L17 Flashcards
Describe 3 components of The Ultrafiltration Barrier
1) Fenestrated endothelium
2) Basement membrane
3) Podocytes (pedicel- secondary process + Filtration slit)
What’s the purpose of Fenestration (pore) of glomerular endothelial cell?
prevents filtration of blood cells but allows all components of blood plasma to pass through
What’s the purpose of Basal lamina of glomerulus:
prevents filtration of larger proteins
What’s the purpose of Slit membrane between pedicels:
prevents filtration of medium-sized proteins
Describe the process of Micropuncture
- Animal anaesthetised
- Micropipette penetrates tubule
- Suck up fluid sample
- Chemical analysis
What purpose does Mircopuncture serve?
to investigate ultrafiltration
Variations on technique of Micropuncture:
- Tubule section separated by oil
- Test fluid injected (to investigate reab./secr.)
- Suck up fluid sample
- Chemical analysis
…. described ultrafiltration. (ludzie z datą)
Wearn and Richards (1929)
…. is formed by filtering out plasma proteins while allowing the free passage of ions (e.g. Na+) and small molecules (e.g. glucose)”
Capsular fluid
The fluid formed by ultrafiltration is ….
GLOMERULAR FILTRATE
•The rate at which the 2 kidney’s form ultrafiltrate is …..
GLOMERULAR FILTRATION RATE or GFR .
The rate at which a single nephron forms ultrafiltrate is ….
SINGLE NEPHRON GFR or snGFR.
Which substances are freely filtered?
Substances of a low molecular weight are freely filtered.
Which substances are restricted?
Large molecules are restricted. e.g. hemoglobin, serum albumin
Negatively charged molecules are restricted. e.g. albumin
What governs GFR?
“A balance of hydrodynamic forces”.
- Hydrostatic pressure (plasma leaves capillaries because of pressure)
- Plasma proteins remain in blood (because of size and charge). Produces osmotic pressure (plasma protein oncotic pressure)
- Oncotic pressure opposes hydrostatic force due to capillary pressure
- ALSO small oncotic pressure from Bowman’s space opposing hydrostatic pressure known as NET FILTRATION PRESSURE
How can GFR be measured?
It can’t be measured, but it can be estimated.
•By measuring the rate of excretion of substances that are:
- Freely filtered.
- Not reabsorbed or secreted by tubules.
- Have no influence on renal function (e.g. blood flow)
Inulin meets these criteria.
The rate of excretion =
concentration in urine (UC) multiplied by amount of urine produced per min (Ů)
Rate of excretion = UC x Ů mg/min
Przypomnienie
The rate of excretion also depends on its concentration in the plasma (PC)
CLEARANCE -
The ratio between rate of excretion and PC is called CLEARANCE (C) and is expressed in ml/min
Thus: C = UC x Ů /PC in ml/min
Definition of Renal Clearance:
the volume of plasma completely cleared of a given substance in 1 min.
The clearance of inulin is used to estimate GFR. GFR for inulin clearance is …. ml/min for adult humans.
120-130
In a single day that’s … litres of plasma that are filtered!
180
If a substance has a clearance
reabsorbed (e.g. glucose) or not freely filtered (e.g. proteins).
If a substance has a clearance >GFR it must be ….
secreted
Why is Inulin not convenient for clinical purposes?
What implications does it have?
as you need a steady concentration in plasma for accurate measurements.
Thus use a substance, that fits the ‘criteria’, already found in plasma is used – creatinine.
However, small amounts of creatinine are secreted into the proximal tubule!
Glomerular filtration rate –
amount of filtrate formed in all the renal corpuscles of both kidneys each minute
What happens when GFR is too high?
substances pass too quickly and are not reabsorbed
What happens when GFR is too low?
nearly all reabsorbed and some waste products not adequately excreted
Wymień 5 steps of maintenance of the internal environment
1) Filtration by Glomerulus
2) Obligatory reabsorption and secretion by PCT (Proximal Convoluted Tubule)
3) Generation of osmotic gradient by loop of Henle
4) Regulated reabsorption and secretion by DCT (Distal Convoluted Tubule)
5) Regulation of water uptake by collecting ducts
Opowiedz o pierwszym etapie (co jest szczególnego we fluidzie)
The first stage in renal function is the transfer of fluid from the vascular space to the nephrons.
Involves selective filtration of the plasma through the glomeruli into the Bowman’s capsule
Fluid has a similar composition to plasma but with NO protein
Regulation of plasma composition occurs via 3 key processes:
- Ultrafiltration
- Reabsorption
- Secretion
ULTRAFILTRATION -
Plasma flows through glomerular capillaries ~1/5 is forced through capillary walls (hydrostatic pressure of blood) into Bowman’s space
The Glomerular filtrate -
cell and protein-free, the concentration of ions and small solutes are the same as in plasma (freely filtered). A filtration barrier restricts movement of solutes on a basis of size and charge.
Molecules size in
Glomerular Filtrate :
Molecules 3.6 nm not filtered
…. are more readily filtered than ….. for the same molecular radius
Cations
anions
Serum albumin has a radius of about … nm but its …. prevents its filtration
3.5
negative charge
Describe the structure of glomerulus and Bowman’s capsule:
.
what are the Evidences for ultrafiltration in glomerulus?
.
explain Role of Starling forces in glomerular filtration:
.
how to Measure GFR by inulin clearance?
.
