histo endo

• Endocrine system


  Comprised of endocrine glands such as the Pituitary, Adrenal, Thyroid, Parathyroid, and the Pancreatic Islets of Langerhans
• Pituitary gland


  • Dual gland consisting of an epithelial component called the adenohypophysis and a neural component called the neurohypophysis
  • Adenohypophysis is derived from an outgrowth of oral ectoderm known as Rathke's pouch
  • Has three parts: pars distalis (anterior lobe), pars tuberalis (enveloping the infundibular stalk), and pars intermedia (rudimentary in adults)
  • Neurohypophysis is a neuroectodermal downgrowth from the floor of the diencephalon (part of the central nervous system) and includes the pars nervosa (posterior lobe) and the infundibulum
• Adrenal gland


  • Outer mesoderm-derived cortex is composed of cells that secrete steroid hormones
  • Neural crest-derived cells of the medulla are innervated by preganglionic fibers of the sympathetic nervous system and secrete catecholamines
• Thyroid gland


  • Consists of two populations of cells of different origin, histological arrangement, and function
  • Follicular cells secrete thyroxine and triiodothyronine, which regulate development and metabolic rate
  • Parafollicular cells are of neural crest origin and secrete calcitonin, which is one of the factors regulating calcium and phosphorous balance in the body
• Parathyroid gland


  • Located on the posterior aspect of the thyroid
  • Cells in these glands secrete parathyroid hormone, which acts to increase calcium resorption from bone and in the renal tubules, and increase the synthesis of the active form of Vitamin D
  • Vitamin D increases the absorption of Ca++ from the small intestine
• Islets of Langerhans


  • Endocrine component of the pancreas consisting of multiple spherical groups of epithelial cells embedded as nodules in the exocrine pancreas
  • Cells are not arranged into acini (as in the exocrine pancreas) but in irregular cords and clumps surrounded by a rich capillary plexus
  • Alpha cells secrete glucagon, which raises blood sugar, and beta cells secrete insulin, which lowers it
  • Delta cells secrete somatostatin, which inhibits both insulin and glucagon secretion