Lecture 32- Glomerular function Flashcards
What is the specific form of filtration that the kidney does? Where does this occur?
- Ultrafiltration, essentially a sieve that acts on a very small scale.
- In the glomerulus.
What does filtration in the kidney create?
A plasma-like filtrate of the blood
Is the glomerulus selective when it filters?
- No, not particularly selective
- Only criteria is size and sometimes charge
How much urine is produced per day? What does this mean?
- Produces only 1.5L of urine per day
- Therefore, 99% of what is filtered goes back
How much of the cardiac output does the kidney get and how does this compare to other organs?
- 20-25% of cardiac output (CO) or 1-1.2L/min
- brain= 13%
- heart= 4%
Why is there a high flow to the kidney?
For filtration (reabsorption + secretion processes) rather than metabolism
What are the three things that make up the filtration barrier?
- Fenestrated endothelium
- Basement membrane and
- Podocytes with foot processes and filtration slits
What does the filtration barrier let through? What does the filtration barrier not let through?
- Small substances (low molecular mass) are freely filtered
- Large substances (high molecular mass) are NOT filtered
What are driving forces determined by?
- forces / pressure gradients between glomerular capillary / capsular space
- permeability of glomerular capillary
- surface area of glomerular capillary
What are the two positive forces influencing glomerular filtration?
- Glomerular hydrostatic pressure (GHP) = blood pressure (+ 50 mmHg)
- Capsular colloid osmotic pressure (CsCOP) = no protein in capsular space (+ 0 mmHg)
What are the two negative forces influencing glomerular filtration?
- Blood colloid osmotic pressure (BCOP) = albumin, proteins left behind (- 25 mmHg)
- Capsular hydrostatic pressure (CsHP) = corpuscule embedded in tissue (- 15 mmHg)
Net filtration pressure is…
calculated by positive forces- negative forces
How can we define renal filtration?
By calculating renal clearance: the rate at which substance S is cleared by the kidneys per unit time
How is renal clearance calculated?
Clearance (Cs) = Us x V / Ps (in mL/min)
Us = concentration of S in urine (mg/L or mol/L) V = volume of urine produced per unit time (mL/min or L/hour) Ps = concentration of S in plasma (mg/L or mol/L)
What does the renal clearance equation apply to?
For all substances that can be detected in plasma and urine
