Regulation of blood composition and blood pH.
The kidneys affect blood composition by regulating
the blood levels of several ions. They also help regulate
blood pH through regulation of the concentrations of
H+ and blood bicarbonate ions (HCO3-).
Production of two hormones. The kidneys produce
calcitriol, the active form of vitamin D, which helps
regulate
calcium
homeostasis.
They also
produce
erythropoietin, which stimulates the production of red
blood cells.
T h e u r in a r y s y s t e m •
F ig u r e 1 5 .1
Excretion of wastes. By forming urine, the kidneys
help excrete wastes—substances that have no useful
function in the body. Some of these wastes result
from metabolic processes in the body, as we saw with
the exercise example that began this chapter. Such
metabolic wastes include ammonia, urea, bilirubin,
creatinine, and uric acid. Other wastes are foreign
substances from a person’s diet, such as drugs and
environmental toxins.
Kidneys
(left and right):
• regulate blood volume
and blood pressure
• help regulate blood
composition and pH
• secrete 2 hormones
• excrete wastes
Ax,
Adrenal ■
gland
J
v
'
Anterior view
Renal artery
Renal vein
Kidney
Ureter
Renal veins
(left and right)
drain blood from the kidneys.
Ureters
(left and right)
drain urine from the
kidneys to the urinary
bladder.
Urinary
bladder
stores
urine and expels it into
the urethra.
Urethra
discharges urine
from the body.
Anterior
view
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