STRUCTURE OF GLANDS & GLANDULAR TISSUES

1. STRUCTURE OF GLANDS & GLANDULAR TISSUES

2. Functional Classification

3. Development of Glands This diagram illustrates how glands may be formed from a proliferation of epithelial cells(A) . Continued cell division leads to a cord of cells growing into the underlying connective tissue (B). In the case of exocrine glands the central cells in the core degenerate leading to the formation of the duct system (D). In the case of endocrine glands the cells connecting the gland to the surface degenerate completely leaving isolated glandular cells in which a network of blood vessels develop (D). Note the two types of endocrine glands; follicular glands as illustrated by the thyroid (E). and the much commoner arrangement of cords of cells. B A C D E capillaries

4. Types of Secretory Cells

5. Protein & Mucin Secreting Cells • Top illustration shows cells from the exocrine pancreas which produce pancreatic enzymes. Cells are characterised by abundant rough endoplasmic reticulum, extensive golgi and presence of granules which may be visible with the light microscope. • Bottom illustration shows mucin secreting cells from the submandibular gland. The cells have a poorly stained cytoplasm in routine LM preparations as most of the mucin is removed during processing. Nuclei are usually found in the basal parts of the cell

6. PancreasH&E These pancreatic acinar cells secrete enzymes which are stored in the apical cytoplasm as zymogen granules (here stained pink with eosin). The bases of the cells are very basophilic due to the large amount of ribosomes.

7. SubmandibularH&E These mucus cells are very pale due the absence of material in most of the cell cytoplasm. Close examination shows that outline of droplets can be seen in some areas (arrow). Most of the cellular organelles are located in the base of the cells which is why they are more deeply stained.

8. Steroid & Ion Pumping Cells • Upper illustration showssteroid secreting cells from the corpus luteum. In LM cells show central nuclei with surrounding eosinophilic zone. Peripherally is a pale staining area. In EM cells have well developed smooth ER located peripherally and abundant mitochochondria with characteristic tubular cristae around the nuclear area • Lower illustration is of an ion pumping cell from ducts of a salivary gland. The basal membranes are folded and in the EM it may be seen that these foldings are associated with accumulations of mitochondria. In addition tight junctions are common between adjacent cells

9. Types of Exocrine Glands Unicellular and Multicellular Unicellular Glands GOBLET CELLS

10. Classification of Multicelluar Exocrine Glands Glands are classified on the basis of the ducts and the arrangement of the secretory cells in the gland. Ducts may be straight or branched giving rise to simple or compound glands Secretory portions may be in the form of tubules or acini (sometimes called alveolae). Combining the features of the ducts and the secretory portions gives rise to a number of different gland varieties.

11. Types of Exocrine Glands Simple tubular unbranched duct secretory cells in tubules Simple coiled tubular “ tubules are coiled Simple branched tubular “ tubules are branched Compound tubular branched duct ducts & tubules branched Simple acinar unbranched duct secretory cells in acini Multiple acinar “ many acini open into one duct Compound acinar ducts & secretory secretory cells in branched Units branched acini FINALLY: In some glands the secretory units are both tubular and acinar with branching of the ducts and secretory units. These are compound Tubuloalveolar glands.

12. Morphological Types of Glands

13. Simple Tubular Glands In simple tubular glands the duct system consists of the space between the secretory cells. (Arrows). This type of gland occurs in the colon & the crypts of lieberkuhn in the small intestine.

14. Coiled Tubular Glands The sweat glands of the skin are typical coiled tubular glands. In section the glandular portion appears as a number of roughly circular tubes lined by a cuboidal epithelium (arrows) The gland has a single duct opening onto the surface of the skin.

15. Simple Branched Tubular Glands The glands in the fundic region of the stomach are typical branched tubular glands which open into the base of a folding of the stomach epithelium which is called a gastric pit (green arrow). The cells within these glands secrete mucus and acid; in this slide only acid secreting cells are clearly visible (blue arrows).

16. Alveolar Glands This section illustrates a sebaceous gland which is an example of a simple alveolar gland. The alveolae (Arrows) all enter into a single duct.

17. Compound Tubular Gland • The tubular nature of this gland is clearly • visible as is the fact the tubules may be • branched (arrows). • Note the pale staining of the secretory cells. • All of the cells visible are mucus secreting. • The pale staining of the cytoplasm is due to the fact that : • the mucus occupies most of the cytoplasm • the mucus is removed during tissue • processing • The organelles in these cells are all located towards the base of the cell. This can be seen in slide 20

18. Compound Acinar Gland This micrograph is from the exocrine pancreas which is an example of a compound acinar gland. In this type of gland the duct system and the acini are branched (arrows indicate branching acini). The base of these serous secreting cells is highly basophilic due to the high content of ribosomes. Numerous zymogen granules can be seen in the cell apices; these are pink as they stain with eosin

19. Compound Tubuloacinar Gland This is a micrograph of the submandibular gland. A compound tubuloacinar gland containing mucus and serous cells (green & blue arrows respectively). Acinar and tubular secretory units are present. The serous cells are often arranged in as serous demilunes (blue arrow). This arrangement consist of a cap of serous cells applied to a mucus acinus

20. Mixed Serous & Mucus Glands In this section of submandibular gland two types of secretory cell can be seen. The light staining cells secrete mucus (stars). The darker cells (green arrows) are serous secreting. In some areas the serous cells are arranged as caps on mucous secreting acini; this arrangement is known as a serous demilune (blue arrows).

21. Endocrine Glands • Endocrine glands lack a duct system. Their secretions pass directly into the • blood vascular system. • Arrangement of the glands is in one of two systems: • cells are arranged in cords e.g. adrenal gland • cells arranged in follicles e.g. thyroid gland

22. Adrenal Gland Note how the cells are arranged in cords and clumps and also the very large numbers of capillaries (some marked with green arrows)

23. Thyroid gland Note how the thyroid is composed of numerous follicles (stars) each lined by a cuboidal epithelium (arrows). Hormone precursor is stored in the follicles as colloid which gives each follicle its pink appearance. At the time of secretion colloid is taken back into the epithelial cells, modified and then secreted into the blood vascular system

24. Methods of Secretion Cells release their secretions in different ways. The terms used are defined below MEROCRINE Release of secretory granules e.g. pancreas APOCRINE Release of a portion of the cell e.g. breast HOLOCRINE Release of all of the cell e.g sebaceous gland ENDOCRINE Secretion into vascular system e.g. adrenal