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Lesson Video: Kidney Failure Biology

In this video, we will learn how to describe and evaluate the treatments for kidney failure.

13:16

Video Transcript

In this video, we will learn about the causes and symptoms of kidney failure. We’ll compare and contrast the costs and benefits of kidney transplant and kidney dialysis. And we’ll investigate how kidney dialysis works.

Your kidneys are fist-sized, bean-shaped organs found near the bottom of the rib cage on either side of the spine. Our kidneys have the excretory function of producing urine. Urine production is essential to allowing our bodies to maintain homeostasis or a constant, normal, internal environment. Our kidneys are so important that they’re one of the few internal organs that comes in a pair, which is super lucky for us since a healthy human can survive with just one properly functioning kidney.

Kidneys produce urine by filtering our blood. A properly functioning kidney maintains the perfect balance of ions, also called salts or minerals, and water in the bloodstream. They also remove soluble waste products like urea. But when our kidneys stop functioning properly due to acute or chronic disease, our blood does not get filtered properly, and homeostasis is disrupted. Water and ions become imbalanced, and waste like urea build up in the blood. This condition is known as kidney failure, and it can quickly lead to serious illness and death.

This diagram shows a simplified cross section of the kidney. Our kidneys are incredibly hardworking organs. They’re able to instantly and constantly adjust to the changing conditions in our bodies and help to maintain homeostasis. This is achieved through the action of the nephrons, shown here, which are microscopic structures that make urine. This diagram is quite simplified. The nephron is a complicated structure made up of blood vessels and of tubules.

When blood enters the nephron, almost all of the small molecules are filtered out of the bloodstream. This includes water, ions, glucose, and soluble wastes, but not the cells or the proteins. Then all of the useful materials are reabsorbed back into the bloodstream. This includes all of the glucose, just the right amount of ions, and nearly all of the water. The wastes, ions, and water that is left behind is excreted in the form of urine. There are about a million tiny nephrons inside of each kidney. At any given moment, our kidneys contain about a fifth of our total blood volume. When an individual’s kidneys fail, their complex function is extremely hard to replace.

Kidney failure occurs when the kidneys stop functioning properly and blood doesn’t get filtered like it should. When the function of the kidneys has dropped to 15 percent or less of their typical function, a patient is said to be an ESRD, or end-stage renal disease, also called kidney failure. Some symptoms that usually go along with decreased kidney function include swelling or edema in the extremities, a change in the quantity or quality of urine, change in appetite, or fatigue, as well as frequent muscle cramps.

The two most common causes of ESRD or kidney failure are high blood pressure and diabetes. Other risk factors include use of drugs, alcohol, or tobacco, a family history of chronic kidney disease, and other kidney and neurological conditions like glomerulonephritis, which is inflammation of the nephrons of the kidney.

There are two possible treatments for kidney failure. One is a kidney transplant, and the other is a treatment called kidney dialysis or renal dialysis. Renal is a word that means related to the kidneys. Kidney transplant is the less common treatment because it can only be done if a kidney becomes available from a donor. It’s a more long-term solution that greatly improves the quality of life for the patient, so it’s generally preferred. While kidney and dialysis is more common, it’s a less permanent solution, and it can be more costly over time. Let’s take a closer look at each of these two treatment options next.

A kidney transplant is when the kidney of a recently deceased person or of a living donor is removed and implanted into the body of a patient with kidney failure. Kidney transplant may seem like the perfect solution, but there are serious risks and drawbacks to the procedure. The transplanted kidney can be rejected by the patient’s body. This means that the patient’s immune system starts to attack the donor kidney like it’s a foreign invader. In these cases, the patient must take immunosuppressant drugs for the rest of their lives. Immunosuppressants suppress or decrease the overall activity of the immune system. These drugs may protect the new kidney, but they also leave the patient vulnerable to infections.

The other drawback to kidney transplant as a treatment for kidney failure is that there simply aren’t enough spare kidneys to go around. Patients with kidney failure may spend their entire life waiting for the right kidney to become available. In the meantime, the function of the kidney can be replaced by a treatment known as dialysis.

In kidney dialysis, an external mechanism is used to filter the blood in place of the kidneys. A dialysis machine controls the flow of blood and fluids through something called a dialyzer, which is also known as an artificial kidney. During dialysis, the patient is hooked up to the dialyzer through two needles inserted into the patient’s blood vessels. Blood flows out of the patient’s body and into the dialyzer where it is filtered and balanced. Then the blood is pumped back into the patient.

Let’s take a closer look. Within the dialyzer, there’s a network of tubing. The tubing is semipermeable, meaning that small molecules can pass through freely while larger molecules and cells cannot. The patient’s blood flows inside of the tubing, and a specialized fluid called dialysis fluid or dialysate flows outside of the tubing. The dialysis fluid contains most of the things found in healthy blood plasma. This includes the right balance of water and ions and no metabolic wastes like urea.

Recall that diffusion is the natural tendency of molecules to move from areas of high concentration to areas of low concentration. This means that if the concentration of ions in the blood is higher than in the dialysis fluid, the ions will flow out of the patient’s blood through the semipermeable tubing and into the dialysis fluid. If the concentration of water is higher in the dialysis fluid than in the patient’s blood, then water will flow from the dialysis fluid through the semipermeable tubing and into the patient’s blood. Since there’s no urea in the dialysis fluid, all of the urea will flow out of the patient’s blood through the semipermeable tubing and into the dialysis fluid. In this way, water and ion balance in the blood is restored , and all of the wastes are removed. Sometimes glucose is present in the dialysis fluid. This prevents the patient from losing too much glucose through diffusion during dialysis.

In a typical dialysis session, about two to four liters of blood are completely filtered. In order to effectively restore balance to this blood, a constant fresh supply of dialysis fluid must be pumped through the dialyzer. The dialysis fluid is pumped through the dialyzer in the opposite direction that the blood is being pumped. This arrangement is known as countercurrent, and it maintains a steep concentration gradient along the length of the dialysis tubing so that the blood filters more effectively.

There are several drawbacks to dialysis as a treatment for kidney failure. A kidney can maintain homeostasis constantly, but dialysis is only working when the patient is attached to a renal dialysis machine. Patients must go to a hospital or a dialysis center several times a week for four to six hours at a time for treatment. Dialysis patients also must eat a severely restricted diet in order to limit the build up of wastes and ions between treatments. Dialysis is not a permanent solution for kidney failure and cannot be used indefinitely. Dialysis patients will eventually need a kidney transplant.

Now that we’ve learned about kidney failure, its causes, symptoms, and treatments, let’s try a practice question.

If the kidneys do not function properly, some substances will not be removed from the body. Which waste substance would you expect to build up in the blood of someone with kidney failure? (A) Urea, (B) carbon dioxide, (C) glucose, (D) dead red blood cells, or (E) bile.

The kidneys are organs that filter waste from the blood. This question lists several substances and then asks us which of them is a waste substance that we would expect to find built up in the blood of someone who has kidney failure. The kidneys are two fist-sized, bean-shaped organs found near the base of the rib cage on either side of the spine. The kidneys are organs in the urinary system, and they’re responsible for producing urine.

Urine is a light-yellow-to-amber-colored liquid that contains water, ions, and soluble waste products such as urea. When our kidneys fail, urine is less efficiently produced, which means that the waste products found in urine, such as urea, are likely to build up in the blood. So the waste substance that you would expect to build up in the blood of someone with kidney failure is urea.

Let’s take a moment to wrap up our lesson by reviewing what we’ve learned. Kidney failure or end-stage renal disease occurs when the kidney function drops to below 15 percent of normal. There are two possible treatments for kidney failure. One is kidney transplant, in which a donor kidney is implanted into the patient. And the other is kidney dialysis, in which the blood is filtered using a dialyzer.

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