3. Pseudostratified columnar epithelium is a type of epithelium that contains only one layer of cells on the basal membrane. However, as the nuclei are positioned at different levels resembling stratification. The functions of pseudostratified epithelia comprise secretion and absorption. The examples include respiratory epithelium of the upper respiratory tract.
4. Holocrine glands release products of secretion which are secreted with the remnants of dead cells. Examples include the sebaceous glands of the skin and the meibomian glands of the eyelid. Apocrine glands are mainly found in the skin and open into hair follicles. They continuously secrete a concentrated fatty sweat into the gland tube. The examples also include the mammary gland, which is a modified sweat gland. Both apocrine and holocrine glands are destroyed during secretion. However, only top of the cell is lost in apocrine glands, while the whole cell is fragmented in holocrine glands.