The Excretory System [Elimination of Body Wastes]

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.