There are basically two types of endocrine glands:
Cordonal endocrine gland – these glands are formed by cells organized as plates or sheets of cells. These plates have different shapes and are surrounded by blood spaces or blood capillaries that receive the secretion products and distribute them throughout the body through the blood circulation.
In histological sections the plates of cells are seen as ribbons of cells. For this reason this type of endocrine gland is called “cordonal”.
Follicular endocrine gland – formed by thousands of small spheres or beads whose wall is usually a simple cubic epithelium. These spheres are called follicles. The follicle contains the secretory product of the gland. The only large follicular endocrine gland in the body is the thyroid.
The image is of a cordonal endocrine gland, an islet of Langerhans in which cords of cells (actually cell plates) can be seen (highlighted in light blue after moving the cursor or clicking). The cords are surrounded by blood spaces highlighted in pink. (The blood spaces in this section is empty of blood because the animal was fixed by intravascular perfusion of the fixative).
The islets of Langerhans are thousands of small glands located inside the pancreas and each islet is surrounded by pancreatic acini, as can be seen in the image.
Other cordonal-type endocrine glands: adrenal (suprarenal), parathyroid , adenohypophysis, corpus luteum.
