in Chemical Coordination and Regulation (Endocrine System) by

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I. Adenohypophysis:

A. Pars tuberalis:

  1. It is made up of columns of epithelial cells.
  2. They form clusters around the infundibulum.
  3. They do not give out any secretions.

B. Pars distalis:

  1. It is the largest part and forms about 75% of the gland.
  2. It consists of epithelioid cells arranged in clusters or cords.
  3. They are the main secretory cells and secrete tropic hormones.
  4. The clusters are seperated from one another by blood sinusoids.
  5. These clusters consist of two types of cells mainly the chromophils and chromophobes.
  • Chromophils: They are large, ovoid and granular cells. Depending upon their staining properties, they are classified as:
    Acidophils: They are stained with acidic dyes (red).
    Basophils: They are stained with basic dyes (purple blue).
  • Chromophobes: They do not contain any secretary granules, hence are poorly stained.

C. Pars intermedia (Intermediate lobe): In humans, it appears as a narrow (rudimentary) region between the Pars distalis and Pars nervosa. These cells do not have any secretory granules.

II. Neurohypophysis:

  1. It comprises of the Infundibulum and the Pars nervosa.
  2. The hypothalamus consists of two groups of cell bodies of neurons, i.e. Supra-optic nuclei and Para-ventricular nuclei.
  3. They are also called as neurosecretory cells because they release hormones.
  4. The axons of these neurons pass downwards through the infundibulum and terminate in the Pars nervosa.
  5. Many spindle-shaped Pituicytes (supportive cells) intermingle with these axonal-endings.
  6. Functions: It receives and stores Vasopressin (ADH) and Oxytocin secreted by the supra-optic nuclei and Para-ventricular nuclei respectively.
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