Endocrine cells do not exist in rat Brunner's glands. An electron microscopic study

Area of Science:

• Cell Biology
• Histology
• Gastroenterology

Background:

• Brunner's glands and duodenal epithelium contain cells with basally located granules.
• These granules, identified ultrastructurally, have been variably classified as mucous, serous, or endocrine cells.
• Previous classifications lacked detailed correlation with organelle morphology and synthesis processes.

Purpose of the Study:

• To correlate ultrastructural morphological criteria of Brunner's gland cells with mucopeptide synthesis.
• To elucidate the distinct phases of mucopeptide synthesis within these cells.

Main Methods:

• Light and electron microscopic examination of human and mammalian duodenal tissues.
• Correlation of nuclear and nucleolar morphology (size, shape, electron density) with cytoplasmic and intranuclear organelles.
• Analysis of organelles involved in mucopeptide synthesis, including ribosomes, endoplasmic reticulum, receptosomes, and lysosomes.

Main Results:

• Mucopeptide synthesis occurs in three distinct phases.
• Phase 1 (euchromatic phase): Intranuclear organelle synthesis characterized by electron-lucent nucleus/nucleolus and minimal cytoplasmic organelles.
• Phase 2 (early heterochromatic phase): Heterochromatic nucleus/nucleolus, with developing receptosome- (endosome) and lysosome-like structures near the basal membrane and perinuclear region.

Conclusions:

• Brunner's gland cells exhibit a dynamic three-phase process for mucopeptide synthesis.
• Intranuclear organelle synthesis precedes cytoplasmic involvement in mucopeptide production.
• Ultrastructural changes provide a detailed map of the cellular machinery for mucopeptide synthesis in the duodenum.