Histology of Endocrine System in a Nutshell

Histology of Endocrine System

• Endocrine System
  • 8 endocrine organs (pineal, pituitary, hypothalamus, thyroid, parathyroid, adrenal gland, islets of langerhans, ovaries and testis)
  • Hormone function is either lipid soluble (hormone diffuses through membrane cell and nucleas,  affects gene translation.  Steriods primary for this) or Water soluble (require surface or transmembrane receptors and use a secondary messenger system cAMP or GMP system.  Phosphorylates enzymes.)
  • Pituatary gland

• Blood supply important. Enters into superior hypophyseal artery and enter into a primary plexus.  These contact hypothalamus, travel to pituitary via portal veins to secondary plexus, then drains via anterior hypophyseal veins.
• Posterior part receives blood from inferior hypophyseal artery, enter capillary process, then excits via posterior hypophyseal veins

• Anterior pituitary makes hormones, the posterior pituitary does not.

• Know pars distalis, nervosa, tuberalis
• Posterior (posterior pituitary proper)
• INfundibular stalk refers to the entire suspension of pituitary)
• Nerve portion retains nervous connection, epithelial (distalis) loses connection with oral cavity. Know origin.
• Rathke’s cysts seen in Pars intermedia in Rathke’s cleft. This colloid should not be confused with that of the thyroid artery.
• Neuroendocrine link- anterior pituitary starts in hypothalamus. Neurosecretory cells make releasing factors that travel down axons and contact capillarys of the primary plexus.  The hormones are then brought down to the pituitary.  They bathe the anterior pituitary cells to stimulate production or inhibition
• Chromophobic-inactive
•  Chromophilic-active
  • Acidophils-growth hormone somatotrophs and mammotrophs (make milk)
  • Basophils- everything else
    • Know the different parts of the pituitary (posterior, anterior)
    • Anterior pituitary: red staining acidophilic cells and darker colored basophilic cells.  Be sure to differentiate between the two.
    • Jxn at pars intermedia: The rathke’s cysts are visible.  They are round spaces filled with extracellular liquid.

• Posterior pituitary
  • Modified axons from hypothalamic nerves.
  • Terminals come in contact with capillaries of pars nervosa
  • Hormone shipped down with neurophysin
  • Secretion is triggered by neuron depolarization
  • Axons run down hypothalamic hypophyseal tract
  • Hormone will accumulate in distal tips of axons (herring bodies) until stimulated to release.
  • Pituacytes serve as support cells in the nervosa (pink nuclei staining)
  • Oxytocin-paraventricular nucleas
  • ADH (vasopressin)-supraoptic nucleas
• Feedback regulations
• • 1^st order: Plama level of hormone itself regulates production:  Oxytocin and vasopressin
  • 2^nd order:  Releasing factor from hypothalamus goes to pituitary gland (or other organ) to stimulate hormone production.  This feeds back to hypothalamus.
  • 3^rd order: Thyroid hormone
  • Everything is controlled by hypothalamus. Does it detect it’s own secretion, another pituitary hormone feedback or target organ feedback.
• Pineal gland
  • Sits off midline of the brain
  • makes melatonin (seasonal breeding, sleep-wake cycles). Sensitive to light secretion.
  • made of pinealcytes (secrete melatonin) and glial cells
  • look for corpora aranacea (brain sand).
  • Commonly used to look for brain cancer before MRI
• Thyroid
  • Above tracheal rings
  • Divided into follicles
  • Follicular cells: makes colloid (precursor to thyroid hormone).  Cuboidal cell shaped.
  • Active cells are high cuboidal and will see ragged edges of the colloid
  • Resting cells look squamous and colloid has a smooth looking appearance
  • Thyroid hormone regulates metabolic rate of cells and energy utilization (resting state)
  • Second type of cells (less numerous, larger, lighter staining) called parafollicular (C-cells). Make calcitonin
  • Each follicle is surrounded by capillaries where the hormone will be dumped into
• Parathyroid
  • Two pairs
  • Made of chords interspersed with sinusoids (just like all of the other cells)
  • Chief (principal) cells make parathyroid hormone (regulates plasma calcium levels). Increases plasma level of calcium by increasing breakdown of bone
  • Oxyphil cells- very large with no relevance and have many mitochondria
• Adrenal Gland
  • Two compartment organ
  • Blood supply by adrenal arteries that anastamose in upper recesses of cortex, dive into reticularis zone into another cortical plexus or into medulla plexus
  • Capsul- release in response to pituitary hormone
    • Zona Glomerulosa-Horshoe shaped cells
      1. Makes aldoesterone (mineralcorticoid hormone)
    • Zona fasciculate-long sinusoidal cells
      1. Corticosteroids
    • Zona reticularis
      1. Weak androgens, normally physiologically irrelevant (unless tumor present or during embryo development)
    • Medulla core
      1. Have modified neurons from neurocrest origin.
      2. Secret catecholimines (epinephrine and epinephrine)
      3. Secrete hormones in response to sympathetic system (nervous)
• Islets of langerhans
  • Lighter staining
  • Secretory epithelial cells with different division
  • Alpha-glucagon (converts glycogen to glucose)
  • Beta- insuline (reduce blood sugar)
  • Delta-somatostatin cells
  • F-cells- pancreatic polypeptide