HYPOTHALAMUS, PITUITARY GLAND...

• Ductless glands


  distinct clusters of cells with certain organs of the body - pituitary gland, thyroid and parathyroid gland, adrenal gland, pineal gland
• Endocrine cells


  islets of Langerhans in the pancreas, Corpus Luteum of the ovary, and the interstitial cells of Leydig in the testis
• Endocrine Glands


  secrete signaling molecules called hormones into a neighboring vascularized compartment for uptake by capillaries and distribution throughout the body, rather than directly into an epithelial duct like exocrine glands
• Endocrine system


  although function in different ways, the __________ and the nervous system interact to modulate and coordinate the metabolic activities of the body
• Major Endocrine Organs


  [parts of endocrine system]

  in which the sole or major function of the organ is the synthesis, storage, and secretion of hormones
• Endocrine components within other solid organs


  [parts of endocrine system]

  the endocrine components of the pancreas, ovary, testis, and kidney, in the form of clusters of endocrine cells within other tissues.
• diffuse endocrine system


  [parts of endocrine system]

  scattered individual hormone cells (or small clumps), usually within an extensive epithelium, e.g. the gastrointestinal and respiratory tract
• specialized cells/endocrine cells

  • are always very close to blood capillaries, which receive the secreted hormones and distributed them throughout the body
  • usually aggregate as endocrine glands, where they typically arrange themselves as cords of cells
  • many endocrine cells however produce hormones or other molecules through different modes of secretion
  • example is APOP cells
  • isolated endocrine cells in the body such as Endocrine cells of the digestive tract, cells of placenta, cells of the heart that produce the ANP, Juxtaglomerular cells of the kidney
• endocrine tissues or organs

  • pertains to endocrine glands
  • components of endocrine system that secrete chemicals directly into the bloodstream
  • examples are pancreas, endocrine components - islet of Langerhans
• secretory organs

  • any of various organs that synthesize substances needed by the body and release it through ducts or directly into the bloodstream
  • examples are pituitary, thyroid, and pineal gland
• embryonic origin

  • all three embryonic germ layers (endoderm, mesoderm, and ectoderm) contribute to the development of the endocrine glands
  • all secretory glands, whether exocrine or endocrine, develop from epithelium
• ectoderm


  hypothalamus, pituitary gland, pineal gland, adrenal medulla
• mesoderm 


  adrenal cortex
• endoderm


  thyroid gland, parathyroid glands, pancreas, thymus
• hormones


  • frequently hydrophilic molecules such as proteins, glycoproteins, peptides, or modified amino acids
  • receptor proteins are on the surface of target cells
  • hydrophobic steroid and thyroid hormones must circulate on transport proteins but can diffuse through the membrane of cells and activate cytoplasmic protein receptor in target cells
• paracrine


  [types of endocrine secretion]

  • localized dispersal in interstitial fluid or through short loops of blood vessels
  • hormones produced act very quickly but only at a short distance
  • example is gastrin
• juxtacrine

  [types of endocrine secretion]

  • a signaling molecule remains on the secreting cell's surface or adjacent extracellular matrix
  • effects target cells when the cells make contact
  • important in developmental tissue interactions
• autocrine


  [types of endocrine secretion]

  • cells may produce molecules that act on themselves or on cells of the same type
  • example is IgF
• pituitary gland (hypophysis)

  • small bean-shaped gland, about 1 cm across, at the base of the brain beneath the third ventricle, sitting in a bony cavity in the base of the skull (the sella turcica)
  • weigh about 0.5 g in adults
  • pituitary-dependent endocrine glands: thyroid gland, adrenal cortex, gonads
• develops from oral ectoderm and developing brain

  • neural component arises as a bud growing down from the floor of the diencephalon and caudally as a stalk or infundibulum still attached to the brain
  • oral component arises as an out pocketing of ectoderm from the roof of the primitive mouth; grows cranially, forming the Rathke's (hypophyseal) pouch - base of this pouch constricts and separates it from the pharynx
• pituitary gland (hypophysis)


  the gland is divided into anterior and posterior parts which have different embryological origins, functions, and control mechanisms
• adenohypophysis


  (anterior pituitary) develops from an evagination of the oral ectoderm (Rathke's pouch) that lines the primitive oral cavity (stomadeum)

  • pars distalis (pars anterior)
  • pars intermedia
  • pars tuberalis
• neurohypophysis


  (posterior pituitary) develops from neural ectoderm as a downgrowth of the diencephalon

  • median eminence
  • infundibulum
  • pars nervosa
• hormones which act directly on non-endocrine tissues


  [pituitary gland (hypophysis) hormones)

  • growth hormone (GH)
  • prolactin (PRL)
  • antidiuretic hormone (ADH)
  • oxytocin
  • melanocyte stimulating hormone (MSH)
• hormones which modulate the secretory activity of the other endocrine glands (trophic hormones)


  [pituitary gland (hypophysis) hormones]

  • thyroid stimulating hormone (TSH)
  • adrenocorticotrophic hormone (ACTH)
  • gonadotrophic hormones
  • follicle stimulating hormone (FSH)
  • luteinizing hormone (LH)
• adenohypophysis

  • derived from oral ectoderm
  • a large pars distalis/anterior lobe
  • parts tuberalis (wraps around the infundibulum)
  • the thin pars intermedia
  • the three parts of the adenohypophysis are derived from the hypophyseal pouch off the embryonic pharynx
• pars distalis

  • 75% of adenohypophysis
  • covered by a thin fibrous capsule
  • main components:
  • epithelial cells interspersed with fenestrated capillaries
  • fibroblasts -> produce reticular fibers -> for structural support
  • two broad groups of cells based on staining affinity:
  • acidophil
  • acidophobe
• pars distalis

  • chromophils:

  1. hormone is stored in cytoplasmic granules
  2. strongly staining cytoplasm

  • acidophils (stains pink or red)
  • somatotropic cells
  • secretes GH or somatotropin
  • central nucleus
  • moderate golgi complex
  • small rod-shaped mitochondria
  • abundant rER
  • numerous secretory granules of moderate size
  • mammotropic or lactotrophic cells
  • secrete PRL
  • arrange as individual cells rather than as clumps or clusters
• basophils (stains a bluish color)

  • gonadotropic cells
  • secrete FSH and LH
  • large round cells with secretory granules
  • well-developed golgi complex
  • abundant RER and mitochondria
  • situated near sinuses
  • corticotropic cells
  • secrete ACTH and lipotropic hormone (LPH)
  • round to ovoid cells
  • eccentric nucleus
  • few organelles
  • sparse secretory granules located extremely peripheral
  • thyrotropic cells
  • secrete TSH and thyrotropin
  • deeply embedded within cords of the parenchymal cells at a distance from the sinusoids
  • smaller granules more peripherally located
• chromophob


  very little cytoplasm; therefore, it doesn't take up stain readily heterogeneous group: stem cells, undifferentiated progenitor cells, degranulated cells
• pars tuberalis

  • funnel-shaped region surrounding the infundibulum of the neurohypophysis
  • separated from the infundibular stalk by thin layers of pia arachnoid-like CT
  • highly vascularized by arteries and the hypophyseal portal system
  • most of the cells are cuboidal to low-columnar basophilic gonadotropic cells that secrete FHS and LH
  • contains small, dense granules, lipid droplets, interspersed colloid droplets, and glycogen
• pars intermedia

  • thin zone of basophilic cells between the pars distalis and the pars nervosa of the neurohypophysis
  • synthesize pro-opiomelanocortin which splits to produce several active hormones
  • develops from the dorsal wall of Rathke's pouch and usually contains Rathke's cysts
  • cuboidal cell-lined colloid-filled cysts
  • remnants of the lumen of Rathke's pouch
  • melanotropic cells
  • produce smaller peptide ormones, including 2 forms of melanocyte-stimulating hormone (MSH), y-LPH, and β-endorphin
  • MSH increases melanocyte activity
• neurohypophysis


  posterior pituitary gland
• neurohypophysis


  • Develops from neural ectoderm as a downgrowth of the diencephalon
  • Composed of neural tissue
• neurohypophysis

  • Contains 100,000 unmyelinated axons of secretory neurons situated in the supraoptic and paraventricular nuclei of the hypothalamus
• Pituicytes


  • Highly branched glial cells
  • Resemble astrocytes
  • Most abundant cell type
  • Contain lipid droplets, lipochrome pigment, and intermediate filaments
  • Have numerous cytoplasmic processes that form gap junctions with each other
• neurosecretory bodies or herring bodies

  • Axonal dilations where hormones accumulate
  • Eosinophilic
  • Contain numerous membrane-enclosed granules with either oxytocin or vasopressin bound to 10 kDa carrier proteins called neurophysin I and II respectively
• vasopressin or anti diuretic hormone, ADH

  • stimulus: higher blood tonicity recognized by osmoreceptor cells in the hypothalamus, which them stimulate synthesis of the hormone in supraoptic nuclei
• oxytocin

  • stimulates contraction of mammary gland myoepithelial cells and uterine smooth muscle during childbirth
  • stimulus: breast-feeding via sensory tract that act on the hypothalamus in a neurohormonal reflex called the milk-ejection reflex
  • secretion is associated with paraventricular nuclei
• hypothalamic neurosecretory hormones

  • manufactured in the hypothalamus and stored in the median eminence
  • enter the primary capillary plexus and are drained by the hypophyseal portal veins
  • which course through the infundibulum and connect to the secondary capillary plexus in the anterior lobe
  • here the neurosecretory hormones leave the blood to stimulate or inhibit the parenchymal cells