Lecture 31 - Glomerular function Flashcards
Filtration:
Movement of plasma from the glomerular capillaries (blood) into the glomerular capsule (nephron)
Most substances in plasma are freely-filtered meaning?
Not very selective at the glomerulus
Creates a plasma-like filtrate of the blood
What determines glomerular filtration?
Filtration barrier
Renal blood flow
Driving forces
Where does filtration occur?
Filtered into capsular space:
small substances (low molecular mass) are freely filtered
large substances (high molecular mass) are NOT filtered
What is renal blood flow equal to in the kidneys?
1/5th of CO per min
1100-1200mL blood/min
Why is high blood flow in the kidneys needed?
High flow for filtration, rather than metabolism
What are the two types of pressures?
Hydrostatic pressures
Pressure due to the volume of fluid
“Pushes” fluid away
Colloid osmotic pressures
Osmotic pressure due to protein
“Pulls” fluid towards
What are the 4 forces in the glomerulus?
Glomerular hydrostatic pressure (GHP),
Blood colloid osmotic pressure (BCOP),
Capsular hydrostatic pressure (CsHP),
Capsular colloid osmotic pressure (CsCOP)
What is Glomerular hydrostatic pressure (GHP) equal to?
+ 50 mmHg
What is Blood colloid osmotic pressure (BCOP) equal to?
- 25 mmHg
What is Capsular hydrostatic pressure (CsHP) equal to?
- 15 mmHg
What is Capsular colloid osmotic pressure (CsCOP) equal to?
0 mmHg, If damaged kidneys, there will be a pressure here
Proportion/percentage of the kidneys plasma flow is filtered is called?
Filtration fraction
Renal plasma flow :
45% of blood is cells
55% of blood is plasma
Filtration factor:
1/5th of the plasma which enters the kidneys (renal plasma flow) is filtered through the glomeruli into the nephrons
≈ 20% of the RPF is filtered in the?
glomerular capsule
nephron
≈ 80% remains in the glomerular capillaries
the efferent arteriole
peritubular capillaries
GFR – Glomerular filtration rate
The amount of plasma filtered per unit time by the kidneys
Renal plasma flow (RPF) x Filtration fraction (FF) =
Glomerular filtration rate (GFR)
GFR = ? (mL/min)
125 mL/min
RPF = ? (mL/min)
625 mL/min
Glomerular filtration rate is?
Tightly regulated
Varies from person to person
Declines slowly from age 30
Renal Filtered Load (RFL)
How much of a substance in the plasma is filtered per minute?
Filtered Load =
the amount of a particular substance (solute) in the plasma is filtered per unit of time (per minute/hour/day)
= GFR x solute plasma conc.
Renal Clearance
How much plasma is cleared of a substance per minute
Clearance?
is the volume (mL) of plasma that is cleared of a substance by the kidneys per unit time (per minute)
Clearance can be used to:
Quantify how a substance is handled by the kidneys
Estimate glomerular filtration rate (GFR)
Creatinine and inulin are?
Freely filtered
Not secreted
Not reabsorbed
ALL filtered is excreted in urine
Clearance of creatinine =
= Volume of plasma filtered per minute = GFR
How much of creatinine is filtered?
20% of plasma filtered
Creatinine will be excreted in urine
Medications and toxins (e.g. PAH) are?
Freely filtered
Entirely secreted
Not reabsorbed
ALL in blood is excreted in urine
Clearance of PAH =
Volume of plasma flowing through the kidneys per minute = RPF
How much of PAH is filtered?
20% of plasma filtered
ALL PAH which is filtered stays in the nephrons
PAH is entirely secreted so ALL PAH in the blood of the peritubular capillaries is secreted into the nephrons
This PAH will be excreted in the urine
Glucose is?
Freely filtered
Not secreted
Fully reabsorbed in the proximal tubule
NONE excreted in urine
Except diabetes
Clearance of Glucose =
NO plasma is cleared of glucose = 0
How much of glucose is filtered?
NO glucose will be excreted in the urine
NO plasma has been “cleared” of glucose
Sodium is?
Freely filtered
Not secreted
Almost fully reabsorbed in most parts of the nephron
Small amount excreted in urine
Clearance of sodium =
Very small volume of plasma per minute
How much of sodium is filtered?
A small amount of sodium is not reabsorbed
This sodium will be excreted in the urine
Almost all of the sodium which is filtered is reabsorbed
A small amount of the plasma which was filtered has been reabsorbed without sodium and has been “cleared” of sodium
Clearance can be used to:
Quantify how a substance is handled by the kidneys
Estimate glomerular filtration rate (GFR)
Estimate renal plasma flow (RPF)
To be used to measure GFR a substance must:
Be freely filtered
NOT be reabsorbed from the tubule
NOT be secreted into the tubule
What two main substances meet the requirements to measure GFR?
Inulin and creatinine
