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Review key Human Excretory System: Kidneys, Nephrons, Ultrafiltration & Dialysis exam facts and rate your mastery to track revision.
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#1
The human excretory system consists of two retroperitoneal kidneys, two tubular ureters, one urinary bladder reservoir, and a single terminal urethra.
#2
Each kidney contains approximately one million microscopic nephrons, which serve as the basic structural and functional units of renal filtration.
#3
A nephron consists of a renal corpuscle (glomerular capillary tuft inside Bowman's capsule) and an epithelial tubular system with distinct segments.
#4
Glomerular ultrafiltration occurs across a three-layered barrier: fenestrated capillary endothelium, basement membrane, and podocyte slit diaphragms.
#5
The normal Glomerular Filtration Rate (GFR) in a healthy human adult averages 125 mL per minute, producing approximately 180 liters of filtrate daily.
#6
More than 99% of glomerular filtrate is reabsorbed along the nephron tubules, yielding an average daily urine output of roughly 1.0 to 1.5 liters.
#7
The proximal convoluted tubule (PCT) reabsorbs 100% of filtered glucose and amino acids, alongside 65% to 70% of filtered sodium and water.
#8
The hairpin-shaped loop of Henle acts as a countercurrent multiplier, establishing an osmotic gradient in the renal medulla reaching 1,200 mOsm/L.
#9
The descending limb of the loop of Henle is permeable to water but impermeable to ions, while the ascending limb actively pumps sodium and chloride.
#10
Antidiuretic hormone (ADH or vasopressin) from the posterior pituitary inserts aquaporin-2 water channels into collecting duct cells to retain water.
#11
The juxtaglomerular apparatus secretes the enzymatic hormone renin during hypotension, initiating the renin-angiotensin-aldosterone system (RAAS).
#12
Aldosterone produced by the adrenal cortex acts on distal convoluted tubules and collecting ducts to stimulate sodium reabsorption and potassium excretion.
#13
Urea, produced in the liver through the Krebs-Henseleit ornithine cycle from toxic ammonia, represents the primary nitrogenous waste in human urine.
#14
Hemodialysis purifies uremic blood extracorporeally across a semipermeable synthetic dialyzer membrane against countercurrent dialysate fluid.
#15
Micturition is an autonomic spinal reflex modified by higher brain centers, triggered when urinary bladder stretch receptors detect 200 to 400 mL of urine.
Subject Specialist Commentary
Analytical perspective & practical exam advice from the Master10 academic board
The human excretory system maintains fluid balance and removes toxic nitrogenous waste. Each kidney houses approximately one million functional units called nephrons. High hydrostatic pressure inside the glomerulus forces blood plasma into Bowman's capsule, generating roughly 180 litres of initial filtrate daily. As fluid travels through renal tubules, specialized segments reabsorb over ninety-nine percent of essential water, glucose, and salts back into circulation, leaving one to two litres of urine for excretion.
In UPSC Prelims and SSC exams, questions regularly target nephron physiology and hormone regulation. A classic exam trap asks where nutrients are reclaimed: the proximal convoluted tubule reabsorbs all filtered glucose and amino acids under normal conditions. In hormone MCQs, remember that antidiuretic hormone acts on collecting ducts to retain water, while aldosterone promotes sodium reabsorption. For general science revision, recall that urea is synthesized in the liver via the ornithine cycle, not within the kidneys.
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