Physiology of Finfish and Shellfish (2+1)

5.2.2.2.2 Anatomy of pituitary gland - Posterior pituitary (Neurohypophysis)

A large number of nerve fibres arise from cells in the hypothalamus and enter the hyophysis forming the neurohypophysis. These fibres branch repeatedly are intimately connected with pars intermedia. Pinocytes and droplets of neurosecretory material are seen in these fibres and are called “Herring bodies”. Lymphocytes and migrating cyanophils have also been reported in some species. The neurosecretory material can be stained with aldehyde fuchsin (AF), chromealum haematoxylin and aldehyde thionin. “Stainable” and “non stainable” fibres have been distinguished depending upon their stainability with AF and other stains. Neurosecretory material is synthesized in the hypothalamus and transported to the pituitary along the fibres.

Hormones of the pituitary gland

Atleast 9 hormones are produced by the pituitary in fish and all hormones are made up of proteins or polypeptides.

Hormones of the adenohypophysis

These hormones are released from the anterior pituitary under the influence of the hypothalamus. Six different hormones produced by the anterior lobe will be studied here. Three of these have direct effects on the body, the other three control other glands. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary system called the hypothalamic-hypophysial portal system. ( A vascular system that transports releasing and inhibiting hormones from the hypothalamus to the anterior pituitary).

Anterior pituitary hormones that directly affect the body are Growth Hormone (GH or Somatotropic Hormone), Prolactin and Melanocyte-Stimulating Hormone (MSH).

Anterior pituitary hormones that regulate other glands

The pituitary also controls other glands and is often referred to as the "master gland".

Three kinds of pituitary hormones that regulate other glands are discussed below. The glands that they regulate will be discussed in the following section.

Thyroid Stimulating Hormone (TSH) →thyroid → thyroxin

Adrenocorticotropic Hormone (ACTH) → adrenal cortex → cortisol

Gonadotropic Hormones (FSH and LH) → ovaries and testes → sex hormones; controls gamete production.