Endocrine glands are specialized for production and secretion of proteins and hormones. They are typically organized as clusters or cords of secretory epithelial cells and differ from exocrine glands in two major ways:

1. Lack a system of ducts
2. Secretory products are released into the extracellular space where they act on nearby target cells or enter into the blood vasculature to travel to their target organs

Take a look at these samples of pituitary gland, adrenal gland, and the Islets of Langerhans in the pancreas, all of which function as endocrine glands. Notice in these specimens and in the images below that the glandular epithelia are organized in clumps or cords, there are no ducts, and blood vessels are located near the clusters of epithelial cells.

Before going on, try this little pop quiz on epithelia. It's a self-assessment and no one but you sees the score.

Let's now take look at connective tissue.