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Glomerular Filtration Notes

Medicine Notes > Renal System Notes

This is an extract of our Glomerular Filtration document, which we sell as part of our Renal System Notes collection written by the top tier of Bristol University students.

The following is a more accessble plain text extract of the PDF sample above, taken from our Renal System Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Lecture 3 & 4 Glomerular Filtration

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Introduction o Occurs at rate ~120ml/min o Urine output ~1ml/min (i.e. over 99% glomerular filtrate normally absorbed) o Varies with: gender, age, body size o Energy comes from hydrostatic pressure of blood (generated by heart beat) o No energy expenditure by kidney in filtering glomerular blood Glomerulus as a filtration barrier o Behaves as though perforated by 'functional' pores of the diameter ~8-10nm (1/1000 diameter of RBC) o Rate of filtration of given substance depends upon
? Molecular weight

* <10,000= freely filtered

* >100,000= excluded from glomerular filtrate

* Rate of filtration ~ inversely proportional to molecular weight
? Shape

* Long, thin molecules filtered more easily than spherical molecules of same molecular weight
? Electrical charge

* Ease of filtering o (+) charge >> Neutral >> (-) charge o Examples
? Albumen

* Molecular weight= ~69,000

* (-) charge

* Normally almost completely retained in blood of glomerular capsule
? Free haemoglobin

* Molecular weight= ~68,000

* Not charged

* Some leaks into Bowman's space if in blood (e.g. IV haemolysis) Anatomical barriers in the Glomerulus and Bowman's capsule (3) o Capillary endothelium
? Has open pores (fenestrations)
? ~100nm wide
? Do not prevent plasma protein filtration o Basement membrane
? Has fixed (-) charge
? Gives the electrical charge selectivity of the filter
? NEPHROTIC SYNDROME removes negative charge o Glomerular epithelium (podocytes)
? Epithelial cells put out primary and secondary processes (podocytes)
? These envelope glomerular capillaries
? Molecules must get through gaps between podocytes The factors involved in glomerular filtration o GFR= K S [(PGC - PT) - (pGC - pT)]

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