EXCRETORY PRODUCTS AND THEIR ELIMINATION · Comparison Tables

1. Ammonotelism vs Ureotelism vs Uricotelism

Feature	Ammonotelism	Ureotelism	Uricotelism
Nitrogenous product	Ammonia	Urea	Uric acid
Toxicity / water requirement	Most toxic; requires large amount of water	Less toxic than ammonia; permits terrestrial life	Least toxic; minimum water loss
Examples	Many bony fishes, aquatic amphibians and aquatic insects	Mammals, many terrestrial amphibians and marine fishes	Reptiles, birds, land snails and insects
Route / form	Diffusion across body or gill surfaces as ammonium ions; kidneys have little role	Ammonia converted to urea in liver, released into blood and excreted by kidneys	Pellets or paste

2. Animal Excretory Structures

Structure	Found in	Main function
Protonephridia / flame cells	Flatworms, rotifers, some annelids and Amphioxus	Primarily osmoregulation: ionic and fluid-volume regulation
Nephridia	Earthworms and other annelids	Nitrogenous-waste removal plus fluid and ionic balance
Malpighian tubules	Most insects including cockroach	Nitrogenous-waste removal and osmoregulation
Antennal / green glands	Crustaceans such as prawns	Excretion
Kidneys	Vertebrates	Complex tubular excretory organs

3. Cortical vs Juxtamedullary Nephrons

Feature	Cortical nephron	Juxtamedullary nephron
Loop of Henle	Short; extends only a little into medulla	Long; runs deep into medulla
Vasa recta	Absent or highly reduced	Well-developed parallel capillary loop
Role in concentration	Limited contribution to deep medullary gradient	Especially important in establishing and preserving medullary gradient

Shared plan Both have a renal corpuscle (glomerulus + Bowman’s capsule), PCT, Henle’s loop, DCT and collecting duct. PCT, DCT and renal corpuscles lie in cortex; loop extends into medulla.

4. Filtration vs Reabsorption vs Secretion

Feature	Glomerular filtration	Tubular reabsorption	Tubular secretion
Where	Glomerulus into Bowman’s capsule	Along renal tubules	Tubular cells into filtrate
Nature	Ultrafiltration through endothelium, Bowman’s epithelium and basement membrane	Selective, active or passive recovery	Selective addition to filtrate
Main materials	Almost all plasma constituents except proteins enter filtrate	Glucose, amino acids, Na⁺, water and other useful materials	H⁺, K⁺ and ammonia
Key outcome	GFR about 125 mL min^-1, 180 L day^-1	Nearly 99% filtrate returned to body	Maintains ionic and acid-base balance

5. Functions of Nephron Segments

Segment	Water handling	Solute handling / special role
PCT	Reabsorbs much water	Reabsorbs nearly all essential nutrients and 70-80% electrolytes; HCO₃^- reabsorption; H⁺ and ammonia secretion.
Descending Henle’s limb	Permeable to water; filtrate concentrates	Almost impermeable to electrolytes
Ascending Henle’s limb	Impermeable to water; filtrate dilutes	Electrolytes transported actively or passively; minimum reabsorption overall
DCT	Conditional water reabsorption	Conditional Na⁺ reabsorption; HCO₃^- recovery; H⁺, K⁺, NH₃ secretion
Collecting duct	Large water reabsorption forms concentrated urine	Small urea passage to medulla; H⁺ and K⁺ secretion

6. Henle’s Loop vs Vasa Recta in Counter Current

Feature	Henle’s loop	Vasa recta
Flow	Filtrate moves in opposite directions in descending and ascending limbs	Blood also moves in counter-current pattern through its two limbs
NaCl movement	Ascending limb transports NaCl into medullary interstitium	NaCl exchanges with descending limb and returns to interstitium from ascending limb
Urea role	Small amount enters thin ascending limb	Works beside the urea-rich medullary interstitium
Combined result	Close parallel arrangement maintains gradient from 300 mOsmol L^-1 cortex to about 1200 mOsmol L^-1 inner medulla. This permits water exit from collecting duct and urine about fourfold more concentrated than initial filtrate.

7. ADH vs RAAS vs ANF

Regulator	Stimulus	Effect on kidney / blood pressure
ADH / vasopressin	Fluid loss activates osmoreceptors; hypothalamus stimulates neurohypophysis	Facilitates water reabsorption from latter tubules, preventing diuresis; constricts vessels and can raise BP.
Renin-angiotensin-aldosterone system	Fall in glomerular blood flow, pressure or GFR activates JG cells	Renin -> angiotensin I -> angiotensin II. Angiotensin II vasoconstricts and promotes aldosterone; aldosterone raises distal Na⁺ and water reabsorption.
ANF	Increased blood flow to atria	Vasodilation lowers BP; counter-checks renin-angiotensin mechanism.

8. Micturition, Other Excretory Organs and Disorders

Topic	NCERT comparison / fact
Micturition	Bladder stretch receptors signal CNS; CNS causes bladder-muscle contraction and urethral-sphincter relaxation. Daily urine: 1-1.5 L, light yellow, pH about 6.0.
Lungs vs liver vs skin	Lungs: CO₂ (~200 mL min^-1) and water. Liver: bile-borne bilirubin, biliverdin, cholesterol, degraded hormones, vitamins and drugs. Skin: sweat with NaCl, small urea and lactic acid; sebum with sterols, hydrocarbons and waxes.
Uremia and haemodialysis	Uremia is harmful urea accumulation in blood. In artificial kidney, nitrogenous wastes diffuse from heparinised blood across cellophane tube into dialysing fluid that lacks them.
Renal calculi vs glomerulonephritis	Renal calculi are crystallised salt stones in kidney; glomerulonephritis is inflammation of glomeruli.
Glycosuria / ketonuria	Glucose or ketone bodies in urine may indicate diabetes mellitus.