Results 1 to 1 of 1

Thread: Pituitary Posterior and Anterior Lobes picture - Endocrine Histology Atlas

  1. #1

    Default Pituitary Posterior and Anterior Lobes picture - Endocrine Histology Atlas

    The pituitary gland is often dubbed the “master gland” because its hormones control other parts of the endocrine system, namely the thyroid gland, adrenal glands, ovaries, and testes. However, the pituitary doesn’t entirely run the show.

    In some cases, the hypothalamus signals the pituitary gland to stimulate or inhibit hormone production. Essentially, the pituitary acts after the hypothalamus prompts it.

    Anatomy of the Pituitary Gland
    The pituitary gland is only about 1/3 of an inch in diameter (that’s about as large as a pea) and located at the base of the brain.

    Since their functions are so intertwined, it’s no surprise that the hypothalamus and pituitary are located near each other. They’re actually connected by the pituitary stalk, or more technically, the infundibulum.

    The pituitary glands are made of the anterior lobe and posterior lobe. The anterior lobe produces and releases hormones. The posterior lobe does not produce hormones per se—this is done by nerve cells in the hypothalamus—but it does release them into the circulation.

    Hormones of the Pituitary Gland
    The hormones of the pituitary gland send signals to other endocrine glands to stimulate or inhibit their own hormone production. For example, the anterior pituitary lobe will release adrenocorticotropic hormone (ACTH) to stimulate cortisol production in the adrenal glands when you’re stressed.

    The anterior lobe releases hormones upon receiving releasing or inhibiting hormones from the hypothalamus. These hypothalamic hormones tell the anterior lobe whether to release more of a specific hormone or stop production of the hormone.
    Pituitary Posterior Anterior Lobes picture attachment.php?s=df5cda61a7d82a02f589c3f8cf3b3197&attachmentid=1320&d=1439063715

    Anterior Pituitary

    Although the hypothalamus does not produce the hormones of the anterior pituitary as in the posterior pituitary, it plays an important role in their production. Releasing hormones synthesized by hypothalamic neurons travel down axons and diffuse into the primary plexus of the hypophyseal portal system. They are then carried by the hypophyseal portal veins to the secondary plexus for distribution to target cells within the anterior pituitary.

    The hormones produced by the anterior pituitary are described in the table below.

    The cells constituting the anterior lobe of the pituitary gland are embryologically derived from an outpouching of the roof of the pharynx, known as Rathke’s pouch. While the cells appear to be relatively homogeneous under a light microscope, there are in fact five different types of cells, each of which secretes a different hormone or hormones. The thyrotrophs synthesize and secrete thyrotropin (thyroid-stimulating hormone; TSH); the gonadotrophs, both luteinizing hormone (LH) and follicle-stimulating hormone (FSH); the corticotrophs, adrenocorticotropic hormone (ACTH; corticotropin); the somatotrophs, growth hormone (GH; somatotropin); and the lactotrophs, prolactin.

    Somatotrophs are plentiful in the anterior pituitary gland, constituting about 40 percent of the tissue. They are located predominantly in the anterior and the lateral regions of the gland and secrete between one and two milligrams of GH each day.

    Structure and function of anterior pituitary hormones
    The hormones of the anterior pituitary are proteins that consist of one or two long polypeptide chains. The gonadotropins (LH and FSH) and thyrotropin are called glycoproteins because they contain complex carbohydrates known as glycosides. Each of these three hormones—LH, FSH, and thyrotropin—is composed of two glycopeptide chains, one of which, the alpha chain, is identical in all three hormones. The other chain, the beta chain, differs in structure for each hormone, thereby explaining the different actions of each of these three hormones. As is the case for all protein hormones, the hormones of the anterior pituitary are synthesized in the cytoplasm of the cells as large, inactive molecules called prohormones. These prohormones are stored in granules, within which they are cleaved into active hormones and are secreted into the circulation.

    Each pituitary hormone plays a vital role in endocrine function. Thyrotropin stimulates the production of thyroid hormone. ACTH stimulates the production of cortisol and androgenic hormones by the adrenal cortex. FSH stimulates the production of estrogens and the growth of egg cells (oocytes) in the ovaries in women and sperm cells in the testes in men. LH stimulates the production of estrogens and progesterone by the ovaries in women and the production of testosterone by the testes in men. GH stimulates linear growth in children and helps to maintain bone and other tissues in adults.

    Regulation of anterior pituitary hormones
    The production of the anterior pituitary hormones is regulated in part by hormones produced in the hypothalamus, the region of the brain that lies just above the pituitary gland. In general, hypothalamic hormones stimulate production of pituitary hormones, except for prolactin, which is inhibited. The hypothalamic hormones are secreted into a portal vein that traverses directly from the hypothalamus to the anterior pituitary gland, thereby carrying these hormones directly to the pituitary.

    The posterior lobe is composed of the endings of nerve cells located in specialized regions of the hypothalamus. These nerve cells produce two hormones, oxytocin and vasopressin (antidiuretic hormone), that are carried down the nerves and stored in the nerve endings that compose the posterior pituitary gland. The hormones are released into the circulation in response to nerve signals that originate in the hypothalamus and are transmitted to the posterior pituitary. Oxytocin causes contraction of the uterus and milk secretion in women, and vasopressin increases reabsorption of water from the kidneys and raises blood pressure.

    References:
    pituitary gland | anatomy | Britannica.com
    Pituitary Gland
    An Overview of the Pituitary Gland - The Endocrine System’s Master Gland











    Last edited by Medical Photos; 08-08-2015 at 07:55 PM.

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
About us
Medical Educational Site for Medical Students and Doctors Contains Free Medical Videos ,Atlases,Books,Drug Index ,Researches ,Health and Medical Technology news.
  • Privacy Policy
  • Join us
    Powered by vBulletin® Version 4.2.0 Copyright © 2015
  • vBulletin®
  • Solutions, Inc. All rights reserved. vBulletin Metro Theme by
  • PixelGoose Studio