Renal Physiology Flashcards
What makes up the glomerular fiiltration barrier?
- Capillary endothelium
- Glomerular basement membrane
- Podocyte epithelium
what size particles will get filtered?
- smaller than 20 A get freely filtered
- those greater than 42 A are not filtered
What are the lamina rara interna and externa composed of? What is the significance?
- Proteoglycans
- predominately heparin sulfate
- These provide a negative charge to the GBM
- important because it will repel other negatively charged molecules such as proteins
What happens if the negative charge of the GBM is removed?
- There will be an increase in filtration of anions
What are the three layers to the GBM?
- Lamina rara externa
- Lamina densa
- Lamina rara interna
What does the glycocalyx form and whats the significance?
- Forms a sticky biogel in the endothelial lumen of the glomerular capillary
- In order for molecules to be filtered they also have to pass through the glycocalyx
- it contributes to the size and charge filterability
Examples of freely filtered molecules?
- Water
- Glucose
- AA
- Electrolytes
- concentrations equal on both side of the membrane
How do you calculate urinary excetion?
- Amount filtered - reabsorbed + secreted
How do you calculate tubular reabsorption?
- Glomerular filtartion - urinary excretion + amount secreted
If excretion is greater than filtration, what happened?
- Tubular secretion
- substances moving from the peritubular capililaries into the renal tubular lumen
What is urine excretion rate?
- Urinary concentration (Ux) of X which is sthe [] of the substance in urine in a given volume
- Ux= concentration/volume
- Urine flow rate (V) is the rate at which urine is produdced, depends on fluid intake and homeostasis
- normally if fluid intake is increased the flow will increase
- V= urinve volume/time
- Urine excretion rate= Ux X V
What does renal clearance mean
- Rate at which subtance is removed from the kidneys
- Volume of plasma completely cleared of a substance by the kidneys per unit time
Ratio of urinary excetion to plasma volume
Calculate renal clearance of urea.
- Purea = 20 mM
- Uurea= 400 mM
- V= 1.44 L/day (1mL/min)
If substance is present in blood at a concentration of 1 mg/mL and in urine at 100 mg/mL and the urine flow rate is 1 mL/min what will the renal clearance be?
What is the GFR?
Volume of plasma filtered into the nephron of both kidneys at the same time
What should the GFR be on average?
- 125 mL/min (180 L/day)
- Filtration fraction is 20% of Renal blood flow
- FF=20% RPF
- GFR=125 mL/min
- what is RBF in mL/min?
FF=GFR/RBF
- 125mL/min/(0.20)= 625 mL/min
What is filtration fraction?
- Fraction of RBF (RPF) that is filtered across the glomerulus
- Influenced by BP and ultrafiltration pressure
- FF=GFR/(RBF)
What happens to oncotic pressure as FF increases?
- Oncotic pressure of the efferent arteriole increaes to facilitate reabsoprtion of tubular fluid
How do you calculate filtered load of X?
- GFR x Px
P is the plasma concentration
What percentage of the filtered load of sodium is reabsorbed per day?
- PNa=140 mEq/L
- GFR=180L/day
When will GFR be directly proportional to renal clearance?
- Substance has to be freely filterable in glomeruli
- Substance cant be reabsorbed or secreted by renal tubule
- Substance can’t be synthesized, broken down or accumulated by kidney
- Substance must be inert and non toxic w/o effect on renal function
What substance meets the four standards for using renal clearance to estimate GFR?
- Inulin
- Creatinine
Effects of systemic sympathetic stimulation?
Local renal sympathetic nerves get activated which
- constricts renal arterioles to decrease GFR
- Increase tubular reabsorption of water and salt
- Activates RAAS which further increases tubular reabsorption
What is PGC?
Pressure within glomerular capillary pushing out
PBC?
Hydrostatic pressure within bowmans capsule pushing in
πGC ?
- Oncotic pressure within glomerular capillary pulling in
πBC?
- Oncotic pressure within bowmans capsule pulling out
- should be zero bc no proteins in capsule
What three physical factors contribute to GFR?
- Hydraulic conductivity (permeabilty of fenestrated endothelium) Lp
- Surface area Sf
- Capillary ultrafiltration pressure PUF
What is the ultrafiltration coefficient? Kf
- Hydraulic conductivity Lp x surface area Sf= Kf
- GFR= Kf x PUF*
What can alter PUF?
- Changing glomerular capillary pressure PGC
- PGC determined by renal arterial BP
- Afferent arteriole resistance
- Efferent arteriole resistance
- PUF= PGC-PBC-πGC
How do you change ultrafiltration coefficient Kf?
- Changing surface area and permeability as Kf was hydraulic conductivity X surface area
What role do glomerular mesangial cells play?
Influence Sf
