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Histology Study Guide
Endocrine System

Introduction to endocrine secretion.
Continue on down this page for an overview of several endocrine glands.
 
Or click on links in this table for pages on each endocrine gland.
 
GI tract
(individual endocrine cells)
Liver
(Yes, the liver is an endocrine gland.)

Zoomified online slides of the endocrine system
Link to LUMEN (Loyola University Medical Education Network), click on "Part 14:  Endocrine Glands".


INTRODUCTION TO ENDOCRINE SECRETION

Many of the body's cells secrete substances which influence other cells, either locally or at some distance.  Cells which are conspicuously specialized for this function are called endocrine cells.  (The suffix -crine refers to secretion; the prefix endo- tells us that the secretory product stays inside the body.)   All endocrine cells share certain characteristics.

The various endocrine cells of the human body are organized in a few distinctive patterns.

CONNECTIVE TISSUE, derived from mesoderm, provides the organizational pattern for endocrine cells of testicular Leydig cells and ovarian stromal cells.
 
OTHER:  Ovarian granulosa and luteal cells defy easy tissue-type classification.

Finally, INDIVIDUAL CELLS may have significant endocrine function.  Examples include the epithelial enteroendocrine cells of the GI tract and the juxtaglomular cells (modified smooth muscle) of the renal cortex.


Overview of Individual Endocrine Glands
(For additional detail, click on the name of the gland.)

The pituitary gland (or hypophysis) consists of two distinct parts, the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).

The anterior pituitary appears glandular (hence adenohypophysis), with clumps of epithelial cells with varying staining properties.  Cells of several species each secrete one of several hormones (e.g., GH, ACTH, FSH, LH, TSH, etc.)  Such secretion from this "master gland" regulates most other endocrine glands and is, in turn, regulated by factors secreted by hypothalamic neurons and delivered to the anterior pituitary by the hypophyseal portal vessels.  

The posterior pituitary consists of secretory endings of axons from nerve cells (hence neurohypophysis) whose cell bodies are located in the hypothalamus.  These secretory processes of the posterior pituitary secrete oxytocin and ADH.

Pituitary adenomas may be "benign" (i.e., not malignant) but can nevertheless cause significant problems either from excess hormone production or from mass effect (e.g., crowding the optic chiasm).  For illustration, see WebPath.

For additional detail, click here:  pituitary gland.


The thyroid consists of characteristic follicles, each with a large lumen surrounded by a simple cuboidal epithelium.  The appearance (as well as evolutionary origin) is that of an exocrine gland which has lost its outlet so that secretory product accumulates in the follicles.  Follicular cells store thyroglobulin in the follicles for subsequent use in production and endocrine secretion of T3 (thyroxin) and T4.  Parafollicular cells (C cells) produce calcitonin.

For additional detail, click here:  thyroid.


The parathyroid consists of several discrete glands, each organized into tangled curvilinear cords of chief cells.  These cells secrete parathyroid hormone, which works in opposition to calcitonin (from thyroid C cells) to regulate blood calcium levels.  

For additional detail, click here:  parathyroid.


Pancreatic islets (also called islets of Langerhans (named after Paul Langerhans, b. 1847) are nests of endocrine cells scattered within the pancreas.  Each islet consists of several cell types which secrete insulin, glucagon, somatostatin, and pancreatic peptide.  The cells are arranged into tangled cords.  

For additional detail, click here:  pancreatic islets.


The adrenal consists of two distinct parts, an outer cortex and an inner medulla.  

The cortex consists of cords of steroid-secreting epithelial cells, separated by parallel sinusoids.  The cords are organized into poorly defined zones.  From the outside inward, these zones secrete mineral corticoids (e.g., aldosterone), glucocorticoids (e.g., cortisol), and androgenic steroids.

The medulla consists of cells similar to sympathetic neurons which secrete catecholamines (epinephrine and norepinephrine).

For additional detail, click here:  adrenal.


The testis contains clusters of interstitial Leydig cells which secrete testosterone.  

For additional detail, click here:  testis.


The ovary includes steroid secreting cells of the theca interna and of the corpus luteum.  

For additional detail, click here:  ovary.

 


The pineal consists of pinealocytes, neuron-like cells which secrete melatonin.  Calcium accumulation ("brain sand") in the pineal gland makes this structure a useful landmark in x-rays.  For images of pineal, as well as more information, see LUMEN or Wikipedia.

Historical note:  According to Rene Decartes, it is through the pineal that the soul controls the body.


For some additional detail on specific endocrine glands,
click on a link in this table.
GI tract
(individual endocrine cells)
Liver
(Yes, the liver is an endocrine gland.)

Comments and questions: dgking@siu.edu

SIUC / School of Medicine / Anatomy / David King

https://histology.siu.edu/erg/enguide.htm
Last updated:  8 May 2022 / dgk