MH 001 Nuclear Morphology

Nuclei

Cells exhibit remarkable diversity in their size, shape, and structural organization, reflecting their specialized functions and roles. In histological sections, the nucleus is often the most prominent cellular component.

When stained with hematoxylin and eosin (H&E), chromatin organization within nuclei reveals two distinct patterns:

• Heterochromatic Nuclei () Toggle Label Visibility
  • Appearance: Small, round, nuclei with uniform, intense basophilic staining by hematoxylin (dark blue-purple)
  • Structure: Tightly condensed chromatin with minimal internal detail
  • Function: Characteristic of cells with low transcriptional and metabolic activity
  • Euchromatic Nuclei () Toggle Label Visibility
    • Appearance: Larger, oval nuclei with variable staining intensity
    • Structure:
      • Narrow rim of condensed chromatin along the nuclear membrane
      • Irregularly distributed, more lightly stained clumps in the nuclear matrix
      • Prominent, darkly stained nucleolus (when present)
    • Function: Loosely organized chromatin allows active gene transcription
      • Typical of cells engaged in protein synthesis

  The distinction between heterochromatic and euchromatic patterns serves as a valuable histological indicator of cellular activity, aiding in tissue diagnosis and the assessment of pathological conditions.

Small Cells

Lymph nodes contain small immune cells that exhibit distinctive morphological characteristics, reflecting their quiescent functional state.

When stained with hematoxylin and eosin (H&E), lymphocytes can be readily identified by their characteristic morphology.

• Cell Size: Small cells measuring 7 to 10 µm in diameter
  • Approximately equivalent to red blood cell diameter
  • Nucleus occupies ~75% of the total cell volume
• Nuclear Morphology: Small, round to slightly oval heterochromatic nuclei
  • Uniform, intense staining by hematoxylin (dark-blue-purple)
  • Tightly condensed chromatin
  • Reflects low transcriptional activity typical of resting immune cells
• Cytoplasm:
  • Thin rim of pale cytoplasm surrounding the nucleus
  • Light acidophilic staining by eosin (pink-red) of barely visible cytoplasm
  • Sparse organelles consistent with a quiescent metabolic state

The small cell size and heterochromatic nuclei of lymphocytes are reliable indicators for identifying lymphoid tissue and reactive lymphocyte populations in other tissues.

Large Cells

Adipose tissue consists primarily of adipocytes, which are designed for lipid storage and metabolic regulation. The morphology of these cells, also known as adipose cells or fat cells, reflects their unique function in energy metabolism.

When examining tissues stained with hematoxylin and eosin (H&E), adipocytes are readily identifiable in the connective tissue that surrounds many organs.

• Cell Size: Large cells measuring 30 to 50 µm in diameter
  • Approximately 4-7 times larger than red blood cells (7-8 µm diameter)
  • Nucleus occupies ~75% of the total cell volume
• Nuclear Morphology: Flattened heterochromatic nuclei displaced to the cell periphery by the large lipid droplet
  • Large cell size means most sections do not pass through the nucleus
• Cytoplasm: Large, centrally located lipid droplet occupying most of the cell volume
  • Lipid droplets remain unstained by both hematoxylin and eosin

Very Large Cells

Motor neurons in the spinal cord represent some of the largest cells in the human body, along with mature ova in the ovary.

When examining spinal cord tissue stained with hematoxylin and eosin (H&E), motor neurons can be identified by their exceptional size and staining characteristics.

• Cell Size: Large stellate cells (star-shaped) measuring 80 to 120 µm in diameter
  • Large cell size means most sections only pass through a couple of processes
  • Compare the cell size to red blood cells (RBC), 7 to 8 µm in diameter, in the nearby capillary
• Nuclear Morphology: Large nucleus measuring 20 to 30 µm in diameter
  • Round to oval euchromatic nucleus
  • Large nucleolus intensely stained with hematoxylin
• Cytoplasm:
  • A wide rim of cytoplasm surrounds the nucleus
  • Strong heterogeneous basophilic staining by hematoxylin (dark blue-purple) due to the large number of ribosomes
  • Reflects the extensive protein synthesis and metabolic activity of these cells

The distinctive morphology of motor neurons reflects their role in neural transmission and the enormous metabolic demands for maintaining extensive dendritic processes and a single, longer axonal process.

Hepatocytes

The liver is composed primarily of hepatocytes, which represent the principal functional cells of this important metabolic organ. Unlike the exceptionally large motor neurons, hepatocytes are closer in size to typical somatic cells.

When examining liver tissue stained with hematoxylin and eosin (H&E), individual hepatocytes can often be difficult to identify.

• Cell Size: Moderately large cells measuring 25 to 30 µm in diameter
  • Nearby red blood cells provide reliable internal measurements despite poor preservation
• Nuclear Morphology: Round to oval heterochromatic nuclei
  • Round to oval heterochromatic nuclei
  • Nucleus occupies less than 5% of the total cell volume
  • Nucleolus intensely stained with hematoxylin
  • May exhibit binucleate cells (containing two nuclei)
• Cytoplasm:
  • Strong acidophilic staining by eosin (pink-red) indicates large amounts of protein
    • Hepatocytes contain large numbers of mitochondria
  • Abundant cytoplasm relative to nuclear size
  • Accommodates numerous organelles required for their wide range of metabolic functions
    • Hepatocytes contain large numbers of mitochondria