Biology Chapter: Excretion and Kidneys

Excretion: The Body's Clean-Up Crew

• Excretion is the removal of metabolic waste to maintain homeostasis
• It's how the body gets rid of waste
• Excretion keeps the body clean
• Removes toxins, excess water, and waste (e.g., CO2, urea).
• Waste removal occurs in a series of processes through different body parts and internal organs

Kidneys - The Body's Bouncers

• Kidneys filter blood and produce urine
• Two bean-shaped organs located in the lower back
• Filtration of Blood: Removes waste and excess substances
• Regulation of Water Balance: Maintains hydration levels
• Regulation of Electrolyte Balance: Controls salts like sodium and potassium levels
• Acid-Base Balance: Maintains pH of the blood
• Production of Hormones: Erythropoietin (stimulates red blood cell production), Renin (regulates blood pressure)

Inside the Kidneys

• Renal Cortex: Outer layer where filtration occurs
• Renal Medulla: Inner layer containing collecting ducts
• Nephrons: Functional units responsible for filtering blood
• Glomerulus: Network of capillaries for filtration
• Bowman's Capsule: Surrounds glomerulus, collects filtered fluid
• Proximal Convoluted Tubule: Reabsorbs useful substances (glucose, salts)
• Loop of Henle: Concentrates urine by reabsorbing water
• Distal Convoluted Tubule: Further regulates urine composition
• Collecting Duct: Final urine passage before entering the renal pelvis

Urine Formation

• Filtration: Blood enters glomerulus, waste (urea, salts) filtered into Bowman's capsule
• Reabsorption: Useful substances (water, glucose, salts) reabsorbed into bloodstream
• Secretion: Additional waste (drugs, hydrogen ions) secreted into nephron
• Excretion: Final filtrate (urine) passes through collecting duct to renal pelvis, then ureter

Lungs

• Exhalation contains a trace of your life's story, revealing metabolism, diet, and stress levels
• Excratory Products:
  • Carbon Dioxide (CO2): Produced during cellular respiration
  • Water Vapour (H2O): Lost during exhalation
• Breathing Rate: Controlled by the medulla oblongata, increases with exercise or high CO2 levels
• Gas Exchange Efficiency: Affected by lung health and environmental factors.

The Skin - Sweating It Out

• Skin eliminates waste products through sweat glands
• Supports the kidneys in maintaining water and salt balance
• Sweat Composition:
  • Water: Primary component
  • Salts (Sodium chloride and others)
  • Urea and Ammonia (by-products of protein metabolism)
• Controlled by the Hypothalamus: Detects body temperature changes, triggers sweating

The Liver - Detoxification HQ

• Largest internal organ
• Plays a central role in metabolism, detoxification, and excretion
• Bile: Contains bilirubin (from hemoglobin breakdown) and bile salts
• Urea: Formed during breakdown of amino acids
• Toxins/Drugs: Neutralized or converted into less harmful substances for excretion
• Regulation of Liver excretion is influenced by hormones and enzymes (CYP450).
• Blood Detoxification: Toxins/drugs checmicaly altered.
• Bile Production: Waste products secreted into bile.
• Elimination via Bile: Bile transported to gallbladder, and intestines
• Excretion through Feces: Bilirubin gives feces the characteristic brown color.

Large Intestines - The Final Stop for Solid Waste

• Solid Waste (Feces): Undigested food, dead cells
• Bacterial Waste Products: Compounds like methane and hydrogen sulfide
• Composition of Feces: ~75% water, ~25% solids (fiber, undigested food)
• Absorption of Water and Salts: Removes water from indigestible residue, converting liquid chyme to solid feces
• Movement of Waste: Peristalsis moves feces to rectum
• Storage in the Rectum: Feces are stored until elimination
• Defecation: Waste expelled through the anus