Lecture Notes: The Excretory System

Introduction

• Focus on the excretory system, specifically kidneys and nephron.
• Importance of maintaining osmotic balance and expelling metabolic waste.

Excretory System Overview

• Organs involved: Skin, liver, lungs, kidneys.
  • Skin: Excretes water and substances.
  • Liver: Detoxification, produces urea.
  • Lungs: Expel carbon dioxide.
  • Kidneys: Major focus, part of the urinary system.

Urinary System Components

• Kidneys: Two, located in the lower back.
• Bladder: Single sac to hold urine.
• Ureters: Two, draining urine from kidneys to bladder.
• Urethra: Single tube for expelling urine.

Kidney Function

• Blood filtration to produce urine.
• Importance of nephron as functional unit.

Nephron Structure and Function

• Each kidney contains about a million nephrons.
• Glomerulus and Bowman's Capsule:
  • Blood pressure forces fluid into Bowman's capsule, forming filtrate.
  • Filtrate includes water, glucose, amino acids, salts, ions, medications, vitamins, and urea.
• Reabsorption and Secretion:
  • Reabsorption into interstitial fluid (e.g., water, NaCl, glucose).
  • Secretion of ions like H+ and ammonium.

Nephron Parts

• Proximal Tubule:
  • Reabsorbs NaCl, water, glucose, amino acids, potassium, bicarbonate.
  • Important for pH regulation.
• Loop of Henle:
  • Descending Limb: Reabsorbs water via aquaporins.
  • Ascending Limb: Reabsorbs NaCl.
• Distal Convoluted Tubule:
  • Secretes ions and reabsorbs substances.
  • Further pH regulation.
• Collecting Duct:
  • Final concentration of urine.
  • Water reabsorption regulated by hormones.
  • Some urea reabsorption.

Hormonal and Osmotic Regulation

• Hormones control water permeability in collecting duct.
• Osmotic balance is crucial for nephron function.

Medical Considerations

• Diuretics: Increase water in filtrate, used for high blood pressure, heart failure.
• Dialysis: For compromised kidney function; includes hemodialysis and peritoneal dialysis.

Careers

• Nephrology is a field focused on kidney function.

Conclusion

• Importance of understanding the complexity and regulation of the excretory system.
• Encouragement to explore more about kidney function and related careers.

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Stay curious!