Page 67 - Atlas of Histology with Functional Correlations

FIGURE 1.10 | Planes of Section of a Round, Solid

Object

To illustrate how the shape of a three-dimensional cell can be altered in a
histologic section, a hard-boiled egg has been sectioned in longitudinal and

transverse (cross) planes. The composition of a hard-boiled egg serves as a good
example of a cell, with the yellow yolk representing the nucleus and the
surrounding egg white (pale blue) representing the cytoplasm. Enclosing these

structures are the soft eggshell membrane and a hard eggshell (red). At the
rounded end of the egg is the air space (blue).

The midline sections of the egg in the longitudinal (a) and transverse
planes (d) disclose its correct shape and size, as they appear in these planes of
section. In addition, these two planes of section reveal the correct appearance,

size, and distribution of the internal contents within the egg.

Similar but more peripheral sections of the egg in the longitudinal (b) and
transverse planes (e) still show the external shape of the egg. However, because
the section was cut peripherally and below the midline, the internal contents of

the egg are not seen in their correct size or distribution within the egg white. In
addition, the size of the egg appears smaller.

The tangential plane (c and f) of the section grazes or only passes through
the outermost periphery of the egg. This section reveals that the egg is oval (c) or
a small round (f) object. The egg yolk is not seen in either section because it was

not located in the plane of section. As a result, such tangential section does not
reveal sufficient detail for correct interpretation of the egg size or of its contents
or their distribution within the internal membrane.

Thus, in a histological section, individual structure, shape, and size vary

depending on the plane of section. Some cells may exhibit full cross sections of
their nuclei, and they appear prominent in the cells. Other cells may exhibit only
a fraction of the nucleus, and the cytoplasm appears large. Still other cells may
appear only as clear cytoplasm, without any nuclei. All these variations are
attributable to different planes of section through the nuclei. Understanding these

variations in cell and tube morphology becomes important in interpreting
different histological sections.

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