Filtration of Blood in the Kidneys

8/8/2019 Filtration of Blood in the Kidneys

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Filtration of Blood in the KidneysGroup #7


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What is Filtration?

Because of theexcretion, some of the

metabolic wastes are thrown into theblood.And, for thecellular processes to go well, wastesmustbeeliminated from theblood stream.

To do such,blood enters the kidneys. The old

blood will filtered inside the kidneys tobecleaner, while wastes areexcreted as urine.

This process is what wecall blood filtration.


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How does Filtration happen?

Inside the kidneys, 3 different processes are

being done to filter theblood. The following arethe different processes in theblood filtration:

1. Glomerular Filtration

2. Tubular Re-absorption

3. Tubular Secretion


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Glomerular Filtration

Blood enters the kidneyvia therenal artery.

This seperates manytimes, eventuallyformingmanyafferent arterioles, each of which deliversblood to an individual kidneynephron.

Renal Artery-> Segmental Arteries ->Interlobar Arteries -> ArcuateArteries ->Interlobular Arteries -> Afferent Arterioles


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The diameter of theafferent (incoming) arteriole isgreater than the diameter of theefferent arteriole (by

whichblood leaves the glomerulus). The pressure of theblood inside the glomerulus is increased due to thedifference in diameter of the incoming and out-goingarterioles.This increasedblood pressure helps to force thefollowing components of theblood out of the glomerularcapillaries:

Most of the water; Most/all of the salts; Most/all of the glucose; Most/all of the urea.

Theaboveare filtered in preference to othercomponents ofbloodbased on particle size. (Water andsolutes of relative molecular mass less than 68,000 formthe filtrate.) Blood cells and plasma proteins are notfiltered through the glomerular capillariesbecause theyare relativelylarger in physical size.


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The water and salts that havebeen forced out

of the glomerular capillaries pass into theBowman's Capsuleand arecalled theglomerular filtrate. This glomerular filtrate isformed at a rate ofabove 125 cm3 per minute in

humans. This volume is approx. 20% of theplasma delivered during that time.

The glomerular filtrate passes from therenalcorpuscle to therenal tubule.


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RenalArteryRenal

Artery

SegmentalArtery

SegmentalArtery

InterlobalArteryInterlobal

Artery

ArcuateArteriesArcuateArteries

Interlobular ArteryInterlobular Artery






Artery







SegmentalArtery

SegmentalArtery


Artery




Arcuate

Arteries

Arcuate

Arteries




Artery








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Tubular Re-absorption

Onlyabout 1% of the glomerular fitrate actuallyleaves thebodybecause the rest (the other 99%) is reabsorbed into theblood whileit passes through the renal tubules and ducts. This is called tubular

reabsorption and occurs via three mechanisms. Theyare:Osmosis

Diffusion, andActive Transport.Reabsorption varies according to thebody's needs, enabling the

bodyto retain most of its nutrients.

The processes of tubular reabsorption occur in the following order:

In the PCTMost of the volume of the fitrate solution is reabsobed in the

proximal convoluted tubule (PCT). This includes some water andmost/all of the glucose (except in thecase of diabetics).


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In the Loop of Henle

The remaining water (together with the dissolved salts andurea) passes from the PCT into the descending limb of Henle. Itthen passes along the Loop of Henle, and up theascending limb ofHenle.

In the DCT

The water, urea, and salts contained within theascending limbof Henle eventuallypass into thedistal convoluted tubule (DCT).


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Tubular Secretion

The third processbywhich the kidneys cleanblood(regulating its composition and volume) is called

tubular secretion and involves substancesbeingadded to the tubular fluid. This removes excessivequantities ofcertain dissolved substances from thebody,and also maintains theblood at a normal healthypH(which is typicallyin the range pH 7.35 to pH 7.45).

The substances that are secreted into the tubular

fluid (for removal from thebody) include Potassium ions(K+), Hydrogen ions (H+), Ammonium ions (NH4

+),creatinine, urea, some hormones, and some drugs (e.g.penicillin).

Tubular secretion occurs from theepithelial cells thatline the renal tubules and collecting ducts.


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Afterbeing filtered,blood willthenbe flowing into the renal

vein. Then, it willbeagainbe

usedbythebody. Afterbeingused, it willbe filtered again.This cycle of filtration continueseverysecond in thebodyto

continue theexcretion ofunwanted wastes.

Filtration of Blood in the Kidneys

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