Histology Spotters - Identification Points

Department of Anatomy - Discussion

1. MUCOUS SALIVARY GLAND

• Mucous acini - large, pale-staining (light with H&E), cells arranged around a wide lumen
• Nuclei are flattened and pushed to the base of cells
• Cytoplasm appears vacuolated/foamy (mucin washes out in processing)
• Demilunes of serous cells may be seen capping mucous acini (in sublingual gland)
• Striated ducts (intralobular) with basal striations visible
• Interlobular ducts and lobular arrangement with connective tissue septa
• Capsule of dense connective tissue
• Sublingual = predominantly mucous; submandibular = mixed (mainly serous)

2. HYALINE CARTILAGE

• Glassy/homogeneous matrix - bluish-purple with H&E (basophilic due to proteoglycans)
• Chondrocytes in lacunae - rounded cells in spaces within matrix; appear shrunken in prepared sections
• Isogenous groups (cell nests) - 2-8 chondrocytes from same parent cell
• Perichondrium - outer layer of dense connective tissue (fibrous outer + chondrogenic inner layer); ABSENT in articular cartilage
• Territorial matrix (capsule) - deeply basophilic zone immediately around each lacuna
• Interterritorial matrix - paler zone between cell groups
• No blood vessels, no nerves, no lymphatics within cartilage
• Young chondrocytes (chondroblasts) at periphery are flattened/elliptical

3. CARDIAC MUSCLE

• Cross striations (A, I, H bands) - but less prominent than skeletal muscle
• Intercalated discs - darkly staining transverse lines connecting adjacent cells (PATHOGNOMONIC)
• Branching muscle fibers forming a network (syncytium-like)
• Single central nucleus (occasionally 2), oval, centrally placed with pale halo
• Endomysium rich in capillaries (mitochondria-rich cells - appears granular)
• Fibers arranged in spiral/whorled bundles
• Perinuclear clear zones (glycogen accumulation around nucleus)
• No satellite cells

4. SENSORY GANGLION (Dorsal Root / Cranial Sensory Ganglion)

• Pseudounipolar neurons - large, rounded cell bodies (perikarya) with single process
• Eccentric/central nucleus with prominent nucleolus ("owl eye" appearance)
• Satellite (capsule) cells - small flattened glial cells completely surrounding each neuron
• Nissl substance (RER) visible as granular cytoplasm
• No dendrites distinguishable (pseudounipolar = single process that divides into central + peripheral branches)
• Neurons arranged in clusters within connective tissue stroma
• Nerve fibers (axons) running between neuron clusters
• Surrounded by a connective tissue capsule
• Differs from autonomic ganglia: NO multipolar neurons, satellite cells more prominent

5. THYMUS

• Cortex - darkly staining (dense lymphocytes = thymocytes), outer zone
• Medulla - paler staining (fewer lymphocytes, more epithelial reticular cells), inner zone
• Hassall's (thymic) corpuscles - concentric whorls of keratinized epithelial cells in medulla (PATHOGNOMONIC)
• Lobular architecture - incomplete lobules separated by connective tissue septa from capsule
• Blood-thymus barrier in cortex (capillary + epithelial sheath)
• Epithelial reticular cells form a framework (stellate cells with tonofilaments)
• No lymphoid follicles (germinal centers)
• No sinuses

6. SKIN - L.S. (Longitudinal Section through hair-bearing skin)

• Epidermis layers (from surface): Stratum corneum → granulosum → spinosum → basale (germinativum)
• Stratum corneum - anucleate, keratinized cells (pink, basket-weave pattern)
• Stratum granulosum - cells with keratohyalin granules (basophilic)
• Rete ridges (epidermal pegs) interdigitating with dermal papillae
• Dermis - papillary (loose CT) + reticular (dense irregular CT) layers
• Hair follicles in longitudinal profile - inner/outer root sheaths, hair shaft, sebaceous gland
• Sebaceous glands - associated with hair follicle, holocrine secretion
• Sweat glands (eccrine) in deep dermis/hypodermis
• Arrector pili muscle (smooth muscle) attached to follicle

7. SKIN - T.S. (Transverse/Cross Section through hair-bearing skin)

• Same layers as above but cut in cross-section
• Hair follicles appear as circular structures in cross-section
  • Hair shaft (cortex + medulla) in center
  • Inner root sheath (IRS)
  • Outer root sheath (ORS)
  • Connective tissue sheath
• Sebaceous glands cut obliquely/transversely - pale foamy cells (lipid-rich)
• Sweat gland ducts - small rounded double-layered epithelium
• Blood vessels cross-sectioned in dermis
• Epidermis seen as a thin strip (if included)

8. UMBILICAL CORD

• Wharton's jelly - abundant gelatinous ground substance (mucous CT), pale blue/purple
• 2 umbilical arteries - thick muscular wall (no elastic laminae), no vasa vasorum
• 1 umbilical vein - larger lumen, thinner wall, no valves
• No adventitia distinguishable from surrounding Wharton's jelly
• Amniotic epithelium covering the surface (simple or stratified squamous/cuboidal)
• Stellate fibroblasts (mucous cells) scattered in jelly matrix
• No nerves in umbilical cord
• Remnant of allantois may be present (urachus - small epithelial channel)

9. PLACENTA

• Chorionic villi - the basic structural unit, floating or anchoring
• Two trophoblast layers:
  • Syncytiotrophoblast - outer, multinucleated, no cell boundaries, darkly staining nuclei
  • Cytotrophoblast (Langhans cells) - inner, distinct cell boundaries, pale cytoplasm (prominent in early pregnancy, diminish at term)
• Fetal mesenchyme core within each villus with fetal capillaries
• Hofbauer cells - large pale macrophages in villus mesenchyme
• Intervillous space filled with maternal blood (no endothelial lining)
• Fibrinoid material (Nitabuch's layer) at basal plate
• Decidua (maternal component) - large polygonal cells with pale cytoplasm

10. SPLEEN

• White pulp - lymphoid tissue surrounding central arteriole (PALS - periarteriolar lymphoid sheath + lymphoid follicles)
• Red pulp - venous sinuses + splenic cords (Billroth's cords)
• Central arteriole - off-center within white pulp (eccentric position)
• Germinal centers may be visible in lymphoid follicles
• Marginal zone between white and red pulp
• Trabeculae with trabecular arteries/veins from the thick capsule
• Capsule of dense CT with smooth muscle (contractile)
• No sinuses with specific lining in cortex (unlike lymph node)
• No afferent lymphatics

11. AORTA

• Tunica intima - endothelium + thin subendothelial CT + internal elastic lamina (may merge with media)
• Tunica media - VERY THICK, with numerous concentric elastic laminae/fenestrated sheets (40-70 layers), smooth muscle cells between them (PATHOGNOMONIC of elastic artery)
• Tunica adventitia - relatively thin, dense CT, contains vasa vasorum and nerve fibers (nervi vasorum)
• With elastic stains (Verhoeff/Orcein): elastic fibers stain dark - multiple concentric rings
• No distinct internal/external elastic lamina (unlike muscular arteries)
• Wide lumen relative to wall thickness
• Distinction from muscular artery: media dominated by elastic > smooth muscle

12. LYMPH NODE

• Capsule of dense CT with trabeculae extending inward
• Cortex:
  • Lymphoid follicles (primary = dense; secondary = with pale germinal center)
  • Germinal centers with large lymphoblasts, mitotic figures
  • Mantle zone of small lymphocytes surrounding germinal center
• Paracortex (deep cortex) - T-cell zone, less organized lymphocytes
• Medulla:
  • Medullary cords - plasma cells, macrophages, lymphocytes
  • Medullary sinuses - macrophage-lined channels
• Subcapsular (marginal) sinus just beneath capsule - receives lymph from afferent vessels
• Afferent lymphatics enter through capsule; single efferent lymphatic exits at hilum
• High endothelial venules (HEV) in paracortex (lymphocyte homing)
• Hilum contains artery, vein, efferent lymphatic

Quick Comparison Summary Table

Sources: Junqueira's Basic Histology - Text and Atlas, 17e | Histology: A Text and Atlas with Correlated Cell and Molecular Biology (Pawlina)