Provided Courtesy of Nutrition411.com
Kidneys: What Your Kidneys
Do for You
Contributed by Elaine M. Koontz, RD, LD/N
Review Date 8/13
R-0626
What Your Kidneys Do
for You
• Remove waste from the body (urea and
ammonia)
• Remove drugs from the body
• Balance the body’s fluids
• Regulate electrolyte levels in the body
• Regulate blood pressure
• Promote strong, healthy bones
• Control the production of red blood cells
• Reabsorb glucose and amino acids
Kidneys
and Homeostasis
• The kidneys need to react appropriately to your
condition
• The kidneys have a tough job, for example:
– If you are dehydrated, the kidneys put less water in
the urine
– If your blood is acidic, the kidneys remove more acid
from the urine
– If your potassium level gets too high, the kidneys
remove more potassium from the urine
Kidney Anatomy
• Two kidneys, each the size of a fist, are located
at the lowest level of the rib cage, near the
middle of the back
• Each kidney contains roughly a million nephrons
• Each nephron contains tiny blood vessels known
as the glomerulus, which is attached to a tubule
• Blood enters the kidneys from the liver
Kidney Anatomy (cont’d)
• Blood enters the glomerulus, where it is filtered:
– Normal proteins and cells are kept in the bloodstream
– Extra fluids and waste pass through the tubule
• In the tubule, chemicals and water are either
added or removed, and eventually are excreted
as urine
Kidney Anatomy (cont’d)
• The ureters are muscular tubes attached to the
kidneys that carry urine to the bladder
• Roughly 200 quarts of fluid are filtered every day
• 2 quarts of waste products and extra water are
sifted out
Waste
• The waste that the kidneys filter out comes from
the normal breakdown of tissues, such as
muscle, and from food
• After the body has taken what it needs from the
food, the waste is sent to the blood and removed
by the kidneys
• If the kidneys are unable to do their job and
remove the waste, waste builds up in the body,
which can prove very harmful
Waste (cont’d)
• The kidneys collect and get rid of waste in three
ways:
– Glomerular filtration—the blood is filtered through the
glomerulus in the nephron
– Tubular reabsorption—the tubules of the nephron
reabsorb the filtered blood in the nearby blood vessels
– Tubular secretion—the filtrate passes through the
tubules and eventually ends up in the bladder
Hormones Released
by the Kidneys
• Erythropoietin—stimulates the bone marrow to
make red blood cells
• Renin—regulates blood pressure; released by the
adrenal glands, which sit on top of the kidneys
• Calcitriol—the active form of vitamin D, which
helps maintain calcium for bones and normal
chemical balance in the body
Measuring
Kidney Function
• If kidney function decreases by 30% to 40%, the
effects are rarely noticeable
• When a person has <25% of kidney function,
serious health problems occur
• When a person has <10% to 15% of kidney
function, dialysis or a kidney transplant becomes
necessary
• The estimated glomerular filtration rate (eGFR) is
used to measure kidney function (the rate at
which the glomeruli filter the blood)
Stages of Chronic
Kidney Disease
Stage
Description
GFR
(mL/min/1.73 m2
1
Slight kidney damage
with increased or normal
filtration
>90
2
Mild decrease in kidney
function
60-89
3
Moderate decrease in
kidney function
30-59
4
Severe decrease in kidney
function
15-29
5
Kidney failure requiring
dialysis or transplantation
<15
GFR=glomerular filtration rate, m2=meters squared, mL=milliliter, min=minute
Most Common Causes
of Kidney Disease
• Diabetes—unused glucose in the bloodstream
damages the nephrons
• High blood pressure—high blood pressure
damages the vessels of the kidneys; the vessels
become unable to filter fluid and waste
• Glomerular diseases—include autoimmune
diseases, infection-related diseases (such as
pyelonephritis), and sclerotic diseases
– Immune diseases that can lead to kidney disease
include lupus, HIV/AIDS, hepatitis B, and hepatitis C
HIV/AIDS=human immunodeficiency virus/acquired immunodeficiency syndrome
Most Common Causes
of Kidney Disease (cont’d)
• Inherited and congenital kidney disease—
includes polycystic kidney disease
• Poisons
• Trauma
• Certain medications
Acute Kidney Failure
• Acute kidney failure occurs very quickly
• A person can recover in some cases, but it
also can lead to a permanent loss of kidney
function
Acute Kidney Failure
(cont’d)
• Causes of acute kidney failure:
–
–
–
–
–
–
–
Injury
Blood infection (septicemia)
Blood loss
Obstruction of urine flow
Pregnancy complications
Sudden breakdown of muscle tissue
Sometimes occurs in dehydrated athletes
Symptoms in Later
Stages of Kidney Disease
•
•
•
•
•
Frequent urination
Fatigue
Loss of appetite
Nausea and vomiting
Swelling of the hands
and feet
• Feeling itchy
• Feeling numb
• Having difficulty
concentrating
• Suffering from muscle
cramps
• Darkening of skin tone
Tests for Kidney Disease
• Blood pressure—high blood pressure can cause
kidney disease or indicate that someone may
already have kidney disease
• Microalbuminuria and proteinuria—when healthy
kidneys take waste from the blood, they leave
these proteins in the blood; if these proteins
show up in the urine, it is a sign that kidney
function is impaired
Tests for Kidney Disease
(cont’d)
• Blood urea nitrogen—healthy kidneys remove
urea from the blood, which is excreted in the
urine; having urea in the blood is a sign of
impaired kidney function
Resources
• Hoenig DM. Kidney anatomy. http://emedicine.medscape.com/article/1948775overview. Medscape Reference Web site. Accessed August 22, 2013.
• How your kidneys work: why are the kidneys so important? National Kidney
Foundation Web site. http://www.kidney.org/kidneydisease/howkidneyswrk.cfm.
Accessed August 22, 2013.
• Kidney anatomy and function. HealthPages.org Web site.
http://healthpages.org/anatomy-function/kidney/. Accessed August 22, 2013.
• National Institute of Diabetes and Digestive and Kidney Disease, National
Institutes of Health. The kidneys and how they work. National Kidney and
Urologic Diseases Information Clearinghouse (NKUDIC) Web site.
http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/. Updated March 23,
2012. Accessed August 22, 2013.
• Understanding kidney disease—the basics. WebMD® Web site.
http://www.webmd.com/a-to-z-guides/understanding-kidney-disease-basicinformation. Accessed August 22, 2013.