Excretory Products and Their Elimination
[PREMIUM NCERT MODULE • RENAL PHYSIOLOGY]
- Ammonotelic: Excrete Ammonia (highly toxic, needs much water). E.g., Bony fishes, aquatic amphibians.
- Ureotelic: Excrete Urea (less toxic). Ammonia converted to urea in Liver. E.g., Mammals, Terrestrial amphibians.
- Uricotelic: Excrete Uric Acid (least toxic, paste form). E.g., Reptiles, Birds, Insects.
Kidneys are bean-shaped, located between T12-L3 levels.
- Nephron: Structural/Functional unit (~1 million per kidney).
--> Glomerulus: Tuft of capillaries (filtration).
--> Bowman's Capsule: Encloses glomerulus.
--> PCT: 70-80% reabsorption of electrolytes and water.
--> Loop of Henle: Descending (permeable to water); Ascending (permeable to electrolytes).
--> DCT: Conditional reabsorption of Na+ and water (regulated by ADH/Aldosterone).
- Glomerular Filtration: Ultrafiltration through 3 layers. GFR = 125 ml/min.
- Reabsorption: 99% of filtrate is reabsorbed.
- Secretion: H+, K+, and Ammonia are secreted into the filtrate to maintain pH/ionic balance.
- ADH (Vasopressin): Released by hypothalamus when osmolarity increases; increases water reabsorption in DCT/Collecting duct.
- JGA (RAAS): Fall in GFR triggers Renin release -> Angiotensin II (vasoconstrictor) -> Aldosterone (Na+ reabsorption).
- ANF: Released by heart; causes vasodilation (opposes RAAS).
Maintains high osmolarity (300 to 1200 mOsmol) in medullary interstitium via Loop of Henle and Vasa Recta. This helps in producing Concentrated Urine.
- Uremia: Accumulation of urea in blood; treated by Hemodialysis.
- Renal Calculi: Kidney stones (oxalates).
- Glomerulonephritis: Inflammation of glomeruli.
- Glycosuria: Presence of glucose in urine (Diabetes marker).
Excretory Products HOTS
[ RENAL CALCULATIONS & NCERT LOGIC ]
During ultrafiltration, blood is filtered through very fine pores (fenestrae and slit pores). All constituents of plasma except large Proteins and blood cells pass into the Bowman's capsule. Hence, the filtrate composition is identical to plasma but without proteins.
Stretch receptors detect the filling of the bladder and send signals to the CNS to initiate the Micturition reflex. If these are removed, the bladder will continue to fill without the person feeling the urge to urinate, eventually leading to overflow incontinence (continuous dribbling).
They have Juxtamedullary nephrons with extremely long Loops of Henle. This allows them to create an incredibly powerful counter-current multiplier system, producing highly concentrated urine. They also rely on metabolic water (produced by fatty acid oxidation).
This differential permeability is central to the Counter-Current Mechanism. Water leaving the descending limb concentrates the filtrate, while the ascending limb actively pumps out NaCl into the medullary fluid without letting water follow, creating the high osmotic gradient needed to concentrate urine later in the collecting duct.
The dialysing fluid has the same composition as plasma except it lacks Nitrogenous wastes (Urea). By the principle of diffusion, urea moves from blood into the dialysing fluid. Glucose and salts stay in the blood because there is no concentration gradient for them.
Senses low GFR and releases Renin to restore blood pressure.
Presence of glucose and ketone bodies in urine; indicates Diabetes Mellitus.
Antagonistic to RAAS; causes vasodilation to lower blood pressure.
Crustaceans like Prawns.
PCT (Proximal Convoluted Tubule).
Inhibits ADH release, leading to increased urine volume (diuresis).
Liver (Ornithine cycle).
About 18 litres per day.
Sterols, hydrocarbons, and waxes via sebum.
Uremia.
U-shaped capillary vessel running parallel to Henle's loop.
Maintaining the balance of water and salts in body fluids.
Always aquatic; ammonia requires huge water volume to eliminate.
Renin: Kidney hormone. Rennin: Milk-digesting enzyme (stomach).
Juxtaglomerular cells of the kidney.
Excretion: 50 Mastery Facts
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