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Questions and Answers
If a patient's GFR decreases, what does this indicate about their renal disease?
If a patient's GFR decreases, what does this indicate about their renal disease?
- The disease is progressing. (correct)
- The patient no longer requires monitoring.
- The disease is stable and not changing.
- The disease is improving.
Why are GFR estimates clinically important?
Why are GFR estimates clinically important?
- To evaluate the patient's liver function.
- To assess the patient's risk of heart disease.
- To index renal function and assess the severity and course of renal disease (correct)
- To determine the patient's blood type.
What is the purpose of calculating fractional excretion (FE)?
What is the purpose of calculating fractional excretion (FE)?
- To measure the amount of protein in the urine.
- To calculate the patient's body mass index (BMI).
- To determine the exact GFR value.
- To express solute excretion as a percentage of its filtered load. (correct)
In the formula for fractional excretion of sodium (FENa), what do UNa, Pcr, Ucr, and PNa represent, respectively?
In the formula for fractional excretion of sodium (FENa), what do UNa, Pcr, Ucr, and PNa represent, respectively?
In the context of acute renal failure (ARF), why is calculating fractional sodium excretion (FENa) useful?
In the context of acute renal failure (ARF), why is calculating fractional sodium excretion (FENa) useful?
Flashcards
Nephron
Nephron
The functional unit of the kidney responsible for filtering blood and producing urine.
Waste Products Cleared by Kidneys
Waste Products Cleared by Kidneys
Three key substances removed during kidney filtration
GFR Estimation Using Clearance
GFR Estimation Using Clearance
A method to assess kidney function and track the progression/recovery of renal disease.
Clinical Significance of GFR
Clinical Significance of GFR
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Fractional Excretion of Sodium (FENa)
Fractional Excretion of Sodium (FENa)
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Study Notes
- Glomerular filtration is a process where plasma is filtered in the blood.
- The nephron is the functional unit of the kidney.
- Urine formation involves glomerular filtration, reabsorption, and secretion.
Glomerulus
- The glomerulus filters plasma in the blood.
- Bowman's capsule is a key part of the glomerulus
- Blood flows into the glomerulus via the afferent arteriole, regulated by sympathetic innervation.
- Blood flows out of the glomerulus via the efferent arteriole, which is not regulated.
- The glomerular tuft, composed of capillaries, is the leakiest blood vessels in the body.
- The juxtaglomerular apparatus, including the macula densa and granule cells, regulates the glomerulus through hormonal mechanisms.
Glomerular Filtration Details
- Approximately 20% of plasma is filtered each time blood passes through the kidneys.
- Approximately 125 ml of plasma is filtered per minute, translating to about 180 liters of fluid per day.
- The total circulation volume is 3-5 liters, which is filtered about 65 times per day on average.
- The filtrate resembles plasma but lacks proteins.
Filtration Barrier Layers
- Filtration occurs through three layers:
- The capillary endothelium is permeable to water, salts, and glucose; filtrate moves between the cells.
- The basement membrane is an acellular gelatinous layer of collagen/glycoproteins, permeable to small proteins, and its glycoproteins repel other proteins.
- The podocyte layer has podocytes' pseudopodia interdigitating to form filtration slits.
Plasma Filtration Forces
- Physical forces are responsible for filtering plasma to form tubular fluid.
- Three forces are involved:
- Hydrostatic pressure in the capillary, regulated as PGC.
- Hydrostatic pressure in Bowman's capsule, PBC.
- Osmotic pressure difference between the capillary and tubular lumen, πGC.
Tubuloglomerular Feedback
- Arterial pressure influences glomerular filtration pressure and GFR (glomerular filtration rate).
- Sodium and water retention occurs in the proximal convoluted tubule (PCT).
- Sodium delivery at the macula densa sends signals to the afferent arteriole.
- Adenosine/ATP leads to afferent arteriole resistance and vasodilation.
- Renin and Angiotensin II increase efferent arteriole resistance and vasoconstriction.
Summary of Reabsorption
- All plasma constituents have the same concentration in the glomerular filtrate as in the plasma.
- Reabsorption is a two-step process: from lumen to interstitium to peritubular capillary
- Movement can be transcellular or paracellular, occurring primarily through cells, unlike glomerular filtration.
- Channels and transporters promote transmembrane flux of solutes that cannot pass through the lipid bilayer, which is energy-dependent.
- Reabsorption of solute and water is linked to active sodium reabsorption.
- Water and solutes reabsorbed into the interstitium are driven into the capillary by Starling forces.
Tubular Secretion
- Tubular secretion involves transepithelial transport mechanisms, similar to tubular reabsorption.
- It provides a second route for solutes to be secreted into the tubular fluid.
- This is useful because only 20% of plasma is filtered each time blood passes through the kidney.
- Substances secreted into the tubular fluid include protons (H+), potassium (K+), organic anions, and cations.
Clearance
- Clearance is defined as the volume of plasma rendered free of a given substance in 1 minute.
- Clearance is calculated as the ratio of the urinary excretion rate to the plasma concentration.
- The formula for calculating clearance: Cp = (Up × V) / Pp
- Cp = Renal clearance of solute P
- Up = Urine concentration of solute P
- V = Urine flow rate
- Pp = Plasma concentration of solute P
Clearance Rate
- P is an imaginary compound. Inulin would be a real "P".
- If a compound behaves like "P," it is completely cleared from the plasma, meaning that the rate it appears in the urine equals the GFR.
Estimating GFR
- Estimates of GFR are clinically used as an index of renal function to assess the severity and course of renal disease.
- A fall in GFR indicates progression, while an increase suggests recovery.
- Clearance is an important concept used to determine GFR
Clinical Significance of GFR
- Knowing the GFR helps determine the severity of renal disease.
- Indicates whether a patient needs a kidney transplant.
- Describes renal function.
Fractional Excretion
- Fractional excretion (FE) expresses solute excretion as a percentage of its filtered load.
- The formula for fractional excretion of sodium (FENa) is: FE Na = (UNa * Pcr) / (Ucr * PNa) * 100
- Calculating FENa is useful in cases of acute renal failure (ARF).
Normal Ranges (Serum Biochemistry)
- Sodium: 136-145 mmol/l
- Potassium: 3.5-5.0 mmol/l
- Bicarbonate: 21-30 mmol/l
- Urea: 3.6-7.1 mmol/l
- Creatinine: 50-120 mmol/l
- Calcium: 2.1-2.5 mmol/l
- pH: 7.38-7.42
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Description
An overview of glomerular filtration in the kidneys. Includes details on the nephron and the function of the glomerulus, Bowman's capsule and the juxtaglomerular apparatus. Also discusses urine formation.