Introduction to the Human Excretory System

Overview

• Commonly known body systems: Circletory, Nervous, Digestive, Muscular systems
• Less familiar but incredible system: Excretory system
• Focus: Kidneys & Nephron

Obstacles for Survival

1. Maintain osmotic balance (manage water and solutes)
2. Remove metabolic wastes (carbon dioxide, nitrogenous wastes from protein breakdown)

Organs and Structures in the Excretory System

• Skin: excretes water and substances
• Liver: detoxification, produces urea
• Lungs: excrete carbon dioxide
• Kidneys: major focus of this lecture
• Urinary system includes:
  • Kidneys: filter blood, produce urine
  • Bladder: holds urine
  • Ureters: two tubes, drain urine from kidneys to bladder
  • Urethra: single tube, conducts urine out of the body

Kidney and Urine Production

• Nephron: functional unit of the kidney (millions per kidney)
• Process waste from blood to create urine
• Glomerulus: mass of capillaries
  • Surrounded by Bowman's Capsule
  • Blood pressure forces fluid into Bowman’s capsule -> filtrate
• Filtrate Contains: water, glucose, amino acids, salts, H+ ions, bicarbonate ions, medications, vitamins, urea
• Reabsorption and Secretion:
  • Reabsorbed: substances crossing back into the body
  • Secreted: substances entering nephron to be excreted
  • Transport: diffusion, facilitated diffusion (no ATP), active transport (requires ATP)

Detailed Nephron Process

1. Bowman's Capsule: Filtrate formed
2. Proximal Tubule:

• Reabsorbed: NaCl, water, glucose, amino acids, potassium, bicarbonate
• Secreted: H+ ions, ammonium ions
• pH regulation

3. Loop of Henle: Descending Limb

• Aquaporins allow water reabsorption by osmosis
• Increasing solute concentration in filtrate

4. Loop of Henle: Ascending Limb

• No aquaporins; NaCl exits (reabsorbed)
• Thin segment: NaCl diffuses out
• Thick segment: NaCl active transport out
• Result: Dilute filtrate

5. Distal Convoluted Tubule:

• Reabsorbed: NaCl, water, bicarbonate
• Secreted: H+, ammonium, potassium
• pH regulation

6. Collecting Duct:

• Urine formation
• NaCl, water reabsorption
• Hormonal control of water permeability
• Urea present, some reabsorbed

Urine Pathway

• Produced by nephrons -> ureters -> bladder -> urethra for excretion

Additional Insights

• Complexity of nephron functions influenced by hormones and osmotic balance
• Diuretics: increase filtrate water, prescribed for high blood pressure, heart failure
• Dialysis: for compromised kidney function, involves blood filtering
• Nephrology: specialized career in kidney function

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Remember to stay curious!