Na ions AT out of the ascending limb of the LOH using ATP provided by the many mitochondria in cells of its wall
2 of 25
What does this create
A low WP (high ion conc in the region of the medulla between the 2 limbs called the interstitial region)
3 of 25
What would happen in normal circumstances
Water would pass out of the ascending limb by osmosis however the thick walls are almost impermable to water and so very little, if any, escapes
4 of 25
What are the walls of the decending limb however
very permeable to water and so it passes out of the filtrate by osmosis into the interstitial space
5 of 25
What does this water do
Enters the blood capillaries in this region by osmosis and is carries away
6 of 25
What does the filtrate do
progressively loses water in this way as it moves down the descending limb lowering its WP.
7 of 25
When does it reach its lowest WP
AT the tip of the hair pin
8 of 25
At the base of ascending limb What do Na+ ions do
diffuse out of the filtrate and as it moves up the ascending limb these ins are also actively pumped out (1) and therefore the filtrate develops a progressively higher WP
9 of 25
In the interstitial space between the ascending limb and the collecting duct what is there
a gradient of WP with the highest WP (lowest conc of ions) in the cortex and an increasingly lower WP (higher conc of ions) the further into the medulla one goes
10 of 25
What is the collecting duct
Permeable to water and so as the filtrate moves down it water passes out of it by osmosis- this water passes by osmosis into the blood vessels that occupy this space and is carried away
11 of 25
As water passes out of the filtrate what happens to its WP
It is lowered
12 of 25
However the WP is also
lowered in the interstitial space and so water continues to move out by osmosis down the whole length of the collecting duct
13 of 25
What does the counter current multiplier ensures
that there is always a WP gradient drawing water out of the tubule
14 of 25
Water that passes out of the collecting duct by osmosis does so through
channel proteins that are specific to water (aquaporins)
15 of 25
What can ADH alter
the number of these channels and so control water loss
16 of 25
By the time the filtrate now called urine leaves the collecting duct on its way to the bladder it has lost most of its
water and so it has a lower WP (is more concentrated) than the blood
17 of 25
What do the cells that make up the walls of the DCT have
microvilli and many mitochondria that allow them to reabsorb material rapidly from the filtrate by AT
18 of 25
The main role of the DCT is to
make final adjustments to the water and salts that are reabsorbed and to control the PH of the blood by selecting which ions to reabsorb
19 of 25
to achieve this the
permeability of its walls become altered under the influence of various hormones
20 of 25
When 2 liquids flow opposite directions past one another
the exchange of substances or heat between them is greater than if they flowed in the same direction next to each other
21 of 25
In the case of the LOH what does the counter current flow mean that
the filtrate in the collecting duct with a lower WP meets interstitial fluid that has an even lower wp
22 of 25
What does this mean
that although the WP gradient b/w the collecting duct and interstitial fluid is small it exists for the whole length of the collecting duct
23 of 25
there is therefore a
steady flow of water into the interstitial fluid so that around 80% of the water enters the interstitial and hence the blood
24 of 25
if the 2 flows were in the same direction (parallel)
less water would enter the blood
25 of 25
Other cards in this set
Card 2
Front
Steps
Back
Na ions AT out of the ascending limb of the LOH using ATP provided by the many mitochondria in cells of its wall
Comments
No comments have yet been made