Experiment 03Mammalian HistologyTissue Microanatomy
Mammalian Histology: Microscopic Identification of Primary Visceral Organ Tissues (Liver & Kidney Cortex)
Lab Duration: 3 Hours • Hematoxylin & Eosin (H&E) Staining • Mammalian Microtomy
🎯 Aim: To examine permanent Hematoxylin and Eosin (H&E) stained transverse histological sections of mammalian visceral organs (Liver and Kidney cortex), identify functional microanatomical subunits (hepatic lobule, central vein, portal triad, renal corpuscle, glomerulus, Bowman’s capsule, PCT and DCT), and correlate cellular architecture with physiological functions.
🔬 Principle & Histochemical Architecture
Routine diagnostic histology relies on the universal counterstain pair Hematoxylin and Eosin (H&E):
- Hematoxylin (Basic/Cationic dye): Binds to acidic, polyanionic basophilic structures (nuclear DNA and ribosomal RNA/heterochromatin), staining nuclei deep blue-purple.
- Eosin Y (Acidic/Anionic dye): Binds to basic, cationic acidophilic/eosinophilic cytoplasmic proteins and extracellular collagen fibers, staining cytoplasm and connective tissue matrix pink/red.
1. Mammalian Liver (Hepatic Lobule):
- Arranged into polygonal/hexagonal classic hepatic lobules centered around a thin-walled Central Vein.
- Plates of polyhedral hepatocytes (with central spherical nuclei and abundant glycogen/mitochondria) radiate outward like wheel spokes from the central vein toward the periphery.
- Between hepatocyte plates lie fenestrated hepatic sinusoids carrying mixed arterial and venous blood, lined by phagocytic reticuloendothelial Kupffer cells.
- At the peripheral corners of adjacent lobules lie the Portal Triads embedded in connective tissue, each containing three diagnostic structures:
– Portal Venule: Large, irregularly shaped lumen with thin endothelial lining.
– Hepatic Arteriole: Smaller lumen with a thick, distinct tunica media of smooth muscle cells.
– Bile Ductule: Lined by uniform simple cuboidal epithelium.
2. Mammalian Kidney (Renal Cortex):
- Features thousands of spherical Renal Corpuscles (Malpighian Bodies), each consisting of:
– Glomerulus: A convoluted tuft of fenestrated anastomosing capillaries covered by visceral podocytes.
– Bowman’s Capsule: Outer parietal layer composed of a single layer of flat simple squamous epithelial cells, separated from the capillary tuft by a distinct, clear Urinary (Bowman’s) space. - Surrounding convoluted tubules in the cortical labyrinth:
– Proximal Convoluted Tubules (PCT): Lined by simple cuboidal epithelial cells possessing an apical brush border of dense microvilli ($> 1,mutext{m}$ high) that stains intensely eosinophilic pink, producing a narrow, fuzzy, star-shaped lumen (specialized for reabsorbing $65%$ of glomerular filtrate).
– Distal Convoluted Tubules (DCT): Lined by smaller simple cuboidal cells lacking a brush border; cytoplasm stains paler pink, producing a clean, wide, well-defined open circular lumen.
Figure 3.1: Microscopic histology of mammalian visceral organs: hepatic lobule with central vein vs renal cortex with glomerulus and convoluted tubules.
📋 Step-by-Step Microscopic Protocol
- Liver Slide Examination: Place the H&E mammalian liver slide on the mechanical stage. Under low power ($100times$), scan for the hexagonal lobular boundaries. Center on a single classic hepatic lobule.
- Liver High-Power Diagnostics: Switch to $400times$. Identify the central vein and trace hepatocyte cords radiating outward. Locate sinusoidal spaces and search for dark, elongated Kupffer cell nuclei lining sinusoidal walls. Move the stage to the perimeter to find a portal canal: confirm the presence of all three portal triad structures (portal vein branch, hepatic artery branch, bile ductule). Sketch and label.
- Kidney Cortex Slide Examination: Mount the mammalian kidney cortex slide. Under $100times$, identify the dense distribution of rounded renal corpuscles in the superficial cortex.
- Renal Corpuscle Diagnostics: Switch to $400times$. Observe the central glomerulus capillary knot, the surrounding translucent Bowman’s urinary space, and the simple squamous nuclei of the outer parietal capsule wall. Locate the vascular pole (where afferent and efferent arterioles enter/exit) and the urinary pole (continuous with the PCT neck).
- Tubular Differentiation: Differentiate cross-sections of proximal convoluted tubules (PCT) from distal convoluted tubules (DCT) based on three diagnostic criteria: lumen appearance (occluded brush border in PCT vs clear open lumen in DCT), cell height, and nuclear density per cross-section (fewer nuclei in PCT cross-section due to larger cell volume; more nuclei in DCT cross-section).
