Efferent arteriole- biology a level

I don’t get the point of the efferent arteriole. When some of the substances pass through the barriers and the proteins don’t, is the role of the efferent allow blood and the remaining substances to leave?

Reply 1

macpatgh-Sheldon

Hi, btw no blue skies this morning sorry - dull UK weather! :frown:

Let me try and guide you in simple terms, yeah?

Ok think of it like this:

We need to get rid of waste products of metabolism, excess water from the body and to maintain a constant pH [the last by adjusting the amount of bicarbonate [HCO3-] ions excreted] and to maintain plasma osmolality within normal limits, with me?

So, there has to be some mechanism to be dreamed up by whoever/whatever you believe in [in my case that is nature and evolutionary pressure, but it might be some superpower in your case] to excrete ONLY the substances that we do not need OR that are toxic, still with me?

OK now we cannot excrete solid particles like birds do (I mean the flying variety, sorry! :colondollar:

) - you might know that birds micturate particles of uric acid lol.

So we need to excrete them in aqueous solution - this "urine-to-be" has to leave the body in some way - so NOW COMING TO YOUR SPECIFIC Q, the efferent arteriole to the glomerulus [which surrounds Bowman's capsule] is the contraption created by nature to filter out liquid that will become urine further down the nephron. The afferent arteriole is significantly wider than the efferent one, so a pressure gradient is generated [a bit like a bottleneck], and fluid with some dissolved substances is forced out by hydrostatic pressure [essentially the blood pressure transmitted from the renal artery], a direct branch of the abdominal aorta.

Look up:
glomerular basement membrane
podocytes [Greek pod = feet as in arthropod [arthro] so animals with jointed legs - you must have seen the lumps on a spider's legs or on insects [andcrabs [Crustacea]] cytos = container here cell]
glomerulonephritis [dw if you don't remember this].
immune complex deposition in basement membrane.

[the last two are diseases - a brief overview of these might help you understand the normal scenario better].

Be safe!
M

Reply 2

Blue_skies124

I assumed that fluid enters through the afferent arteriole and the hydrostatic pressure forces the fluid in to the pct having passed through the three barriers. So urea doesn’t became a part of the glomerular filtrate but enters the efferent arteriole alongside the remaining fluid instead?

Reply 3

macpatgh-Sheldon

Ok I see where you are coming from - the filtration of fluid is first into the Bowman's capsule - proximal tubule comes after that.

The 2nd sentence [Q] is not correct - urea is filtered into Bowman's capsule together with the water and other substances. Then later a lot of it is reabsorbed in the PCT as well as secreted back into the urine compartment in the convoluted tubule partly by diffusion and partly by solvent drag. Oc we need to get rid of this substance [urea] because it is the final waste product of protein/amino acid metabolism [nitrogen waste] generated by the ornithine cycle [also called urea cycle] in the liver; hence the re-secretion mored

Reply 4

macpatgh-Sheldon

sry st went wrong - was trying to say that secretion must occur more distally so that urea is excreted - oc we do not want to have urine with no urea in it - would defeat the purpose!

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Efferent arteriole- biology a level

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