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    This is for GCSE(Higher) btw.

    Can someone please explain to me basically how the kidney and reabsorption works?

    Here is what I understand:

    The blood in the renal artery is under high pressure, which moves ions, water, urea and sugars out of the artery to Bowman's Capsule. There is a membrane between the artery and Bowman's Capsule that prevents large molecules such as proteins moving.

    After this I'm not so sure:

    The blood moves through capillaries to nephrons which filter out waste materials. The substances that the body needs are reabsorbed whilst the waste materials are passed through the kidney as urine, which is stored in the bladder and then removed from the body.

    I'm don't really understand how all this works and I'm a bit confused. Am I right? and how does the kidney know how much of each substance is needed?
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    (Original post by ThatPerson)
    This is for GCSE(Higher) btw.

    Can someone please explain to me basically how the kidney and reabsorption works?

    Here is what I understand:

    The blood in the renal artery is under high pressure, which moves ions, water, urea and sugars out of the artery to Bowman's Capsule. There is a membrane between the artery and Bowman's Capsule that prevents large molecules such as proteins moving.

    After this I'm not so sure:

    The blood moves through capillaries to nephrons which filter out waste materials. The substances that the body needs are reabsorbed whilst the waste materials are passed through the kidney as urine, which is stored in the bladder and then removed from the body.

    I'm don't really understand how all this works and I'm a bit confused. Am I right? and how does the kidney know how much of each substance is needed?
    The kidney doesn't "know" as such . . . Selective reabsorption works by something called co-transport. Which basically is a type of "facilitated diffusion" dependent on the concentration gradient of certain ions to work.
    Here's some reading material:
    http://en.wikipedia.org/wiki/Selective_reabsorption
    http://en.wikipedia.org/wiki/Co-transport
    I wouldn't worry if you don't really understand all of it. Its covered on the AS spec.
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    (Original post by joostan)
    The kidney doesn't "know" as such . . . Selective reabsorption works by something called co-transport. Which basically is a type of "facilitated diffusion" dependent on the concentration gradient of certain ions to work.
    Here's some reading material:
    http://en.wikipedia.org/wiki/Selective_reabsorption
    http://en.wikipedia.org/wiki/Co-transport
    I wouldn't worry if you don't really understand all of it. Its covered on the AS spec.
    Thanks I remember now, I learnt about co-transport earlier in the year, although I was a bit confused then.

    One more thing to clarify, when the receptors in the hypothalamus detect there is a low blood water content, they send messages to the pituarity gland to produce more ADH, which increases the permeability of the membrane so more water is absorbed. Does this also include the ions and sugars as well? Also what membrane does this affect?
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    (Original post by ThatPerson)
    Thanks I remember now, I learnt about co-transport earlier in the year, although I was a bit confused then.

    One more thing to clarify, when the receptors in the hypothalamus detect there is a low blood water content, they send messages to the pituarity gland to produce more ADH, which increases the permeability of the membrane so more water is absorbed. Does this also include the ions and sugars as well? Also what membrane does this affect?
    Water is a funny one. It's a large polar molecule that is not lipid soluble. It has to pass through specific channel proteins called aquaporins to enter the cell.
    It is perfectly possible to increase water retention without increasing retention of ions, by simply accelerating the rate by which water can move by osmosis into the cells of the kidney.
    http://en.wikipedia.org/wiki/Vasopressin#Kidney
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    (Original post by ThatPerson)
    This is for GCSE(Higher) btw.

    Can someone please explain to me basically how the kidney and reabsorption works?

    Here is what I understand:

    The blood in the renal artery is under high pressure, which moves ions, water, urea and sugars out of the artery to Bowman's Capsule. There is a membrane between the artery and Bowman's Capsule that prevents large molecules such as proteins moving.
    This part is incorrect. The filtration does not occur from the Renal artery to the Bowman's Capsule.

    The Renal Artery is under high pressure because a lot of blood is pumped to it, but no substances leave because the wall is too thick.

    The substances leave after in smaller capillaries

    I will explain below.


    (Original post by ThatPerson)
    After this I'm not so sure:

    The blood moves through capillaries to nephrons which filter out waste materials. The substances that the body needs are reabsorbed whilst the waste materials are passed through the kidney as urine, which is stored in the bladder and then removed from the body.
    The part in bold is slightly wrong.

    I will go through it step by step, just so it is easy to point out which bit you don't understand.


    1) The blood goes from the Renal artery to the Kidney.

    2) Once in the kidney, the renal artery becomes lots of small capillaries

    3) The blood is distributed to lots of small nephrons using tiny capillaries from the Renal Artery.

    4) The capillary takes blood to the nephron and to the Bowmans capsule ( part of the nephron).

    5) It gets to bowman capsule where substances are filtered under high pressure (like you correctly wrote above).

    6) This all happens in huge numbers of tiny nephrons throughout the kidney.

    7) A capillary leaves the bowman's capsule and winds around the tubes of the nephron like in this picture

    http://www.google.co.uk/imgres?imgur...9QEwAQ&dur=368

    8) The Capillary then is involved in a complex system of re-absorption with different parts of the nephron again.

    That is why it winds around the nephron. So it can reabsorb substances.

    9) The substances that are filtered in the Bowmans capsule is NOT always waste. Some of it is. Not all.

    So there are two important things. The first is filtration in the Bowmans Capsule. The second is the re-absorption of substances between the capillary and the nephron.

    I will explain below.



    (Original post by ThatPerson)
    and how does the kidney know how much of each substance is needed?
    Through a complex system of hormones.

    Say you are low on water. Your body sends out a hormone called ADH ( also known as Vasopressin).

    The ADH tells the nephron to reabsorb more water back from the nephron and into the capillary around the nephron. I can go into more detail if you wish.

    Another example would be phosphate. IF you are low on phosphate, more Parathyroid hormone. This causes the Kidney to absorb more phosphate back into capillary around the nephron.

    This all happens AFTER the capillary has left the Bowmans Capsule.
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    (Original post by DorianGrayism)
    This part is incorrect. The filtration does not occur from the Renal artery to the Bowman's Capsule.

    The Renal Artery is under high pressure because a lot of blood is pumped to it, but no substances leave because the wall is too thick.

    The substances leave after in smaller capillaries

    I will explain below.




    The part in bold is slightly wrong.

    I will go through it step by step, just so it is easy to point out which bit you don't understand.


    1) The blood goes from the Renal artery to the Kidney.

    2) Once in the kidney, the renal artery becomes lots of small capillaries

    3) The blood is distributed to lots of small nephrons using tiny capillaries from the Renal Artery.

    4) The capillary takes blood to the nephron and to the Bowmans capsule ( part of the nephron).

    5) It gets to bowman capsule where substances are filtered under high pressure (like you correctly wrote above).

    6) This all happens in huge numbers of tiny nephrons throughout the kidney.

    7) A capillary leaves the bowman's capsule and winds around the tubes of the nephron like in this picture

    http://www.google.co.uk/imgres?imgur...9QEwAQ&dur=368

    8) The Capillary then is involved in a complex system of re-absorption with different parts of the nephron again.

    That is why it winds around the nephron. So it can reabsorb substances.

    9) The substances that are filtered in the Bowmans capsule is NOT always waste. Some of it is. Not all.

    So there are two important things. The first is filtration in the Bowmans Capsule. The second is the re-absorption of substances between the capillary and the nephron.

    I will explain below.





    Through a complex system of hormones.

    Say you are low on water. Your body sends out a hormone called ADH ( also known as Vasopressin).

    The ADH tells the nephron to reabsorb more water back from the nephron and into the capillary around the nephron. I can go into more detail if you wish.

    Another example would be phosphate. IF you are low on phosphate, more Parathyroid hormone. This causes the Kidney to absorb more phosphate back into capillary around the nephron.

    This all happens AFTER the capillary has left the Bowmans Capsule.
    So does it go to bowman's capsule before the Nephrons or after?
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    (Original post by ThatPerson)
    So does it go to bowman's capsule before the Nephrons or after?
    Bowman's capsule is part of the nephron.

    The Bowmans capsule represents the point where capillaries ( from the Renal Artery) meet the nephron for the first time and filter their substances into the nephron.

    http://www.google.co.uk/imgres?imgur...9QEwAQ&dur=239

    The yellow tube is a nephron.

    The red tube is a capillary.

    The blood and substances start in the left hand corner and follow the tubes to the right.

    If you look in the top left corner, there is the bowman's capsule. It is where filtration first takes place.

    The capillary then reabsorbs whatever it needs after.
 
 
 
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