hormone has a well established physiological role in aiding reabsorption of water from tetrapod kidney tubules, but it may also raise the blood pressure of anaesthetized mammals,
elevate blood glucose levels, increase renal sodium excretion, initiate release of
adenohypophysial, adrenocortical and thyroid hormones and increase the motility of the
gut. These latter effects are most probably all pharmacological and reflect the actions of
quantities of hormone that do not normally appear in the circulation. It should also be remembered that after removal from a moribund animal, tissues are often subjected to a multitude of chemical insults; boiling, freezing , thawing, extraction in various solvents and the
like. Substances that are not normally secreted may be decocted, while novel materials may
appear as a result of tissue degradation.
d) Histological Procedures
Histological and cytological methods, using the light and electron microscopes, play an integral part in the study of endocrinology. Such techniques provide information about the
morphology of endocrine glands and their vascular and nerve connections that is relevant
to their function . The cytological appearance of the gland assists in the identif ication of
homologus tissues in other species, or even in different parts of the same animal. In addition
such precedures aid the precise localization of the cells in which the hormones originate
and are stored, and also may provide an index of activity .
Endocrine tissues and their secretions can be stained in am ulritude of ways that facilitate
observations of their structure. Some of these procedures are histochemical, being directed
towards the staining of specific substances like lipids , glycoproteins and cholesterol. Many
staining routines are, however, more arbitrary, their success being judged by their ability
to differentiate between various cells and to make secretory products visible. A vast number
of dyes, which may give comparable results in homologous tissues from a wide range of
species, can be used for such purposes. In many instances, however, a rarticular staining
technique may be peculiarly adapted to a particular species or group 0 animals.
D ifferential staining of the various cells in the pituitary gland provides a good example of
the types of procedures used. In the adenohypophysis a broad distinction can be made between cells which are stained by acid (acidophils) and basic (basophils) dyes .The basophils can
be stained by the periodic acid - SCHIFF (PAS) method, while the acidophils are exposed
by a modified MALLORY stain or HERLANT'S tetrachrome. These two groups of cells can
each be further subdivided, by differential staining with other dyes, to distinguish five or
six different types of cells. In the neurohypophysis, secretory material can be seen in nerve
cells after staining the tissue with GOMORI chrome-alum haematoxylin or paraldehyde-fuchsin. In adrenocortical tissue more precise histochemical procedures can be used, as this contains lipid droplets, cholesterol and ascorbic acid, all of which may be associated with its
endocrine activity. The lipid droplets can be seen after staining with fat soluble SUDAN dyes,
and specific methods are also available for the other materials. The thyroid hormones are
associated with the colloidal material stored in the follicles of.the gland, and this stains with
periodic acid - SCHIFF reagent . Suitable histological procedures have been described for all
endocrine tissues in a large variety of species.
Once the types of cells present in an endocrine tissue have been histologically characterized by their situation, shape, size and reaction to dyes, an attempt can be made to identify
the role of each in the production and storage of the different hormones that may be present.
This can be quite a problem, even if only one or two hormones are involved. Thus, the pituicytes present in the neurohypophysis were for a long time thought to be the site of formation of the antidiuretic hormone, though it is now clear this hormone originates in the
nerve cells that extend into this tissue . BARGMANN, using the chrome-alum haematoxylin
stain, was able to identify secretory material in the nerve terminals and axons of the neural
lobe, and was able to trace such material back along the nerve fibre to its site of origin in
the hypothalamus. The distribution and quantity of this material paralleled that of antidiuretic hormone, and so initiated our contemporary views on the cellular sites for the formation and storage of this hormone. The problem may be somewhat greater, when, as in
the instance of the adenohypophysis, six or seven hormones may originate in proximity
to each other. Cytological changes in each cell type can be observed under a variety of natural
43
elevate blood glucose levels, increase renal sodium excretion, initiate release of
adenohypophysial, adrenocortical and thyroid hormones and increase the motility of the
gut. These latter effects are most probably all pharmacological and reflect the actions of
quantities of hormone that do not normally appear in the circulation. It should also be remembered that after removal from a moribund animal, tissues are often subjected to a multitude of chemical insults; boiling, freezing , thawing, extraction in various solvents and the
like. Substances that are not normally secreted may be decocted, while novel materials may
appear as a result of tissue degradation.
d) Histological Procedures
Histological and cytological methods, using the light and electron microscopes, play an integral part in the study of endocrinology. Such techniques provide information about the
morphology of endocrine glands and their vascular and nerve connections that is relevant
to their function . The cytological appearance of the gland assists in the identif ication of
homologus tissues in other species, or even in different parts of the same animal. In addition
such precedures aid the precise localization of the cells in which the hormones originate
and are stored, and also may provide an index of activity .
Endocrine tissues and their secretions can be stained in am ulritude of ways that facilitate
observations of their structure. Some of these procedures are histochemical, being directed
towards the staining of specific substances like lipids , glycoproteins and cholesterol. Many
staining routines are, however, more arbitrary, their success being judged by their ability
to differentiate between various cells and to make secretory products visible. A vast number
of dyes, which may give comparable results in homologous tissues from a wide range of
species, can be used for such purposes. In many instances, however, a rarticular staining
technique may be peculiarly adapted to a particular species or group 0 animals.
D ifferential staining of the various cells in the pituitary gland provides a good example of
the types of procedures used. In the adenohypophysis a broad distinction can be made between cells which are stained by acid (acidophils) and basic (basophils) dyes .The basophils can
be stained by the periodic acid - SCHIFF (PAS) method, while the acidophils are exposed
by a modified MALLORY stain or HERLANT'S tetrachrome. These two groups of cells can
each be further subdivided, by differential staining with other dyes, to distinguish five or
six different types of cells. In the neurohypophysis, secretory material can be seen in nerve
cells after staining the tissue with GOMORI chrome-alum haematoxylin or paraldehyde-fuchsin. In adrenocortical tissue more precise histochemical procedures can be used, as this contains lipid droplets, cholesterol and ascorbic acid, all of which may be associated with its
endocrine activity. The lipid droplets can be seen after staining with fat soluble SUDAN dyes,
and specific methods are also available for the other materials. The thyroid hormones are
associated with the colloidal material stored in the follicles of.the gland, and this stains with
periodic acid - SCHIFF reagent . Suitable histological procedures have been described for all
endocrine tissues in a large variety of species.
Once the types of cells present in an endocrine tissue have been histologically characterized by their situation, shape, size and reaction to dyes, an attempt can be made to identify
the role of each in the production and storage of the different hormones that may be present.
This can be quite a problem, even if only one or two hormones are involved. Thus, the pituicytes present in the neurohypophysis were for a long time thought to be the site of formation of the antidiuretic hormone, though it is now clear this hormone originates in the
nerve cells that extend into this tissue . BARGMANN, using the chrome-alum haematoxylin
stain, was able to identify secretory material in the nerve terminals and axons of the neural
lobe, and was able to trace such material back along the nerve fibre to its site of origin in
the hypothalamus. The distribution and quantity of this material paralleled that of antidiuretic hormone, and so initiated our contemporary views on the cellular sites for the formation and storage of this hormone. The problem may be somewhat greater, when, as in
the instance of the adenohypophysis, six or seven hormones may originate in proximity
to each other. Cytological changes in each cell type can be observed under a variety of natural
43