endocrine system

• ENDOCRINE SYSTEM - Consists of a group of glands (known as the endocrine glands) which are widely separated and have no physical connections with each other
• Endocrine glands - Typically epithelial in origin, that aggregated as cords or clusters and surrounded by extensive networks of capillaries
• Endocrine glands - Referred to as ductless glands because hormones diffuse directly into the bloodstream into the neighboring vascularized compartment for uptake by capillaries and distribution throughout the body
• HORMONES - Chemical substances that act like messenger molecules in the body. After being made in one part of the body, they travel to other parts of the body where they influence cell growth and metabolism
• HORMONES - Maintains the constancy of the chemical composition of extracellular and intracellular fluid
• Hormones are directly released from the tissue into the bloodstream and carried to the site
• Each hormone act to a specific site or target cell to induce certain characteristic biochemical changes and is produced by a specific gland
• DISTRIBUTION OR SECRETION OF HORMONES

  • PARACRINE SECRETION OR PARACRINE
  • JUXTACRINE SECRETION
  • AUTOCRINE SECRETION
• PARACRINE SECRETION OR PARACRINE - dispersal in interstitial fluid or through short loops of blood vessels
• PARACRINE SECRETION OR PARACRINE - distribution of secretion that Occurs between cells in close proximity with each other
• Gastrin - example of paracrine secretion or paracrine
• Gastrin made by pyloric G cells reaches target cells in the fundic glands
• JUXTACRINE SECRETION - signaling molecule remains on the secreting cell’s surface or adjacent extracellular matrix and affects target cells when the cells make contact
• Embryonic and regenerative tissue interactions - example of juxtacrine secretion
• AUTOCRINE SECRETION - Cells may produce molecules that act on themselves
• Insulin-like growth factor (IGF) - example of autocrine secretion
• Insulin-like growth factor (IGF) produced by several cell types may act on the same cells that produced it
• PITUITARY GLAND - Also known as hypophysis, lies below the brain in a small cavity on the sphenoid bone, the sella turcica
• Neurohypophyseal Bud - pituitary gland from Neural Component
• Hypophyseal (Rathke) Pouch - pituitary gland from Oral Component
• Two major parts of pituitary gland

  • Posterior pituitary (Neurohypophysis)
  • Anterior pituitary (Adenohypophysis)
• Posterior pituitary (Neurohypophysis) – has a part called the pars nervosa develops as a downgrowth of the developing brain and is attached in the hypothalamus by the infundibulum
• Anterior pituitary (Adenohypophysis) – includes the large pars distalis, the pars tuberalis that surrounds the infundibulum, and the thin pars intermedia adjacent to the pars nervosa
• PITUITARY GLAND - Develops from developing brain and oral cavity
• Hypothalamic-hypophyseal portal system has great importance because it carries neuropeptides to the adenophypophysis where they either stimulate or inhibit hormone release by the endocrine cells there. - Network of vessels
• Components of Hypothalamic-hypophyseal portal system

  • Primary capillary plexus
  • Secondary plexus
• Primary capillary plexus - Components of Hypothalamic-hypophyseal portal system in the infundibulum and lower hypothalamus
• Secondary plexus - Components of Hypothalamic-hypophyseal portal system in the pars distalis, connected by portal veins and draining to the hypophyseal vein.
• Hypothalamic-hypophyseal tract – a bundle of axons from two important hypothalamic nuclei
• two important hypothalamic nuclei

  • Supraoptic nuclei
  • Paraventricular nuclei
• Supraoptic nuclei – nuclei that release ADH (Antidiuretic hormone) or Vasopressin
• ADH – is released in response to increase blood tonicity (hypertonic), sensed by osmoreceptor cells in the hypothalamus; increases the permeability of the renal collecting ducts to water so that more water is reabsorbed from the filtrate in these tubules and osmotic balance of body fluids is restored.
• Paraventricular nuclei – nuclei release oxytocin
• Oxytocin – stimulates contraction of uterine smooth muscle during childbirth and the myoepithelial cells in the mammary gland
• Bundle of axons called the hypothalamic-hypophyseal tract courses into the neurohypophysis from two important hypothalamic nuclei
• Vasopressin and Oxytocin - Both hormones undergo axonal transport and accumulate temporarily in the axons of the hypothalamic-hypophyseal tract before their release and uptake by capillaries branching from the inferior arteries
• Endocrine cells of the anterior pituitary can be called acidophils, basophils, or chromophobes based on their general staining properties; the latter lack secretory granules and stain poorly
• Acidophils and basophils can be identified as to which pituitary hormone they produce using immunohistochemistry and antibodies against specific hormones
• Chromophils (acidophils and basophils)
• Chromophils - Are secretory cells in which hormone is stored in cytoplasmic granules