Functions of the Human Urinary System
Each part of the urinary system performs important functions -
both for the efficient operation of the urinary system itself,
and also therefore, for the body as a whole.
Functions of the Kidneys:
- Regulation of blood volume:
The kidneys conserve or eliminate water from
the blood, which regulates the volume of blood in
- Regulation of blood pressure:
The kidneys regulate blood pressure in 3 ways, by:-
the volume of
the quantity of water in the blood - see above),
- Adjusting the flow of blood both into, and out of, the kidneys, and
- Via the action of the enzyme renin.
The kidneys secret renin, which activates the
- Regulation of the pH of the blood:
The kidneys excrete H+ ions (hydrogen
atoms that lack their single electron), into urine.
At the same time, the kidneys also conserve bicarbonate
ions (HCO3-), which are an important
buffer of H+.
- Regulation of the ionic composition of blood:
The kidneys also regulate the quantties in
the blood of the ions (charged particles) of several
important substances. Important examples
of the ions whose quantities in the blood are regulated
by the kidneys include sodium ions (Na+),
potassium ions (K+), calcium ions (Ca2+),
chloride ions (Cl-), and phosphate ions
- Production of Red blood cells:
The kidneys contribute to the production
of red blood cells by releasing the hormone erythropoietin
- which stimulates erythropoiesis (the production
of red blood cells).
- Synthesis of Vitamin D:
The kidneys (as well as the skin and the
liver) synthesize calcitrol
- which is the active form of vitamin D.
- Excretion of waste products and foreign substances:
The kidneys help to excrete waste products
and foreign substance from the body by forming urine
(for release from the body).
Examples of waste products from metabolic reactions
within the body include ammonia (from
the breakdown of amino
acids), bilirubin (from the breakdown
of haemoglobin), and creatinine (from
the breakdown of creatine phosphate in muscle fibres).
Examples of foreign substances that may also be exceted
in urine include pharmaceutical drugs
and environmental toxins.
Functions of the Ureters:
- There are two ureters, one leading from each kidney to the
urinary bladder. Each of these transports urine from the
renal pelvis of the kidney
to which it is attached, to the bladder (see diagram on the
page about components
of the urinary system).
- Both of the ureters pass beneath
the urinary bladder, which results in the bladder compressing
ureters and hence preventing back-flow of urine when pressure
in the bladder is high during urination. This prevention of back-flow
is important because when it is not operating correctly cystitis,
which is inflammation of the ureter / urinary bladder, may
develop into a kidney infection.
Functions of the Bladder:
- The purpose of the urinary bladder is to store urine prior
to elimination of the urine from the body.
- The bladder
also expels urine into the urethra by a process called micturition (also
known as urination). Micturition involves the actions of
both voluntary and involuntary muscles. Lack of voluntary
over this process is referred to as incontinence.
Functions of the Urethra:
- The urethra is the passageway through which urine is
discharged from the body.
- In males the urethra also serves as the duct through
which semen is ejaculated (see the section about reproduction
for further detail about this function).
Quick Summary: The
Functions of the Urinary System
- The kidneys regulate blood volume and composition, help
to regulate blood pressure and pH, participate in red blood
cell production and synthesis of vitamin D, and excrete waste
products and foreign substances.
- The ureters transport urine from the kidneys to the urinary
- The urinary bladder stores urine and expels urine into
- The urethra discharges urine from the body.