The Excretory System [Elimination of Body Wastes] Short notes and Selected PYQs

Excretion: Process of removal of metabolic waste products from the body. Essential for homeostasis.
Excretory Organs: (1) Kidneys (main), (2) Lungs (CO₂ and water vapor), (3) Skin (sweat), (4) Liver (bile pigments), (5) Intestines (undigested food).
Importance: (1) Removes toxic wastes, (2) Maintains water and salt balance, (3) Regulates pH, (4) Prevents accumulation of harmful substances.
Excretion vs Egestion: Excretion - removal of metabolic wastes. Egestion - removal of undigested food.
Nitrogenous Wastes: Ammonia (toxic, in aquatic animals), Urea (mammals), Uric acid (birds, reptiles).
Diagram Importance: Overview diagram of human excretory system showing kidneys, ureters, bladder, urethra is essential.

Kidneys: Bean-shaped organs. Located on either side of vertebral column. Right kidney slightly lower than left.
Size: 10-12 cm long, 5-7 cm wide, 2-3 cm thick. Weight: 120-170 g each.
Structure: (1) Renal capsule (outer covering), (2) Cortex (outer region), (3) Medulla (inner region with renal pyramids), (4) Renal pelvis (collects urine).
Functions: (1) Filtration of blood, (2) Formation of urine, (3) Regulation of blood pressure, (4) Acid-base balance, (5) Erythropoietin production (RBC formation).
Renal Artery: Brings oxygenated blood to kidney. Branches into arterioles.
Renal Vein: Takes filtered blood back to heart.
Diagram Importance: Longitudinal section of kidney showing cortex, medulla, pyramids, pelvis is crucial for ICSE.

Nephron: Microscopic functional unit of kidney. About 1 million per kidney.
Parts: (1) Bowman's capsule, (2) Glomerulus, (3) Proximal convoluted tubule (PCT), (4) Loop of Henle, (5) Distal convoluted tubule (DCT), (6) Collecting duct.
Bowman's Capsule: Cup-shaped structure surrounding glomerulus. Site of filtration.
Glomerulus: Network of capillaries. High pressure filtration occurs here.
PCT: Reabsorbs glucose, amino acids, salts, water (selective reabsorption).
Loop of Henle: Creates concentration gradient. Reabsorbs water and salts.
DCT: Reabsorbs water and salts under hormone control (ADH, aldosterone).
Collecting Duct: Collects urine from multiple nephrons. Final adjustment of urine concentration.
Diagram Importance: Detailed labeled diagram of nephron showing all parts and blood flow is frequently asked.

Three Processes: (1) Glomerular filtration, (2) Tubular reabsorption, (3) Tubular secretion.
Glomerular Filtration: Blood filtered in glomerulus. Water, salts, glucose, urea pass into Bowman's capsule. Proteins and blood cells retained.
Filtration Pressure: Hydrostatic pressure in glomerulus (55 mm Hg) minus osmotic pressure (30 mm Hg) and capsular pressure (15 mm Hg) = Effective filtration pressure (10 mm Hg).
Glomerular Filtrate: 180 liters/day filtered. Contains water, salts, glucose, urea.
Tubular Reabsorption: Useful substances reabsorbed back into blood. PCT reabsorbs 65% water and salts, glucose (100%), amino acids.
Tubular Secretion: Active secretion of wastes (H⁺, K⁺, creatinine) into tubules from blood.
Urine Formation: Final urine = 1-2 liters/day. Concentrated due to water reabsorption in DCT and collecting duct.
Diagram Importance: Diagram showing processes of urine formation with arrows indicating flow is important.

Hormonal Control: (1) ADH (Antidiuretic Hormone) - increases water reabsorption, reduces urine volume, (2) Aldosterone - increases Na⁺ reabsorption, water follows, (3) Renin-Angiotensin system - regulates blood pressure and Na⁺ balance.
Neural Control: Autonomic nervous system. Sympathetic stimulation reduces urine formation during stress.
Atrial Natriuretic Factor (ANF): Released from heart when blood volume high. Increases Na⁺ excretion, reduces blood pressure.
Importance: Maintains homeostasis of water, electrolytes, and blood pressure.

Urinary System Components: (1) Kidneys (filtration), (2) Ureters (transport urine), (3) Urinary bladder (storage), (4) Urethra (elimination).
Urine Composition: 95% water, 5% solutes (urea, uric acid, creatinine, salts, pigments).
Urine Characteristics: Straw-colored, slightly acidic (pH 6), specific gravity 1.015-1.025, odor due to bacteria.
Micturition: Process of urine expulsion. Controlled by nervous system. Bladder fills → stretch receptors → spinal cord → brain → voluntary control.
Abnormal Constituents: Glucose (diabetes), proteins (kidney disease), blood (infection/injury), ketones (diabetes/starvation).

Lungs: Excrete CO₂ and water vapor during respiration.
Skin: Sweat glands excrete water, salts, urea (small amount). Helps in thermoregulation.
Liver: Removes bile pigments, detoxifies drugs, converts ammonia to urea.
Intestines: Excrete undigested food, excess salts, cholesterol, bile pigments.
Significance: All organs contribute to waste removal, but kidneys are primary for nitrogenous wastes.

Kidney Stones (Renal Calculi): Hard deposits of salts in kidney. Causes: dehydration, high calcium intake. Treatment: surgery, lithotripsy.
Urinary Tract Infection (UTI): Bacterial infection. Symptoms: burning sensation, frequent urination.
Nephritis: Inflammation of kidneys. Causes: infections, autoimmune diseases.
Kidney Failure: Acute (sudden) or chronic (gradual). Treatment: dialysis or transplant.
Diabetes Insipidus: ADH deficiency. Causes excessive urine production.
Edema: Swelling due to fluid retention. Caused by kidney or heart problems.
Prevention: Drink plenty of water, balanced diet, regular exercise, avoid smoking.

The Excretory System [Elimination of Body Wastes]