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