Sebaceous glands consist of bulbous multilayered epithelium cones, termed sebaceous bulbs or sacs, which lack a luminal space (cf. Figs. 612, 613). The neck of the main bulb opens to the hair shaft. The cells inside the bulb grow larger, produce sebum and consequently, change into sebum cells [2. Their nuclei then die (apoptosis). In the usual preparations used for teaching purposes, the fat droplets are removed. This leads to more and more vacuoles in the cells at the center. While producing the secretory product, the cells die and are extruded together with the secretory material (sebum): holocrine extrusion, holocytosis, (cell lysis). New cells arrive from a supply line, which start at the peripheral cell layer (substitute cells, basal cells) 0.
1 Sebum in the neck of the gland
2 Sebaceous gland cells
3 Peripheral cells (substitute cells, basal cells) gg 4 Dense regular connective tissue
Mesenchymal cells are specific cells of the embryonic connective tissue. They will give rise to the adult connective and supporting tissue. The mesenchyme itself originates with the mesoderm early in the embryonic development. Mesenchymal cells have little cytoplasm; their large (euchromatin) nuclei show weak basophilia and contain one or more nucleoli. Mesenchymal cells show many cytoplasmic processes: thin, branched cell processes connect with each other and form a loose, spongy network that spans an intercellular substance (extracellular matrix) that is not specifically differentiated. Mesenchymal cells from a 10-day old mouse embryo.
Stain: Heidenhain iron hematoxylin; magnification: x 200
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