WEEK 1: Assessment of Kidney Function Flashcards
Outline at least 5 kidney functions.
*Maintain water balance
*Maintain body fluid osmolarity
*Regulates the quantity & concentration of most ECF ions
*Maintain proper plasma volume
*Participates in acid-base balance
*Metabolic waste product elimination
*Exogenous compounds elimination
*Erythropoietin production
*Renin production
*Converts vitamin D into its active form
Define osmolarity.
State the units for osmolarity.
Osmolarity refers to the concentration of osmotically active particles, or solutes, in a solution.
Osmolarity is expressed in osmoles per liter (osmol/L) or milliosmoles per liter (mOsm/L).
State the formula for calculating osmolarity.
Osmolarity can be calculated if you know 2 things:
1. The molar concentration of the solution and
2. The number of osmotically active particles present in solution
In simpler terms, you sum up the concentrations of all individual solutes in the solution, each multiplied by the number of particles it produces when it dissociates in the solution.
Calculate the osmolarity of a solution that contains the following solutes:
0.2 moles of NaCl (sodium chloride)
0.3 moles of glucose (C₆H₁₂O₆)
0.1 moles of CaCl₂ (calcium chloride), which dissociates into three ions when it dissolves.
- Sodium Chloride (NaCl):
Concentration: 0.2 moles/L
Number of particles produced: NaCl dissociates into two ions (Na⁺ and Cl⁻).
Contribution to osmolarity:
0.2 × 2 = 0.4 mOsm/L
- Glucose (C₆H₁₂O₆):
Concentration: 0.3 moles/L
Glucose does not dissociate, so the number of particles produced is 1.
Contribution to osmolarity:
0.3×1=0.3mOsm/L
- Calcium Chloride (CaCl₂):
Concentration: 0.1 moles/L
Number of particles produced: CaCl₂ dissociates into three ions (Ca²⁺, 2Cl⁻).
Contribution to osmolarity:
0.1×3=0.3mOsm/L
Now, sum up the contributions from each solute:
Osmolarity=0.4+0.3+0.3=1.0mOsm/L
So, the osmolarity of the solution is 1.0 mOsm/L.
State the osmolarities in the different parts of the nephron.
Proximal Convoluted Tubule (PCT):
Osmolarity: ~300 mOsm/kg
Descending Limb of the Loop of Henle:
Osmolarity: Increases from ~300 mOsm/kg at the cortex to ~1200 mOsm/kg at the medulla.
Ascending Limb of the Loop of Henle:
Osmolarity: Decreases from ~1200 mOsm/kg at the medulla to ~100 mOsm/kg at the cortex.
Distal Convoluted Tubule (DCT) and Connecting Tubule (CNT):
Osmolarity: Varies, but generally remains lower than that of the medulla.
Collecting Duct:
Osmolarity: Varies depending on the body’s needs, ranging from ~100 mOsm/kg to as high as ~1200-1400 mOsm/kg under the influence of antidiuretic hormone (ADH).
What is tonicity?
It is the effects of various osmotic solutions on cells.
A solution can be either; Hypotonic or Hypertonic or Isotonic.
Define the 3 terms.
An isotonic solution does not cause an osmotic flow of water into or out of a cell (no change in cell volume).
A hypotonic solution will cause osmotic flow of water into the cell, causing the cell to swell. If the osmotic gradient is large enough, the cell may eventually burst/lyse. (An extreme example of a hypotonic solution is water)
A hypertonic solution will result in osmotic flow of water from inside to outside the cell, causing the cell to shrink.
State the formula for rate of excretion.
Filtration (GF) + Secretion (TS) = Reabsorption (TR) + Excretion
or
Rate of excretion = rate of filtration + rate of secretion - rate of reabsorption
What is renal blood flow?
It is the volume of blood that comes into the kidney in a given period of time.
What is Renal plasma flow?
What is the standard RPF?
It is the proportion of this RBF that is plasma.
The volume of plasma that passes through the kidneys per unit of time.
600 to 700 milliliters per minute (mL/min) per kidney.
*650mL/min
What is glomerular filtration rate?
What is the standard GFR?
It is the volume of plasma filtered per minute.
125ml/min
The ratio of filtered blood (GFR) to the renal plasma (RPF) can also be calculated.
This is referred to as____________and is expressed in percentage.
Filtration fraction.
Calculate the filtration fraction.
Therefore,
Filtration fraction= GFR/RPF x 100
= 125mL/min/650mL/min X 100
= 19.2%
State the net filtration pressure?
10mmHg
What is the Filtration coefficient?
State the filtration coefficient.
We can express GFR in terms of net filtration pressure.
This is referred to as the filtration coefficient.
Therefore,
Filtration coefficient= 125mL/min / 10mmHg
= 12.5 mL.min-1.mmHg-1
What is Plasma Clearance?
Units?
Plasma clearance= volume of plasma completely cleared of a particular substance per minute.
UNITS: mL/min
State the 3 parameters that are determined using Plasma Clearance.
GFR
Renal plasma flow
Renal blood flow (indirectly)
To measure plasma clearance of particular substance what are the 3 things we need to know?
Volume of urine excreted per unit time
Concentration of the substance in the urine
Concentration of the substance in the blood
State the formula for plasma clearance.
Clearance (C)= (U * V)/ P
Where U= conc of substance in urine (mg/mL)
P= conc of the substance in plasma (mg/mL)
V= volume of urine flow (mL/min)
Remember C1 * V1 = C2 * V2
To determine GFR, we need a substance that is completely filtered, BUT not reabsorbed or secreted.
Name the substance used.
Inulin is completely filtered by the body; it is neither reabsorbed nor secreted.
State the Inulin clearance.
Name the parameter which has the same value as Inulin clearance.
Inulin clearance= GFR=125mL/min
What really is the meaning of inulin clearance?
It means that 125mL of inulin-free plasma is returned to the circulation every minute!! (in 1 minute the kidneys have removed (cleared) all the inulin present in 125mL of plasma)
__________ clearance is now used to determine GFR (Partially secreted in small amounts!!).
Creatinine clearance is now used to determine GFR (Partially secreted in small amounts!!).
Name the substance clinically to measure renal plasma flow (= 650 ml/min).
State its properties.
Para-amino hippuric acid (PAH) = exogenous organic anion
*Complete filtration
*Complete secretion
*Not reabsorbed
PAH is
1) freely filtered at glomerulus,
2) secreted into the tubule (not reabsorbed) & 3) completely cleared from the plasma
i.e. all the PAH in the plasma that escapes filtration is secreted from the peritubular capillaries.
