Page 38 - Textbook of Pathology, 6th Edition

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SECTION I

General Pathology and Basic Techniques

Figure 3.2 Schematic diagram of the structure of an epithelial cell.

receptors are probably related to the microtubules and micro- Nucleus
filaments of the underlying cytoplasm. The microtubules The nucleus consists of an outer nuclear membrane enclosing
connect one receptor with the next. The microfilaments are nuclear chromatin and nucleoli.
contractile structures so that the receptor may move within
the cell membrane. Bundle of microfilaments along with NUCLEAR MEMBRANE. The nuclear membrane is the
cytoplasm and protein of cell membrane may form outer envelop consisting of 2 layers of the unit membrane
projections on the surface of the cell called microvilli. which are separated by a 40-70 nm wide space. The outer
Microvilli are especially numerous on the surface of layer of the nuclear membrane is studded with ribosomes
absorptive and secretory cells (e.g. small intestinal mucosa) and is continuous with endoplasmic reticulum. The two
increasing their surface area. layers of nuclear membrane at places are fused together
In brief, the cell membrane performs the following forming circular nuclear pores which are about 50 nm in
important functions: diameter. The nuclear membrane is crossed by several factor
i) Selective permeability that includes diffusion, membrane which regulate the gene expression and repair the DNA
pump (sodium pump) and pinocytosis (cell drinking). damage as soon as it occurs.
ii) Bears membrane antigens (e.g. blood group antigens, NUCLEAR CHROMATIN. The main substance of the
transplantation antigen). nucleus is comprised by the nuclear chromatin which is in
iii) Possesses cell receptors for cell-cell recognition and the form of shorter pieces of thread-like structures called
communication. chromosomes of which there are 23 pairs (46 chromosomes)