Glandular Epithelium (Glands): Some of the epithelial cells get specialised for secretion and are called
glandular epithelium.
(i) Exocrine glands: They are glands which drain out their
secretion to the epithelial surface through ducts, HJ, gastric
glands, mucous glands, intestinal glands, salivary glands,
sweat glands, sebaceous glands and mammary glands.
(ii) Endocrine glands: They are glands which pour their
secretion directly into blood vascular system. Endocrine
glands are commonly called ductless glands as they lack
draining ducts, HJ, thyroid, adrenal, pituitary, etc.
(iii) Heterocrine glands: They have both exocrine part and
endocrine part. The exocrine part sends its secretion by way
of a duct whereas the endocrine part releases its secretion
directly into blood and lymph, HJ, pancreas and gonads.(i) Unicellular glands: They consist of isolated glandular
cells, HJ, goblet cells (mucous cells), serous cells.
(ii) Multicellular glands: They consist of cluster of cells,
HJ, salivary glands. These are further classified in two types:
tubular and saccular glands.Types of GlandsSecretory
product in
lumen of glandA vesicle
releasing
its contents
Merocrine glandIntact cell(i) Merocrine glands: Discharge the
secretion by simple diffusion from the cell
without any loss or damage to cell part,
HJ, sweat gland and intestinal gland.Holocrine glandA disintegrating
cell releasing its
contents
Cell with secretory
product
New cells forming(iii) Holocrine glands: An entire
cell gets filled with secretory
products, disintegrates and gets
discharged as secretion, HJ,
sebaceous glands.Pinched off portion
of cell releasing
secretory productApocrine glandPinched off
portion of cell(ii) Apocrine glands: Glands accumulate
their secretory product in the apical part
of the cell. This portion of the cell breaks
off from the rest of the cell and is released
as secretion, HJ, mammary glands.Based on cell number Based on mode of secretionBased on site of secretion