179. The Paraganglionic System: The Paraganglia

  1. Introduction: the primordial neural crest cells of the sympathetic ganglia are not all transformed into nervous cells. Some of the sympathogonia migrate beyond the sympathetic chain and take on a glandular character. They form the paraganglionic or chromaffin body system, so named because the paraganglia are often associated with the sympathetic ganglia, and their cells are also derived from the same cells. The mechanism of regulation of their migration is unknown
    1. PARAGANGLIONIC TISSUE is found dispersed in relation to the sympathetic ganglia, the abdominal aorta (the organs of Zuckerkandl), and beginning in embryos of about 10 mm, similar cells migrate into the primordium of the suprarenal gland to form the suprarenal medulla
    2. THE CELLS OF THE SYMPATHOCHROMAFFIN SYSTEM combine some of the properties of secretory cells and of nerve cells and are homologous in the suprarenal gland with postganglionic neurons
      1. The other elements of this system undergo a slow atrophy after birth
  2. The paraganglia
    1. INTRODUCTION: the sympathogonia detach themselves from the sympathetic primordium and differentiate into glandular cells during month 2 of gestation
      1. Small groups of cells are formed behind the peritoneum (retroperitoneal), in the connective tissue capsule of the suprarenal gland, in the thoracic and abdominal sympathetic chains, in the genital glands, in the epicardium, near and around the kidneys, and elsewhere
    2. MANY OF THESE PARAGANGLIA REGRESS when the adrenal medulla becomes functional after birth, e.g., the aortic chromaffin body called the body of Zuckerkandl, located near the origin of the inferior mesenteric artery
      1. Other large cell clusters persist but are usually fragmented, and the resulting paraganglia come in contact with sympathetic ganglionic cells or even some blood vessels
    3. FUNCTION OF THE PARAGANGLIA: they are probably involved in the production of epinephrine (adrenaline) or norepinephrine (noradrenaline)
      1. The above 2 hormones are secreted in the fetus near the end of month They help maintain the fetal blood pressur After birth, the adrenal medulla and the autonomic nervous system take over this function
      2. Some paraganglia cells are located near the vagus (X) nerve and are found to secrete acetylcholin These cells, however, do not show the same staining reaction as those of the adrenaline-producing paraganglia, which selectively take up chromium salts and account for the chromaffin reaction
      3. The cells of the paraganglionic system are distinguished from the neuroblasts by their smaller size and by their characteristic reaction to staining with dichromate salts (yellow) and to ferric chloride (green)
        1. The staining is probably due to the presence of cytoplasmic droplets which have been tentatively identified with the precursors of epinephrine and norepinephrine
      4. Paraganglionic tissue liberates adrenaline and acetylcholine more abundantly than do the ordinary nerve endings, thus, can be considered to be in support of organs that function continuously, like the heart or the vasosensory system that controls circulation
  3. Pathology of the paraganglionic system
    1. PHEOCHROMOCYTOMA AND PARAGANGLIOMA are tumors that involve this system
      1. The tumor may affect the adrenal medulla or the adrenal-producing paraganglia
      2. An abnormally persisting organ of Zuckerkandl may become tumorous
    2. THE MOST FREQUENT SYMPTOM of involvement of this system is paroxysmal hypertension

the paraganglionic system:  the paraganglia: image #1