Excretory Products and their Elimination
கழிவுப் பொருட்களும் அவற்றின் வெளியேற்றமும்
- 1Modes of Excretion
Ammonia is the most toxic waste but needs the most water to remove; uric acid is the least toxic and needs the least. Match the animal's water supply to its waste and you can answer every 'ammonotelic vs uricotelic' question.
- 2Human Excretory System and Nephron
Most nephrons are cortical with a short loop of Henle; only some are juxtamedullary with a long loop. Reverse this and an assertion–reason question is lost.
- 3Urine Formation
Out of about 180 litres of filtrate formed each day, only about 1.5 litres leaves as urine — nearly 99% is reabsorbed. That one number explains why tubules matter more than the filter.
- 4Function of the Tubules
Descending limb: water out, salts stay. Ascending limb: salts out, water stays. Get these two opposite rules right and the concentration questions solve themselves.
- 5Mechanism of Concentration of the Filtrate
Concentrated urine is possible only because the kidney keeps its inner medulla salty — up to about 1200 mOsmolL-1. The counter-current mechanism exists to build and protect that gradient.
- 6Regulation of Kidney Function
ADH and the renin-angiotensin system both raise blood pressure and save water; ANF does the opposite. If an option has ANF 'released when blood pressure falls', it is wrong.
- 7Micturition and Role of Other Organs in Excretion
Urea is made in the liver, so the vessel leaving the liver — the hepatic vein — carries the most urea, not the renal artery and certainly not the renal vein.
- 8Disorders of the Excretory System
Glycosuria plus ketonuria points to diabetes mellitus; uremia points to kidney failure. Read the urine and you read the disease.