Introduction to the Excretory System

Overview

• Some body systems are well-known: circulatory, nervous, digestive, muscular.
• Excretory system often not understood well.
• Focus on excretory system and specifically kidneys and nephrons.

Key Challenges for Survival

1. Osmotic Balance: Managing water and solutes.
2. Metabolic Wastes Disposal: Carbon dioxide, nitrogenous wastes from protein breakdown.

Organs Involved in Excretion

• Skin: Excretes water and substances.
• Liver: Detoxification, produces urea.
• Lungs: Excrete carbon dioxide.
• Kidneys: Central role in the urinary system.

The Urinary System

• Kidneys: Two organs in the lower back.
• Bladder: Stores urine.
• Ureters: Transport urine from kidneys to bladder.
• Urethra: Excretes urine from the body.

Function of the Kidneys

• Filter blood to produce urine.
• Urine contains waste products for excretion.
• Simplified explanation of complex processes.

The Nephron

Structure and Function

• Functional unit of the kidney.
• Processes waste from blood to create urine.

The Glomerulus and Bowman's Capsule

• Fluid is forced from blood into Bowman's capsule, becomes filtrate.
• Filtrate contains: water, glucose, amino acids, salts, H+ ions, bicarbonate ions, medications, vitamins, urea.

Reabsorption and Secretion

• Some filtrate reabsorbed into interstitial fluid.
• Components moved by diffusion, facilitated diffusion, or active transport.
• Reabsorption and secretion regulate various substances.

Nephron Pathway

Proximal Tubule

• NaCl reabsorption; water follows osmotically.
• Glucose, amino acids, potassium, bicarbonate also reabsorbed.
• Important for pH regulation.
• H+ ions and ammonium ions secreted.

Loop of Henle

• Descending Limb: Water reabsorbed due to aquaporins; solute concentration increases inside.
• Ascending Limb: NaCl reabsorbed (diffusion then active transport); water can't leave.

Distal Convoluted Tubule

• H+, ammonium, potassium secreted into filtrate.
• NaCl, water, bicarbonate reabsorbed.
• Contributes to pH regulation.

Collecting Duct

• Filtrate becomes urine.
• NaCl and water reabsorbed; water regulated by hormones.
• Urea reabsorbed by diffusion at high concentration.

Final Stages of Urine Formation

• Urine travels down ureters to bladder, then expelled via urethra.

Additional Information

• Hormonal control influences reabsorption and secretion.
• Diuretics increase water in urine to manage conditions like high blood pressure.
• Dialysis options for compromised kidney function.

Careers in Kidney Function

• Nephrologists specialize in kidney function.

Conclusion

• Excretory system has intricate processes.
• Nephrons play a critical role in regulating body fluid and solute balance.