Human physiology / by William Furneaux.

  • William Samuel Furneaux
Date:
1909
Catalogue details

Licence: In copyright

Credit: Human physiology / by William Furneaux. Source: Wellcome Collection.

    105/270 page 93
    LESSON XVII. GLANDS—THE SALIVARY GLANDS AND INSALIVATION. A gland is an organ which has the power of separating certain materials from the blood which flows through it. Glands are of 3 _ through two kinds ; secreting and excreting. A secreting gland (Lat. se, aside; and cerno, I separate) is one which prepares a substance from the materials of the blood ; in other words, it manufactures a material which did not pre-exist in the blood; this substance being set apart for some future use in the body. Each secreting gland is provided with a system of blood- vessels, and generally a duct or tube which conveys away the material prepared. An excreting gland (Lat. ex, out; and cerno) does not prepare a substance, but simply separates a ma- terial from the blood which is afterwards to be expelled from the body. These glands also are provided with ducts for the removal of the ex- cretion— the substance ex- creted. The sweat glands of the skin are an example of this kind of gland. Fig. 91.—Simple Secreting Glands. 1, straight tube ; 2, sac ; 3, coiled tube. Fig. 92.- -Simple Glands, with, pouched sides. There are other bodies known as ductless glands, which, as their name implies, have no ducts. The functions of these organs are not well understood, but they generally appear to be concerned in the elaboration of the blood. The spleen is one of the ductless glands. Many of the membranes which line the cavities of the body and its organs also have the power of secretion, hence they are called secreting membranes. The amount of substance secreted obviously depends on the extent of the secreting surface. Hence we sometimes find the membrane drawn up into folds in order that its surface may be increased. On the other hand, we often find the secreting membrane dipping down into the substance beneath in such a manner as to form a multitude of minute tubes, each one having an opening at the general surface. This forms the simplest kind of gland, called the simple tubular gland. In many cases the tubular gland is developed into a coil or convolution, thus adding still more to the secreting surface. The tubular gland is also sometimes enlarged till its shape is somewhat globular;
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