La fonction glomérulaire (ll) / Le système rénine-angiotensine-aldostérone / Introduction à la fonction tubulaire Flashcards
Where can you find the glomerular capillaries?
Between the afferent and efferent arteriole
Where does filtration glomérulaire happen?
capillaires glomérulaires which is then collected in Bowman’s capsule
What is the normal GFR for men and women?
men: 2 mL/sec (120 ± 25 mL/min)
women: 1.6 mL/sec (95 ± 20 mL/min)
Why is the daily GFR so high?
to keep the blood clean and decrease waste in the blood —> maintain equilibrium
Information for the GFR:
After 20 years old… GFR starts decreasing by around 1 mL/min each year
What are the categories and respective GFR for kidney function?
What is the “débit de filtration glomérulaire”?
volume of filtrate produced by glomérules for a certain period of time
What is renal clearance?
Renal clearance of a substance refers to the how quickly a particular substance is removed from the plasma by the kidney and excreted in urine
What can renal clearance be used for?
- to calculate the volume of blood that was filtered of the “traceur” expressed in mL
- it is a sorta direct measure of DFG (GFR)
What is a “traceur”?
- Substance X in the blood
- Stable plasmatic concentration
- Filtered 100% in the glomerulus —> identical concentration in the filtrate and plasma
- Substance isn’t reabsorbed or secreted in the tubule —> excretion = amount actually filtered out in the glomerulus
What is the ideal “traceur”?
Inuline: polysaccharide exogène mais très $$$ —> used mostly in research
Radio-isotopes: once again, mostly used in research
What is typically used as the “traceur” in clinical context?
Créatinine —> produced by muscular metabolism
Clearance measured using creatinine is overestimated by around 10-20%… why?
it its secreted by the tubule
How is creatinine used to determine renal function?
Créatininémie increases with decreasing renal function BUT BE CAREFUL… it is dependent on 2 factors:
- Renal function (elimination)
- Muscle mass (production)
What can cause elevated creatinine levels?
high muscle mass —> clearance is normal but high creatinine
renal insufficiency —> high levels due to decreased clearance
How can you determine the GFR? CRÉATININÉMIE MUST BE STABLE
Measuring —> blood test with 24hr urine collection (creatinine)
Estimating —> two different formulas availableFormule de Cockcroft et Gault (1976) —> measures the creatinine clearance
How can GFR be estimated?
Formule de Cockcroft et Gault (1976) —> measures the creatinine clearance
- done on 225 white men… not very accurate
- multiply answer by 85% for women
Formule MDRD puis CKD-EPI —> measures the DFGe based on 4 parameters? what are they?
- age, sex, race and creatinine levels
- Why is this one better?
- Larger and more diverse sample population
- Calculated on computers in the lab
- Answer is normalized according to standard body surface
- Directly estimates DFG not creatinine clearance
What do you do if the patient does not have an “approximately normal body shape”? (determining GFR)
Measure it directly
What are the four stages of chronic kidney failure (maladie rénale chronique)?
Stage 1: renal lesions with normal GF or elevated GF (normalized filtration rate: > 90)
Stage 2: mild kidney failure, slightly decreased GF (normalized filtration rate: 60-89)
Stage 3: moderate kidney failure, moderately decreased GF (30-59)
Stage 4: severe kidney failure, severely decreased GF (15-29)
Stage 5: terminal kidney failure, terminal GF (< 15 or patient on dialysis)
Where is renin stored and produced?
In the afferent arteriole… if the pressure here decreases enough, renin will be released into blood from epithelial cells
What is the purpose of the SRAA?
Maintain TA and volume
How does the SRAA work?
When does renin secretion increase?
When there is a noticeable decrease in effective circulating volume, blood pressure, or overall volume
Why are the glomerular capillaries the only capillaries in the body situated between two arterioles?
In systemic capillaries, filtration will happen on the arteriolar side due to a high hydrostatic pressure and reabsorption will happen on the venular side due to low hydrostatic pressure…
In glomerular capillaries you want filtration the entire time —> ULTRAFILTRATION therefore… you need arterioles on both sides
So where does the reabsorption happen?
Peritubular capillaries
Why were filtration and absorption separated in the kidneys?
to have one time of capillary in ultrafiltration and the other in reabsorption mode
Overview of pressure levels in the vascularization of the kidneys:
What are the 8 “principes de la fonction tubaire”?
- Reabsorption and secretion
- Membrane transport
- Passive diffusion
- Facilitated diffusion
- Transporteur
- Canal ion-spécificque
- Active transport
- Typical tubular cell
- Energized by basolateral Na+K+ ATPase
- What does it do?
- Sodium in, which decreases cytoplasmic sodium levels this then draws intraluminal sodium into the cell which is done through cotransporters
- Polarity of epithelial cells (vectorial transport)
- Tight junctions
- Proximal tubules vs distal tubules
- What does the distal nephron include?
- Tubule distale et le tubule collecteur
- What does the distal nephron include?
- Transcellular and paracellular reabsorption
- Certain substances can pass by trans or paracellular route and be reabsorbed back into the blood depending on the Starling forces at the moment
- Tm (maximum tubulaire)
How does the schéma d’hydratation work?
Horizontal axis: volume on each side
Vertical axis: osmolality —> should be consistent between LEC and LIC
Why is there double the amount of liquid in your cells compared to outside of them?
the osmoles are distributed 1/3 —> LEC and 2/3 —> LIC
What happens to the schéma d’hydratation if you either:
- diminish extracellular volume,
- lower the osmolality or
- increase the intracellular volume
What happens if you drink a lot of water… lets say 3 glasses?
Water will evenly distribute between LEC and LIC depending on the osmoles ∴ 1/3 to LEC and 2/3 to LIC
