Lecture Notes: Detailed Structure of Nephrons

Introduction

• Main focus: Understanding the detailed structure of nephrons
• Key aspects to be covered:
  1. General structure of nephrons
  2. Blood circulation in nephrons
  3. Types of nephrons

Key Points

1. Nephrons as Functional Unit of Kidney

   • Nephrons are the basic functional units of kidneys.
   • Each kidney contains approximately 1-1.3 million nephrons.
   • Nephron numbers cannot increase after birth, only decrease due to aging, injury, or disease.
   • Nephron size can increase depending on individual physiology and lifestyle factors.

2. General Structure of Nephrons

   • Parts of a Nephron: Two main parts
     • Renal corpuscle (non-tubular part): Consists of glomerulus and Bowman’s capsule.
     • Renal tubule (tubular part): Includes proximal convoluted tubule (PCT), loop of Henle (LH), distal convoluted tubule (DCT), and collecting duct (CD).
   • Renal Corpuscle: Further consists of:
     • Glomerulus: A network of blood capillaries for filtration.
     • Bowman’s capsule: Encloses the glomerulus.
   • Renal Tubule: Composed of:
     • Proximal Convoluted Tubule (PCT): Located near the glomerulus, responsible for reabsorption, features brush border with microvilli.
     • Loop of Henle (LH): Has descending and ascending limbs, critical for concentrating urine.
     • Distal Convoluted Tubule (DCT): Located away from the glomerulus, involved in further reabsorption and secretion.
     • Collecting Duct (CD): Collects urine from multiple nephrons and passes it into the renal pelvis.

3. Detailed Examination of Glomeruli and Bowman’s Capsule

   • Structure: Glomerulus inside Bowman’s capsule.
   • Filtration Process: Involves three layers:
     1. Endothelium of glomerular blood vessels (contains pores).
     2. Basement membrane (extra-cellular matrix, blocks large molecules).
     3. Podocytes of Bowman’s capsule (has foot-like extensions creating filtration slits).

4. Blood Circulation in Nephrons

   • Renal blood flow: From heart → Aorta → Renal artery → Arterioles → Capillaries (glomerulus) → Efferent arterioles → Peritubular capillaries → Renal vein → Inferior Vena Cava → Heart.
   • Pressure regulation: Afferent arteriole has larger diameter than efferent, creating high pressure for filtration in glomerulus.

5. Types of Nephrons

   • Cortical Nephrons:
     • Located mainly in the renal cortex.
     • Shorter loops of Henle.
     • Majority (about 80%) of nephrons.
   • Juxtamedullary Nephrons:
     • Located close to the medulla.
     • Longer loops of Henle extending deep into the medulla.
     • Crucial for producing concentrated urine.
     • Lesser in number (about 20%).

Summary

• General Structure: Nephrons consist of renal corpuscle and renal tubules.
• Blood Circulation: Key for filtration and maintains high pressure needed for filtration.
• Types: Cortical and Juxtamedullary, each with distinct roles and structures related to their functions.