The kidney and nephron

Overview of how the nephrons in the kidney filter blood and reabsorb water and other molecules.

The kidney and nephron

Discussion and questions for this video
This process seems to involve a lot of functional redundancy. Doesn't that waste energy?
Redundancy is not necessarily bad, what if something fails?
I only have one kidney, so i was wondering if your kidney stops functioning can you tell right away?? And since I was born with one kidney (and since my one kidney is performing like the operation of two kidneys does that mean I have a greater risk for that kidney to stop functioning?) And people can live without a kidney right (if they like go for a few hours a week or so to get their blood cleaned right??)
As Kokomazz mentions, you should talk to your doctor about this. Some things you should know anyway:
What you probably have is called Renal agenesis, which means exactly what you think it means: renal (kidney) a (not/no) genesis (formation/creation). You could easily live the rest of your life with one kidney, but you need to be aware of a few things: First, you are at a higher risk for high blood pressure, which it turn puts you at a higher risk of stroke and heart disease. You need to limit your intake of salt and maintain a healthy weight for your entire life (everyone needs to do these things, but you especially). Check the labels on everything you eat to make sure it is low in sodium and try to exercise frequently. Finally, avoid activities where blunt trauma is possible, since you don't want to hurt your only kidney (so no rugby! :p ).

Have your blood pressure checked regularly and be vigilant with your salt intake. If you do these things, in addition to regular checkups with a doctor, your life will be fine.
respiration. all cells need to respire. everything in are bodies is made out of cells. cells->tissues->organs->organ systems->organism
respiration needs glucose to combine with oxygen to form water carbon dioxide and energy. Energy is needed in our body obviously. Kidneys are also made from cells therefore they must respire. Kidneys are excretory organs.
how big is the actual kidney? and I heard that you can survive with only one kidney, is that possible? if yes, can you tell me how you can survive with only one kidney?
A kidney is about 10-12 centimetres long and weighs 150 grams. Men usually have bigger kidneys then woman.

It is possible to live a long time with just one kidney. Normally kidneys don't work at full capacity. In fact kidneys are made with extra capacity so that the body can keep working if they kidneys are damaged and/or loose some of their filtering ability. When a kidney stops working or is removed the other kidney takes over the work. The nephrons in the remaining kidney actually grow a little in compensation.

However one kidney can never filter as much blood as two can. People with just one kidney there for need be careful with their diet and exercise.
What are the wastes which are actually staying in the filtrate?
actually substances in the glomerular filtrate can be divided into high threshold,low threshold and athreshold substances....high threshold substances are very useful and are to be reabsorbed(like glucose)...low threshold substances are absorbed in very little quantities(like urea(remember that urea is passed into the descending limb to increase the osmolarity of the glomerular filtrate),uric acid)...creatinine etc are the athreshold and are the actual excretory products...
How does the kidney function as part of the immune system? (it's in the Immunology section)
The Kidney helps in osmoregulation and maintains the osmotic pressure of blood which in turn helps in maintaining the immune system.
video 1833 question; where does the fluid go that's in the renal medulla

The only fluid leaving the body is that of which is emptied into the collecting ducts. The osmotic gradient is maintained by the counter-current exchange system of the vasa recta. Essentially the vasa recta is a capillary network in which the blood flows parallel to the loop of henle but the fluid flows in the opposite direction. This allows for reabsorption of fluid and solute without messing with the gradient created.
where does the maximum water re-absorption occur? in which part of the nephron?
Descending loop of Henley is the part of nephron which is highly permeable to water. Osmosis is a passive mechanism of reabsorption water from glomerulus filtrate in the descending loop of Henley.
How does aldosterone work in retaining sodium and water? Does it work on the nephron as well? And where does it do that?
Aldosterone causes the kidneys to retain sodium and to excrete potassium
yes it works in nephron too
Q.1. Do the nephrons carry blood?
Q.2. Is "The Bowman's capsule", a part of another nephron?
Q.3. When Sally uses pink and yellow to demonstrate two different 'nephrons', does the pink nephron also have a bowman's capsule(touching another nephron), a proximal tubule, loop of henle, a distal convoluted tubule and a collecting tubule?
Q.4. Are the bowman's capsule and glomerulus collectively known as "Malphigian body"?
1. The nephron does not carry actual blood in itself. It carries blood filtrate, whatever is able to run through the cells lining the artery and bowman's capsule. The afferent arteriole pumps blood towards the glomerulus, where the blood's high pressure squeezes some substances out into the Bowman's Capsule (amino acids, sodium, glucose, water, but not red blood cells for example). This filtered blood is known as the *filtrate*, not actual blood, and this filtrate is what is carried around the nephron.

2. The "Bowman's capsule" is the part of a nephron which receives the filtrate. It is a part of a nephron, and only delivers filtrate to a single nephron. The afferent artery and efferent artery are *not* nephrons, they are arteries outside the nephron that run around the kidney (the red lines that run around the large kidney diagram to the right).

3. If you're talking about near 11:20, the pink blood vessel is *not* another nephron. That is the blood stream. The nephron _filters sodium and other products that can still be used by the body- such as glucose, animo acids and a little bit of water (only a small bit) back into the blood_. The Proximal Convoluted Tubule is near to another blood vessel, which allows useful substances to be pumped back out of the filtrate back into the blood.

Just to make sure you understand, that pink/orangey structure is *not* a nephron, it is a capillary- a blood stream. Through the thin cell walls, _some_ water, glucose and _some_ salts (as well as any other useful products that might find their way into the filtrate within the nephron), the particles are able to diffuse back into the bloodstream wehre the body can use them more. No point wasting those perfectly good materials!

4. They are collectively known as the Malphigian body, but, in an exam/test, it would be better to list the components rather than the collective name for them- just to show the examiner that you know what you're talking about. The Malphigian body is the name for the initial filtration site in the nephron.

If you have any more questions, just comment them below.
They are aggregates of minerals such as calcium in your kidneys from filtering your blood. They hurt a lot when they are large because that particular pathway is only supposed to handle liquid and very tiny particles instead of relatively large jagged rocks.
The collecting *ducts* are tubes in the kidney that collect filtered urine from the nephrons and carry it to the ureter.
In a healthy person it's around one litre, on average.
Basically,these are located near or in kidneys thats why thay are called "RENAL artery and vein"...Renal is a term when relating to kidneys or involving kidney.

The renal artery branches off from the aorta and brigs oxygenated blood to kidneys from heart..
The renal vein takes deoxygenated blood away from kidneys then to heart((VENA CAVA))...
in the video it was said about collecting duct going back to medulla but no mention of collecting tubule . is it there or is my textbook wrong ?
The collecting duct is the more widely accepted name for the structure but it is also called a collecting tubule. To make things worse, there is also a "connecting" tubule and an initial collecting tubule before the nephron joins with other outputs to become a collecting duct.
Humans do not need two kidneys to live, as one kidney efficiently performs the tasks of both. Much like limbs, eyes, ears, lungs, reproductive parts and the brain, it is possible that kidneys formed as a pair due to symmetrical evolution of the organs. Humans may have adapted to develop two kidneys, due to the vital function provided by the organs, so that if one is destroyed, the body can continue to survive.
Nephrons are small units present in the kidney that filter the wastes
Does anybody know how the kidney plays part in urinary system?
If you know please tell me. Thanks
its the complex in the kidneys where the blood vessels and arteries and kidney filtering system is. it filters the water concentrations and such and pulls wastes from the blood to create urine for excretion.
how much pressure is given on the bowman's capsule? is it more than capillaries or less?
Inside the bowman's capsule, we have a ball of capillaries called the glomerulus, and there is a pressure gradient drawing fluid out of these capillaries into the capsular space. We have the glomerular hydrostatic pressure: the pressure pushing plasma from the capillaries INTO the capsular space, producing filtrate. We also have two opposing pressures that push the filtrate back into the capillaries. These are: capsular hydrostatic pressure and blood colloid osmotic pressure. We consider both of these pressures to calculate the overall pressure gradient. We often refer to this as "Net Filtration Pressure." For normal functioning kidneys, the approximate NFP is ~10 mmHg. That is, we have a net flow of blood plasma into the capsular space. The reason this happens is because the glomerular hydrostatic pressure is larger in magnitude than the combination of the two opposing pressures pushing fluid back in. If you are interested, here are the approximate pressures and the calculation:

(Hg) Glomerular Hydrostatic Pressure (OUT): 55 mmHg
(Pc) Blood Colloid Osmotic Pressure (back IN): 30 mmHg
(Hc) Capsular Hydrostatic Pressure (back IN): 15 mmHg

NFP: Hg - (Pc + Hc): 55 mmHg - (30 mmHg + 15 mmHg)
NFP: 10 mmHg
Is the renal cortex the most outermost layer of kidney.
Is there no protective layer like we have in the heart and the brain?
The kidney is protected by the renal capsule, surrounding renal fat, and Gerota's fascia. All surround the renal cortex and help protect the functioning part of the kidney.
At around 7:30 Sal says only small molecules diffuse into the Bowman's Capsule, but then he includes glucose. Glucose is fairly large, I thought. C 6 H 12 O 6. So does it diffuse through? Or is it only small molecules? Or is glucose a small molecule?
I think in this case, glucose would be considered small in comparison to larger cells like red blood cells or larger polypeptides, etc.
I love this. As a science major, I use all your videos with every science class I take. I would love to see more videos on anatomy and physiology. It would be so helpful while I take these classes but I know its not easy as pie to make these videos. Im really looking forward to the future of Khan Academy.
what happens if we drink more and more water ? it won't keep any pressure on our kidneys?
In a word, yes. Drinking too much water can lead to a condition known as water intoxication and to a related problem resulting from the dilution of sodium in the body, hyponatremia. Water intoxication is most commonly seen in infants under six months of age and sometimes in athletes. A baby can get water intoxication as a result of drinking several bottles of water a day or from drinking infant formula that has been diluted too much. Athletes can also suffer from water intoxication. Athletes sweat heavily, losing both water and electrolytes. Water intoxication and hyponatremia result when a dehydrated person drinks too much water without the accompanying electrolytes.
How do the concentrations compare before and after the filtrate passes through the Loop of Henle? It seems water removed from the filtrate while descending the loop and ions are removed ascending the loop. How much of each is removed during each direction relative to the other?
At the end of the proximal tubule, about 2/3 of your filtrate has been reabsorbed, including water, sodium, chloride, and calcium. Certain solutes have been reabsorbed completely, like bicarbonate and glucose or amino acids.

The descending loop of Henle reabsorbs 15% of the filtrate as water, so tubular fluid volume decreases and osmolarity increases. In the ascending limb, there is no change in volume, but osmolarity decreases below normal plasma concentrations, first in thin ascending permeable to Na and Cl, and then through the Na/Cl/K symport and Na/H antiport in apical side of the thick ascending limb.

Fine adjustments are made by the distal convoluted tubule and collecting duct under the direction of aldosterone and ADH.
Could someone explain a little about the renal artery and the renal vein? Are the renal arterial capillaries the only blood vessels that are filtered by the nephron?
In a way the renal arteries are, but all blood vessels share the same blood...
If you only have one kidney, how big is the difference compared to a person with two kidneys?
No, the kidneys are organs, so they receive oxygenated blood and return deoxygenated blood to the heart via the renal vein.
what happens in cholera to the person? is it related to the kidney?
Cholera is an acute, diarrheal illness caused by infection of the intestine with the bacterium Vibrio cholerae. The infection is often mild or without symptoms, but sometimes it can be severe. Approximately one in 20 infected persons has severe disease characterized by profuse watery diarrhea, vomiting, and leg cramps. In these persons, rapid loss of body fluids leads to dehydration and shock. Without treatment, death can occur within hours.

A person may get cholera by drinking water or eating food contaminated with the cholera bacterium. In an epidemic, the source of the contamination is usually the feces of an infected person. The disease can spread rapidly in areas with inadequate treatment of sewage and drinking water.

The cholera bacterium may also live in the environment in brackish rivers and coastal waters. Shellfish eaten raw have been a source of cholera, and a few persons in the United States have contracted cholera after eating raw or undercooked shellfish from the Gulf of Mexico. The disease is not likely to spread directly from one person to another; therefore, casual contact with an infected person is not a risk for becoming ill.
What happens to the water which is pumped out in the medulla? How is the water used again by the body if it is in the medulla?
The process of osmosis is a dynamic one, and in the assumption of an ideal kidney, it is also under equilibrium What this means is that once the requisite concentratins gradients are set up, as much water is pumped out into the medulla at some place as much water enters from the medulla at some other place. The amount in medulla is fixed and there is no further *net* transfer of water.
I've never known but.. I'm curious, is your liver, your "Stomach"?
(Just curious, please do not just answer yes or no, I'd like an explanation, please, thank you!)
There is actually an organ called the stomach, and it is where the food you eat goes before the intestines. The liver, is, however involved, as it does produce/store enzymes that go into the stomach to help break down food.
What if someone has a stone in the kidney? How to remove it without an operation? Is there any way to remove it by doing some type of home remedy?
One the ways to remove the stone is to keep drinking water. Without water there will be no Liquid in the guitex. The stone will then just come out after going to the toilet
Those nephrons are really small. If it leads into the urinary tract, then how would someone possibly get a kidney stone? 2:45
Kidney stones are very tiny. They form from minerals in your diet that crystallize out of the fluid solution passed through the kidneys.
This might be more of a chemistry question, but I was wondering if anyone could answer it. At 13:10, Sal describes how the Loop of Henle pumps out salts, and then describes salts including sodium ions, potassium ions and chloride ions. I was puzzled by this, as I'd only have described Na+ and NaCl as salts. What exactly constitutes a salt?
A salt is any alkali/alkaline metal that is ionically paired with its counter part halide/halogen on the other side of the periodic table. NaCl is but one of the many possible combinations ranging from CaO to NaF.

*Pysiologically*, salts do thier work as ions of Ca+2,Na+,F- etc.
i really love this site but i find it annoying that it's only the American curriculum :/ Sal said in interviews he wants to spread this worldwide and i know it takes time but is there a chance it'll be soon?
Does anyone know if there is a digestive system video on Khan Academy? Just wondering.
in "crash course: Biology" there appears to be a video of the type you are looking for.
So if you accidentally drink pool water with alot of chlorine, alot of it will be filtered in our kidney?
You would get sick and may die but ONLY IF you drank it out of the bottle, not in a pool.
i hope ur not planning on doing that...
Can any one relate the structure of kidney with its function?Like why kideny is bean shaped or have renal pyramids in pyramids shape?
The blood full with renal waste comes to the glomerulus section and gets ultrafiltrated.Then goes to the body again.So golmerulus works as a filter
Could anyone explain why is the descending part only permeable for water and ascending only for salt? Wouldn't it be easier if the kidney first pumps out salts and then water, since the length the water would be pumped out would be approximately the same. Kill two birds with one stone...
Thanks in advance! :)
Can you please make a detailed video on kidney and on gcse biology (b3) physics (p3) and chemistry (c3) chapters biology contains active transport,osmosis, diffusion, kidney function and fake kidneys. and there is no detialed explanation on any of them. Also i would suggest making a GCSE/and O'level, ASlevel/Colloge science section for us all
In the ascending loop of henle K+ is actively filtered out. Then why is it reabsorbed in the distal convoluted tubule?
Also, it is reabsorbed since K+ is a nutrient that our body somehow needs. Though it varies depending on our diet or diagnosis.
Without at least one functional kidney, your body can't perform several functions, like 'filtering' your blood, for example. There are two main options for people: kidney transplants, or the use of a dialysis machine, an external machine that tries to perform the function of a kidney for you.
if glucose gets selectively reabsorbed from the ultra filtrate,why is glucose found in the urine of diabetic patients?
Diabetics have high glucose values because the insulin is not working properly or there is not enough of it (type I or II depending). As a result, the body cannot convert the glucose to a smaller molecule or store it as glycogen. The kidney tries to filter it, but after a while, glucose (large molecules) damages the kidney filtration system and still gets trough.
Sal says that proteins are not filtrated in the Bowman's Capsule. But, in my textbook it says that they are filtrated, thanks to diffusion (passive transport), since there are actually no proteins in the Capsule. Can someone clarify this for me, please? :)
Sal says that the LARGER proteins are not filtered. Simply put, only amino acids and protein chains that are small enough to diffuse through the membrane will become part of the filtrate.
Larger proteins shouldn't pass through unless the membrane between the Bowman's Capsule and the Glomerulus is damaged--which can happen for example if the pressure in the Bowman's Capsule exceeds that of the Glomerulus.

That's why it's not a good idea to "hold it in" for too long.
Our kidneys excrete waste, regulate blood pressure, regulate extracellular fluid volume, regulate osmolality (solvents/plasma), regulate pH, make EPO (hormone responsible for making new red blood cells) and "activate" vitamine-D
Medulla is Latin for pith or marrow, which derives from the Latin word medius, which means middle. Medulla in modern times refers to the inner region of a structure, like adrenal medulla.

The medulla was called the marrow because it was the portion of the hindbrain continuous with the spinal cord. The marrow is probably in reference to the spinal cord, which is the soft-spongy tissue within the vertebral column.

(In case you were wondering, myelin is the greek word for marrow.)
Will salt move out of the nephron by diffusion since it's moving from a high concentration to a low concentration?
The job of the loop of Henle is to make the tissue fluid in the medulla hypertonic compared to the filtrate in the nephron, i.e. plays an important role in osmoregulation.
The first part of the loop (the descending limb) is impermeable to ions, but some water leaves by osmosis.
The second part of the loop (the ascending limb) contains a Na+ ( and a Cl-) pump, so these ions are actively pumped out of the filtrate into the surrounding tissue fluid.
Water would follow by osmosis, but it can't, because the ascending limb is impermeable to water.
So the tissue fluid becomes more salty (hypertonic) and the filtrate becomes less salty (hypotonic).
Water is therefore reabsorbed from the distal convoluted tubule and the collecting duct.
The amount of water reabsorbed is controlled by ADH (anti diuretic hormone).
Secretion of Na+ and Cl- is controlled by the hormone aldosterone secreted from the adrenal cortex.
I know that is doesn't exactly answer your question, but I hope that it helps!
The kidney consist of functional units called "nephrons". A glomerulus is a part of the nephron and is responsible for the filtartion of the blood. Through a mesh built from special cells only water and small molecules (but not the blood cells) are filtered. This is the primary urine which gets concentrated further down the nephron.
If glucose concentration is high in blood, wouldn't less water be diffused out from glomerulus to Bowmans capsule? Therefore, less urine? I mean, high glucose concentration means high osmolarity which will eventually wants to draw in fluid.. the book says the opposite: high glucose concentration in blood will cause increase in urine excretion. I'm so confused. Can someone please answer? I'm sorry if I'm not making any sense.. I'm so confused!!
The first step in urine production is some type of pressure filtration, not a plain diffusion. The blood pressure squeezes a constant amount of very thin urine through the Bowman's capsule which is later concentrated by taking the water back.
Glucose itself cannot be filtered, it is too small and has to be recovered actively from the urine later not to be lost. So a constant part of your blood sugar goes into the urine first, but if you have very, very high blood sugar (like in diabetes) then not all glucose can be recovered. It stays in the urine and keeps the extra water from being resorbed (high osmolarity in the urine), so you loose sugar and extra water together.
Sugar is an important form of energy in the body. The kidney filters your blood to remove toxins, but if it didn't allow your body to retain sugars, you would need to eat much much more to survive, and would be wasting tons of energy.
Yes, very much indeed! The kidneys are powerful chemical factories that perform the following functions:

1) Remove waste products from the body
2) Remove drugs from the body
3) Balance the body's fluids
4) Release hormones that regulate blood pressure
5) Produce an active form of vitamin D that promotes strong, healthy bones
6) Control the production of red blood cells

All parts of the body are uniquely important due to the parts they play.
Information provided by The National Kidney Foundation. Visit their website at
iam confused, if we have high fever we feel to cold but the other person who toches
us says that our body is hot esspicially in our neck & for head . how ??
This is actually a very nice question. The answer lies in the physiological response of our body. In order to maintain the homeostasis or in other words the balance of the body. Say if you get an infection, by a bacteria. This bacteria has entered in the body. So, immediately our immune system will detect this bacteria and the main cells involved are macrophages. So, what these cells will do is they will secrete chemical substances known as pyrogens inorder to kill this bacteria. These pyrogens will go the the hypothalamus which is like a Central Processing Unit of the brain. The main function of hypothalamus is to maintain a particular temperature of the body. In other words it is like a thermostat fixed in your room's air conditioner or heater. So, normally, the hypothalamus maintains or sets the bodies temperature to 37 degree Celsius. Now, when macrophage releases pyrogens due to bacteria infections, these pyrogens go to the hypothalamus and resets the body temperature to say below 37 degree Celsius. So now what will happen is with this new reduced temperature as compared to the previous one, our body will think that its cold outside that's why the body's internal temperature has fallen down, so we will start to feel cold. Now in response to this cold condition, and also to maintain the homeostasis, out body will start to increase the temperature and thus the body temperature starts to rise and it rises even more than 37 degree Celsius so as to counter act the cold conditions (which it has created on it own). Thus now if any one who touches us will feel that we are hot because our internal body temperature is increasing slowly and we will feel cold because our normal body temperature has been reset to below 37 degree Celsius. Remember, the temperature of the body actually decreases due to the actions of the pyrogen and it is set to a lower value so that the body recognizes that the outside conditions are cool and thus the internal temperature begins to rise, this whole condition is just a pre-planned strategy so as to kill the invading bacteria via increase in the internal temperature of the body. Its like a simple microbiology exercise that you heat things to decontaminate to to kill the bacteria present in it. I hope that's helpful. :)
Actually the answer to this simple question is a complicated one. For understanding this you must recall that the body is made up of individual cells and these cells have mitochondria which is the power house of the cell. Inside the mitochondria we make ATP aka "the energy currency of the cell". So, in the process of breakdown of glucose and formation of ATP, the carbon skeleton of glucose molecule is broken down and these carbons are released as carbon oxide. Also, in the same process we make energy rich intermediates like NAD and NADH which pass their electrons in the electron transport chain, and finally these electrons are accepted by the "terminal electron acceptor" i.e. oxygen. Thus, after accepting these electrons it gets reduced to water. Thus to summarize, cellular respiration makes carbon dioxide and water as waste products which we release as we exhale the air, in a process called breathing. Thus this exhaled breath is mixed up of water and CO2 which are the metabolic waste products. Thus, when we exhale our breath on window panes or glassy surfaces, our breath forms a mist because it has water and CO2 present in it. I hope that's clear. :)
Are both the kidneys in our body same in size or do they differ?
The left kidney is slightly larger than the right
also the right one is lower than the left to accommodate the liver
Peritoneal cavity is the abdominal space where all the organs such as stomach, intestine, kidney, spleen, liver, reproductive organs, are suspended. It occupies the space below the diaphragm.
The bowman's capsule is the place where the filtrate is collected from the blood.
Just out of curiosity, how long could you live if both kidneys shut down?
And how many cycles can glucose and amino acids etc. be reabsorbed during the passage through the proximal convoluted tubule before leaving the body?
Thanks in advance.
A couple of weeks would be the maximum life expectancy.
i have a question regarding the capillaries and vessels,
that why arterioles they r changed to capillaries..??
do this change of vessels have any effect on filtration...??
do answer :)
Arterioles change into capillaries because capillaries have epithelial walls that are only 1 cell thick and these walls allow for efficient transfer of blood between the capillaries, the interstitial fluid, and the tissues they are replenishing. Arterioles are larger, and have muscular walls that would prevent such exchange from happening efficiently. As for your second question, filtration is possible because of the ability of a capillary to exchange blood with the basement membrane of the Bowman's capsule.
Sodium and Potassium are important ions especially for neurons and other excitable cells. These cells use the concentrations of these ions to create tiny electrical currents that travel down our nerves. Without these ions, the electrical currents could not be generated and your nerves would stop functioning, leading to a whole assortment of problems.
At 15:47 Sal says that the Distal Convulated Tubule passes very close to the Bowman's Capsule
But distal means at a distance and so it must be moving away from the Bowman's Capsule.??
So basically from where does that tubule pass from?
The distal convoluted tubule is distant from where the tube starts (Bowman's capsule) but travels a fair distance away as the loop of Henle before coming back and passing close to the capsule again.
Is there any specific reason why urine/glomerular filtrate is usually yellow? Is it due to the urea? (Or is urea colourless?)
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