{I have just written what the doctor said but in organized way and delete many repeating sentence in his talk .. so u can get more benefit and good luck }

Today we will take the last lecture in urinal system

In the last lecture , We started to talk about absorption or reobsorption in the tubular system , sodium in details and also we discuss the glucose reobsorption , amino acid which is almost same as glucose ( it’s a co-transporter active with the sodium co-transporter) , vitamins and finally hydrogen which works in the opposite way which is secretion

We also talk about the Tmax and the renal threshold

» threshold: it’s a term that retain to the plasma concentration

» Tmax: it’s the amount of substance in the tubular system or the filtered load

* Phosphate and calcium

-They both are reabsorbed actively

- They are regulated by the renal reabsorption (kidneys )

As we know the renal threshold for an element means : the normal concentration of this element in the blood

And we also know that the renal system has specific T max for each element …..

So in the normal concentration of phosphate or calcium ( Tmax = renal threshold) the absorption of renal system will works probably .

Now if the calcium concentration is higher than the normal that’s mean the calcium that would be filtered in the tubule is extra than of Tmax ( on the top of Tmax ) in this case the extra calcium won’t be absorbed because the capacity of the absorpty system is the Tmax , after Tmax no absorption.

» Conclusion:

The renal reabsorption of phosphate and calcium occur only if the Tmax of the renal system for them equal the threshold otherwise no absorption will occur

Extra amount of phosphate and calcium will be excreted

As we know ,

-the sodium absorption mainly occur in the proximal tubule by different ways {many means} but mainly active reabsorption.

-67% of sodium will be reabsorbed in the proximal tubule and about 20% in the tube of henle , So about 8- 10 % remaining in the collecting duct .

-In the basoretinal side {don’t know what does it mean} , the absorption of the sodium occur by the sodium potassium pump

Now let’s talk about the reaming percent = 13% in the distal and collecting tubules .

In the distal and collecting tubules, sodium is absorbed by the sodium potassium pump but with a control , This control is the ALDASTERONE LEVEL .

So the present aldosterone secretion in our body is responsible for the sodium reabsorption in collecting and distal duct , and the absent of it, causes the closure in tubules from sodium reabsorption ( in other word , no absorption occur )

Ʊ Now what affects the aldosterone secretion??

sodium concentration >> if we have normal sodium concentration in the blood , aldosterone won’t be secreted ( the blood don’t need any more sodium ) , and if the sodium concentration decreases , it will be secreted , so that sodium will be conserved { or reserved back }

Aldosterone is a yellow steroid hormone . produced by the outer-section (zone of glomerulosa ) of the adrenal cortex in the adrenal gland, and acts on the distal tubules and collecting ducts of the nephrons , the functioning unit of the kidney to cause the conservation of sodium, secretion of potassium, increased water retention, and increased blood pressure. (Wikipedia)

The doctor said that he won’t ask about the details of the mechanism

Ʊ How is aldosterone secreted ?

By : Renin angiotensin system (Renin angiotensin aldosterone system )

Mechanism of Renin angiotensin system .

Renin is the substance that it is secreted in Costa apparatus glomerulus in the kidney controlling GFR

- When we have low concentration of sodium in blood so low conc. In distal tubules and filtrate , The kidney releases Renin , which activate the angiotensin in liver . -The angiotensin will converted into angiotensin1 .

-The angiotensin1 will flow in the blood until it reaches the capillaries and blood circulation of the lung

- There the angiotensin1 will converted to angiotensin2

- At last angiotensin2 will release the aldosterone.

» The affect of aldosterone :

1- constriction of efferent arterioles so increase the GFR 2- increase sodium reabsorption in the kidney

3-increase chloride and water reabsorption ( NACL will follow the sodium , when NACL is absorbed , water will follow the Salt , the water will be reabsorb )

» The RESULT:

1- return back to the normal sodium reabsorption in the blood

2- increase the water volume in the blood so increase the blood pressure ( when we constrict the arteriole)

SO THIS IS HOW THE RNEN SYSTEM CONTROL BLOOD PRESURE &SODUIM CONCENTRATIN IN THE BLOOD .

atrial natriuretic peptide (ANP)

It’s a peptide but it’s a hormone like substance

and it is released from the heart muscle . it has the opposite effect of aldosterone

Ʊ when it releases?

When there is a stretch in the heart muscles .

-that means the blood volume is huge , so the blood pressure high so ANP will be released

» The Affect of ANP:

It will inhibit the sodium and water reabsorption >> (less sodium and water in the blood) >> (so more sodium excreted and water ) , no chloride reabsorption and Less blood volume , so the blood pressure will go down .

Chloride reabsorption is a passive process in whole way

Water reabsorption

-Water is absorbed passively in the whole tubular system

- 65% of water will be free reabsorbed in the proximal tubule ( means no control – no inhibition – no stimulation ) just be osmosis

- 60% of water will be reabsorbed in loop of henle

» Loop of henle

The ascending limb The descending limb

No absorption happens free water reabsorption

( never )

- 20% reaming in the distal and collecting duct .

In the first part of distal tubule , there is no water reabsorption (never ) >>> after that , in the late part of distal tubule and collecting duct , water reabsorption happened depending on hormone called antidiuretic hormone ( البول الدرار مضاد which opens their ( هرمونchannel for water reabsorption

If we have it >> there is water reabsorption, If we don’t have >> No water reabsorption

So we can say that absent of antidiuretic hormoneMakes the distal tubules and collecting ducts works as ascending limb of loop of henle ( no water reabsorption ) , and it is the different .

metabolic waste

Urea – creatinine – phenol - drugs and toxic material All of them metabolic waste that shouldn’t have full capacity for reabsorption .

» LET’S TALK ABOUT EACH OF THEM :

-Urea : when it’s inside the tubular system it is absorbed about 50% , (not as water = 99% - sodium = 99 % - glucose = 100% )

≠ Urea is absorbed because it have a physiological benefit.

-Toxic material : they shouldn’t be reabsorb - creatinine : we don’t absorb it- phenol : we don’t at all ( whatever filter is goes for the Uren )

NOW WE HAVE TO DEFRENCIATE BETWEEN TWO CONCEPTS :

- IN REABSOBTION : we divided the material into :

Very good nutrition (we take it back 100% ) Partially back material Toxic material ( we don’t take them back )

- tubular secretion : it is related to the very very toxic material so we don’t want them to circulate back in our body .

-Examples of those: hydrogen– potassium ( has a special case, not as toxic and very toxic ) - organic material like : penicillin – drugs – food additive – histamine and nor-epinephrine

- We filter them , but we don’t reabsorb them -They are secreted from the peritubular capillary to the tubular system

percentage of secretion in each cycle of blood circulation : Percentage of secretion =

20% (which is the filtrated from glomerulus) + percentage of secreted material from peritubular capillary to the tubular system. (Depends on the material )

» Examples:

-If the material (x) will be secreted extra 10 % and we will lose 20% by filtration SO total secretion will be 30 %

-If the secretion rate is 50% for material (y) , and we will lose 20% filtration SO we will lose 70% in each cycle of blood flow

But if we lose 80% in secretion that means : this material will be lost from ur body from the first cycle of blood flow

» Explanation:

when the blood coming to the kidney , 20% of that material will be filtered not reabsorbed because it’s toxic material , and 80% will follow from peritubular capillary to the tubule , So the sum is 100%

there is only one substance can follow this way : paraaminoheporic acid ( freely filtered – not reabsorbed – completely secreted ) and we can call this : plasma clearness