Lecture 32: Glomerular function Flashcards
Filtration is a specific form of what?
Ultrafiltration
What is ultrafiltration?
Filtration on a micro scale
Filtration creates what?
A plasma-like filtrate of the blood
Filtration at the glomeruli is what?
Not particularly selective
What is filtration at the glomeruli influenced slightly by?
Charge and size of molecules
What is the average rate of filtration?
125mL/min or 180L/day
Filtration produces how much urine?
1.5L per day
The glomerulus has afferent and efferent arterioles supplying it with what?
Blood for filtration
What % of cardiac output does the renal blood supply receive?
20-25%
At what rate does the renal blood supply receive blood?
1-1.2L/min
What is the high flow of renal blood supply for?
Filtration rather than metabolism
Where does filtration take place?
In the glomerulus
What is the filtration membrane of the glomerulus composed of?
(3)
- Fenestrated endothelium
- Basement membrane
- Podocytes with foot processes and filtration slits
Small substances with low molecular mass are what?
Freely filtered
Large substances with high molecular mass are what?
Not filtered
What is glomerular filtration determined by?
3
- Forces/pressure gradients between glomerular capillary/capsular space
- Permeability of glomerular capillary
- Surface area of glomerular capillary
What are the 4 forces determining net filtration pressure?
- Glomerular hydrostatic pressure (GHP)
- Blood colloid osmotic pressure (BCOP)
- Capsular hydrostatic pressure(CsHP)
- Capsular colloid osmotic pressure (CsCOP)
What does the Glomerular hydrostatic pressure (GHP) =?
Blood pressure
What does the Blood colloid osmotic pressure (BCOP) =?
Albumin
What does the Capsular hydrostatic pressure(CsHP) =?
Corpuscle embedded in tissue
What does the Capsular colloid osmotic pressure (CsCOP) =?
No protein in the capsular space
What force cause filtration into the glomerular space from the capillary?
Glomerular hydrostatic pressure (GHP)
What forces cause filtration into the capillary from the capsular space?
- Blood colloid osmotic pressure (BCOP)
- Capsular hydrostatic pressure(CsHP)
What is the equation for the clearance of a substance?
Clearance (C) = U x V / P (in mL/min)
What does U =?
Concentration of S in urine (mg/L or mol/L)
What does V=?
Volume of urine produced per unit time (mL/min or L/hour)
What does P=?
Concentration of S in plasma (mg/L or mol/L)
What does the equation for renal clearance describe?
The rate at which substance is cleared by the kidney per unit time
The equation for renal clearance describes the clearance via the kidneys for what?
All substances that can be detected in plasma and urine
What does GFR stand for?
Glomerular filtration rate
What is glomerular filtration rate?
Amount of fluid filtered per unit time
What is the GFR normally?
Approximately 180 L/day or 125mL/minute
GFR is/does what?
3
- Tightly regulated
- Varies from person to person
- Declines slowly from age 30
To be used as a measure of GFR a substance must what?
3
- Not be reabsorbed
- Not be secreted into the tubule
- Not be metabolised
What 2 substance fit the conditions to be used as a measurer of GFR?
- Insuline
- Creatinine
What is insulin?
2
- A polysaccharide not metabolised by the body
- Not found in the body, must be injected
What is creatine?
2
- Waste product produced by muscles
- Already in the body so most commonly used clinically
What happens to creatine at the glomerulus?
It is filtered freely but not reabsorbed/secreted/metabolised
Plasma creatine is an indicator for what?
Kidney function
What happens to plasma creatine levels if both kidneys are working?
It is low
What happens to plasma creatine if only one kidney is working?
It is still fairly normal
What happens if there is critical kidney function?
Kidneys are not working properly and it is important to consider for drug application
How much renal blood is filtered?
Only about 20%
half of the CO is plasma therefore it is only 20% of the 1/2 of CO that is filtered
What is the filtration fraction?
GFR/RPF
What does RPF mean?
Renal plama flow
What is filtered load?
The amount of a particular substance (solute) filtered per minute
What does filtered load =?
GFR x solute plasma conc.
What is a typical value for GFR?
125mL/min
