The Kidneys

Urine for a Great Time!!!
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Waste removal
Several organs are important in removing waste from the body.
The lungs remove
carbon dioxide.
The skin provides
a surface for small
amounts of water
and salt to move
out of the body.
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The liver
converts excess
protein into urea.
The kidneys
remove unwanted
substances such
as urea, excess
water and salt.
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What is urea?
Excess amino acids in the body are
broken down by the liver, producing
a waste substance called urea.
This process is important because
it converts toxic ammonia to urea,
which is done using carbon dioxide.
Once formed, urea is transported by the
circulatory system to the kidneys.
The kidneys filter the blood, removing
urea and excess water and salt, which
forms urine. Urine is stored in the bladder
before being excreted from the body.
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What are the different parts of a kidney?
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How does the kidney work?
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Stages in the nephron
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Controlling water levels
Osmoregulation is the process by which organisms
regulate the water content of the body.
Mammals need to ensure the volume of blood plasma
and concentration of dissolved substances in the blood
and tissue fluid stay relatively constant.
Osmoreceptors in the hypothalamus
monitor the water potential of the blood.
This varies the amount of antidiuretic
hormone (ADH) released into the
bloodstream. The kidneys respond to a
change in ADH concentration by adjusting
the volume and concentration of the urine.
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change detected by
osmoreceptors in the
decrease in
water potential
increase in
water potential
change detected by
osmoreceptors in the
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pituitary gland
releases more ADH
must conserve
normal water
potential of
must expel
excess water
ADH increases
permeability of
collecting ducts
concentrated urine
dilute urine
decrease in
permeability of
collecting ducts
pituitary gland
releases less ADH
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Controlling water content
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Analysing urine
Changes in the color, clarity, pH and the presence of certain
substances in urine can help doctors diagnose medical
 Protein or red blood cells in
urine can indicate kidney
damage or disease, as these
substances would not normally
filter through the glomerulus.
 Glucose in urine is often an
indication of diabetes. A person
with diabetes will have a high
level of glucose in the blood.
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What happens if the kidneys fail?
Humans can survive with just one functioning kidney. If both
kidneys become diseased or damaged, it can be fatal.
Kidney failure can occur
due to infection, diabetes,
long-term high blood
pressure or damage in an
accident. If left untreated,
urea and other toxins can
build up in the blood,
poisoning the patient.
To counteract this, people with kidney failure can undergo
regular kidney dialysis, or receive a kidney transplant.
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What is dialysis?
Dialysis involves diverting the blood through an 'artificial
kidney' machine that cleans it and returns it to the body.
What happens during kidney dialysis?
1. A tube is connected to a vein
in the patient’s arm.
2. The patient’s blood flows along
the tube, into the machine.
3. Inside the machine, the blood is pumped through semipermeable tubes surrounded by dialysis fluid. Dialysis
fluid contains sodium, magnesium, calcium chloride and
potassium chloride and sodium acetate, in the same
concentrations as the blood plasma of a healthy person.
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Dialysis machine
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Disadvantages of dialysis
It is difficult to control the
diffusion of substances in a
dialysis machine as well as in
a kidney so people on dialysis
often have to carefully control
their fluid intake and diet.
Dialysis can involve a patient
going to hospital up to three
times a week and being
connected up to the dialyser
for about four hours at a time.
This could have a large
impact on a person’s lifestyle.
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What is a kidney transplant?
Kidney failure can also be treated by giving a patient a kidney
transplant. This involves replacing the damaged kidney with
a healthy kidney from a donor.
Healthy organs can come from a living or recently deceased
person. Living donors are often close friends or relatives of
the patient.
In the US there is an organ donor
register. By joining this people agree to
the donation of their organs and tissue
for transplantation after their death.
Other organs and tissues that can be
donated include blood, bone marrow,
heart, lungs and cornea.
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Kidney transplant data
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Preventing organ rejection
All cells contain markers on the surface, called antigens.
These help the immune system identify a cell as a cell
from the body or a foreign cell.
If the immune system detects a transplanted organ as a foreign
object, it may mount an immune response against it. This is
called organ rejection. Several steps are taken to prevent this:
 A donor kidney of a similar ‘tissue type’ as the patient, is
used. This means that the antigens on the new organ will
be as similar as possible to those of the patient.
 Before and after a transplant operation, a patient takes
immunosuppressant drugs. These drugs inhibit the
activity of the immune system.
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Problems relating to transplants
A kidney transplant can give a patient a better quality of life,
as it provides freedom from dialysis.
However, a transplant operation
can put the body under a lot of
strain and there is potential for
problems related to surgery.
Immunosuppressant drugs lower a
patients resistance to infection and
can make infections hard to treat.
Blood tests are regularly carried out to make sure that
the organ is functioning and to monitor the effect of the
immunosuppressant drugs.
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What do you think?
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Labelling the kidney
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