Veterinary Histology UFF
Department of Morphology - Biomedic Institute
LaBEc - Laboratory of Cellular and Extracellular Biomorphology
Veterinary Histology Atlas
    Versão em Português
Endocrine System

• It has a dense connective tissue capsule that comes from the dura mater that sends septa into the organ.
• It has three portions: the anterior portion(or adenohypophysis), the posterior portion (or neurohypophysis) and the intermediate portion.
• The adenohypophysis originates from the epithelium that evaginates and stands out from the hard palate (Rathke Pouch), migrating towards the neural tube.
• The neurohypophysis is an evagination of the floor of the diencephalus
• It is a gland that produces numerous important hormones and therefore is acknowledged as the master-gland of the nervous system.
• Responsible for regulating the activity of other glands and various other functions of the organism such as growth and the secretion of milk from the mammary glands.
It is richly vascularized as all endocrine glands are since the hormones it produces are released into the blood vessels.


It connects itself to the hypothalamus through the infundibulum.
• The hormones are produced in the cell body of the neurons in the hypothalamus and these hormones are then transported through the axons of the neurons towards the neurohypophysis that releases these hormones when stimulated.
The hormones that are secreted through the posterior hypophysis are: Oxytocin and ADH.

• It comes from the paraventricular nucleus of the hypothalamus.
• It acts on the uterus helping it contract during labor and in mammary terms it facilitates the secretion of milk

Antidiuretic Hormone (ADH, Vasopressin or AVP-Arginine Vasopressin)
• It comes from the supraoptic nucleus of the hypothalamus
• It regulates the contraction of blood vessels, regulating the pressure and antidiuretic action on the kidney tubules

Amyelinic Axons
• Fibrillary extensions of the hypothalamic neurons, where deposits of neurosecretion can be observed in its extremities (Herring corpuscles)
• Presence of Fenestrated capillaries


• Constituent cells of the neurohypophyseal parenchyma
• It has an irregular shape with countless extensions.


• Through the vascular connection of the adenohypophysis with the hypothalamus, the hypothalamus integrates central and peripheral stimulatory and inhibitory signals to the five types of phenotypically distinct hypophysis cells.
• Histologically, we observe 3 cell types, differed by staining, which are:
- Chromophobic cells (cytoplasm does not have an affinity for stains; only the nuclei stained with hematoxylin are observed)
- Chromophilic cells
A) Acidophilic (cytoplasm stained by eosin)
B) Basophilic (cytoplasm stained by hematoxylin)






Chromophobic Cells


Chromophilic Cells



Chromophilic Cells

Stains (Type)
Cell Type
Growth H. (GH) GHRH( Growth hormone releasing hormone)
Prolactin Secretion inhibited by DA (dopamine)
Follicle Stimulating H. (FSH) GnRH(Gonadotropin releasing hormone)
Luteinizing H. (LH) GnRH(Gonadotropin releasing hormone)
Thyroid Stimulating H. TRH( Tireotropin releasing hormone)
Adrenocorticotrophic H. CRH (Corticotropin Releasing Hormone)
Endorphins -


Intermediate Portion
• Stimulates the melanocytes (MSH): regulates the distribution of pigments.


Adrenal Glands
• They are endocrine glands covered by a fibrous, innerved and vascularized connective capsule.
• Its main function is to stimulate the conversion of proteins and fat into glucoses at the same time it reduces the capture of glucoses by cells, therefore increasing the use of fat, and consists on the synthesis and release of corticosteroid hormones and cathecolamines, such as cortisol and adrenaline.
Histologically, it is divided into a cortex and medulla.



• Outer part of the gland with a yellowish color due to the great amount of cholesterol there.
• It has an embryonic origin in the mesodermis. It subdivides itself into three regions due to their different histological aspects.

Glomerular Zone
• The outermost zone, presents cell cords disposed in arches.
There are juxta-vascularly disposed columnar cells in such a way that resembles a glomerulus

Fasciculate Zone
• It is of intermediate location. The cells arrange themselves parallel to each other and perpendicular to the capsule of the gland
The cells are cuboidal and arrange themselves axially and juxta-vascularly
• The cytoplasm of its cells contains numerous vacuoles giving them a spongy aspect and therefore are called spongiocytes.

Reticulated Zone
• The innermost zone, it presents cords of cells arranged in a net-like way
• The cells are polyhedral and arrange themselves in a way that resembles a juxtavascular reticulum


- Glomerular Zone: synthesizes mineralocorticoids (aldosterone)
- Fasciculate and Reticulated Zone: secrete glucocorticoids, of which the most important is cortisol. Also secrete sexual steroids such as testosterone.



• Inner part; derives from the neural crest. Its secreting cells are polyhedral and organized into a network.
• There are two types of cells: Chromaffin cells and Ganglionary cells that neighbor the capillary network.
• Synthesis and release of neuromediators, specially adrenaline and noradrenaline.

> The Cortex is essential to life, the Medulla is not.

• It is a endocrine gland, covered by a fibrous connective tissue capsule
• It has different shapes depending on the animal species and is formed by two lobes united by an isthmus.
• The lobes are subdivided into lobules.
• The lobules are formed by vesicles or follicles lined by simple cuboidal epithelium.
• Inside the vesicles we find the secreting material stored in the form of colloid.
• The lining cells of the vesicles are called follicular cells.
• Between the follicles, in the interstice, are the C (clear) or parafollicular cells that produce calcitonin.
• The follicles are limited by a simple cuboidal epithelium of follicular cells. These cells secrete into the follicle the hormones and other substances that form the gelatin-like colloid inside it.
• The colloid stores the thyroid hormone that is absorbed once again by the follicular cells and released into the bloodstream.



Thyroid Follicles


Follicular Cells

• The main function is to produce and store the thyroid hormones, T3(tri-iodothyronine) and T4 (thyroxine);
• The production of these hormones occurs after the stimulation of the cells by the hypophyseal hormone TSH
• The thyroid hormones T3 and T4 stimulate the cellular metabolism by stimulating the mitochondria.
• The C cells produce calcitonin, a hormone that leads to the reduction in the level of calcium in the blood(stimulating bone formation)
• The thyroid is the only endocrine gland that stores its secreting product.


• They are endocrine glands covered by a thin connective tissue capsule of which thin septa emanate and penetrate the gland.
• It is not a lobulated gland
• The cells are densely grouped, in contrast to the follicular structure in the thyroid.
• There are two kinds of cells, the main and the oxyphilic cells, supported by a matrix of reticular and adipose connective tissue.
• The main cells (eosinophilic) are smaller and secrete the parathyroid hormone(PTH)
• The oxyphilic cells are larger and more basophilic and have no known function.

Parathryoid Hormone
• Stimulates the osteolytic activities of osteoclasts
• Increases the renal absorption of calcium
• Increases the absorption of vitamin D
• Increases the intestinal absorption of calcium
All this can be translated into a rapid and sustained increase in the amount of calcium in the blood.
• It also influences the concentration of phosphate in the blood, increasing the renal excretion of this ion by diminishing its absorption in the renal tubules.


Endocrine Pancreas
• Composed of agglomerations of special cells called Langerhans islets
• There are 4 types of cells in the Langerhans islets. They are relatively difficult to distinguish by average staining techniques , but they can be classified according to their secretions:

Name of Cells
% of Cells in the Islet
Beta Cells Insulin and Amylin
Reduces the level of sugar in the blood
Alpha Cells Glucagon
Increases the level of sugar in the blood
Delta Cells Somatostatin
Inhibits the endocrine pancreas
PP Cells Pancreatic Polypeptide
Inhibits the exocrine pancreas






Langerhans Islets

Accessory Gls.
Male Reprod.
Female Reprod.
Birds Histology