Which of the following is freely filtered by Kidney across glomerular capillaries:
C i.e. CreatinineElectrolytes such as sodium (Na+), water and small orgaic compounds like glucose, inulin and creatinine are freely filtered across glomerular capillaries (i.e. filterability =1).As the plasma volume is 3 liters and GFR is 180 L/day (7.5L/h or 125 mL/min) the entire plasma is filltered & processed about 60 times each day.Filterability of 1 means that the substance is filtered as freely as water. Electrolytes such as sodium (Na+) , and small organic compounds such as glucose, inulin are freely filteredQ (filterability = 1).Filterability of solutes is inversely related to their size. As the molecular weight of molecule approaches that of albumin, the filterability rapidly decreases, approaching zero0.75 filterability means that the substance is filtered only 75% as rapid as water. Myoglobin (F = 0.75) and albumin (F = 0.005) are not freely filteredQ.Glomerular filtrate is protein free, and devoid of any cellular element, including RBCQ. The concentration of other constituents including most salts & organic molecules, are similar to the concentration in plasma (i.e., are freely filtered). Exception to this generalization are few low molecular weight substances, such as calcium & fatty acidQ, which are paially bound to plasma proteins and thus not filtered freely.Neutral substances with molecular diameter of < 4 nanometers are filtered freely and filtration of substance > 8 nm approaches zero, as the pores of glomerular membrane are of - 8 nm (80 angstroms) size. Between 4 - 8 nm, filtration is inversely propoional to diameter. However, negatively charged large molecules are filtered less easily than positively charged molecules of equal molecular sizeQ, and even neutral molecule are filtered much more easily than negatively charged molecules of same size. This is because, the negative charges of basement membrane & podocytes restrict and repel large negatively charged and attract positively charged molecules. This explains, only 0.2% filtrability of negatively charged albumin with an effective diameter of - 7 nm.Inulin (a polymer of fructose found in dahalia tubers, MW 5200) that is freely filtered, neither reabsorbed nor secreted in tubules, and creatinine (that is freely filtered, secreted & reabsorbed in some amount) are used to measure glomerular filtration rate (GFR).
Albumin (across glomerular capillaries)
Globulin
Creatinine
HCO3