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.