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Technical Discussion The pituitary gland
is often portrayed as the "master gland" of the body. Such praise is
justified in the sense that the anterior and posterior pituitary
secrete a battery of hormones that collectively influence all cells
and affect virtually all physiologic processes.
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Lay Interpretation
The pituitary gland is called the Master Gland as almost all
significant functions within the body fall under the influence of
the pituitary gland at some point. |
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The pituitary gland may be king, but the power
behind the throne is clearly the hypothalamus. As alluded to in
the last section, some of the neurons within the hypothalamus -
neurosecretory neurons - secrete hormones that strictly control
secretion of hormones from the anterior pituitary.
The hypothalamic
hormones are referred to as releasing hormones and
inhibiting hormones, reflecting their influence on anterior
pituitary hormones.
Hypothalamic releasing and inhibiting hormones are
carried directly to the anterior pituitary gland via
hypothalamic-hypophyseal portal veins. Specific hypothalamic
hormones bind to receptors on specific anterior pituitary cells,
modulating the release of the hormone they produce.
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Whilst the pituitary gland is called the master gland, it is in fact
the hypothalamus which is the power behind the throne. The
hypothalamus is responsible for stimulating and inhibiting pretty
much all of the functions of the pituitary gland.
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As an example, thyroid-releasing hormone from the
hypothalamus binds to receptors on anterior pituitary cells called
thyrotrophs, stimulating them to secrete thyroid-stimulating hormone
or TSH. The anterior pituitary hormones enter the systemic
circulation and bind to their receptors on other target organs. In
the case of TSH, the target organ is the thyroid gland.
Clearly, robust control systems must be in place
to prevent over or under-secretion of hypothalamic and anterior
pituitary hormones.
A prominent mechanism for control of the
releasing and inhibiting hormones is
negative feedback. Details on the control of specific
hypothalamic and anterior pituitary hormones is presented in the
discussions of those hormones.
The following table summarizes the major hormones
synthesized and secreted by the pituitary gland, along with summary
statements about their major target organs and physiologic effects.
Keep in mind that summaries are just that, and ongoing research
continues to delineate additional, sometimes very important effects.
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Needless to detail beyond outline, correct function of the
hypothalamus and pituitary are critical to life. |
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Hormone |
Major
target organ(s) |
Major Physiologic
Effects |
Anterior
Pituitary |
Growth hormone |
Liver, adipose tissue |
Promotes growth (indirectly),
control of protein, lipid and carbohydrate metabolism |
| Thyroid-stimulating
hormone |
Thyroid gland |
Stimulates secretion of thyroid
hormones |
| Adrenocorticotropic
hormone |
Adrenal gland (cortex) |
Stimulates secretion of
glucocorticoids |
| Prolactin |
Mammary gland |
Milk production |
| Luteinizing hormone |
Ovary and testis |
Control of reproductive function |
| Follicle-stimulating
hormone |
Ovary and testis |
Control of reproductive function |
Posterior
Pituitary |
Antidiuretic hormone |
Kidney |
Conservation of body water |
| Oxytocin |
Ovary and testis |
Stimulates milk ejection and
uterine contractions |
A final point to be made is that individual
cells within the anterior pituitary secrete a single hormone
(or possibly two in some cases). Thus, the anterior pituitary
contains at least six distinctive endocrinocytes.
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The anterior (front) pituitary gland is responsible for production
of many hormones. The table to the left shows the amazing array of
functions ultimately dependant upon the function of the pituitary
gland.
The pituitary gland is made up of many different types of cells,
each producing a single hormone. Thus, this gland contains at
least six distinctive cell types, each with very different
functions.
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The cells that secrete thyroid-stimulating hormone do not
also secrete growth hormone, and they have receptors for
thyroid-releasing hormone, not growth hormone-releasing hormone.
The image below is of a section of canine anterior pituitary
that was immunologically stained for luteinising hormone (black
stain) and prolactin (purple stain). The unstained cells in the
image are those that secrete the other pituitary hormones.
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The technical information on these pages is the work of
Professor Bowen et al, Colorado State University and are reproduced
without endorsement of any kind. The "lay" interpretations are
the work of this site and do not necessarily reflect Professor
Bowen's opinions. |
