Pituitary gland

The pituitary gland, or hypophysis, is located at the base of the brain just below the hypothalamus. It is composed of two functionally and anatomically distinct lobes (see Figure 10.2):

Figure 10.2 Anatomical and functional relationship between the hypothalamus and pituitary gland. The neurohypophysis is derived from the hypothalamus, an anatomical connection that allows the hypothalamus to influence the function of the neurohypophysis directly. Action potentials conducted by neurosecretory cells originating in the hypothalamus cause the release of hormones stored in the neurohypophysis. The adenohypophysis is derived from glandular tissue and therefore has no anatomical connection to the hypothalamus. The release of hormones from the adenohypophysis is regulated by hypothalamic hormones carried to the adenohypophysis through the hypothalamic-hypophyseal portal veins. Hypothalamic hormones enter the tissue of the adenohypophysis and influence production of adenohypophyseal hormones. Hormones released from both regions of the pituitary gland (the neurohypophysis and adenohypophysis) are removed from the pituitary gland by the venous outflow blood and transported to target tissues throughout the body.

Figure 10.2 Anatomical and functional relationship between the hypothalamus and pituitary gland. The neurohypophysis is derived from the hypothalamus, an anatomical connection that allows the hypothalamus to influence the function of the neurohypophysis directly. Action potentials conducted by neurosecretory cells originating in the hypothalamus cause the release of hormones stored in the neurohypophysis. The adenohypophysis is derived from glandular tissue and therefore has no anatomical connection to the hypothalamus. The release of hormones from the adenohypophysis is regulated by hypothalamic hormones carried to the adenohypophysis through the hypothalamic-hypophyseal portal veins. Hypothalamic hormones enter the tissue of the adenohypophysis and influence production of adenohypophyseal hormones. Hormones released from both regions of the pituitary gland (the neurohypophysis and adenohypophysis) are removed from the pituitary gland by the venous outflow blood and transported to target tissues throughout the body.

PITUITARY GLAND

PITUITARY GLAND

• Neurohypophysis (posterior pituitary)

• Adenohypophysis (anterior pituitary)

As its name implies, the neurohypophysis is derived embryonically from nervous tissue. It is essentially an outgrowth of the hypothalamus and is composed of bundles of axons, or neural tracts, of neurosecretory cells originating in two hypothalamic nuclei. These neurons are referred to as neurosecretory cells because they generate action potentials as well as synthesize hormones. The cell bodies of the neurosecretory cells in the supraoptic nuclei produce primarily antidiuretic hormone (ADH) and the cell bodies of the paraventricular nuclei produce primarily oxytocin. These hormones are then transported down the axons to the neurohypophysis and stored in membrane-bound vesicles in the neuron terminals. Much like neurotransmitters, the hormones are released in response to the arrival of action potentials at the neuron terminal.

The adenohypophysis is derived embryonically from glandular tissue, specifically, Rathke's pouch. This tissue originates from the oropharynx, or the roof of the mouth. It then migrates toward the embryonic nervous tissue destined to form the neurohypophysis. When these two tissues come into contact, Rathke's pouch loses its connection with the roof of the mouth and the pituitary gland is formed. Unlike the neurohypophysis, which releases hormones originally synthesized in the hypothalamus, the adenohypophysis synthesizes its own hormones in specialized groups of cells. Similar to the neurohypophysis, however, the release of these hormones into the blood is regulated by the hypothalamus.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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