Excretory Products and Their Elimination Mind Map
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Visual Mind Map & Concept Tree (English)
Structured concept hierarchy, subtopic relationships, and exam revision tree.
Excretory Products and Their Elimination
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Introduction
- Definition of Excretion
- Removal of nitrogenous wastes
- Maintenance of homeostasis (osmoregulation)
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Modes of Excretion
- Ammonotelism
- Most toxic; requires large water volume
- Examples: Bony fishes, aquatic amphibians, aquatic insects
- Ureotelism
- Less toxic; requires moderate water
- Examples: Mammals, land amphibians, marine fishes
- Uricotelism
- Least toxic; conserved water (paste/pellet form)
- Examples: Reptiles, birds, land snails, insects
- Ammonotelism
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Human Excretory System
- Kidneys
- Reddish-brown, bean-shaped
- Located between T12 and L3 vertebrae
- Structure: Hilum, renal cortex, renal medulla, renal pyramids, Calyces, Renal pelvis
- Accessory Organs
- Ureters (pair)
- Urinary Bladder
- Urethra
- Kidneys
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Nephron: The Structural & Functional Unit
- Glomerulus
- Tuft of capillaries
- Formed by afferent arteriole and efferent arteriole
- Bowman's Capsule
- Cup-shaped end of nephron
- Forms Malphigian body (Renal corpuscle) along with glomerulus
- Renal Tubule
- Proximal Convoluted Tubule (PCT)
- Henle's Loop (Descending and Ascending limbs)
- Distal Convoluted Tubule (DCT)
- Collecting Duct
- Types of Nephrons
- Cortical nephrons (Short Henle's loop, mostly in cortex)
- Juxtamedullary nephrons (Long Henle's loop, deep into medulla)
- Glomerulus
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Urine Formation
- Glomerular Filtration
- Ultrafiltration under high pressure
- GFR (Glomerular Filtration Rate): ~125 mL/min
- Reabsorption
- 99% of filtrate reabsorbed
- Active and passive mechanisms (e.g., in PCT, Henle's loop)
- Secretion
- Addition of ions ($H^+$, $K^+$) and ammonia into filtrate
- Maintains ionic and acid-base balance
- Glomerular Filtration
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Function of the Tubules
- PCT: Reabsorbs essential nutrients, $HCO_3^-$, water; secretes $H^+$, $K^+$, ammonia
- Henle's Loop: Concentration of urine
- Descending limb: Permeable to water, impermeable to electrolytes
- Ascending limb: Impermeable to water, permeable to electrolytes
- DCT: Conditional reabsorption of $Na^+$ and water
- Collecting Duct: Large water reabsorption to produce concentrated urine
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Mechanism of Concentration of Filtrate (Counter-Current Mechanism)
- Counter-current multiplier (Henle's loop)
- Counter-current exchanger (Vasa recta)
- Maintains medullary gradient (NaCl and Urea)
- Produces concentrated urine (up to 4 times concentrated)
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Regulation of Kidney Function
- Hypothalamus
- Releases ADH (Antidiuretic Hormone) / Vasopressin during fluid loss
- Stimulates water reabsorption
- JGA (Juxtaglomerular Apparatus)
- Fall in GFR activates Renin-Angiotensin-Aldosterone System (RAAS)
- Renin $\rightarrow$ Angiotensinogen $\rightarrow$ Angiotensin II $\rightarrow$ Aldosterone
- Increases blood pressure and Na+ reabsorption
- ANF (Atrial Natriuretic Factor)
- Vasodilator; acts as a check on RAAS
- Hypothalamus
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Micturition
- Process of release of urine
- Micturition reflex
- Stretch of urinary bladder $\rightarrow$ CNS signals $\rightarrow$ Contraction of detrusor muscle $\rightarrow$ Relaxation of urethral sphincter
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Role of Other Organs in Excretion
- Lungs: Eliminate $CO_2$ (~18L/day) and water
- Liver: Secretes bilirubin, biliverdin, cholesterol, degraded hormones (via bile)
- Skin: Sweat and sebaceous glands (NaCl, urea, small amount of wastes in sebum)
- Saliva: Eliminates small amounts of nitrogenous wastes
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Disorders of the Excretory System
- Uremia: Accumulation of urea in blood
- Renal Failure: Malfunctioning of kidneys
- Calculi: Stone (insoluble mass of crystallized salts) in kidney
- Glomerulonephritis: Inflammation of glomeruli
- Dialysis: Artificial kidney method for blood filtration in renal failure patients