Med Simplified: Human Excretory System

Introduction

• The human excretory system is crucial for filtering blood and removing excess materials, maintaining chemical homeostasis and preventing bodily damage.
• The term "excretory system" generally refers to the urinary system but includes other organs such as skin, lungs, gut, nails, and hair.

Urinary System Overview

• Components:
  • Pair of kidneys
  • Pair of ureters
  • Urinary bladder
  • Urethra
• Blood Supply:
  • Renal artery supplies fresh blood to the kidneys
  • Renal vein drains blood from the kidneys

Kidneys

• Function: Main organs for filtering blood.
• Location: Bean-shaped, on either side of the spine at the umbilical level; the left kidney is slightly larger and higher due to the liver's position.
• Size: Approximately 11 to 13 centimeters in length.
• Structure:
  • Borders: Convex and concave, with the concave border having a notch called the hilum (point where blood vessels enter/leave).
  • Regions:
    • Renal Cortex: Outer region, contains most nephrons
    • Renal Medulla: Contains 12-15 cone-shaped structures (medullary pyramids)
• Nephrons: Basic functional unit, ~1 million per kidney.
  • Blood Filtration: Occurs in the Bowman’s capsule, where blood vessels form a tuft of capillaries.
  • Urine Formation: Waste products and water are filtered, exiting through collecting ducts into the renal calyx.

Urine Transport

• Ureters: 25-30 cm tubes carrying urine from kidneys to the bladder.
  • Smooth muscle walls propel urine forward.
  • Kidney stones can cause blockages.
• Urinary Bladder:
  • Function: Stores urine (300-500 ml capacity) and propels urine out of the body.
  • Neck of Bladder: Contains sphincter muscles that control urine leakage.
• Urethra:
  • Transports urine out of the body; longer in males (20 cm) than females (4 cm).
  • Females are more prone to urinary tract infections.

Kidney Functions Beyond Excretion

• Fluid volume regulation
• Ion balance
• pH regulation
• Blood pressure regulation
• Vitamin D formation

Other Excretion Organs

• Skin:
  • Sweat glands secrete sweat (temperature control), minimal excretory function; trace materials (e.g., urea) are lost.
• Large Intestine:
  • Excretes indigestible waste, collects and transports waste elements.
• Lungs:
  • Expel carbon dioxide as waste.
• Liver:
  • Metabolizes drugs and excretes waste into bile.
  • Bile aids in excreting metabolites and heavy metals.
• Nails and Hair:
  • Excrete heavy metals.

Conclusion

• For a detailed understanding of urine formation, watch the video on the structure and function of nephron.