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Histology of Pituitary gland \ Hypophysis Cerebri

The pituitary (also known as the hypophysis) is found at the base of the brain, about 1cm in diameter, lying beneath the third ventricle in a bony cavity (sella turcica) in the base of the skull. It has a complex structure The anterior and posterior parts of the pituitary have different embryological origins. show labels This picture of the pituitary has been stained with PAS and orange G. You should be able to identify the anterior and posterior pituitary. (The brightly stained part is the anterior). Rathke's pouch (vestiges of) is stained bright purple, by this stain. The posterior part of the pituitary has its embryological origins in nervous tissue. It is formed from a downgrowth of the diencephalon that forms the floor of the third ventricle. The anterior part is derived from an upgrowth from the oral ectoderm of the primitive oral cavity called Rathke's pouch. Along the posterior part of the the anterior lobe there is a narrow region called the pars intermedia, which also has its embryological origin in Rathke's pounch. The pars intermedia is poorly developed in humans. The glandular epithelial part of the pituitary is also called the adenohypophysis - (anterior pituitary, pars intermedia and pars tuberalis). These different origins are reflected in the histological structure of the anterior and posterior parts of the pituitary. show labels This is a magnified image of the anterior pituitary, stained with H&E showing two types of chromophils; pink - acidophils, which are more common, and purple - basophils. (Occasionally, you may be able to identify a third type, which are poorly stained, these are resting/degranulated chromophils) Anterior Pituitary You should also be able to see two types of chromophils (cells which take up stain) called acidophils and basophils. Acidophils and basophils are divided into different classes of cells which have different secretory products and target organs. The subtypes of acidophils and basophils, are described in the table below. These cannot be distinguished by H&E or other histological stains, but can be stained specifically by immunohistochemical techniques. The anterior pituitary secretes five different types of hormone. See the table below. The capillaries in this gland are fenestrated, to enable passage of hormones from the secretory cells into the bloodstream. Glandular Disorders and diseases The anterior pituitary also contains one type of chromophobe (cells which stain only weakly) These are resting/degranulated chromophils. Posterior Pituitary. The posterior pituitary looks very different to the anterior pituitary (see adjacent image). It contains non-myelinated axons which are the neurosecretory cells. The cell bodies of these cells are located in the hypothalamus. It only secretes two hormones: Antidiuretic hormone (ADH) which acts on the kidney, and oxytocin, which acts on the uterus.