You know when a medical student explore medicine he tries to explore and learn more about the brain , heart , muscles and bones but only few among them hardly tries an forgotten organ named -"Kidney" . People usually find this organ and renal system as less useful and hardly tries to understand this and just read this for passing their exams but it is not so , In the upcoming article we will be learning and exploring the world of kidneys (physiology , some part of pathology and some parts of pharmacology too.)
This article is purely focussed on the basic functions of renal system .
So to introduce renal system , I will be talking about the functions of the kidneys...
Note:- Article may look a bit lengthy inspite of the fact that i am only talking about function of kidneys but i will be talking about them in great detail...
Let's start:-
Function of kidneys:-
There are hell lot of functions of kidneys so i will be dividing them in 4 categories and we will explore each category one by one in great detail
- Excretory functions.
- Regulatory functions.
- Endocrine functions.
- Metabolic functions.
Excretory Functions :-
Well we all are aware that the renal system is the excretory system of our body and it excretes out the waste material out from our body.
Here is a question for you :- Can you name same of the waste material that is excreted out by the kidneys... I want you think and try to remember which are the waste material which the kidney secretes?
The most common waste products secreted by the kidneys are
- Urea
- Creatinine
- Drugs and hormones
- Toxic substance (some of them)
1:- let's talk about Urea , you know humans are ureotelic and our body convert the toxic ammonia gas obtained from various metabolic reactions into urea and that urea is excreted out in the urine.
Note:- Serum urea level tests are diagnostic tests for kidney functioning , Elevated serum urea level indicates improper functioning of kidneys.
2:- let's talk about Creatinine now , for those who does not know about the creatinine or what it is ?
Let me introduce you to creatinine . Creatinine is an molecule made up of 3 amino acids , it is not a essential nutrient as body can produce it via methionine, glycine and arginine amino acids
Creatinine is generally found in muscles and brain and used as energy reservior in these organs . you know when you are extensively using your muscles and ATP supply gets limited , for such condition our muscles have a chemical compound called - creatinine monophosphate , whenever the ATP use in muscle is increased and it overtakes the ATP production in muscles mitochondria , at that moment creatinine monophosphate donate their phosphate group to ADP producing ATP instantly and thus providing a continous chain of supply of ATP until all the creatinine monophosphate gets depleted in the muscles and when all the creatinine monophosphates are dephosphorylated , that is the point where muscle switch to anaerobic respiration
So in short Creatinine is like an invertor for muscle providing a continous flow of energy to muscles when muscle are performing heavy tasks (like vigrous exercise, weight lifting , brutual fighting)
So let me link more about creatinine in your life :- more you exercise, more are the mitochondria in your muscles and creatinine stores get utilised much later as you have a lot of mitochondria and higher the creatinine levels in your muscle , muscle will involve the anaerobic respiration for energy production much later it means larger amount of creatinine monophosphate stores in your muscle me
Clinical relation of creatinine and renal diseases :-
Let me tell you that the body builders and athletes often take creatinine as nutritional supplement to enchance their performance in the games.
see below :-
Well taking creatinine is not a bad thing at all and several researches also proved that taking creatinine does boost up muscles and brain performance under heavy tasks as compared to those who are not taking it as supplement .
Clinical relevance.
Well everything has its advantages and its disadvantages too so the main disadvantage of taking creatinine as supplement is that, it can actually burden up your kidneys a lot,Now you know why , because kidneys filters and excrete out the creatinine from the blood and if there is lot of creatinine , kidneys need to work much harder and this puts your kidney at a higher risk
Note :- Serum creatinine levels are also tested for diagnosis of proper kidney function
So both the Creatinine and serum urea levels are being tested for kidney functioning but which one is the best and more accurate test for relating kidney functioning ??
It is Creatinine test which is more important and related more specifically for the kidney functioning although both test can be used to assess kidney function but urea level get increased easily in other conditions too(like heavy protein diet, dehydration) while on the other hand Creatinine level in the blood are not usually increased and their increase usually point towards kidney dysfunction
3:- let's talk about Drugs and hormones now.
Let me ask you a very basic question now
The drugs we take in our daily life, do they stay forever in our body, Obviously it does not.
Thank god, that does not happen if it would have happened our body would have become walking jar of medicines
So where does these drugs go? If they do not stay forever in our body how they are thrown out of the body
Actually there is a process called Biotransformation of drugs, ever heared about it?
Also popularly read under the topic - "Metabolism of Xenobiotics", the actual process of Biotransformation is quite lengthy and is covered under pharmacology basic concepts and some of its aspects are also discussed in biochemistry
That is not our topic today, what j want you to notice is, that both the liver and kidney are involved in throwing out the drugs from our body
Drugs undergo Biotransformation in the liver by 2 step reaction (includes conjugation reactions ) and then the conjugated polar substance is secreted out from the body either by the heaptobilloary system and finally through faeces or the conjugated polar product from liver can enter in blood and ultimately get secreted by the kidneys in the urine as waste product
Same things happens with the hormones too. Think yourself hormones which are secreted by the glands, do they remain in our body forever
Answer is obviously no, but again the question is where do they go? and again the answer is that they also undergoes the Biotransformation reaction and secreted out of body either via faeces or by the kidney in urine.
Evolutionary link
so let me ask you an another question about 1 million years ago there were no drugs then why did our liver evolved these biotransformation mechanism ?
Actually the answer is the biotransformation is not just for the drugs but it is for many hormones , xenobiotics and also for many toxins and about a million years ago altohough drugs were not there but these substances were there so liver evolved more complex and efficient mechanism of biotransformation
Clinical relevance
the clinical thing regarding this is, that you have to remember what will happen to a person of chronic renal failure ?
If kidneys are not functioning properly than accumulation of toxins and harmful substance will be started although liver will try his best to counteract but still not be able to match kidney efficiency, so the patient will be having a problem in excreting these drugs and hormones out of the body .
4:- Certain toxins are also secreted by the kidneys except anesthetic gases which are secreted out by our lungs.
Regulatory functions
Kidney regulates amount of various substances and maintain a proper concentration of those in your blood some of the material which are regulated by the kidneys are :-
- water
- Electrolytes
- Acid base balance
1:- No doubt, water content is maintained by kidney very efficiently and kidney just maintains the right amount of water for proper functioning of the body system , Extra excretion of water outside can cause problem like dehydration and under-excretion of water may cause overhydration in the body which will cause other protein to become diluted and may cause edema and other harmful complication and may even cause death (water poisoning or water intoxication)
2:- Electrolytes , Kidneys play major role in homeostasis of various electrolytes in your plasma , they work every second just to maintain the right amount of elctrolyte in your plasma. some of the most common electrolyte are Na+ ,k+,Cl-,Ca+2 .
Normal ranges
1:- Na+ =135-145 mEq/L.
2:-K+ = 3.5-5.5 mEq/L.
3:-Cl- =about 100 mEq/L.
4:-Ca+2=near about 2.5 mEq/L.
Clinical Relevance:-
The amount of potassium needs to be regulated super precisely in our body even more than the sodium as slightly wrong fluctuation in our body can lead to cardiac tachy-arrythmia and may cause death of the individual although all the electrolytes need to be regulated.
3:- Acid base balance is also maintained by kidneys and problem in the kidney can lead to alkalosis and acidosis
Endocrine Functions:-
So what are the hormones that kidney secretes ?
They are :-
- Erythropoietin
- Renin
- Prostaglandin
1:- Erythropoietin , secreted by Endothelial cells of peritubular capillaries regulates erythropoiesis by acting on bone marrow
Clinical relevance :- Chronic renal failure causes Severe anemia in the patients due to deficiency of erythropoietin and patients are given genetically engineered Erythropoietin injection to counter this severe anemia.
2:- Renin, Secreted by Juxtaglomerular cells of JGA
3:- Prostaglandins - Released by the kidneys are vasodilators for the vessels with in the kidneys to maintain blood flow.
Metabolic functions
Kidneys are involved in production of active vitamin D . 25 hydroxy chole-calciferol that kidney recieves from liver get hydroxylated again in kidneys by alpha-hydroxylases enzyme with in the kidneys to produce -"1,25 dihydroxy chole-calciferol" active form of vitamin D.
Clinical Relevance
Patient with chronic kidney failure also suffer from low calcium level and weak bones , even the parathyroid hormones shots in their blood are unable to increase the calcium level in the body as the active form of vitamin D is not getting synthesized.
This is all about the kidney functions , i hope that now you will be having a very clear idea about function of kidneys and complication that kidney failure can generate .
That,s all from my side.
Signing off----
Bhavesh saini (student from KCGMC,Karnal)
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