Renal System Flashcards
Regulator of extracellular volume
Aldosterone
Regulator of extracellular osmolality
ADH or vasopressin
concentration
Amount/volume
Solute/solvent
Osmolality
Na concentration
Na salts are 90% of total osmolality
Normal osmolality number
300 mOsm/kg
Range: 270-310
Kidney functions
- Maintenance of extracellular fluid composition
- Maintenance of extracellular fluid volume
- Regulation of arterial blood pressure
- Endocrine functions
Endocrine functions of kidney
- Erythropoietin
- RAS
- Vitamin D- conversion to active form Vitamin D3
Vit D life
- Born in skin
- Liver (adolescence)- adds OH group
- Kidney- another OH group makes it Vit D3
Endocrine implications of CKD
- Anemic because of lack of erythropoietin
2. Hypocalcemia because Ca absorption from intestine is impaired with decreased vitamin D
Renal blood flow
20-25% of blood pumped by heart
1-1.2 L/min
GFR
125 mL/min
180 L filtered per day
Nephron functions
- Filtration
- Reabsorption
- Secretion
Excretion- NOT a kidney process but is a result of 1-3
Blood flow in glomerulus
Enters via afferent arteriole
Exists via efferent arteriole
Reabsorption
2/3 of what is filtered is reabsorbed in proximal tubule
Any ? Asking where something is reabsorbed should choose proximal tubule
Parts of nephron in cortex
Glomeruli
Proximal tubule
Distal tubule
Parts of nephron in medulla
Loops of Henle
Collecting duct
Most vulnerable part to ischemia
Inner stripe of outer medulla
Secondary to hypotension
Glomerular filtration
From glomerular capillary into Bowman’s capsule
Pressure for this created by beat of heart causing glomerular capillary hydrostatic pressure
Tubular reabsorption
Out of the lumen of renal tubule
Tubular secretion
Into the lumen of the renal tubule
Loop of Henle
Establishes and maintains an osmotic gradient in medulla of kidney
Countercurrent multiplier
Distal tubule and collecting duct
Make final adjustments on urine pH, osmolality, and ionic compositions
Thick ascending limb of Henle
Countercurrent multiplier
Creates the osmotic gradient
Impermeable to water
Sodium is reabsorbed into medullary interstitium, water can’t follow
Vasa recta
Countercurrent exchanger
Maintains osmotic gradient created by loop of Henle
Interstitial osmolality created by deposition of sodium
600 mOsm/kg
Total osmolality at tip of medullary pyramid
1200 mOsm/kg
Additional 600 from urea
Urea
Partially reabsorbed in proximal tubules
Secreted into tubules in TAL- increases concentration in tubules
High concentration drives reabsorption at collecting ducts
Urea is recycled
Renal control of glucose
Proximal tubule has maximum capacity for reabsorbing
All filtered glucose is usual completely reabsorbed by active transport here
Renal transport of glucose in DM
Amount of glucose filtered exceeds transport maximum
All segment beyond proximal tubule impermeable to glucose=glucose excreted
Glucose appears in urine
Causes osmotic diuresis
Life of vasopressin (aVP, ADH)
- Synthesized in hypothalamus cell bodies- paraventricular nucleus, supraoptic nucleus
- Stored before release in posterior pituitary (neurohypophysis)
- Secreted into blood
- Stimulus for release is increase in extracellular osmolality
- Site of action is collecting duct
Absence of ADH/AVP/vasopressin
Collecting duct and distal tubule impermeable to water
Causes large volume (up to 25 mL/min) of dilute urine (50-100 mOsm) to be formed
ADH/AVP/vasopressin in circulation
Causes reabsorption of H2O in collecting duct Small amount (0.5 mL/min or 0.5mL/kg/hr) of concentrated urine (1200-1500 mOsm) is formed
Ascending loop of Henle
Impermeable to H2O
Reabsorbed NaCl
DI
Failure of vaso synthesis or release
Insensitivity of DT and CD to vaso
SIADH
Inappropriate secretion of vaso
From intracranial tumors, hypothyroid, porphyria, and small cell carcinoma of lung
Diagnosed by increased urine sodium concentration and osmolality in the presence of hyponatremia and decreased plasma osmolality
Actions of aldosterone
Increases Na reabsorption from late installments tubule and collecting duct (decreases Na excretion)
Increase rate of K secretion into late signal tubule and collecting cute (increases rate of K excretion)
Production of aldosterone
In Zona glomerulus a of adrenal cortex
Atrial natriuretic peptide
Released from R atria
Acts on kidney to increase sodium excretion
Determinants of K excretion
- Aldosterone- increases rate of K secretion in distal tubule and collecting duct
- Distal tubular flow rate- excretion is increased when flow through distal tubule is increased and vice versa
- Bicarbonate ion concentration - increased bicarb concentration in distal tubule increased (alkaline urine)= K secretion increase
Loop diuretics example
Furosemide
Bumetanide
Ethacrynic acid
Torsemide
Loop diuretics
Site of action- thick ascending limb
Bind to Na K 2Cl symporter and inhibiting reabsorption of these ions
Osmolality of medulla decreases causing water excretion
SE-hypokalemia, fluid volume deficit, orthostatic hypotension, reversible deafness
Thiazides examples
Chlorothiazide
Hydrochlorothizide
Chlortahidone
Metolazone
Thiazides
Work in early distal tubule
Inhibit sodium reabsorption
SE-hypokalemia
K sparing examples
Spironolactone
Traiamterene
Amiloride
K sparing
Spironolactone-competitive aldosterone antagonist, works in late distal tubule and collective duct (mostly)
Others- decrease Na reabsorption from late distal tubule and collecting duct
SE- hyperkalemia
Carbonic anhydrase inhibitor example
Acetazolamide
Carbonic anhydrase inhibitor
Works in proximal tubule
Inhibits carbonic anhydrase inhibits bicarb reabsorption
Diminishes Na reabsorption
SE- hyerchloremic metabolic acidosis, decreased intraocular pressure by decreased rate of aqueous humor formation
Osmotic diuretics
Loop of henle or Bowman’s capsule- controversial
Exerts osmotic force and hinders reabsorption of water
SE- hypokalemia
Intraoperative acute renal failure stats
Accounts for 50% of patients requiring acute dialysis
Associated with mortality of 40-90%
Prerenal vs renal failure sodium
Prerenal (prerenal oliguria)- FENa <0.01 (1%)
Extensive Na reabsorption due to slow flow through tubule
Renal failure (acute tubular necrosis)- FENA >0.03 (3%) Reabsorbed sodium poorly so there is a large amount in the urine
Best test of renal reserve
Creatinine clearance
Measures GFR
Electrolyte abnormalities in CKD
Hyperkalmia
Hypocalcemia
Hypermagnesemia
Hyperphosphatemia
Decrease of K with hyperventilation
0.5 mEq/L for each 10 mmHg decrease in PaCO2
