Flashcards in Renal 2 Deck (7)
Describe glomerular filtration
- Movement from glomerular capillary into bowman's space in corpuscle
- Fluid called FILTRATE or ULTRAFILTRATE
○ No proteins
- Similar to our blood components minus proteins (can't cross the barrier)
- Glomerular filtration rate (GFR): volume filtered per unit of time (80-120 ml/min for healthy person) collectively
○ Damaged glomeruli, older person, the filtration rate decreases.
- Use filtration fraction (FF): of renal plasma flow, how much is filtered into glomerulus
- Rate/flow = filtration fraction of 0.2
Describe barriers to glomerular filtration.
1. Fenestrated endothelium: innermost surface: lining, large openings are fenetrations: allow larger stuff to get through
2. Glomerular basement membrane: barrier to filtration
3. Podocytes: epithelial cells (extensions with little feet) Line vessels on the outside, inside bowman's space.
Only capillary bed without interstitial tissue.
Needs other support (Intraglomerular cells which support area around capillaries)
Connect with basement membrane to solidity it via contractile properties
Respond to signalling molecules.
□ Relaxation/contration of interglomerular/messengial cells
□ Surface area for filtration regulation
- Slit diaphragm
□ Protiens that interact with each other and other components.
□ Structural integrity
□ Neg charge found on filtration barrier
Types of substances able to cross the barrier
What are the main components that determine what is filtered? What are the names of fluid in different components?
Same as what we see in blood in filtrate (without proteins)
Free filtration depends on
- Radius. Smaller than 15 angstroms, freely pass
- Molecular weight: Lighter (under 5000 daltons), better passing
- Charge of the substance: neg charge on filtration barrier, easier to filter cations (positive charge)
- Neutral: permeate a little harder
- Negative: really hard time
Albumin: -17 charge, and high weight, can't pass barrier. That’s why it remains in our blood.
Anything found in renal corpuscle: filtrate.
Now in nephron: tubular fluid
- In renal corpuscle: fluid can't be altered
- In tubular fluid: epithelial cells can alter the fluid.
How do you measure GFR?
Same properties apply
- Non toxic
- Not produced/broekn down by kidney
- Largely extreted substance (eliminate venous output part of equation)
Arterial blood measurement (blood from arm)
GFR: 100 % excreted
- Filter reliant
- Can't be reabsorbed or filtration
- Because we want to look at the glomerulus SPECFICALLY.
Inulin and creatinine: no reabsorption or secretion.
Creatinine: breakdown of creatine (metabolism within muscles)
- No injection required
- Injection of creatine breakdown in body
Values can change during this assessment
Good quick but less accurate measurement. (they can change, less controlled )
INULIN: injected, more reliable
- Look at inulin in blood
- Look at inulin in urine
Using inulin or creatinin: GFR
PAH: delivery overall to kidney
- Use them together to get filtration fraction, want 20% or 0.2
what does GFR tell us?
Of the the plasma that's being delivered, how much is filtered by the glomerulus
- Substance that relies totally on filtration for its excretion.
- Inulin and creatinine are this!
Impaired filtration: age or damage, reduced ability to filter. See a change to the GFR. GFR will be reduced, but RPF will remain the same.
- See a change in filtration fraction!
- Impaired GFR, filtration fraction will go down.
describe glomerular filtration rate (GFR) and the starling forces that apply to it. Where are pressures favoured?
180 L a day goes into the nephron, mostly goes back into our bloodflow
Pressures determine amount of filtration
Starlings Forces (2 forces determine if it goes in or out)
- Oncotic pressure (proteins)
- Hydrostatic pressure (hydrolic pressure, from blood)
- Early capillary, greater hydrostatic than oncotic, fluid goes out
- Later capillary (BP drops), greater oncotic than hydrolic, fluid comes in
Within Glomererular cappilary: hydraulic pressure
Proteins within blood: Oncotic pressure
Pressure in bowman's space: fluid pressure within
- Oncotic pressure within should be zero.
- No proteins within bowman's space
Efferent end changes from Afferent end:
hydrolic pressure goes down
Within bownman's space doesn't change
Ontotic pressure within capillary gets more negative (concentration within blood increases)
(afferent) end: ultrafiltration pressure POSITIVE value
- Favor fluid moving into bowman's from capillary
(efferent)end: positive value, still favor movement from glomerulus into bowman's space.
*** Along the whole capillary bed, favour movment into bowmans capsule ****