolysis
causes of increased potassium intake (hyperkalemia)
oral or intravenous potassium replacement therapy
causes of artifactual hyperkalemia
- sample hemolysis
- thrombocytosis
- prolonged tourniquet use or excessive fist clenching
causes of hyperchloremia
- excess loss of bicarbonate because of gastrointestinal loss
- renal tubular acidosis
- metabolic acidosis
causes of hypochloremia
- prolonged vomiting
- diabetic ketoacidosis
- aldosterone deficiency
- salt-losing renal diseases
- high bicarbonate concentrations
causes of hypocalcemia
- primary hypoparathyroidism
- vitamin d deficiency
- pseudohypoparathyroidism
- hypomagnesemia
- hypermagnesemia
- hypoalbuminemia
- acute pancreatitis
- renal disease
- rhabdomyolysis
causes of hypercalcemia
- primary hyperparathyroidism
- hyperthyroidism
- increased vitamin d
- benign familial hypocalciuria
- malignancy
- multiple myeloma
- milk alkali syndrome
- thiazide diuretics
- prolonged immobilization
general causes of hypomagnesemia
- increased excretion
- decreased absorption
- reduced intake
causes of increased excretion (hypomagnesemia)
- tubular disorder, glomerulonephritis, pyelonephritis
- hyperparathyroidism, hyperaldosteronism, hyperthyroidism, hypercalcemia, diabetic ketoacidosis
- diuretics
causes of decreased absorption (hypomagnesemia)
- malabsorption syndrome
- pancreatitis
- vomiting
- diarrhea
causes of reduced intake (hypomagnesemia)
- poor diet/starvation
- prolonged magnesium
- deficient intravenous therapy
- chronic alcoholism
general causes of hypermagnesemia
- decreased excretion
- increased intake
- miscellaneous causes
causes of decreased excretion (hypermagnesemia)
- acute/chronic renal failure
- hypothyroidism
- hypoaldosteronism
- hypopituitarism
causes of increased intake (hypermagnesemia)
- antacids
- enemas
- cathartics
- therapeutic
miscellaneous causes (hypermagnesemia)
- dehydration
- bone carcinoma
- bone metastases
causes of hypophosphatemia
- diabetic ketoacidosis
- chronic obstructive pulmonary disease
- asthma
- anorexia nervosa
- alcoholism
- increased renal excretion
- decreased intestinal absorption
causes of hyperphosphatemia
- increased intake
- increase release of cellular phosphate
- increased breakdown of cells
- severe infections
- intensive exercise
- neoplastic disorders
- intravascular hemolysis
ion-selective electrode (ISE)
an analytical technique used to determine the activity of ions in aqueous solution by measuring the electrical potential
- used for sodium, potassium, chloride, calcium
colorimetric assay
based on the use of spectrophotometer to determine concentration of a chemical compounds in a solution by measuring spectral absorbance of the compound at a particular wavelength
- used for chloride, magnesium
co-oximetry
a device that measures the oxygen carrying state of hemoglobin in a blood specimen
- used for bicarbonate
dye binding assay
based on the principle that certain strongly anionic dyes form insoluble complexes with proteins at low pH
- used for magnesium, calcium
uv absorption
based on protein absorbing uv light at the wavelength of 280 nm due to the presence of aromatic amino acids
- used for phosphate
differences between indirect and direct ise for sodium
- direct: measures sodium in undiluted plasma
- indirect: measures sodium in diluted plasma; more commonly used in high, throughput, fully automated analyzers
renin-angiotensin-aldosterone system
- initiated by low blood pressure, low blood volume
- stimulates kidney to release renin and liver to release angiotensinogen
- renin converts angiotensinogen to angiotensin i
- angiotensin i converted to angiotensin ii by angiotensin converting enzyme (ACE)
- increases water reabsorption and constricting blood vessels to increase blood pressure
blood urea nitrogen (BUN)
- measure of kidney health
- increased kidney failure, decreased blood volume, CHF
- decreased malnutrition, syndrome of antidiuretic hormone
creatinine clearance equation
(volume of urine over 24 hours/1440) x (creatinine in urine/creatinine in plasma) x (1.73/actual body surface area)
anion gap
- difference between measured cations and measured anions
- used in acid/base balance and toxic alcohol
- normal range is 4-12
osmolal gap
- difference between measured osmolality and calculated osmolality
- increased gap indicates ethylene glycol, isopropanol, methanol, antifreeze
- normal range is <10
bicarbonate
- second most common extracellular anion
- accounts for 90% of total carbon dioxide; carbon dioxide measured, not bicarbonate
- diffuses out of the cell in exchange for chloride to maintain neutrality
- reabsorbed in proximal tubule, maybe distal
- reference range: 22-33 mmol/L
what does bicarbonate concentration look like in alkalosis?
relative increase of bicarbonate compared to carbon dioxide, kidneys increase excretion carrying a cation
- losing bicarbonate in urine corrects pH by increasing amount of hydrogen ions
what does bicarbonate concentration look like in acidosis?
body will reabsorb bicarbonate and excrete hydrogen to decrease the ratio of acid to base
