Anatomy of Nephrons and Collecting System

Overview of Nephrons and Collecting System

• Review of previous question about the regions of the kidney with filtrate:
  • Filtrate found in renal cortex and renal medulla (D answer).
  • Once filtrate exits the renal medulla, it becomes urine in the renal pelvis.

Nephron Structure

• Nephrons have two main parts:
  • Renal Corpuscle: Where filtrate is formed.
  • Includes Glomerulus (capillary bed) and Glomerular Capsule (Bowman's Capsule).
  • Renal Tubule: Where filtrate travels and is modified.
• The Collecting System: Not part of the nephron but collects filtrate from multiple nephrons.

Components of Renal Corpuscle

• Glomerulus: Fenestrated capillaries that increase substance diffusion.
• Glomerular Capsule:
  • Composed of two layers:
  • Parietal Layer: Simple squamous epithelium; provides a container.
  • Visceral Layer: Podocytes (foot cells) with extensions called foot processes, forming filtration slits (slits are critical for filtration).
• Capsular Space: Area between parietal and visceral layers where filtrate accumulates.

Filtration Process

• Filtrate is formed from blood pushed into the glomerular capsule and accumulates in the capsular space before entering the renal tubule.

Renal Tubule Structure

• Divided into three parts:
  1. Proximal Tubule:
  • Lined with simple cuboidal epithelium (with microvilli).
  • Function: Involved in absorption due to increased surface area; closest to the renal corpuscle.
  1. Nephron Loop (Loop of Henle):
  • Two parts:
    • Thin Descending Limb: Simple squamous epithelium.
    • Thick Ascending Limb: Simple cuboidal epithelium (no microvilli).
  1. Distal Tubule:
  • Lined with simple cuboidal epithelium (few microvilli).

Collecting System

• Composed of Cortical and Medullary Collecting Ducts:
  • Cortical Collecting Duct: Located in the renal cortex.
  • Medullary Collecting Duct: Located in the renal medulla where filtrate exits to become urine.

Juxtaglomerular Apparatus (JGA)

• Formed where the distal tubule & afferent/efferent arterioles meet.
• Contains different types of cells:
  • Macula Densa Cells:
  • Part of distal tubule wall; monitor sodium and chloride concentrations in filtrate.
  • Juxtaglomerular (JG) Cells:
  • Located in afferent/efferent arterioles; serve as mechanoreceptors monitoring blood pressure and produce Renin (enzyme that regulates blood pressure).

Importance of Histology in Nephron Function

• Different types of epithelial tissues in each part of the nephron reflect their specific functions (e.g., absorption vs. secretion).
• Changes in permeability correspond to the differing structural makeup of nephron components.

Summary

• Understanding the structure and function of the nephron is crucial for grasping how the kidneys filter blood and produce urine.