The excretory system works to remove waste products and maintain the body's
chemical balance through several key organs and processes: 1. Filtration by
the Kidneys
The kidneys filter blood to separate waste products and excess substances from
useful nutrients. Blood enters the kidneys where tiny filtering units called
nephrons remove urea (a waste product formed from protein breakdown), excess
water, and other wastes, forming urine. Essential nutrients, vitamins, and
minerals are reabsorbed back into the bloodstream
. 2. Transport of Urine
Urine formed in the kidneys travels down two narrow tubes called ureters to
the bladder. Muscles in the ureter walls contract rhythmically to push urine
downward, preventing backflow and infection
. 3. Storage in the Bladder
The bladder is a hollow, muscular organ that stores urine until it is
convenient to expel it. It can hold about two cups of urine for several hours.
The bladder walls relax and expand to store urine, then contract to release it
. 4. Excretion via the Urethra
When urinating, the brain signals the bladder muscles to contract and the
sphincter muscles around the urethra to relax, allowing urine to exit the body
through the urethra
. Additional Waste Removal
- The lungs expel gaseous wastes like carbon dioxide during respiration.
- The liver detoxifies chemicals and converts ammonia into urea, which the kidneys then filter out.
- The large intestine removes solid waste by absorbing water and expelling indigestible food residues as feces
Overall, the excretory system maintains the body's internal environment by removing liquid, gaseous, and solid wastes, regulating fluid and electrolyte balance, and supporting other functions like blood pressure regulation and red blood cell production
