Excretion By Rakshita Singh
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Title
Excretion by Rakshita Singh
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Nitrogenous Waste in Animals
Animals ingest food and accumulate nitrogenous wastes.
Major forms: Ammonia, Urea, Uric Acid, CO2, ions (Na+, K+, etc.)
These wastes must be removed completely or partially to maintain balance, from most toxic (Ammonia) to least toxic (Uric Acid).
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Ammonotelism
Definition: Excreting ammonia.
Example organisms: Bony fishes, aquatic amphibians, aquatic insects.
Ammonia is soluble and excreted through diffusion, primarily across gill surfaces.
Kidneys are not significantly involved in this process.
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Terrestrial Adaptation
To conserve water, organisms excrete less toxic nitrogenous wastes, primarily Urea and Uric Acid.
Examples: Mammals, Reptiles, Birds, Amphibians, Marine Fishes.
Urea is excreted by kidneys and maintains osmolarity in the blood.
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Excretory Structures
Invertebrates: Simple tubular forms
Vertebrates: Complex tubular organs (kidneys)
Ex: Protonephridia in Platyhelminthes, Nephridia in Annelids, Malpighian Tubules in Insects, Green glands in Crustaceans.
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Human Excretory System Components
Kidneys (1 Pair)
Ureters (1 Pair)
Urinary Bladder
Urethra
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Kidney Anatomy
Shape: Reddish brown, bean-shaped
Location: Between last thoracic and third lumbar vertebrae
Dimensions: Length ~10-12 cm, Width ~5.7 cm, Thickness ~2-3 cm
Average weight: ~10 g
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Kidney Structure
Outer Cortex and Inner Medulla with conical masses (pyramids) and calyces.
Hilum: point of entry for blood through the renal artery.
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Kidney Diagram Overview
Medulla features: Renal Artery, Renal Vein, Pelvis, Calyx, etc.
Cortex extends between medullary pyramids.
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Nephrons
Each kidney contains nearly a million nephrons, the functional units.
Nephrons consist of Renal Tubule and Glomerulus.
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Nephron Structure
Components: Afferent Arteriole, Efferent Arteriole, Glomerulus, Bowman's Capsule, Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule, Collecting Duct.
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Bowman's Capsule
Double-walled structure surrounding the Glomerulus.
Key role: Filtration of blood.
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Nephron Tubules
PCT (Proximal Convoluted Tubule): Highly coiled.
Loop of Henle: U-shaped, includes descending and ascending limbs.
DCT (Distal Convoluted Tubule): Also highly coiled.
Collecting Duct: Straight tube in medullary pyramid leading to renal pelvis.
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Medullary Loop Description
Describes the structure and function of the Loop of Henle.
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Nephron Types
Types of Nephrons: Cortical Nephrons (most common) and Juxtamedullary Nephrons (deeper in medulla with long loops).
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Capillary Network
Efferent arterioles form capillary networks around nephron tubules (peritubular capillaries).
Vasa Recta: specialized capillaries around Loop of Henle.
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Glomerular Filtration
Blood filtration occurs at the glomerulus, 1100-1200 mL/min.
Filtration layers: Endothelium, Bowman's Capsule, Basement Membrane.
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Bowman's Capsule Structure
Epithelial cells called podocytes and how they filter blood through slit pores.
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Glomerular Filtration Rate
Normal GFR: 125 mL/min, around 180 liters of filtrate formed daily.
Regulation by Juxtaglomerular Apparatus (JGA).
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Urine Formation
Urine released: 1.5 liters/day, 99% of filtrate reabsorbed.
Reabsorption: passive and active of ions, glucose, amino acids, etc.
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PCT Function
PCT: Reabsorbs essential nutrients and maintains ionic balance (70-80% of water, Na+, etc.).
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Loop of Henle Reabsorption
Description of water and electrolyte reabsorption in loop limbs.
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DCT Functions
Conditional reabsorption of Na+ and water; secretion of H+ and K+ ions.
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Collecting Duct Function
Final reabsorption in the collecting duct contributes to urine concentration.
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Diagram of Reabsorption
Illustration of the reabsorption and secretion at different nephron parts.
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Mechanism of Concentration
Countercurrent mechanism in loops of Henle and vasa recta for urine concentration.
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Osmotic Gradient
Maintenance of urine concentration gradient through vasa recta and loop of Henle.
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Water Passage
Water moves from medullary interstitium to filtrate, influencing urine concentration.
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Hormonal Regulation
Hormonal feedback: Antidiuretic Hormone (ADH) regulates water reabsorption.
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Body Fluid Regulation
Mechanism includes osmoregulation and blood pressure influence.
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Renin-Angiotensin System
Activates renin release and the effects on blood pressure and fluid balance.
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Atrial Natriuretic Factor
Released from heart's atria affecting blood pressure regulation.
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Micturition Process
Urinary bladder control involving neural signaling for muscle contractions.
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Urine Characteristics
Typical urine: light yellow, slightly acidic (pH=6), approx 25-30g urea excreted daily.
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Excretion via Other Organs
Additional waste elimination through glands and their functions.
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Disorders of the Excretory System
Renal calculi: kidney stones formed from crystallized salts.
Glomerulonephritis: inflammation of glomeruli.
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Kidney Failure and Treatment
Uremia: harmful urea accumulation in blood.
Hemodialysis: blood purification method for kidney failure.
Kidney transplantation as a long-term solution for renal failure.