Kidney, Loop of Henle, Medulla, ..............

[Toothguy80]

Ok so here is another question from Achiever:

Question: Why the lower portions of the loop of henle and the collecting ducts are selectively permeable to NaCl, urea and H2O?

Answer: Because osmolarity of interestial fluid in the inner medulla help prevent H2O loss from the nephronic filtrate.

So this is what I know, the medulla is the inner-most region of the kidney and takes away water so urine is more concentrated. What does osmolarity mean? What is the nephronic filtrate? Is that the thing that filters all the stuff?




Another question, why is there no homolgous chromosomes in mitosis? they only occur in meiosis 1? Why? what's the reasoning? please explain so I dont have to memorize this.

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[Sillygirl]

Okay i kinda know. First as you go down the loop of henle, the surrounding tissue becomes more and more concentrated hence a higher osmolarity. The Na and Cl ions diffuse out of the loop of henle (the curved part) and the ascending loop passively until you get to the top. By doing this you are keeping the solute concentration of the surrounding tissues high (and the solute concentration gets higher as you go from the top of the medulla which is near the cortex to the center). As you get to the top of the ascending loop and the distal convoluted tubule, you don't need such a high concentration so the ions have to be actively transported out. The reason for this high concentration tissue is so that as you are going down the descending loop of henle and down the collecting duct, due to the higher concentration of solute, water will passively diffuse out into the tissue so you can conserve water.

The way I reason my way through the homologous chromosome question is that in Prophase I of meiosis, you have synapsis which makes the homologous chromosomes pair to form a tetrad. You need the same chromosomes to be next to each other for crossing over to occur where as the same chromosomes are in mitosis but they don't need to be physically next to each other to just divide into two cells. I hope that helps! Good Luck!

 

[Dotoday]

Hey Sillygirl is mostly correct. The only thinkg that I`d like to add to this is that osmolarity means mOsm (miliosmoles). All that means is 1 mOsm = 1mole/1000. Tat is what mOsm is. Fluids in the kidneys are measured in osmoles because of their minute concentrations.
Now- mitosis vs meiosis. Mitosis is just a replicative division. It occurs with most of our cells, the cells that divide. Most of our cells divide(multiply) through mitosis. Meiosis however, is a reductive division. It basically reduces one cell into two, so that each of the cells produced have only one half of the original pair of chromosomes. Therefore they are called homologous chromosomes. There is no duplication (replication) of these chromosomes like it is in mitosis. After that reductive division happens, sex cells of the mother are ready to combine with sex cells of the father and they will generate a full 46 chromosome (in humans there are 46 chromosomes) cell.
I hope this makes more sense.
Good luck.

 

[Sillygirl]

agreed