pore(redirected from alveolar pore)
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in plant anatomy, a thin, microscopic area in the primary cell membrane. Pores, which are more commonly called pits, usually appear in pit fields, intertwined with plasmodesmata of cytoplasm. They are formed during the uneven secondary thickening of the cell membrane. Pores may appear in the membranes of adjacent cells (pit-pairs). A distinction is made between simple pits, which are found in parenchyma tissues and in fibers, and bordered pits, which form chiefly in the water-conducting elements of woody tissue. In the tracheids of conifers, the membrane of bordered pits of adjacent cells has a thickening in the center called a torus, which can function as a valve. Pores play an important role in the vital activity of cells and in the conduction of substances to all the tissues. Pores are also present in the cell membranes of lower plants. Sometimes the conducting elements of vessels in higher plants develop contiguous openings in the membranes of adjacent cells (at the site of the pores) called perforations.
I. S. MIKHAILOVSKAIA
The pores of animals included the openings of the efferent ducts of the sweat glands on the surface of the epidermis (sweat pores) and the openings of the canals by which the taste receptors communicate with the surface of the epithelium of the oral cavity (taste pores).
In karyology, pores are round spots filled with a solid substance in the membrane of the cell nucleus. They are circumscribed by the fused surface of the internal and external nuclear membrane, which forms a small ring containing eight granules joined together by thin fibrils. The substance filling the pore sometimes presses deep into the karyoplasm in the form of a cylinder and protrudes slightly into the cytoplasm surrounding the nucleus, forming a pore complex with the ring. A pore is 200–1,000 A in diameter. Pores occupy 5 to 10 percent of the entire nuclear membrane surface. Owing to the nature of permeability, pores play an important role in the transport of macromolecular substances from the nucleus to the cytoplasm and back.