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Excretion
involved in excretion are the kidneys, essential substances like glucose
lungs, skin, and liver, each playing a and amino acids are reabsorbed into
specific role in waste removal. The the bloodstream. Tubular secretion
main excretory substances include ensures additional waste removal
carbon dioxide, water, salts, urea, and before urine is collected in the bladder.
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other nitrogenous compounds.
5. The common complications and
2. The human excretory system consists disorders of excretory system
of several specialized organs. The which can affect its normal function
kidneys filter blood to remove includes: Kidney failure which occurs
nitrogenous wastes, excess salts, when the kidneys lose their ability to
and water, forming urine. The lungs filter blood properly, leading to toxin
expel carbon dioxide and water vapor buildup. This can result from high
produced during cellular respiration. blood pressure, diabetes, infections,
The skin eliminates some metabolic or toxic substances. Kidney stones,
waste through sweat, which contains solid deposits of minerals and salts,
water, salts, and small amounts of may form in the urinary tract and
urea. The liver processes toxins, cause severe pain. Another common
breaking down old red blood cells, disorder is urinary tract infection
and converts excess amino acids into (UTI), often caused by bacterial
urea. invasion of the urethra and bladder.
Symptoms include painful urination
3. The urinary system plays a major
role in excretion and homeostasis. and frequent urges to urinate.
It comprises the kidneys, ureters, Uraemia develops when excess urea
bladder, and urethra. The kidneys filter accumulates in the bloodstream due to
blood, regulate water and salt balance, kidney dysfunction, leading to severe
and remove nitrogenous wastes. Urine complications.
formed in the kidneys travels through 6. The liver also experiences excretory-
the ureters to the bladder, where it related complications. Liver cirrhosis
is temporarily stored before being occurs when liver cells are damaged
expelled through the urethra. and replaced by scar tissue, impairing
its ability to process toxins. This
4. Urine formation occurs in three
key steps: ultrafiltration, selective condition can be caused by excessive
reabsorption, and tubular secretion. alcohol intake, infections, or
During ultrafiltration, blood is filtered autoimmune diseases. Gout, another
at high pressure in the glomerulus, excretory disorder, results from excess
allowing small molecules like water, uric acid accumulation, leading to
urea, and salts to pass into the painful joint inflammation.
nephrone. In selective reabsorption,
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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 99
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 99 KAMISHNA 23/10/2025 11:52:45
KAMISHNA
