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1

Describe glomerular filtration

Glomerular Filtratoin
- Movement from glomerular capillary into bowman's space in corpuscle
- Fluid called FILTRATE or ULTRAFILTRATE
○ H20
○ Electrolytes
○ 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

2

Describe barriers to glomerular filtration.

Filtration barrier
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

3

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.

4

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)
Urine sample







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

5

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.

6

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 ****

7

How does resistance changes in afferent vs efferent arterioles work?

VASOCONSTRICT AFFERENT OR EFFERET, BOTH DECREASE RENAL BLOOD FLOW.
DEPENDING ON AFFERENT OR EFFERENT ARTERIOLE, SEE DIFFERENT EFFECTS ON GFR.
- Afferent: filtration rate goes down, less pressure
Efferent: increase filtration rate because pressure increased.

detailed
Arteriols on both sides of capillary bed, selective resistance changes to afferent or efferent component or both.
- Alter amount of blood to the kidneys (renal blood flow)
- Alter amount of filtration at glom (GFR)

1. Selectively vasoconstrict in efferent arteriole.
- Make it harder for blood to pass efferent portion
- Shunt blood elsewhere, decrease RBF
- Still blood enters
- Pressure within capillary increases
- Increased filtration rate.
- Decreased blood delivered to kidney
- Of blood that is delivered, higher filtration rate. (cause found before high pressure section)
2. Selective vasoconstrict afferent arteriole.
- Squeeze part before glomerulus
- Difficult delivery blood to kidney
- Increase bloodflow to other regions
- Reduction in amount of blood going into glomerulus.
Decrease in pressure, decrease in filtration rate.