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Updated: Jan 6 2022

Pituitary (Hypophysis)

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Images
https://upload.medbullets.com/topic/109002/images/pituitary gland.jpg
https://upload.medbullets.com/topic/109002/images/screen shot 2012-04-03 at 12.45.05 am.jpg
https://upload.medbullets.com/topic/109002/images/pomc.jpg
https://upload.medbullets.com/topic/109002/images/growth hormone.jpg
https://upload.medbullets.com/topic/109002/images/pituitary_gland.jpg
  • Overview
    • Overview
      • pituitary, or hypophysis, rests in sella turcica, a depression of the sphenoid bone
      • primary function of pituitary is secretion of hormones
      • anatomically, pituitary is divided into anterior and posterior pituitary
  • Anterior Pituitary: Anatomy and Embryology
    • Anterior pituitary
      • anterior pituitary, or adenohypophysis, is the glandular component of the pituitary
        • a collection of endocrine cells
          • responsible for synthesis and secretion of anterior pituitary hormones
      • consists of pars distalis, pars intermedia,and pars tuberalis
      • embryological origin
        • oral ectoderm (Rathke's pouch)
          • upgrowth of oral ectoderm
          • primitive oral cavity
    • Anterior pituitary cell types
      • various cell types are responsible for synthesis and secretion of various hormones
      • gonadotrophs
        • FSH and LH
      • corticotrophs
        • ACTH
      • thyrotrophs
        • TSH
      • lactotrophs
        • prolactin
      • somatotrophs
        • growth hormone (somatotropin)
    • Histology
      • chromophils
        • anterior pituitary cells that contain granules that react with acidophilic/basophilic stains
          • acidophils
            • anterior pituitary cells (pars distalis) that contain granules that react with acidophilic stains
            • responsible for synthesis and secretion of PiG hormones
              • prolactin and growth hormone
          • basophils
            • anterior pituitary cells (pars distalis) that contain granules that react with basophilic stains
            • responsible for synthesis and secretion of FLAT hormones
              • FSH, LH, ACTH, TSH
                • granules that contain FLAT hormones are PAS+
      • chromophobes
        • anterior pituitary cells that lack granules and that do not react with acidophilic/basophilic stains
          • e.g., stromal cells and degranulated chromophils
  • Anterior Pituitary: Hormones
    • Anterior pituitary hormones
      • FLAT PiG
        • FSH (follicle-stimulating hormone)
        • LH (luteinizing hormone)
        • ACTH (adrenocorticotropic hormone)
        • TSH (thyroid-stimulating hormone)
        • Prolactin
        • Growth hormone (somatotropin)
      • categories of hormones
        • corticolipotropins
          • ACTH and MSH (melanocyte-stimulating hormone)
        • glycoprotein hormones
          • FSH, LH, TSH
        • somatomammotropins
          • prolactin and growth hormone
    • Cortiolipotropins
      • synthesis
        • overview
          • corticolipotropins are derived from a single precursor, POMC
            • POMC = pro-opiomelanocortin
        • pathway details
        • MSH
          • corticolipotropin synthesis products (aka fragments) contain MSH
          • increased MSH levels → skin pigmentation
          • e.g., Addison's disease
            • ↑ ACTH → ↑ MSH → skin pigmentation
    • Glycoprotein hormones
      • subunits of peptide hormones
        • glycoprotein hormones contain 2 subunits: α and β subunit
          • α subunits identical, β subunits non-identical
            • hormone specificity determined by β subunit
        • human chorionic gonadotropin (hCG) structurally related to glycoprotein hormone
          • hCG contains identical α subunit
    • Somatomammotropins
      • prolactin
      • growth hormone
        • secretion
          • pulsatile secretory pattern
            • secretory bursts approximately every 2 hours
              • ↑ in secretory bursts during exercise and sleep
        • functions
          • ↑ linear growth and muscle mass
            • growth mediated by production of somatomedins
              • aka insulin-like growth factors (IGFs)
          • diabetogenic effect
            • insulin resistance
              • decreases glucose uptake and utilization
            • "diabetogenic"
              • growth hormone produces increases in blood glucose
        • pathophysiology
          • GH deficiency
            • before puberty
              • symptoms
                • failure to grow
                • short stature
                • mild obesity
                • delayed puberty
            • treatment
              • growth hormone replacement
          • GH excess
            • growth-hormone secreting pituitary adenoma causes acromegaly
            • symptoms differ from pre-puberty vs post-puberty
              • before puberty
                • gigantism
                  • aka increased linear growth
              • after puberty
                • increased organ size
                • increased hand and foot size
                • enlargement of tongue
                • coarsening of facial features
                • insulin resistance and glucose intolerance
            • treatment
              • somatostatin analog (e.g., octreotide)
  • Posterior Pituitary: Anatomy and Embryology
    • posterior pituitary
      • posterior pituitary, or neurohypophysis, is the neural portion of the pituitary
        • a collection of unmyelinated axons
          • axons extend from cell bodies in hypothalamus
      • consists of pars nervosa, infundibular stalk, and median eminence
      • neurophysins carry hormones made in the hypothalamus (ADH and oxytocin) from the hypothalamus to the posterior pituitary
      • embryological origin
        • neural ectoderm
          • downgrowth of neural ectoderm (diencephalon)
  • Posterior Pituitary: Hormones
    • Antidiuretic hormone (ADH; vasopressin)
      • synthesis
        • hypothalamic supraoptic nucleus neuronal cell bodies synthesize ADH pro-hormone
          • ADH pro-hormone contains ADH and neurophysin II
        • ADH pro-hormones are packaged in secretory vesicles
          • secretory vesicles are transported via axonal transport to nerve terminals
            • nerve terminals in pars nervosa of posterior pituitary
        • ADH pro-hormone processing occurs in secretory vesicles during axonal transport
          • cleavage of neurophysin II and release of ADH hormone
      • secretion
        • action potential depolarizes nerve terminals
          • neurosecretory vesicles fuse with plasma membrane
            • releases ADH and neurophysin II into perivascular space of highly fenestrated capillaries by which ADH enters systemic circulation
    • Oxytocin
      • synthesis
        • neuronal cell bodies of the hypothalamic paraventricular nucleus synthesize oxytocin pro-hormone
          • oxytocin pro-hormone contains oxytocin and neurophysin I
        • oxytocin pro-hormones are packaged in secretory vesicles
          • secretory vesicles are transported via axonal transport to nerve terminals
            • nerve terminals in pars nervosa of posterior pituitary
        • oxytocin pro-hormone processing occurs in secretory vesicles during axonal transport
          • cleavage of neurophysin I and release of oxytocin hormone
      • secretion
        • action potential depolarizes nerve terminals
          • neurosecretory vesicles fuse with plasma membrane
            • releases oxytocin and neurophysin I into perivascular space of highly fenestrated capillaries by which oxytocin enters systemic circulation
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